/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
** DAV extension module for Apache 2.0.*
**  - various utilities, repository-independent
*/

#include "apr_strings.h"
#include "apr_lib.h"

#define APR_WANT_STRFUNC
#include "apr_want.h"

#include "mod_dav.h"

#include "http_request.h"
#include "http_config.h"
#include "http_vhost.h"
#include "http_log.h"
#include "http_protocol.h"

DAV_DECLARE(dav_error*) dav_new_error(apr_pool_t *p, int status, int error_id,
                                      apr_status_t aprerr, const char *desc)
{
    dav_error *err = apr_pcalloc(p, sizeof(*err));

    /* DBG3("dav_new_error: %d %d %s", status, error_id, desc ? desc : "(no desc)"); */

    err->status = status;
    err->error_id = error_id;
    err->desc = desc;
    err->aprerr = aprerr;

    return err;
}

DAV_DECLARE(dav_error*) dav_new_error_tag(apr_pool_t *p, int status,
                                          int error_id, apr_status_t aprerr,
                                          const char *desc,
                                          const char *namespace,
                                          const char *tagname)
{
    dav_error *err = dav_new_error(p, status, error_id, aprerr, desc);

    err->tagname = tagname;
    err->namespace = namespace;

    return err;
}


DAV_DECLARE(dav_error*) dav_push_error(apr_pool_t *p, int status,
                                       int error_id, const char *desc,
                                       dav_error *prev)
{
    dav_error *err = apr_pcalloc(p, sizeof(*err));

    err->status = status;
    err->error_id = error_id;
    err->desc = desc;
    err->prev = prev;

    return err;
}

DAV_DECLARE(dav_error*) dav_join_error(dav_error *dest, dav_error *src)
{
    dav_error *curr = dest;

    /* src error doesn't exist so nothing to join just return dest */
    if (src == NULL) {
        return dest;
    }

    /* dest error doesn't exist so nothing to join just return src */
    if (curr == NULL) {
        return src;
    }

    /* find last error in dest stack */
    while (curr->prev != NULL) {
        curr = curr->prev;
    }

    /* add the src error onto end of dest stack and return it */
    curr->prev = src;
    return dest;
}

DAV_DECLARE(void) dav_check_bufsize(apr_pool_t * p, dav_buffer *pbuf,
                                    apr_size_t extra_needed)
{
    /* grow the buffer if necessary */
    if (pbuf->cur_len + extra_needed > pbuf->alloc_len) {
        char *newbuf;

        pbuf->alloc_len += extra_needed + DAV_BUFFER_PAD;
        newbuf = apr_palloc(p, pbuf->alloc_len);
        memcpy(newbuf, pbuf->buf, pbuf->cur_len);
        pbuf->buf = newbuf;
    }
}

DAV_DECLARE(void) dav_set_bufsize(apr_pool_t * p, dav_buffer *pbuf,
                                  apr_size_t size)
{
    /* NOTE: this does not retain prior contents */

    /* NOTE: this function is used to init the first pointer, too, since
       the PAD will be larger than alloc_len (0) for zeroed structures */

    /* grow if we don't have enough for the requested size plus padding */
    if (size + DAV_BUFFER_PAD > pbuf->alloc_len) {
        /* set the new length; min of MINSIZE */
        pbuf->alloc_len = size + DAV_BUFFER_PAD;
        if (pbuf->alloc_len < DAV_BUFFER_MINSIZE)
            pbuf->alloc_len = DAV_BUFFER_MINSIZE;

        pbuf->buf = apr_palloc(p, pbuf->alloc_len);
    }
    pbuf->cur_len = size;
}


/* initialize a buffer and copy the specified (null-term'd) string into it */
DAV_DECLARE(void) dav_buffer_init(apr_pool_t *p, dav_buffer *pbuf,
                                  const char *str)
{
    dav_set_bufsize(p, pbuf, strlen(str));
    memcpy(pbuf->buf, str, pbuf->cur_len + 1);
}

/* append a string to the end of the buffer, adjust length */
DAV_DECLARE(void) dav_buffer_append(apr_pool_t *p, dav_buffer *pbuf,
                                    const char *str)
{
    apr_size_t len = strlen(str);

    dav_check_bufsize(p, pbuf, len + 1);
    memcpy(pbuf->buf + pbuf->cur_len, str, len + 1);
    pbuf->cur_len += len;
}

/* place a string on the end of the buffer, do NOT adjust length */
DAV_DECLARE(void) dav_buffer_place(apr_pool_t *p, dav_buffer *pbuf,
                                   const char *str)
{
    apr_size_t len = strlen(str);

    dav_check_bufsize(p, pbuf, len + 1);
    memcpy(pbuf->buf + pbuf->cur_len, str, len + 1);
}

/* place some memory on the end of a buffer; do NOT adjust length */
DAV_DECLARE(void) dav_buffer_place_mem(apr_pool_t *p, dav_buffer *pbuf,
                                       const void *mem, apr_size_t amt,
                                       apr_size_t pad)
{
    dav_check_bufsize(p, pbuf, amt + pad);
    memcpy(pbuf->buf + pbuf->cur_len, mem, amt);
}

/*
** dav_lookup_uri()
**
** Extension for ap_sub_req_lookup_uri() which can't handle absolute
** URIs properly.
**
** If NULL is returned, then an error occurred with parsing the URI or
** the URI does not match the current server.
*/
DAV_DECLARE(dav_lookup_result) dav_lookup_uri(const char *uri,
                                              request_rec * r,
                                              int must_be_absolute)
{
    dav_lookup_result result = { 0 };
    const char *scheme;
    apr_port_t port;
    apr_uri_t comp;
    char *new_file;
    const char *domain;

    /* first thing to do is parse the URI into various components */
    if (apr_uri_parse(r->pool, uri, &comp) != APR_SUCCESS) {
        result.err.status = HTTP_BAD_REQUEST;
        result.err.desc = "Invalid syntax in Destination URI.";
        return result;
    }

    /* the URI must be an absoluteURI (WEBDAV S9.3) */
    if (comp.scheme == NULL && must_be_absolute) {
        result.err.status = HTTP_BAD_REQUEST;
        result.err.desc = "Destination URI must be an absolute URI.";
        return result;
    }

    /* the URI must not have a query (args) or a fragment */
    if (comp.query != NULL || comp.fragment != NULL) {
        result.err.status = HTTP_BAD_REQUEST;
        result.err.desc =
            "Destination URI contains invalid components "
            "(a query or a fragment).";
        return result;
    }

    /* If the scheme or port was provided, then make sure that it matches
       the scheme/port of this request. If the request must be absolute,
       then require the (explicit/implicit) scheme/port be matching.

       ### hmm. if a port wasn't provided (does the parse return port==0?),
       ### but we're on a non-standard port, then we won't detect that the
       ### URI's port implies the wrong one.
    */
    if (comp.scheme != NULL || comp.port != 0 || must_be_absolute)
    {
        /* ### not sure this works if the current request came in via https: */
        scheme = r->parsed_uri.scheme;
        if (scheme == NULL)
            scheme = ap_http_scheme(r);

        /* insert a port if the URI did not contain one */
        if (comp.port == 0)
            comp.port = apr_uri_port_of_scheme(comp.scheme);

        /* now, verify that the URI uses the same scheme as the current.
           request. the port must match our port.
        */
        port = r->connection->local_addr->port;
        if (strcasecmp(comp.scheme, scheme) != 0
#ifdef APACHE_PORT_HANDLING_IS_BUSTED
            || comp.port != port
#endif
            ) {
            result.err.status = HTTP_BAD_GATEWAY;
            result.err.desc = apr_psprintf(r->pool,
                                           "Destination URI refers to "
                                           "different scheme or port "
                                           "(%s://hostname:%d)" APR_EOL_STR
                                           "(want: %s://hostname:%d)",
                                           comp.scheme ? comp.scheme : scheme,
                                           comp.port ? comp.port : port,
                                           scheme, port);
            return result;
        }
    }

    /* we have verified the scheme, port, and general structure */

    /*
    ** Hrm.  IE5 will pass unqualified hostnames for both the
    ** Host: and Destination: headers.  This breaks the
    ** http_vhost.c::matches_aliases function.
    **
    ** For now, qualify unqualified comp.hostnames with
    ** r->server->server_hostname.
    **
    ** ### this is a big hack. Apache should provide a better way.
    ** ### maybe the admin should list the unqualified hosts in a
    ** ### <ServerAlias> block?
    */
    if (comp.hostname != NULL
        && strrchr(comp.hostname, '.') == NULL
        && (domain = strchr(r->server->server_hostname, '.')) != NULL) {
        comp.hostname = apr_pstrcat(r->pool, comp.hostname, domain, NULL);
    }

