mod_headers.c

Apache HTTP Server 是一个功能强大的灵活的与HTTP/1.1相兼容的web服务器.这里给出的是Apache HTTP服务器的源码。

/* Copyright 1999-2005 The Apache Software Foundation or its licensors, as
 * applicable.
 *
 * Licensed 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.
 */

/*
 * mod_headers.c: Add/append/remove HTTP response headers
 *     Written by Paul Sutton, [e-mail], 1 Oct 1996
 *
 * The Header directive can be used to add/replace/remove HTTP headers
 * within the response message.  The RequestHeader directive can be used
 * to add/replace/remove HTTP headers before a request message is processed.
 * Valid in both per-server and per-dir configurations.
 *
 * Syntax is:
 *
 *   Header action header value
 *   RequestHeader 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 and RequestHeader directives 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 "apr.h"
#include "apr_lib.h"
#include "apr_strings.h"
#include "apr_buckets.h"

#include "apr_hash.h"
#define APR_WANT_STRFUNC
#include "apr_want.h"

#include "httpd.h"
#include "http_config.h"
#include "http_request.h"
#include "http_log.h"
#include "util_filter.h"
#include "http_protocol.h" /* ap_hook_insert_error_filter */

/* format_tag_hash is initialized during pre-config */
static apr_hash_t *format_tag_hash;

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_echo = 'e'              /* echo headers from request to response */
} hdr_actions;

/*
 * magic cmd->info values
 */
static char hdr_in  = '0';  /* RequestHeader */
static char hdr_out = '1';  /* Header onsuccess */
static char hdr_err = '2';  /* Header always */

/*
 * There is an array of struct format_tag per Header/RequestHeader 
 * config directive
 */
typedef struct {
    const char* (*func)(request_rec *r,char *arg);
    char *arg;
} format_tag;

/*
 * There is one "header_entry" per Header/RequestHeader config directive
 */
typedef struct {
    hdr_actions action;
    char *header;
    apr_array_header_t *ta;   /* Array of format_tag structs */
    regex_t *regex;
    const char *condition_var;
} header_entry;

/* echo_do is used for Header echo to iterate through the request headers*/
typedef struct {
    request_rec *r;
    header_entry *hdr;
} echo_do;

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

module AP_MODULE_DECLARE_DATA headers_module;

/*
 * Tag formatting functions
 */
static const char *constant_item(request_rec *r, char *stuff)
{
    return stuff;
}
static const char *header_request_duration(request_rec *r, char *a)
{
    return apr_psprintf(r->pool, "D=%" APR_TIME_T_FMT, 
                        (apr_time_now() - r->request_time)); 
}
static const char *header_request_time(request_rec *r, char *a)
{
    return apr_psprintf(r->pool, "t=%" APR_TIME_T_FMT, r->request_time);
}
static const char *header_request_env_var(request_rec *r, char *a)
{
    const char *s = apr_table_get(r->subprocess_env,a);

    if (s)
        return s;
    else
        return "(null)";
}
/*
 * Config routines
 */
static void *create_headers_config(apr_pool_t *p, char *dummy)
{
    headers_conf *conf = apr_palloc(p, sizeof(*conf));

    conf->fixup_in = apr_array_make(p, 2, sizeof(header_entry));
    conf->fixup_out = apr_array_make(p, 2, sizeof(header_entry));
    conf->fixup_err = apr_array_make(p, 2, sizeof(header_entry));

    return conf;
}

static void *merge_headers_config(apr_pool_t *p, void *basev, void *overridesv)
{
    headers_conf *newconf = apr_palloc(p, sizeof(*newconf));
    headers_conf *base = basev;
    headers_conf *overrides = overridesv;

    newconf->fixup_in = apr_array_append(p, base->fixup_in, overrides->fixup_in);
    newconf->fixup_out = apr_array_append(p, base->fixup_out, overrides->fixup_out);
    newconf->fixup_err = apr_array_append(p, base->fixup_err, overrides->fixup_err);

    return newconf;
}
 
static char *parse_misc_string(apr_pool_t *p, format_tag *tag, const char **sa)
{
    const char *s;
    char *d;

    tag->func = constant_item;

    s = *sa;
    while (*s && *s != '%') {
        s++;
    }
    /*
     * This might allocate a few chars extra if there's a backslash
     * escape in the format string.
     */
    tag->arg = apr_palloc(p, s - *sa + 1);

    d = tag->arg;
    s = *sa;
    while (*s && *s != '%') {
        if (*s != '\\') {
            *d++ = *s++;
        }
        else {
            s++;
            switch (*s) {
            case '\\':
                *d++ = '\\';
                s++;
                break;
            case 'r':
                *d++ = '\r';
                s++;
                break;
            case 'n':
                *d++ = '\n';
                s++;
                break;
            case 't':	
                *d++ = '\t';
                s++;
                break;
            default:
                /* copy verbatim */
                *d++ = '\\';
                /*
                 * Allow the loop to deal with this *s in the normal
                 * fashion so that it handles end of string etc.
                 * properly.
                 */
                break;
            }
        }
    }
    *d = '\0';

    *sa = s;
    return NULL;
}

static char *parse_format_tag(apr_pool_t *p, format_tag *tag, const char **sa)
{ 
    const char *s = *sa;
    const char * (*tag_handler)(request_rec *,char *);

    /* Handle string literal/conditionals */
    if (*s != '%') {
        return parse_misc_string(p, tag, sa);
    }
    s++; /* skip the % */
    tag->arg = '\0';
    /* grab the argument if there is one */
    if (*s == '{') {
        ++s;
        tag->arg = ap_getword(p,&s,'}');
    }

    tag_handler = (const char * (*)(request_rec *,char *))apr_hash_get(format_tag_hash, s++, 1);

    if (!tag_handler) {
        char dummy[2];
        dummy[0] = s[-1];
        dummy[1] = '\0';
        return apr_pstrcat(p, "Unrecognized Header or RequestHeader directive %",
                           dummy, NULL);
    }
    tag->func = tag_handler;

    *sa = s;
    return NULL;
}

/*
 * A format string consists of white space, text and optional format 
 * tags in any order. E.g., 
 *
 * Header add MyHeader "Free form text %D %t more text"
 *
 * Decompose the format string into its tags. Each tag (struct format_tag)
 * contains a pointer to the function used to format the tag. Then save each 
 * tag in the tag array anchored in the header_entry.
 */
static char *parse_format_string(apr_pool_t *p, header_entry *hdr, const char *s)
{
    char *res;

    /* No string to parse with unset and copy commands */
    if (hdr->action == hdr_unset ||
        hdr->action == hdr_echo) {
        return NULL;
    }

    hdr->ta = apr_array_make(p, 10, sizeof(format_tag));

    while (*s) {
        if ((res = parse_format_tag(p, (format_tag *) apr_array_push(hdr->ta), &s))) {
            return res;
        }
    }
    return NULL;
}