http_protocol.c

    for (i = 0; i < 5; i++) {
        status -= 100;
        if (status < 100) {
            pos = (status + shortcut[i]);
            if (pos < shortcut[i + 1] && status_lines[pos] != NULL) {
                return pos;
            }
            else {
                return LEVEL_500;            /* status unknown (falls in gap) */
            }
        }
    }
    return LEVEL_500;                         /* 600 or above is also illegal */
}

AP_DECLARE(const char *) ap_get_status_line(int status)
{
    return status_lines[ap_index_of_response(status)];
}

/* Build the Allow field-value from the request handler method mask.
 */
static char *make_allow(request_rec *r)
{
    apr_int64_t mask;
    apr_array_header_t *allow = apr_array_make(r->pool, 10, sizeof(char *));
    apr_hash_index_t *hi = apr_hash_first(r->pool, methods_registry);
    /* For TRACE below */
    core_server_config *conf =
        ap_get_core_module_config(r->server->module_config);

    mask = r->allowed_methods->method_mask;

    for (; hi; hi = apr_hash_next(hi)) {
        const void *key;
        void *val;

        apr_hash_this(hi, &key, NULL, &val);
        if ((mask & (AP_METHOD_BIT << *(int *)val)) != 0) {
            APR_ARRAY_PUSH(allow, const char *) = key;
        }
    }

    /* TRACE is tested on a per-server basis */
    if (conf->trace_enable != AP_TRACE_DISABLE)
        *(const char **)apr_array_push(allow) = "TRACE";

    /* ### this is rather annoying. we should enforce registration of
       ### these methods */
    if ((mask & (AP_METHOD_BIT << M_INVALID))
        && (r->allowed_methods->method_list != NULL)
        && (r->allowed_methods->method_list->nelts != 0)) {
        apr_array_cat(allow, r->allowed_methods->method_list);
    }

    return apr_array_pstrcat(r->pool, allow, ',');
}

AP_DECLARE(int) ap_send_http_options(request_rec *r)
{
    if (r->assbackwards) {
        return DECLINED;
    }

    apr_table_setn(r->headers_out, "Allow", make_allow(r));

    /* the request finalization will send an EOS, which will flush all
     * the headers out (including the Allow header)
     */

    return OK;
}

AP_DECLARE(void) ap_set_content_type(request_rec *r, const char *ct)
{
    if (!ct) {
        r->content_type = NULL;
    }
    else if (!r->content_type || strcmp(r->content_type, ct)) {
        r->content_type = ct;
    }
}

AP_DECLARE(void) ap_set_accept_ranges(request_rec *r)
{
    core_dir_config *d = ap_get_core_module_config(r->per_dir_config);
    apr_table_setn(r->headers_out, "Accept-Ranges",
                  (d->max_ranges == AP_MAXRANGES_NORANGES) ? "none"
                                                           : "bytes");
}
static const char *add_optional_notes(request_rec *r,
                                      const char *prefix,
                                      const char *key,
                                      const char *suffix)
{
    const char *notes, *result;

    if ((notes = apr_table_get(r->notes, key)) == NULL) {
        result = apr_pstrcat(r->pool, prefix, suffix, NULL);
    }
    else {
        result = apr_pstrcat(r->pool, prefix, notes, suffix, NULL);
    }

    return result;
}

/* construct and return the default error message for a given
 * HTTP defined error code
 */
static const char *get_canned_error_string(int status,
                                           request_rec *r,
                                           const char *location)
{
    apr_pool_t *p = r->pool;
    const char *error_notes, *h1, *s1;