    /* now, if a hostname was provided, then verify that it represents the
       same server as the current connection. note that we just use our
       port, since we've verified the URI matches ours */
#ifdef APACHE_PORT_HANDLING_IS_BUSTED
    if (comp.hostname != NULL &&
        !ap_matches_request_vhost(r, comp.hostname, port)) {
        result.err.status = HTTP_BAD_GATEWAY;
        result.err.desc = "Destination URI refers to a different server.";
        return result;
    }
#endif

    /* we have verified that the requested URI denotes the same server as
       the current request. Therefore, we can use ap_sub_req_lookup_uri() */

    /* reconstruct a URI as just the path */
    new_file = apr_uri_unparse(r->pool, &comp, APR_URI_UNP_OMITSITEPART);

    /*
     * Lookup the URI and return the sub-request. Note that we use the
     * same HTTP method on the destination. This allows the destination
     * to apply appropriate restrictions (e.g. readonly).
     */
    result.rnew = ap_sub_req_method_uri(r->method, new_file, r, NULL);

    return result;
}

/* ---------------------------------------------------------------
**
** XML UTILITY FUNCTIONS
*/

/* validate that the root element uses a given DAV: tagname (TRUE==valid) */
DAV_DECLARE(int) dav_validate_root(const apr_xml_doc *doc,
                                   const char *tagname)
{
    return doc->root &&
        doc->root->ns == APR_XML_NS_DAV_ID &&
        strcmp(doc->root->name, tagname) == 0;
}

/* find and return the (unique) child with a given DAV: tagname */
DAV_DECLARE(apr_xml_elem *) dav_find_child(const apr_xml_elem *elem,
                                           const char *tagname)
{
    apr_xml_elem *child = elem->first_child;

    for (; child; child = child->next)
        if (child->ns == APR_XML_NS_DAV_ID && !strcmp(child->name, tagname))
            return child;
    return NULL;
}

/* gather up all the CDATA into a single string */
DAV_DECLARE(const char *) dav_xml_get_cdata(const apr_xml_elem *elem, apr_pool_t *pool,
                              int strip_white)
{
    apr_size_t len = 0;
    apr_text *scan;
    const apr_xml_elem *child;
    char *cdata;
    char *s;
    apr_size_t tlen;
    const char *found_text = NULL; /* initialize to avoid gcc warning */
    int found_count = 0;

    for (scan = elem->first_cdata.first; scan != NULL; scan = scan->next) {
        found_text = scan->text;
        ++found_count;
        len += strlen(found_text);
    }

    for (child = elem->first_child; child != NULL; child = child->next) {
        for (scan = child->following_cdata.first;
             scan != NULL;
             scan = scan->next) {
            found_text = scan->text;
            ++found_count;
            len += strlen(found_text);
        }
    }

    /* some fast-path cases:
     * 1) zero-length cdata
     * 2) a single piece of cdata with no whitespace to strip
     */
    if (len == 0)
        return "";
    if (found_count == 1) {
        if (!strip_white
            || (!apr_isspace(*found_text)
                && !apr_isspace(found_text[len - 1])))
            return found_text;
    }

    cdata = s = apr_palloc(pool, len + 1);

    for (scan = elem->first_cdata.first; scan != NULL; scan = scan->next) {
        tlen = strlen(scan->text);
        memcpy(s, scan->text, tlen);
        s += tlen;
    }

    for (child = elem->first_child; child != NULL; child = child->next) {
        for (scan = child->following_cdata.first;
             scan != NULL;
             scan = scan->next) {
            tlen = strlen(scan->text);
            memcpy(s, scan->text, tlen);
            s += tlen;
        }
    }

    *s = '\0';

    if (strip_white) {
        /* trim leading whitespace */
        while (apr_isspace(*cdata)) {     /* assume: return false for '\0' */
            ++cdata;
            --len;
        }

        /* trim trailing whitespace */
        while (len-- > 0 && apr_isspace(cdata[len]))
            continue;
        cdata[len + 1] = '\0';
    }

    return cdata;
}

DAV_DECLARE(dav_xmlns_info *) dav_xmlns_create(apr_pool_t *pool)
{
    dav_xmlns_info *xi = apr_pcalloc(pool, sizeof(*xi));

    xi->pool = pool;
    xi->uri_prefix = apr_hash_make(pool);
    xi->prefix_uri = apr_hash_make(pool);

    return xi;
}

DAV_DECLARE(void) dav_xmlns_add(dav_xmlns_info *xi,
                                const char *prefix, const char *uri)
{
    /* this "should" not overwrite a prefix mapping */
    apr_hash_set(xi->prefix_uri, prefix, APR_HASH_KEY_STRING, uri);

    /* note: this may overwrite an existing URI->prefix mapping, but it
       doesn't matter -- any prefix is usable to specify the URI. */
    apr_hash_set(xi->uri_prefix, uri, APR_HASH_KEY_STRING, prefix);
}

DAV_DECLARE(const char *) dav_xmlns_add_uri(dav_xmlns_info *xi,
                                            const char *uri)
{
    const char *prefix;

    if ((prefix = apr_hash_get(xi->uri_prefix, uri,
                               APR_HASH_KEY_STRING)) != NULL)
        return prefix;

    prefix = apr_psprintf(xi->pool, "g%d", xi->count++);
    dav_xmlns_add(xi, prefix, uri);
    return prefix;
}

DAV_DECLARE(const char *) dav_xmlns_get_uri(dav_xmlns_info *xi,
                                            const char *prefix)
{
    return apr_hash_get(xi->prefix_uri, prefix, APR_HASH_KEY_STRING);
}

DAV_DECLARE(const char *) dav_xmlns_get_prefix(dav_xmlns_info *xi,
                                               const char *uri)
{
    return apr_hash_get(xi->uri_prefix, uri, APR_HASH_KEY_STRING);
}

DAV_DECLARE(void) dav_xmlns_generate(dav_xmlns_info *xi,
                                     apr_text_header *phdr)
{
    apr_hash_index_t *hi = apr_hash_first(xi->pool, xi->prefix_uri);

    for (; hi != NULL; hi = apr_hash_next(hi)) {
        const void *prefix;
        void *uri;
        const char *s;

        apr_hash_this(hi, &prefix, NULL, &uri);

        s = apr_psprintf(xi->pool, " xmlns:%s=\"%s\"",
                         (const char *)prefix, (const char *)uri);
        apr_text_append(xi->pool, phdr, s);
    }
}

/* ---------------------------------------------------------------
**
** Timeout header processing
**
*/

/* dav_get_timeout:  If the Timeout: header exists, return a time_t
 *    when this lock is expected to expire.  Otherwise, return
 *    a time_t of DAV_TIMEOUT_INFINITE.
 *
 *    It's unclear if DAV clients are required to understand
 *    Seconds-xxx and Infinity time values.  We assume that they do.
 *    In addition, for now, that's all we understand, too.
 */
DAV_DECLARE(time_t) dav_get_timeout(request_rec *r)
{
    time_t now, expires = DAV_TIMEOUT_INFINITE;

    const char *timeout_const = apr_table_get(r->headers_in, "Timeout");
    const char *timeout = apr_pstrdup(r->pool, timeout_const), *val;

    if (timeout == NULL)
        return DAV_TIMEOUT_INFINITE;

    /* Use the first thing we understand, or infinity if
     * we don't understand anything.
     */

    while ((val = ap_getword_white(r->pool, &timeout)) && strlen(val)) {
        if (!strncmp(val, "Infinite", 8)) {
            return DAV_TIMEOUT_INFINITE;
        }

        if (!strncmp(val, "Second-", 7)) {
            val += 7;
            /* ### We need to handle overflow better:
             * ### timeout will be <= 2^32 - 1
             */
            expires = atol(val);
            now     = time(NULL);
            return now + expires;
        }
    }

    return DAV_TIMEOUT_INFINITE;
}

/* ---------------------------------------------------------------
**
** If Header processing
**
*/

