mod_headers.c

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/*
 * mod_headers.c: Add/append/remove HTTP response headers
 *     Written by Paul Sutton, [e-mail], 1 Oct 1996
 *
 * New directive, Header, can be used to add/replace/remove HTTP headers.
 * Valid in both per-server and per-dir configurations.
 *
 * Syntax is:
 *
 *   Header action header value
 *
 * Where action is one of:
 *     set    - set this header, replacing any old value
 *     add    - add this header, possible resulting in two or more
 *              headers with the same name
 *     append - append this text onto any existing header of this same
 *     unset  - remove this header
 *
 * Where action is unset, the third argument (value) should not be given.
 * The header name can include the colon, or not.
 *
 * The Header directive can only be used where allowed by the FileInfo 
 * override.
 *
 * When the request is processed, the header directives are processed in
 * this order: firstly, the main server, then the virtual server handling
 * this request (if any), then any <Directory> sections (working downwards 
 * from the root dir), then an <Location> sections (working down from 
 * shortest URL component), the any <File> sections. This order is
 * important if any 'set' or 'unset' actions are used. For example,
 * the following two directives have different effect if applied in
 * the reverse order:
 *
 *   Header append Author "John P. Doe"
 *   Header unset Author
 *
 * Examples:
 *
 *  To set the "Author" header, use
 *     Header add Author "John P. Doe"
 *
 *  To remove a header:
 *     Header unset Author
 *
 */

#include "httpd.h"
#include "http_config.h"

typedef enum {
    hdr_add = 'a',              /* add header (could mean multiple hdrs) */
    hdr_set = 's',              /* set (replace old value) */
    hdr_append = 'm',           /* append (merge into any old value) */
    hdr_unset = 'u'             /* unset header */
} hdr_actions;

typedef struct {
    hdr_actions action;
    char *header;
    char *value;
} header_entry;

/*
 * headers_conf is our per-module configuration. This is used as both
 * a per-dir and per-server config
 */
typedef struct {
    array_header *headers;
} headers_conf;

module MODULE_VAR_EXPORT headers_module;

static void *create_headers_config(pool *p, server_rec *s)
{
    headers_conf *a =
    (headers_conf *) ap_pcalloc(p, sizeof(headers_conf));

    a->headers = ap_make_array(p, 2, sizeof(header_entry));
    return a;
}

static void *create_headers_dir_config(pool *p, char *d)
{
    return (headers_conf *) create_headers_config(p, NULL);
}

static void *merge_headers_config(pool *p, void *basev, void *overridesv)
{
    headers_conf *a =
    (headers_conf *) ap_pcalloc(p, sizeof(headers_conf));
    headers_conf *base = (headers_conf *) basev, *overrides = (headers_conf *) overridesv;

    a->headers = ap_append_arrays(p, base->headers, overrides->headers);

    return a;
}


static const char *header_cmd(cmd_parms *cmd, headers_conf * dirconf, char *action, char *hdr, char *value)
{
    header_entry *new;
    server_rec *s = cmd->server;
    headers_conf *serverconf =
    (headers_conf *) ap_get_module_config(s->module_config, &headers_module);
    char *colon;

    if (cmd->path) {
        new = (header_entry *) ap_push_array(dirconf->headers);
    }
    else {
        new = (header_entry *) ap_push_array(serverconf->headers);
    }

    if (!strcasecmp(action, "set"))
        new->action = hdr_set;
    else if (!strcasecmp(action, "add"))
        new->action = hdr_add;
    else if (!strcasecmp(action, "append"))
        new->action = hdr_append;
    else if (!strcasecmp(action, "unset"))
        new->action = hdr_unset;
    else
        return "first argument must be add, set, append or unset.";

    if (new->action == hdr_unset) {
        if (value)
            return "Header unset takes two arguments";
    }
    else if (!value)
        return "Header requires three arguments";

    if ((colon = strchr(hdr, ':')))
        *colon = '\0';

    new->header = hdr;
    new->value = value;

    return NULL;
}

static const command_rec headers_cmds[] =
{
    {"Header", header_cmd, NULL, OR_FILEINFO, TAKE23,
     "an action, header and value"},
    {NULL}
};

static void do_headers_fixup(request_rec *r, array_header *headers)
{
    int i;

    for (i = 0; i < headers->nelts; ++i) {
        header_entry *hdr = &((header_entry *) (headers->elts))[i];
        switch (hdr->action) {
        case hdr_add:
            ap_table_addn(r->headers_out, hdr->header, hdr->value);
            break;
        case hdr_append:
            ap_table_mergen(r->headers_out, hdr->header, hdr->value);
            break;
        case hdr_set:
            ap_table_setn(r->headers_out, hdr->header, hdr->value);
            break;
        case hdr_unset:
            ap_table_unset(r->headers_out, hdr->header);
            break;
        }
    }

}

static int fixup_headers(request_rec *r)
{
    void *sconf = r->server->module_config;
    headers_conf *serverconf =
    (headers_conf *) ap_get_module_config(sconf, &headers_module);
    void *dconf = r->per_dir_config;
    headers_conf *dirconf =
    (headers_conf *) ap_get_module_config(dconf, &headers_module);

    do_headers_fixup(r, serverconf->headers);
    do_headers_fixup(r, dirconf->headers);

    return DECLINED;
}

module MODULE_VAR_EXPORT headers_module =
{
    STANDARD_MODULE_STUFF,
    NULL,                       /* initializer */
    create_headers_dir_config,  /* dir config creater */
    merge_headers_config,       /* dir merger --- default is to override */
    create_headers_config,      /* server config */
    merge_headers_config,       /* merge server configs */
    headers_cmds,               /* command table */
    NULL,                       /* handlers */
    NULL,                       /* filename translation */
    NULL,                       /* check_user_id */
    NULL,                       /* check auth */
    NULL,                       /* check access */
    NULL,                       /* type_checker */
    fixup_headers,              /* fixups */
    NULL,                       /* logger */
    NULL,                       /* header parser */
    NULL,                       /* child_init */
    NULL,                       /* child_exit */
    NULL                        /* post read-request */
};