    switch (status) {
    case HTTP_MOVED_PERMANENTLY:
    case HTTP_MOVED_TEMPORARILY:
    case HTTP_TEMPORARY_REDIRECT:
    case HTTP_PERMANENT_REDIRECT:
        return(apr_pstrcat(p,
                           "<p>The document has moved <a href=\"",
                           ap_escape_html(r->pool, location),
                           "\">here</a>.</p>\n",
                           NULL));
    case HTTP_SEE_OTHER:
        return(apr_pstrcat(p,
                           "<p>The answer to your request is located "
                           "<a href=\"",
                           ap_escape_html(r->pool, location),
                           "\">here</a>.</p>\n",
                           NULL));
    case HTTP_USE_PROXY:
        return(apr_pstrcat(p,
                           "<p>This resource is only accessible "
                           "through the proxy\n",
                           ap_escape_html(r->pool, location),
                           "<br />\nYou will need to configure "
                           "your client to use that proxy.</p>\n",
                           NULL));
    case HTTP_PROXY_AUTHENTICATION_REQUIRED:
    case HTTP_UNAUTHORIZED:
        return("<p>This server could not verify that you\n"
               "are authorized to access the document\n"
               "requested.  Either you supplied the wrong\n"
               "credentials (e.g., bad password), or your\n"
               "browser doesn't understand how to supply\n"
               "the credentials required.</p>\n");
    case HTTP_BAD_REQUEST:
        return(add_optional_notes(r,
                                  "<p>Your browser sent a request that "
                                  "this server could not understand.<br />\n",
                                  "error-notes",
                                  "</p>\n"));
    case HTTP_FORBIDDEN:
        s1 = apr_pstrcat(p,
                         "<p>You don't have permission to access ",
                         ap_escape_html(r->pool, r->uri),
                         "\non this server.<br />\n",
                         NULL);
        return(add_optional_notes(r, s1, "error-notes", "</p>\n"));
    case HTTP_NOT_FOUND:
        return(apr_pstrcat(p,
                           "<p>The requested URL ",
                           ap_escape_html(r->pool, r->uri),
                           " was not found on this server.</p>\n",
                           NULL));
    case HTTP_METHOD_NOT_ALLOWED:
        return(apr_pstrcat(p,
                           "<p>The requested method ",
                           ap_escape_html(r->pool, r->method),
                           " is not allowed for the URL ",
                           ap_escape_html(r->pool, r->uri),
                           ".</p>\n",
                           NULL));
    case HTTP_NOT_ACCEPTABLE:
        s1 = apr_pstrcat(p,
                         "<p>An appropriate representation of the "
                         "requested resource ",
                         ap_escape_html(r->pool, r->uri),
                         " could not be found on this server.</p>\n",
                         NULL);
        return(add_optional_notes(r, s1, "variant-list", ""));
    case HTTP_MULTIPLE_CHOICES:
        return(add_optional_notes(r, "", "variant-list", ""));
    case HTTP_LENGTH_REQUIRED:
        s1 = apr_pstrcat(p,
                         "<p>A request of the requested method ",
                         ap_escape_html(r->pool, r->method),
                         " requires a valid Content-length.<br />\n",
                         NULL);
        return(add_optional_notes(r, s1, "error-notes", "</p>\n"));
    case HTTP_PRECONDITION_FAILED:
        return(apr_pstrcat(p,
                           "<p>The precondition on the request "
                           "for the URL ",
                           ap_escape_html(r->pool, r->uri),
                           " evaluated to false.</p>\n",
                           NULL));
    case HTTP_NOT_IMPLEMENTED:
        s1 = apr_pstrcat(p,
                         "<p>",
                         ap_escape_html(r->pool, r->method), " to ",
                         ap_escape_html(r->pool, r->uri),
                         " not supported.<br />\n",
                         NULL);
        return(add_optional_notes(r, s1, "error-notes", "</p>\n"));
    case HTTP_BAD_GATEWAY:
        s1 = "<p>The proxy server received an invalid" CRLF