/* add_if_resource returns a new if_header, linking it to next_ih.
 */
static dav_if_header *dav_add_if_resource(apr_pool_t *p, dav_if_header *next_ih,
                                          const char *uri, apr_size_t uri_len)
{
    dav_if_header *ih;

    if ((ih = apr_pcalloc(p, sizeof(*ih))) == NULL)
        return NULL;

    ih->uri = uri;
    ih->uri_len = uri_len;
    ih->next = next_ih;

    return ih;
}

/* add_if_state adds a condition to an if_header.
 */
static dav_error * dav_add_if_state(apr_pool_t *p, dav_if_header *ih,
                                    const char *state_token,
                                    dav_if_state_type t, int condition,
                                    const dav_hooks_locks *locks_hooks)
{
    dav_if_state_list *new_sl;

    new_sl = apr_pcalloc(p, sizeof(*new_sl));

    new_sl->condition = condition;
    new_sl->type      = t;

    if (t == dav_if_opaquelock) {
        dav_error *err;

        if ((err = (*locks_hooks->parse_locktoken)(p, state_token,
                                                   &new_sl->locktoken)) != NULL) {
            /* If the state token cannot be parsed, treat it as an
             * unknown state; this will evaluate to "false" later
             * during If header validation. */
            if (err->error_id == DAV_ERR_LOCK_UNK_STATE_TOKEN) {
                new_sl->type = dav_if_unknown;
            }
            else {
                /* ### maybe add a higher-level description */
                return err;
            }
        }
    }
    else
        new_sl->etag = state_token;

    new_sl->next = ih->state;
    ih->state = new_sl;

    return NULL;
}

/* fetch_next_token returns the substring from str+1
 * to the next occurrence of char term, or \0, whichever
 * occurs first.  Leading whitespace is ignored.
 */
static char *dav_fetch_next_token(char **str, char term)
{
    char *sp;
    char *token;

    token = *str + 1;

    while (*token && (*token == ' ' || *token == '\t'))
        token++;

    if ((sp = strchr(token, term)) == NULL)
        return NULL;

    *sp = '\0';
    *str = sp;
    return token;
}

/* dav_process_if_header:
 *
 *   If NULL (no error) is returned, then **if_header points to the
 *   "If" productions structure (or NULL if "If" is not present).
 *
 *   ### this part is bogus:
 *   If an error is encountered, the error is logged.  Parent should
 *   return err->status.
 */
static dav_error * dav_process_if_header(request_rec *r, dav_if_header **p_ih)
{
    dav_error *err;
    char *str;
    char *list;
    const char *state_token;
    const char *uri = NULL;        /* scope of current production; NULL=no-tag */
    apr_size_t uri_len = 0;
    apr_status_t rv;
    dav_if_header *ih = NULL;
    apr_uri_t parsed_uri;
    const dav_hooks_locks *locks_hooks = DAV_GET_HOOKS_LOCKS(r);
    enum {no_tagged, tagged, unknown} list_type = unknown;
    int condition;

    *p_ih = NULL;

    if ((str = apr_pstrdup(r->pool, apr_table_get(r->headers_in, "If"))) == NULL)
        return NULL;

    while (*str) {
        switch(*str) {
        case '<':
            /* Tagged-list production - following states apply to this uri */
            if (list_type == no_tagged
                || ((uri = dav_fetch_next_token(&str, '>')) == NULL)) {
                return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                     DAV_ERR_IF_TAGGED, 0,
                                     "Invalid If-header: unclosed \"<\" or "
                                     "unexpected tagged-list production.");
            }

            /* 2518 specifies this must be an absolute URI; just take the
             * relative part for later comparison against r->uri */
            if ((rv = apr_uri_parse(r->pool, uri, &parsed_uri)) != APR_SUCCESS
                || !parsed_uri.path) {
                return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                     DAV_ERR_IF_TAGGED, rv,
                                     "Invalid URI in tagged If-header.");
            }
            /* note that parsed_uri.path is allocated; we can trash it */

            /* clean up the URI a bit */
            ap_getparents(parsed_uri.path);

            /* the resources we will compare to have unencoded paths */
            if (ap_unescape_url(parsed_uri.path) != OK) {
                return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                     DAV_ERR_IF_TAGGED, rv,
                                     "Invalid percent encoded URI in "
                                     "tagged If-header.");
            }

            uri_len = strlen(parsed_uri.path);
            if (uri_len > 1 && parsed_uri.path[uri_len - 1] == '/') {
                parsed_uri.path[--uri_len] = '\0';
            }

            uri = parsed_uri.path;
            list_type = tagged;
            break;

        case '(':
            /* List production */

            /* If a uri has not been encountered, this is a No-Tagged-List */
            if (list_type == unknown)
                list_type = no_tagged;

            if ((list = dav_fetch_next_token(&str, ')')) == NULL) {
                return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                     DAV_ERR_IF_UNCLOSED_PAREN, 0,
                                     "Invalid If-header: unclosed \"(\".");
            }

            if ((ih = dav_add_if_resource(r->pool, ih, uri, uri_len)) == NULL) {
                /* ### dav_add_if_resource() should return an error for us! */
                return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                     DAV_ERR_IF_PARSE, 0,
                                     "Internal server error parsing \"If:\" "
                                     "header.");
            }

            condition = DAV_IF_COND_NORMAL;

            while (*list) {
                /* List is the entire production (in a uri scope) */

                switch (*list) {
                case '<':
                    if ((state_token = dav_fetch_next_token(&list, '>')) == NULL) {
                        /* ### add a description to this error */
                        return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                             DAV_ERR_IF_PARSE, 0, NULL);
                    }

                    if ((err = dav_add_if_state(r->pool, ih, state_token, dav_if_opaquelock,
                                                condition, locks_hooks)) != NULL) {
                        /* ### maybe add a higher level description */
                        return err;
                    }
                    condition = DAV_IF_COND_NORMAL;
                    break;

                case '[':
                    if ((state_token = dav_fetch_next_token(&list, ']')) == NULL) {
                        /* ### add a description to this error */
                        return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                             DAV_ERR_IF_PARSE, 0, NULL);
                    }

                    if ((err = dav_add_if_state(r->pool, ih, state_token, dav_if_etag,
                                                condition, locks_hooks)) != NULL) {
                        /* ### maybe add a higher level description */
                        return err;
                    }
                    condition = DAV_IF_COND_NORMAL;
                    break;

                case 'N':
                    if (list[1] == 'o' && list[2] == 't') {
                        if (condition != DAV_IF_COND_NORMAL) {
                            return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                                 DAV_ERR_IF_MULTIPLE_NOT, 0,
                                                 "Invalid \"If:\" header: "
                                                 "Multiple \"not\" entries "
                                                 "for the same state.");
                        }
                        condition = DAV_IF_COND_NOT;
                    }
                    list += 2;
                    break;

                case ' ':
                case '\t':
                    break;

                default:
                    return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                         DAV_ERR_IF_UNK_CHAR, 0,
                                         apr_psprintf(r->pool,
                                                     "Invalid \"If:\" "
                                                     "header: Unexpected "
                                                     "character encountered "
                                                     "(0x%02x, '%c').",
                                                     *list, *list));
                }

                list++;
            }
            break;

        case ' ':
        case '\t':
            break;

        default:
            return dav_new_error(r->pool, HTTP_BAD_REQUEST,
                                 DAV_ERR_IF_UNK_CHAR, 0,
                                 apr_psprintf(r->pool,
                                             "Invalid \"If:\" header: "
                                             "Unexpected character "
                                             "encountered (0x%02x, '%c').",
                                             *str, *str));
        }

        str++;
    }

    *p_ih = ih;
    return NULL;
}

static int dav_find_submitted_locktoken(const dav_if_header *if_header,
                                        const dav_lock *lock_list,
                                        const dav_hooks_locks *locks_hooks)
{
    for (; if_header != NULL; if_header = if_header->next) {
        const dav_if_state_list *state_list;

        for (state_list = if_header->state;
             state_list != NULL;
             state_list = state_list->next) {

            if (state_list->type == dav_if_opaquelock) {
                const dav_lock *lock;

                /* given state_list->locktoken, match it */

                /*
                ** The resource will have one or more lock tokens. We only
                ** need to match one of them against any token in the
                ** If: header.
                **
                ** One token case: It is an exclusive or shared lock. Either
                **                 way, we must find it.
                **
                ** N token case: They are shared locks. By policy, we need
                **               to match only one. The resource's other
                **               tokens may belong to somebody else (so we
                **               shouldn't see them in the If: header anyway)
                */
                for (lock = lock_list; lock != NULL; lock = lock->next) {

                    if (!(*locks_hooks->compare_locktoken)(state_list->locktoken, lock->locktoken)) {
                        return 1;
                    }
                }
            }
        }
    }

    return 0;
}

/* dav_validate_resource_state:
 *    Returns NULL if path/uri meets if-header and lock requirements
 */
static dav_error * dav_validate_resource_state(apr_pool_t *p,
                                               const dav_resource *resource,
                                               dav_lockdb *lockdb,
                                               const dav_if_header *if_header,
                                               int flags,
                                               dav_buffer *pbuf,
                                               request_rec *r)
{
    dav_error *err;
    const char *uri;
    const char *etag;
    const dav_hooks_locks *locks_hooks = (lockdb ? lockdb->hooks : NULL);
    const dav_if_header *ifhdr_scan;
    dav_if_state_list *state_list;
    dav_lock *lock_list;
    dav_lock *lock;
    int num_matched;
    int num_that_apply;
    int seen_locktoken;
    apr_size_t uri_len;
    const char *reason = NULL;

    /* DBG1("validate: <%s>", resource->uri); */

    /*
    ** The resource will have one of three states:
    **
    ** 1) No locks. We have no special requirements that the user supply
    **    specific locktokens. One of the state lists must match, and
    **    we're done.
    **
    ** 2) One exclusive lock. The locktoken must appear *anywhere* in the
    **    If: header. Of course, asserting the token in a "Not" term will
    **    quickly fail that state list :-). If the locktoken appears in
    **    one of the state lists *and* one state list matches, then we're
    **    done.
    **
    ** 3) One or more shared locks. One of the locktokens must appear
    **    *anywhere* in the If: header. If one of the locktokens appears,
    **    and we match one state list, then we are done.
    **
    ** The <seen_locktoken> variable determines whether we have seen one
    ** of this resource's locktokens in the If: header.
    */

    /*
    ** If this is a new lock request, <flags> will contain the requested
    ** lock scope.  Three rules apply:
    **
    ** 1) Do not require a (shared) locktoken to be seen (when we are
    **    applying another shared lock)
    ** 2) If the scope is exclusive and we see any locks, fail.
    ** 3) If the scope is shared and we see an exclusive lock, fail.
    */

    if (lockdb == NULL) {
        /* we're in State 1. no locks. */
        lock_list = NULL;
    }
    else {
        /*
        ** ### hrm... we don't need to have these fully
        ** ### resolved since we're only looking at the
        ** ### locktokens...
        **
        ** ### use get_locks w/ calltype=PARTIAL
        */
        if ((err = dav_lock_query(lockdb, resource, &lock_list)) != NULL) {
            return dav_push_error(p,
                                  HTTP_INTERNAL_SERVER_ERROR, 0,
                                  "The locks could not be queried for "
                                  "verification against a possible \"If:\" "
                                  "header.",
                                  err);
        }

        /* lock_list now determines whether we're in State 1, 2, or 3. */
    }

    /*
    ** For a new, exclusive lock: if any locks exist, fail.
    ** For a new, shared lock:    if an exclusive lock exists, fail.
    **                            else, do not require a token to be seen.
    */
    if (flags & DAV_LOCKSCOPE_EXCLUSIVE) {
        if (lock_list != NULL) {
            return dav_new_error(p, HTTP_LOCKED, 0, 0,
                                 "Existing lock(s) on the requested resource "
                                 "prevent an exclusive lock.");
        }

        /*
        ** There are no locks, so we can pretend that we've already met
        ** any requirement to find the resource's locks in an If: header.
        */
        seen_locktoken = 1;
    }
    else if (flags & DAV_LOCKSCOPE_SHARED) {
        /*
        ** Strictly speaking, we don't need this loop. Either the first
        ** (and only) lock will be EXCLUSIVE, or none of them will be.
        */
        for (lock = lock_list; lock != NULL; lock = lock->next) {
            if (lock->scope == DAV_LOCKSCOPE_EXCLUSIVE) {
                return dav_new_error(p, HTTP_LOCKED, 0, 0,
                                     "The requested resource is already "
                                     "locked exclusively.");
            }
        }

        /*
        ** The locks on the resource (if any) are all shared. Set the
        ** <seen_locktoken> flag to indicate that we do not need to find
        ** the locks in an If: header.
        */
        seen_locktoken = 1;
    }
    else {
        /*
        ** For methods other than LOCK:
        **
        ** If we have no locks or if the resource is not being modified
        ** (per RFC 4918 the lock token is not required on resources
        ** we are not changing), then <seen_locktoken> can be set to true --
        ** pretending that we've already met the requirement of seeing one
        ** of the resource's locks in the If: header.
        **
        ** Otherwise, it must be cleared and we'll look for one.
        */
        seen_locktoken = (lock_list == NULL
                          || flags & DAV_VALIDATE_NO_MODIFY);
    }

    /*
    ** If there is no If: header, then we can shortcut some logic:
    **
    ** 1) if we do not need to find a locktoken in the (non-existent) If:
    **    header, then we are successful.
    **
    ** 2) if we must find a locktoken in the (non-existent) If: header, then
    **    we fail.
    */
    if (if_header == NULL) {
        if (seen_locktoken)
            return NULL;

        return dav_new_error(p, HTTP_LOCKED, 0, 0,
                             "This resource is locked and an \"If:\" header "
                             "was not supplied to allow access to the "
                             "resource.");
    }
    /* the If: header is present */

    /*
    ** If a dummy header is present (because of a Lock-Token: header), then
    ** we are required to find that token in this resource's set of locks.
    ** If we have no locks, then we immediately fail.
    **
    ** This is a 400 (Bad Request) since they should only submit a locktoken
    ** that actually exists.
    **
    ** Don't issue this response if we're talking about the parent resource.
    ** It is okay for that resource to NOT have this locktoken.
    ** (in fact, it certainly will not: a dummy_header only occurs for the
    **  UNLOCK method, the parent is checked only for locknull resources,
    **  and the parent certainly does not have the (locknull's) locktoken)
    */
    if (lock_list == NULL && if_header->dummy_header) {
        if (flags & DAV_VALIDATE_IS_PARENT)
            return NULL;
        return dav_new_error(p, HTTP_BAD_REQUEST, 0, 0,
                             "The locktoken specified in the \"Lock-Token:\" "
                             "header is invalid because this resource has no "
                             "outstanding locks.");
    }

    /*
    ** Prepare the input URI. We want the URI to never have a trailing slash.
    **
    ** When URIs are placed into the dav_if_header structure, they are
    ** guaranteed to never have a trailing slash. If the URIs are equivalent,
    ** then it doesn't matter if they both lack a trailing slash -- they're
    ** still equivalent.
    **
    ** Note: we could also ensure that a trailing slash is present on both
    ** URIs, but the majority of URIs provided to us via a resource walk
    ** will not contain that trailing slash.
    */
    uri = resource->uri;
    uri_len = strlen(uri);
    if (uri[uri_len - 1] == '/') {
        dav_set_bufsize(p, pbuf, uri_len);
        memcpy(pbuf->buf, uri, uri_len);
        pbuf->buf[--uri_len] = '\0';
        uri = pbuf->buf;
    }

    /* get the resource's etag; we may need it during the checks */
    etag = (*resource->hooks->getetag)(resource);

    /* how many state_lists apply to this URI? */
    num_that_apply = 0;

    /* If there are if-headers, fail if this resource
     * does not match at least one state_list.
     */
    for (ifhdr_scan = if_header;
         ifhdr_scan != NULL;
         ifhdr_scan = ifhdr_scan->next) {

        /* DBG2("uri=<%s>  if_uri=<%s>", uri, ifhdr_scan->uri ? ifhdr_scan->uri : "(no uri)"); */

        if (ifhdr_scan->uri != NULL
            && (uri_len != ifhdr_scan->uri_len
                || memcmp(uri, ifhdr_scan->uri, uri_len) != 0)) {
            /*
            ** A tagged-list's URI doesn't match this resource's URI.
            ** Skip to the next state_list to see if it will match.
            */
            continue;
        }

        /* this state_list applies to this resource */

        /*
        ** ### only one state_list should ever apply! a no-tag, or a tagged
        ** ### where S9.4.2 states only one can match.
        **
        ** ### revamp this code to loop thru ifhdr_scan until we find the
        ** ### matching state_list. process it. stop.
        */
        ++num_that_apply;

        /* To succeed, resource must match *all* of the states
         * specified in the state_list.
         */
        for (state_list = ifhdr_scan->state;
             state_list != NULL;
             state_list = state_list->next) {

            switch(state_list->type) {
            case dav_if_etag:
            {
                const char *given_etag, *current_etag;
                int mismatch;