            "response from an upstream server.<br />" CRLF;
        return(add_optional_notes(r, s1, "error-notes", "</p>\n"));
    case HTTP_VARIANT_ALSO_VARIES:
        return(apr_pstrcat(p,
                           "<p>A variant for the requested "
                           "resource\n<pre>\n",
                           ap_escape_html(r->pool, r->uri),
                           "\n</pre>\nis itself a negotiable resource. "
                           "This indicates a configuration error.</p>\n",
                           NULL));
    case HTTP_REQUEST_TIME_OUT:
        return("<p>Server timeout waiting for the HTTP request from the client.</p>\n");
    case HTTP_GONE:
        return(apr_pstrcat(p,
                           "<p>The requested resource<br />",
                           ap_escape_html(r->pool, r->uri),
                           "<br />\nis no longer available on this server "
                           "and there is no forwarding address.\n"
                           "Please remove all references to this "
                           "resource.</p>\n",
                           NULL));
    case HTTP_REQUEST_ENTITY_TOO_LARGE:
        return(apr_pstrcat(p,
                           "The requested resource<br />",
                           ap_escape_html(r->pool, r->uri), "<br />\n",
                           "does not allow request data with ",
                           ap_escape_html(r->pool, r->method),
                           " requests, or the amount of data provided in\n"
                           "the request exceeds the capacity limit.\n",
                           NULL));
    case HTTP_REQUEST_URI_TOO_LARGE:
        s1 = "<p>The requested URL's length exceeds the capacity\n"
             "limit for this server.<br />\n";
        return(add_optional_notes(r, s1, "error-notes", "</p>\n"));
    case HTTP_UNSUPPORTED_MEDIA_TYPE:
        return("<p>The supplied request data is not in a format\n"
               "acceptable for processing by this resource.</p>\n");
    case HTTP_RANGE_NOT_SATISFIABLE:
        return("<p>None of the range-specifier values in the Range\n"
               "request-header field overlap the current extent\n"
               "of the selected resource.</p>\n");
    case HTTP_EXPECTATION_FAILED:
        s1 = apr_table_get(r->headers_in, "Expect");
        if (s1)
            s1 = apr_pstrcat(p,
                     "<p>The expectation given in the Expect request-header\n"
                     "field could not be met by this server.\n"
                     "The client sent<pre>\n    Expect: ",
                     ap_escape_html(r->pool, s1), "\n</pre>\n",
                     NULL);
        else
            s1 = "<p>No expectation was seen, the Expect request-header \n"
                 "field was not presented by the client.\n";
        return add_optional_notes(r, s1, "error-notes", "</p>"
                   "<p>Only the 100-continue expectation is supported.</p>\n");
    case HTTP_UNPROCESSABLE_ENTITY:
        return("<p>The server understands the media type of the\n"
               "request entity, but was unable to process the\n"
               "contained instructions.</p>\n");
    case HTTP_LOCKED:
        return("<p>The requested resource is currently locked.\n"
               "The lock must be released or proper identification\n"
               "given before the method can be applied.</p>\n");
    case HTTP_FAILED_DEPENDENCY:
        return("<p>The method could not be performed on the resource\n"
               "because the requested action depended on another\n"
               "action and that other action failed.</p>\n");
    case HTTP_UPGRADE_REQUIRED:
        return("<p>The requested resource can only be retrieved\n"
               "using SSL.  The server is willing to upgrade the current\n"
               "connection to SSL, but your client doesn't support it.\n"
               "Either upgrade your client, or try requesting the page\n"
               "using https://\n");
    case HTTP_PRECONDITION_REQUIRED:
        return("<p>The request is required to be conditional.</p>\n");
    case HTTP_TOO_MANY_REQUESTS:
        return("<p>The user has sent too many requests\n"
               "in a given amount of time.</p>\n");
    case HTTP_REQUEST_HEADER_FIELDS_TOO_LARGE:
        return("<p>The server refused this request because\n"
               "the request header fields are too large.</p>\n");