                /* Do a weak entity comparison function as defined in
                 * RFC 2616 13.3.3.
                 */
                if (state_list->etag[0] == 'W' &&
                    state_list->etag[1] == '/') {
                    given_etag = state_list->etag + 2;
                }
                else {
                    given_etag = state_list->etag;
                }
                if (etag[0] == 'W' &&
                    etag[1] == '/') {
                    current_etag = etag + 2;
                }
                else {
                    current_etag = etag;
                }

                mismatch = strcmp(given_etag, current_etag);

                if (state_list->condition == DAV_IF_COND_NORMAL && mismatch) {
                    /*
                    ** The specified entity-tag does not match the
                    ** entity-tag on the resource. This state_list is
                    ** not going to match. Bust outta here.
                    */
                    reason =
                        "an entity-tag was specified, but the resource's "
                        "actual ETag does not match.";
                    goto state_list_failed;
                }
                else if (state_list->condition == DAV_IF_COND_NOT
                         && !mismatch) {
                    /*
                    ** The specified entity-tag DOES match the
                    ** entity-tag on the resource. This state_list is
                    ** not going to match. Bust outta here.
                    */
                    reason =
                        "an entity-tag was specified using the \"Not\" form, "
                        "but the resource's actual ETag matches the provided "
                        "entity-tag.";
                    goto state_list_failed;
                }
                break;
            }

            case dav_if_opaquelock:
                if (lockdb == NULL) {
                    if (state_list->condition == DAV_IF_COND_NOT) {
                        /* the locktoken is definitely not there! (success) */
                        continue;
                    }

                    /* condition == DAV_IF_COND_NORMAL */

                    /*
                    ** If no lockdb is provided, then validation fails for
                    ** this state_list (NORMAL means we were supposed to
                    ** find the token, which we obviously cannot do without
                    ** a lock database).
                    **
                    ** Go and try the next state list.
                    */
                    reason =
                        "a State-token was supplied, but a lock database "
                        "is not available for to provide the required lock.";
                    goto state_list_failed;
                }

                /* Resource validation 'fails' if:
                 *    ANY  of the lock->locktokens match
                 *         a NOT state_list->locktoken,
                 * OR
                 *    NONE of the lock->locktokens match
                 *         a NORMAL state_list->locktoken.
                 */
                num_matched = 0;
                for (lock = lock_list; lock != NULL; lock = lock->next) {

                    /*
                    DBG2("compare: rsrc=%s  ifhdr=%s",
                         (*locks_hooks->format_locktoken)(p, lock->locktoken),
                         (*locks_hooks->format_locktoken)(p, state_list->locktoken));
                    */

                    /* nothing to do if the locktokens do not match. */
                    if ((*locks_hooks->compare_locktoken)(state_list->locktoken, lock->locktoken)) {
                        continue;
                    }

                    /*
                    ** We have now matched up one of the resource's locktokens
                    ** to a locktoken in a State-token in the If: header.
                    ** Note this fact, so that we can pass the overall
                    ** requirement of seeing at least one of the resource's
                    ** locktokens.
                    */
                    seen_locktoken = 1;

                    if (state_list->condition == DAV_IF_COND_NOT) {
                        /*
                        ** This state requires that the specified locktoken
                        ** is NOT present on the resource. But we just found
                        ** it. There is no way this state-list can now
                        ** succeed, so go try another one.
                        */
                        reason =
                            "a State-token was supplied, which used a "
                            "\"Not\" condition. The State-token was found "
                            "in the locks on this resource";
                        goto state_list_failed;
                    }

                    /* condition == DAV_IF_COND_NORMAL */

                    /* Validate auth_user:  If an authenticated user created
                    ** the lock, only the same user may submit that locktoken
                    ** to manipulate a resource.
                    */
                    if (lock->auth_user &&
                        (!r->user ||
                         strcmp(lock->auth_user, r->user))) {
                        const char *errmsg;

                        errmsg = apr_pstrcat(p, "User \"",
                                            r->user,
                                            "\" submitted a locktoken created "
                                            "by user \"",
                                            lock->auth_user, "\".", NULL);
                        return dav_new_error(p, HTTP_FORBIDDEN, 0, 0, errmsg);
                    }

                    /*
                    ** We just matched a specified State-Token to one of the
                    ** resource's locktokens.
                    **
                    ** Break out of the lock scan -- we only needed to find
                    ** one match (actually, there shouldn't be any other
                    ** matches in the lock list).
                    */
                    num_matched = 1;
                    break;
                }

                if (num_matched == 0
                    && state_list->condition == DAV_IF_COND_NORMAL) {
                    /*
                    ** We had a NORMAL state, meaning that we should have
                    ** found the State-Token within the locks on this
                    ** resource. We didn't, so this state_list must fail.
                    */
                    reason =
                        "a State-token was supplied, but it was not found "
                        "in the locks on this resource.";
                    goto state_list_failed;
                }

                break;

            case dav_if_unknown:
                /* Request is predicated on some unknown state token,
                 * which must be presumed to *not* match, so fail
                 * unless this is a Not condition. */

                if (state_list->condition == DAV_IF_COND_NORMAL) {
                    reason =
                        "an unknown state token was supplied";
                    goto state_list_failed;
                }
                break;

            } /* switch */
        } /* foreach ( state_list ) */

        /*
        ** We've checked every state in this state_list and none of them
        ** have failed. Since all of them succeeded, then we have a matching
        ** state list and we may be done.
        **
        ** The next requirement is that we have seen one of the resource's
        ** locktokens (if any). If we have, then we can just exit. If we
        ** haven't, then we need to keep looking.
        */
        if (seen_locktoken) {
            /* woo hoo! */
            return NULL;
        }

        /*
        ** Haven't seen one. Let's break out of the search and just look
        ** for a matching locktoken.
        */
        break;

        /*
        ** This label is used when we detect that a state_list is not
        ** going to match this resource. We bust out and try the next
        ** state_list.
        */
      state_list_failed:
        ;

    } /* foreach ( ifhdr_scan ) */

    /*
    ** The above loop exits for one of two reasons:
    **   1) a state_list matched and seen_locktoken is false.
    **   2) all if_header structures were scanned, without (1) occurring
    */

    if (ifhdr_scan == NULL) {
        /*
        ** We finished the loop without finding any matching state lists.
        */

        /*
        ** If none of the state_lists apply to this resource, then we
        ** may have succeeded. Note that this scenario implies a
        ** tagged-list with no matching state_lists. If the If: header
        ** was a no-tag-list, then it would have applied to this resource.
        **
        ** S9.4.2 states that when no state_lists apply, then the header
        ** should be ignored.
        **
        ** If we saw one of the resource's locktokens, then we're done.
        ** If we did not see a locktoken, then we fail.
        */
        if (num_that_apply == 0) {
            if (seen_locktoken)
                return NULL;

            /*
            ** We may have aborted the scan before seeing the locktoken.
            ** Rescan the If: header to see if we can find the locktoken
            ** somewhere.
            **
            ** Note that seen_locktoken == 0 implies lock_list != NULL
            ** which implies locks_hooks != NULL.
            */
            if (dav_find_submitted_locktoken(if_header, lock_list,
                                             locks_hooks)) {
                /*
                ** We found a match! We're set... none of the If: header
                ** assertions apply (implicit success), and the If: header
                ** specified the locktoken somewhere. We're done.
                */
                return NULL;
            }

            return dav_new_error(p, HTTP_LOCKED, 0 /* error_id */, 0,
                                 "This resource is locked and the \"If:\" "
                                 "header did not specify one of the "
                                 "locktokens for this resource's lock(s).");
        }
        /* else: one or more state_lists were applicable, but failed. */

        /*
        ** If the dummy_header did not match, then they specified an
        ** incorrect token in the Lock-Token header. Forget whether the
        ** If: statement matched or not... we'll tell them about the
        ** bad Lock-Token first. That is considered a 400 (Bad Request).
        */
        if (if_header->dummy_header) {
            return dav_new_error(p, HTTP_BAD_REQUEST, 0, 0,
                                 "The locktoken specified in the "
                                 "\"Lock-Token:\" header did not specify one "
                                 "of this resource's locktoken(s).");
        }

        if (reason == NULL) {
            return dav_new_error(p, HTTP_PRECONDITION_FAILED, 0, 0,
                                 "The preconditions specified by the \"If:\" "
                                 "header did not match this resource.");
        }

        return dav_new_error(p, HTTP_PRECONDITION_FAILED, 0, 0,
                             apr_psprintf(p,
                                         "The precondition(s) specified by "
                                         "the \"If:\" header did not match "
                                         "this resource. At least one "
                                         "failure is because: %s", reason));
    }

    /* assert seen_locktoken == 0 */

    /*
    ** ifhdr_scan != NULL implies we found a matching state_list.
    **
    ** Since we're still here, it also means that we have not yet found
    ** one the resource's locktokens in the If: header.
    **
    ** Scan all the if_headers and states looking for one of this
    ** resource's locktokens. Note that we need to go back and scan them
    ** all -- we may have aborted a scan with a failure before we saw a
    ** matching token.
    **
    ** Note that seen_locktoken == 0 implies lock_list != NULL which implies
    ** locks_hooks != NULL.
    */
    if (dav_find_submitted_locktoken(if_header, lock_list, locks_hooks)) {
        /*
        ** We found a match! We're set... we have a matching state list,
        ** and the If: header specified the locktoken somewhere. We're done.
        */
        return NULL;
    }

    /*
    ** We had a matching state list, but the user agent did not specify one
    ** of this resource's locktokens. Tell them so.
    **
    ** Note that we need to special-case the message on whether a "dummy"
    ** header exists. If it exists, yet we didn't see a needed locktoken,
    ** then that implies the dummy header (Lock-Token header) did NOT
    ** specify one of this resource's locktokens. (this implies something
    ** in the real If: header matched)
    **
    ** We want to note the 400 (Bad Request) in favor of a 423 (Locked).
    */
    if (if_header->dummy_header) {
        return dav_new_error(p, HTTP_BAD_REQUEST, 0, 0,
                             "The locktoken specified in the "
                             "\"Lock-Token:\" header did not specify one "
                             "of this resource's locktoken(s).");
    }

    return dav_new_error(p, HTTP_LOCKED, 1 /* error_id */, 0,
                         "This resource is locked and the \"If:\" header "
                         "did not specify one of the "
                         "locktokens for this resource's lock(s).");
}

/* dav_validate_walker:  Walker callback function to validate resource state */
static dav_error * dav_validate_walker(dav_walk_resource *wres, int calltype)
{
    dav_walker_ctx *ctx = wres->walk_ctx;
    dav_error *err;

    if ((err = dav_validate_resource_state(ctx->w.pool, wres->resource,
                                           ctx->w.lockdb,
                                           ctx->if_header, ctx->flags,
                                           &ctx->work_buf, ctx->r)) == NULL) {
        /* There was no error, so just bug out. */
        return NULL;
    }

    /*
    ** If we have a serious server error, or if the request itself failed,
    ** then just return error (not a multistatus).
    */
    if (ap_is_HTTP_SERVER_ERROR(err->status)
        || (*wres->resource->hooks->is_same_resource)(wres->resource,
                                                      ctx->w.root)) {
        /* ### maybe push a higher-level description? */
        return err;
    }

    /* associate the error with the current URI */
    dav_add_response(wres, err->status, NULL);

    return NULL;
}

/* If-* header checking */
static int dav_meets_conditions(request_rec *r, int resource_state)
{
    const char *if_match, *if_none_match;
    int retVal;

    /* If-Match '*' fix. Resource existence not checked by ap_meets_conditions.
     * If-Match '*' request should succeed only if the resource exists. */
    if ((if_match = apr_table_get(r->headers_in, "If-Match")) != NULL) {
        if (if_match[0] == '*' && resource_state != DAV_RESOURCE_EXISTS)
            return HTTP_PRECONDITION_FAILED;
    }

    retVal = ap_meets_conditions(r);

    /* If-None-Match '*' fix. If-None-Match '*' request should succeed
     * if the resource does not exist. */
    if (retVal == HTTP_PRECONDITION_FAILED) {
        /* Note. If if_none_match != NULL, if_none_match is the culprit.
         * Since, in presence of If-None-Match,
         * other If-* headers are undefined. */
        if ((if_none_match =
            apr_table_get(r->headers_in, "If-None-Match")) != NULL) {
            if (if_none_match[0] == '*'
                && resource_state != DAV_RESOURCE_EXISTS) {
                return OK;
            }
        }
    }

    return retVal;
}

/*
** dav_validate_request:  Validate if-headers (and check for locks) on:
**    (1) r->filename @ depth;
**    (2) Parent of r->filename if check_parent == 1
**
** The check of parent should be done when it is necessary to verify that
** the parent collection will accept a new member (ie current resource
** state is null).
**
** Return OK on successful validation.
** On error, return appropriate HTTP_* code, and log error. If a multi-stat
** error is necessary, response will point to it, else NULL.
*/
DAV_DECLARE(dav_error *) dav_validate_request(request_rec *r,
                                              dav_resource *resource,
                                              int depth,
                                              dav_locktoken *locktoken,
                                              dav_response **response,
                                              int flags,
                                              dav_lockdb *lockdb)
{
    dav_error *err;
    int result;
    dav_if_header *if_header;
    int lock_db_opened_locally = 0;
    const dav_hooks_locks *locks_hooks = DAV_GET_HOOKS_LOCKS(r);
    const dav_hooks_repository *repos_hooks = resource->hooks;
    dav_buffer work_buf = { 0 };
    dav_response *new_response;
    int resource_state;
    const char *etag;
    int set_etag = 0;

#if DAV_DEBUG
    if (depth && response == NULL) {
        /*
        ** ### bleck. we can't return errors for other URIs unless we have
        ** ### a "response" ptr.
        */
        return dav_new_error(r->pool, HTTP_INTERNAL_SERVER_ERROR, 0, 0,
                             "DESIGN ERROR: dav_validate_request called "
                             "with depth>0, but no response ptr.");
    }
#endif

    if (response != NULL)
        *response = NULL;

    /* Set the ETag header required by dav_meets_conditions() */
    etag = apr_table_get(r->headers_out, "ETag");
    if (!etag) {
        etag = (*resource->hooks->getetag)(resource);
        if (etag && *etag) {
            apr_table_set(r->headers_out, "ETag", etag);
            set_etag = 1;
        }
    }
    /* Do the standard checks for conditional requests using
     * If-..-Since, If-Match etc */
    resource_state = dav_get_resource_state(r, resource);
    result = dav_meets_conditions(r, resource_state);
    if (set_etag) {
        /*
         * If we have set an ETag to headers out above for
         * dav_meets_conditions() revert this here as we do not want to set
         * the ETag in responses to requests with methods where this might not
         * be desired.
         */
        apr_table_unset(r->headers_out, "ETag");
    }
    if (result != OK) {
        return dav_new_error(r->pool, result, 0, 0, NULL);
    }

    /* always parse (and later process) the If: header */
    if ((err = dav_process_if_header(r, &if_header)) != NULL) {
        /* ### maybe add higher-level description */
        return err;
    }

    /* If a locktoken was specified, create a dummy if_header with which
     * to validate resources.  In the interim, figure out why DAV uses
     * locktokens in an if-header without a Lock-Token header to refresh
     * locks, but a Lock-Token header without an if-header to remove them.
     */
    if (locktoken != NULL) {
        dav_if_header *ifhdr_new;

        ifhdr_new = apr_pcalloc(r->pool, sizeof(*ifhdr_new));
        ifhdr_new->uri = resource->uri;
        ifhdr_new->uri_len = strlen(resource->uri);
        ifhdr_new->dummy_header = 1;

        ifhdr_new->state = apr_pcalloc(r->pool, sizeof(*ifhdr_new->state));
        ifhdr_new->state->type = dav_if_opaquelock;
        ifhdr_new->state->condition = DAV_IF_COND_NORMAL;
        ifhdr_new->state->locktoken = locktoken;

        ifhdr_new->next = if_header;
        if_header = ifhdr_new;
    }

    /*
    ** If necessary, open the lock database (read-only, lazily);
    ** the validation process may need to retrieve or update lock info.
    ** Otherwise, assume provided lockdb is valid and opened rw.
    */
    if (lockdb == NULL) {
        if (locks_hooks != NULL) {
            if ((err = (*locks_hooks->open_lockdb)(r, 0, 0, &lockdb)) != NULL) {
                /* ### maybe insert higher-level comment */
                return err;
            }
            lock_db_opened_locally = 1;
        }
    }

    /* (1) Validate the specified resource, at the specified depth.
     * Avoid the walk there is no if_header and we aren't planning
     * to modify this resource. */
    if (resource->exists && depth > 0 && !(!if_header && flags & DAV_VALIDATE_NO_MODIFY)) {
        dav_walker_ctx ctx = { { 0 } };
        dav_response *multi_status;

        ctx.w.walk_type = DAV_WALKTYPE_NORMAL;
        ctx.w.func = dav_validate_walker;
        ctx.w.walk_ctx = &ctx;
        ctx.w.pool = r->pool;
        ctx.w.root = resource;

        ctx.if_header = if_header;
        ctx.r = r;
        ctx.flags = flags;

        if (lockdb != NULL) {
            ctx.w.lockdb = lockdb;
            ctx.w.walk_type |= DAV_WALKTYPE_LOCKNULL;
        }

        err = (*repos_hooks->walk)(&ctx.w, DAV_INFINITY, &multi_status);
        if (err == NULL) {
            *response = multi_status;
        }
        /* else: implies a 5xx status code occurred. */
    }
    else {
        err = dav_validate_resource_state(r->pool, resource, lockdb,
                                          if_header, flags, &work_buf, r);
    }