    case HTTP_INSUFFICIENT_STORAGE:
        return("<p>The method could not be performed on the resource\n"
               "because the server is unable to store the\n"
               "representation needed to successfully complete the\n"
               "request.  There is insufficient free space left in\n"
               "your storage allocation.</p>\n");
    case HTTP_SERVICE_UNAVAILABLE:
        return("<p>The server is temporarily unable to service your\n"
               "request due to maintenance downtime or capacity\n"
               "problems. Please try again later.</p>\n");
    case HTTP_GATEWAY_TIME_OUT:
        return("<p>The gateway did not receive a timely response\n"
               "from the upstream server or application.</p>\n");
    case HTTP_LOOP_DETECTED:
        return("<p>The server terminated an operation because\n"
               "it encountered an infinite loop.</p>\n");
    case HTTP_NOT_EXTENDED:
        return("<p>A mandatory extension policy in the request is not\n"
               "accepted by the server for this resource.</p>\n");
    case HTTP_NETWORK_AUTHENTICATION_REQUIRED:
        return("<p>The client needs to authenticate to gain\n"
               "network access.</p>\n");
    case HTTP_MISDIRECTED_REQUEST:
        return("<p>The client needs a new connection for this\n"
               "request as the requested host name does not match\n"
               "the Server Name Indication (SNI) in use for this\n"
               "connection.</p>\n");
    case HTTP_UNAVAILABLE_FOR_LEGAL_REASONS:
        s1 = apr_pstrcat(p,
                         "<p>Access to ", ap_escape_html(r->pool, r->uri),
                         "\nhas been denied for legal reasons.<br />\n",
                         NULL);
        return(add_optional_notes(r, s1, "error-notes", "</p>\n"));
    default:                    /* HTTP_INTERNAL_SERVER_ERROR */
        /*
         * This comparison to expose error-notes could be modified to
         * use a configuration directive and export based on that
         * directive.  For now "*" is used to designate an error-notes
         * that is totally safe for any user to see (ie lacks paths,
         * database passwords, etc.)
         */
        if (((error_notes = apr_table_get(r->notes,
                                          "error-notes")) != NULL)
            && (h1 = apr_table_get(r->notes, "verbose-error-to")) != NULL
            && (strcmp(h1, "*") == 0)) {
            return(apr_pstrcat(p, error_notes, "<p />\n", NULL));
        }
        else {
            return(apr_pstrcat(p,
                               "<p>The server encountered an internal "
                               "error or\n"
                               "misconfiguration and was unable to complete\n"
                               "your request.</p>\n"
                               "<p>Please contact the server "
                               "administrator at \n ",
                               ap_escape_html(r->pool,
                                              r->server->server_admin),
                               " to inform them of the time this "
                               "error occurred,\n"
                               " and the actions you performed just before "
                               "this error.</p>\n"
                               "<p>More information about this error "
                               "may be available\n"
                               "in the server error log.</p>\n",
                               NULL));
        }
        /*
         * It would be nice to give the user the information they need to
         * fix the problem directly since many users don't have access to
         * the error_log (think University sites) even though they can easily
         * get this error by misconfiguring an htaccess file.  However, the
         * e error notes tend to include the real file pathname in this case,
         * which some people consider to be a breach of privacy.  Until we
         * can figure out a way to remove the pathname, leave this commented.
         *
         * if ((error_notes = apr_table_get(r->notes,
         *                                  "error-notes")) != NULL) {
         *     return(apr_pstrcat(p, error_notes, "<p />\n", NULL);
         * }
         * else {
         *     return "";
         * }
         */
    }
}