    /* (2) Validate the parent resource if requested */
    if (err == NULL && (flags & DAV_VALIDATE_PARENT)) {
        dav_resource *parent_resource;

        err = (*repos_hooks->get_parent_resource)(resource, &parent_resource);

        if (err == NULL && parent_resource == NULL) {
            err = dav_new_error(r->pool, HTTP_FORBIDDEN, 0, 0,
                                "Cannot access parent of repository root.");
        }
        else if (err == NULL) {
            err = dav_validate_resource_state(r->pool, parent_resource, lockdb,
                                              if_header,
                                              flags | DAV_VALIDATE_IS_PARENT,
                                              &work_buf, r);

            /*
            ** This error occurred on the parent resource. This implies that
            ** we have to create a multistatus response (to report the error
            ** against a URI other than the Request-URI). "Convert" this error
            ** into a multistatus response.
            */
            if (err != NULL) {
                new_response = apr_pcalloc(r->pool, sizeof(*new_response));

                new_response->href = parent_resource->uri;
                new_response->status = err->status;
                new_response->desc =
                    "A validation error has occurred on the parent resource, "
                    "preventing the operation on the resource specified by "
                    "the Request-URI.";
                if (err->desc != NULL) {
                    new_response->desc = apr_pstrcat(r->pool,
                                                    new_response->desc,
                                                    " The error was: ",
                                                    err->desc, NULL);
                }

                /* assert: DAV_VALIDATE_PARENT implies response != NULL */
                new_response->next = *response;
                *response = new_response;

                err = NULL;
            }
        }
    }

    if (lock_db_opened_locally)
        (*locks_hooks->close_lockdb)(lockdb);

    /*
    ** If we don't have a (serious) error, and we have multistatus responses,
    ** then we need to construct an "error". This error will be the overall
    ** status returned, and the multistatus responses will go into its body.
    **
    ** For certain methods, the overall error will be a 424. The default is
    ** to construct a standard 207 response.
    */
    if (err == NULL && response != NULL && *response != NULL) {
        apr_text *propstat = NULL;

        if ((flags & DAV_VALIDATE_USE_424) != 0) {
            /* manufacture a 424 error to hold the multistatus response(s) */
            return dav_new_error(r->pool, HTTP_FAILED_DEPENDENCY, 0, 0,
                                 "An error occurred on another resource, "
                                 "preventing the requested operation on "
                                 "this resource.");
        }

        /*
        ** Whatever caused the error, the Request-URI should have a 424
        ** associated with it since we cannot complete the method.
        **
        ** For a LOCK operation, insert an empty DAV:lockdiscovery property.
        ** For other methods, return a simple 424.
        */
        if ((flags & DAV_VALIDATE_ADD_LD) != 0) {
            propstat = apr_pcalloc(r->pool, sizeof(*propstat));
            propstat->text =
                "<D:propstat>" DEBUG_CR
                "<D:prop><D:lockdiscovery/></D:prop>" DEBUG_CR
                "<D:status>HTTP/1.1 424 Failed Dependency</D:status>" DEBUG_CR
                "</D:propstat>" DEBUG_CR;
        }

        /* create the 424 response */
        new_response = apr_pcalloc(r->pool, sizeof(*new_response));
        new_response->href = resource->uri;
        new_response->status = HTTP_FAILED_DEPENDENCY;
        new_response->propresult.propstats = propstat;
        new_response->desc =
            "An error occurred on another resource, preventing the "
            "requested operation on this resource.";

        new_response->next = *response;
        *response = new_response;

        /* manufacture a 207 error for the multistatus response(s) */
        return dav_new_error(r->pool, HTTP_MULTI_STATUS, 0, 0,
                             "Error(s) occurred on resources during the "
                             "validation process.");
    }

    return err;
}

/* dav_get_locktoken_list:
 *
 * Sets ltl to a locktoken_list of all positive locktokens in header,
 * else NULL if no If-header, or no positive locktokens.
 */
DAV_DECLARE(dav_error *) dav_get_locktoken_list(request_rec *r,
                                                dav_locktoken_list **ltl)
{
    dav_error *err;
    dav_if_header *if_header;
    dav_if_state_list *if_state;
    dav_locktoken_list *lock_token = NULL;

    *ltl = NULL;

    if ((err = dav_process_if_header(r, &if_header)) != NULL) {
        /* ### add a higher-level description? */
        return err;
    }

    while (if_header != NULL) {
        if_state = if_header->state;        /* Beginning of the if_state linked list */
        while (if_state != NULL)        {
            if (if_state->condition == DAV_IF_COND_NORMAL
                && if_state->type == dav_if_opaquelock) {
                lock_token = apr_pcalloc(r->pool, sizeof(dav_locktoken_list));
                lock_token->locktoken = if_state->locktoken;
                lock_token->next = *ltl;
                *ltl = lock_token;
            }
            if_state = if_state->next;
        }
        if_header = if_header->next;
    }
    if (*ltl == NULL) {
        /* No nodes added */
        return dav_new_error(r->pool, HTTP_BAD_REQUEST, DAV_ERR_IF_ABSENT, 0,
                             "No locktokens were specified in the \"If:\" "
                             "header, so the refresh could not be performed.");
    }

    return NULL;
}

#if 0 /* not needed right now... */

static const char *strip_white(const char *s, apr_pool_t *pool)
{
    apr_size_t idx;

    /* trim leading whitespace */
    while (apr_isspace(*s))     /* assume: return false for '\0' */
        ++s;

    /* trim trailing whitespace */
    idx = strlen(s) - 1;
    if (apr_isspace(s[idx])) {
        char *s2 = apr_pstrdup(pool, s);

        while (apr_isspace(s2[idx]) && idx > 0)
            --idx;
        s2[idx + 1] = '\0';
        return s2;
    }

    return s;
}
#endif

#define DAV_LABEL_HDR "Label"

/* dav_add_vary_header
 *
 * If there were any headers in the request which require a Vary header
 * in the response, add it.
 */
DAV_DECLARE(void) dav_add_vary_header(request_rec *in_req,
                                      request_rec *out_req,
                                      const dav_resource *resource)
{
    const dav_hooks_vsn *vsn_hooks = DAV_GET_HOOKS_VSN(in_req);

    /* ### this is probably all wrong... I think there is a function in
       ### the Apache API to add things to the Vary header. need to check */

    /* Only versioning headers require a Vary response header,
     * so only do this check if there is a versioning provider */
    if (vsn_hooks != NULL) {
        const char *target = apr_table_get(in_req->headers_in, DAV_LABEL_HDR);

        /* If Target-Selector specified, add it to the Vary header */
        if (target != NULL) {
            const char *vary = apr_table_get(out_req->headers_out, "Vary");

            if (vary == NULL)
                vary = DAV_LABEL_HDR;
            else
                vary = apr_pstrcat(out_req->pool, vary, "," DAV_LABEL_HDR,
                                   NULL);

            apr_table_setn(out_req->headers_out, "Vary", vary);
        }
    }
}

/* dav_can_auto_checkout
 *
 * Determine whether auto-checkout is enabled for a resource.
 * r - the request_rec
 * resource - the resource
 * auto_version - the value of the auto_versionable hook for the resource
 * lockdb - pointer to lock database (opened if necessary)
 * auto_checkout - set to 1 if auto-checkout enabled
 */
static dav_error * dav_can_auto_checkout(
    request_rec *r,
    dav_resource *resource,
    dav_auto_version auto_version,
    dav_lockdb **lockdb,
    int *auto_checkout)
{
    dav_error *err;
    dav_lock *lock_list;

    *auto_checkout = 0;

    if (auto_version == DAV_AUTO_VERSION_ALWAYS) {
        *auto_checkout = 1;
    }
    else if (auto_version == DAV_AUTO_VERSION_LOCKED) {
        if (*lockdb == NULL) {
            const dav_hooks_locks *locks_hooks = DAV_GET_HOOKS_LOCKS(r);

            if (locks_hooks == NULL) {
                return dav_new_error(r->pool, HTTP_INTERNAL_SERVER_ERROR, 0, 0,
                                     "Auto-checkout is only enabled for locked resources, "
                                     "but there is no lock provider.");
            }

            if ((err = (*locks_hooks->open_lockdb)(r, 0, 0, lockdb)) != NULL) {
                return dav_push_error(r->pool, HTTP_INTERNAL_SERVER_ERROR, 0,
                                      "Cannot open lock database to determine "
                                      "auto-versioning behavior.",
                                      err);
            }
        }

        if ((err = dav_lock_query(*lockdb, resource, &lock_list)) != NULL) {
            return dav_push_error(r->pool,
                                  HTTP_INTERNAL_SERVER_ERROR, 0,
                                  "The locks could not be queried for "
                                  "determining auto-versioning behavior.",
                                  err);
        }

        if (lock_list != NULL)
            *auto_checkout = 1;
    }

    return NULL;
}

/* see mod_dav.h for docco */
DAV_DECLARE(dav_error *) dav_auto_checkout(
    request_rec *r,
    dav_resource *resource,
    int parent_only,
    dav_auto_version_info *av_info)
{
    const dav_hooks_vsn *vsn_hooks = DAV_GET_HOOKS_VSN(r);
    dav_lockdb *lockdb = NULL;
    dav_error *err = NULL;

    /* Initialize results */
    memset(av_info, 0, sizeof(*av_info));

    /* if no versioning provider, just return */
    if (vsn_hooks == NULL)
        return NULL;

    /* check parent resource if requested or if resource must be created */
    if (!resource->exists || parent_only) {
        dav_resource *parent;

        if ((err = (*resource->hooks->get_parent_resource)(resource,
                                                           &parent)) != NULL)
            goto done;

        if (parent == NULL || !parent->exists) {
            err = dav_new_error(r->pool, HTTP_CONFLICT, 0, 0,
                                apr_psprintf(r->pool,
                                            "Missing one or more intermediate "
                                            "collections. Cannot create resource %s.",
                                            ap_escape_html(r->pool, resource->uri)));
            goto done;
        }

        av_info->parent_resource = parent;

        /* if parent versioned and not checked out, see if it can be */
        if (parent->versioned && !parent->working) {
            int checkout_parent;

            if ((err = dav_can_auto_checkout(r, parent,
                                             (*vsn_hooks->auto_versionable)(parent),
                                             &lockdb, &checkout_parent))
                != NULL) {
                goto done;
            }

            if (!checkout_parent) {
                err = dav_new_error(r->pool, HTTP_CONFLICT, 0, 0,
                                    "<DAV:cannot-modify-checked-in-parent>");
                goto done;
            }

            /* Try to checkout the parent collection.
             * Note that auto-versioning can only be applied to a version selector,
             * so no separate working resource will be created.
             */
            if ((err = (*vsn_hooks->checkout)(parent, 1 /*auto_checkout*/,
                                              0, 0, 0, NULL, NULL))
                != NULL)
            {
                err = dav_push_error(r->pool, HTTP_CONFLICT, 0,
                                     apr_psprintf(r->pool,
                                                 "Unable to auto-checkout parent collection. "
                                                 "Cannot create resource %s.",
                                                 ap_escape_html(r->pool, resource->uri)),
                                     err);
                goto done;
            }

            /* remember that parent was checked out */
            av_info->parent_checkedout = 1;
        }
    }

    /* if only checking parent, we're done */
    if (parent_only)
        goto done;

    /* if creating a new resource, see if it should be version-controlled */
    if (!resource->exists
        && (*vsn_hooks->auto_versionable)(resource) == DAV_AUTO_VERSION_ALWAYS) {

        if ((err = (*vsn_hooks->vsn_control)(resource, NULL)) != NULL) {
            err = dav_push_error(r->pool, HTTP_CONFLICT, 0,
                                 apr_psprintf(r->pool,
                                             "Unable to create versioned resource %s.",
                                             ap_escape_html(r->pool, resource->uri)),
                                 err);
            goto done;
        }

        /* remember that resource was created */
        av_info->resource_versioned = 1;
    }

    /* if resource is versioned, make sure it is checked out */
    if (resource->versioned && !resource->working) {
        int checkout_resource;

        if ((err = dav_can_auto_checkout(r, resource,
                                         (*vsn_hooks->auto_versionable)(resource),
                                         &lockdb, &checkout_resource)) != NULL) {
            goto done;
        }

        if (!checkout_resource) {
            err = dav_new_error(r->pool, HTTP_CONFLICT, 0, 0,
                                "<DAV:cannot-modify-version-controlled-content>");
            goto done;
        }

        /* Auto-versioning can only be applied to version selectors, so
         * no separate working resource will be created. */
        if ((err = (*vsn_hooks->checkout)(resource, 1 /*auto_checkout*/,
                                          0, 0, 0, NULL, NULL))
            != NULL)
        {
            err = dav_push_error(r->pool, HTTP_CONFLICT, 0,
                                 apr_psprintf(r->pool,
                                             "Unable to checkout resource %s.",
                                             ap_escape_html(r->pool, resource->uri)),
                                 err);
            goto done;
        }

        /* remember that resource was checked out */
        av_info->resource_checkedout = 1;
    }

done:

    /* make sure lock database is closed */
    if (lockdb != NULL)
        (*lockdb->hooks->close_lockdb)(lockdb);

    /* if an error occurred, undo any auto-versioning operations already done */
    if (err != NULL) {
        dav_auto_checkin(r, resource, 1 /*undo*/, 0 /*unlock*/, av_info);
        return err;
    }

    return NULL;
}

/* see mod_dav.h for docco */
DAV_DECLARE(dav_error *) dav_auto_checkin(
    request_rec *r,
    dav_resource *resource,
    int undo,
    int unlock,
    dav_auto_version_info *av_info)
{
    const dav_hooks_vsn *vsn_hooks = DAV_GET_HOOKS_VSN(r);
    dav_error *err = NULL;
    dav_auto_version auto_version;

    /* If no versioning provider, this is a no-op */
    if (vsn_hooks == NULL)
        return NULL;

    /* If undoing auto-checkouts, then do uncheckouts */
    if (undo) {
        if (resource != NULL) {
            if (av_info->resource_checkedout) {
                if ((err = (*vsn_hooks->uncheckout)(resource)) != NULL) {
                    return dav_push_error(r->pool, HTTP_INTERNAL_SERVER_ERROR, 0,
                                          apr_psprintf(r->pool,
                                                      "Unable to undo auto-checkout "
                                                      "of resource %s.",
                                                      ap_escape_html(r->pool, resource->uri)),
                                          err);
                }
            }

            if (av_info->resource_versioned) {
                dav_response *response;

                /* ### should we do anything with the response? */
                if ((err = (*resource->hooks->remove_resource)(resource,
                                                               &response)) != NULL) {
                    return dav_push_error(r->pool, HTTP_INTERNAL_SERVER_ERROR, 0,
                                          apr_psprintf(r->pool,
                                                      "Unable to undo auto-version-control "
                                                      "of resource %s.",
                                                      ap_escape_html(r->pool, resource->uri)),
                                          err);
                }
            }
        }

        if (av_info->parent_resource != NULL && av_info->parent_checkedout) {
            if ((err = (*vsn_hooks->uncheckout)(av_info->parent_resource)) != NULL) {
                return dav_push_error(r->pool, HTTP_INTERNAL_SERVER_ERROR, 0,
                                      apr_psprintf(r->pool,
                                                  "Unable to undo auto-checkout "
                                                  "of parent collection %s.",
                                                  ap_escape_html(r->pool, av_info->parent_resource->uri)),
                                      err);
            }
        }

        return NULL;
    }

    /* If the resource was checked out, and auto-checkin is enabled,
     * then check it in.
     */
    if (resource != NULL && resource->working
        && (unlock || av_info->resource_checkedout)) {

        auto_version = (*vsn_hooks->auto_versionable)(resource);

        if (auto_version == DAV_AUTO_VERSION_ALWAYS ||
            (unlock && (auto_version == DAV_AUTO_VERSION_LOCKED))) {

            if ((err = (*vsn_hooks->checkin)(resource,
                                             0 /*keep_checked_out*/, NULL))
                != NULL) {
                return dav_push_error(r->pool, HTTP_INTERNAL_SERVER_ERROR, 0,
                                      apr_psprintf(r->pool,
                                                  "Unable to auto-checkin resource %s.",
                                                  ap_escape_html(r->pool, resource->uri)),
                                      err);
            }
        }
    }

    /* If parent resource was checked out, and auto-checkin is enabled,
     * then check it in.
     */
    if (!unlock
        && av_info->parent_checkedout
        && av_info->parent_resource != NULL
        && av_info->parent_resource->working) {

        auto_version = (*vsn_hooks->auto_versionable)(av_info->parent_resource);

        if (auto_version == DAV_AUTO_VERSION_ALWAYS) {
            if ((err = (*vsn_hooks->checkin)(av_info->parent_resource,
                                             0 /*keep_checked_out*/, NULL))
                != NULL) {
                return dav_push_error(r->pool, HTTP_INTERNAL_SERVER_ERROR, 0,
                                      apr_psprintf(r->pool,
                                                  "Unable to auto-checkin parent collection %s.",
                                                  ap_escape_html(r->pool, av_info->parent_resource->uri)),
                                                  err);
            }
        }
    }

    return NULL;
}