/* We should have named this send_canned_response, since it is used for any
 * response that can be generated by the server from the request record.
 * This includes all 204 (no content), 3xx (redirect), 4xx (client error),
 * and 5xx (server error) messages that have not been redirected to another
 * handler via the ErrorDocument feature.
 */
AP_DECLARE(void) ap_send_error_response(request_rec *r, int recursive_error)
{
    int status = r->status;
    int idx = ap_index_of_response(status);
    char *custom_response;
    const char *location = apr_table_get(r->headers_out, "Location");

    /* At this point, we are starting the response over, so we have to reset
     * this value.
     */
    r->eos_sent = 0;

    /* and we need to get rid of any RESOURCE filters that might be lurking
     * around, thinking they are in the middle of the original request
     */

    r->output_filters = r->proto_output_filters;

    ap_run_insert_error_filter(r);

    /*
     * It's possible that the Location field might be in r->err_headers_out
     * instead of r->headers_out; use the latter if possible, else the
     * former.
     */
    if (location == NULL) {
        location = apr_table_get(r->err_headers_out, "Location");
    }
    /* We need to special-case the handling of 204 and 304 responses,
     * since they have specific HTTP requirements and do not include a
     * message body.  Note that being assbackwards here is not an option.
     */
    if (status == HTTP_NOT_MODIFIED) {
        ap_finalize_request_protocol(r);
        return;
    }

    if (status == HTTP_NO_CONTENT) {
        ap_finalize_request_protocol(r);
        return;
    }

    if (!r->assbackwards) {
        apr_table_t *tmp = r->headers_out;

        /* For all HTTP/1.x responses for which we generate the message,
         * we need to avoid inheriting the "normal status" header fields
         * that may have been set by the request handler before the
         * error or redirect, except for Location on external redirects.
         */
        r->headers_out = r->err_headers_out;
        r->err_headers_out = tmp;
        apr_table_clear(r->err_headers_out);

        if (ap_is_HTTP_REDIRECT(status) || (status == HTTP_CREATED)) {
            if ((location != NULL) && *location) {
                apr_table_setn(r->headers_out, "Location", location);
            }
            else {
                location = "";   /* avoids coredump when printing, below */
            }
        }

        r->content_languages = NULL;
        r->content_encoding = NULL;
        r->clength = 0;

        if (apr_table_get(r->subprocess_env,
                          "suppress-error-charset") != NULL) {
            core_request_config *request_conf =
                        ap_get_core_module_config(r->request_config);
            request_conf->suppress_charset = 1; /* avoid adding default
                                                 * charset later
                                                 */
            ap_set_content_type(r, "text/html");
        }
        else {
            ap_set_content_type(r, "text/html; charset=iso-8859-1");
        }

        if ((status == HTTP_METHOD_NOT_ALLOWED)
            || (status == HTTP_NOT_IMPLEMENTED)) {
            apr_table_setn(r->headers_out, "Allow", make_allow(r));
        }

        if (r->header_only) {
            ap_finalize_request_protocol(r);
            return;
        }
    }

    if ((custom_response = ap_response_code_string(r, idx))) {
        /*
         * We have a custom response output. This should only be
         * a text-string to write back. But if the ErrorDocument
         * was a local redirect and the requested resource failed
         * for any reason, the custom_response will still hold the
         * redirect URL. We don't really want to output this URL
         * as a text message, so first check the custom response
         * string to ensure that it is a text-string (using the
         * same test used in ap_die(), i.e. does it start with a ").
         *
         * If it's not a text string, we've got a recursive error or
         * an external redirect.  If it's a recursive error, ap_die passes
         * us the second error code so we can write both, and has already
         * backed up to the original error.  If it's an external redirect,
         * it hasn't happened yet; we may never know if it fails.
         */
        if (custom_response[0] == '\"') {
            ap_rputs(custom_response + 1, r);
            ap_finalize_request_protocol(r);
            return;
        }
    }
    {
        const char *title = status_lines[idx];
        const char *h1;

        /* Accept a status_line set by a module, but only if it begins
         * with the correct 3 digit status code
         */
        if (r->status_line) {
            char *end;
            int len = strlen(r->status_line);
            if (len >= 3
                && apr_strtoi64(r->status_line, &end, 10) == r->status
                && (end - 3) == r->status_line
                && (len < 4 || apr_isspace(r->status_line[3]))
                && (len < 5 || apr_isalnum(r->status_line[4]))) {
                /* Since we passed the above check, we know that length three
                 * is equivalent to only a 3 digit numeric http status.
                 * RFC2616 mandates a trailing space, let's add it.
                 * If we have an empty reason phrase, we also add "Unknown Reason".
                 */
                if (len == 3) {
                    r->status_line = apr_pstrcat(r->pool, r->status_line, " Unknown Reason", NULL);
                } else if (len == 4) {
                    r->status_line = apr_pstrcat(r->pool, r->status_line, "Unknown Reason", NULL);
                }
                title = r->status_line;
            }
        }

        /* folks decided they didn't want the error code in the H1 text */
        h1 = &title[4];

        /* can't count on a charset filter being in place here,
         * so do ebcdic->ascii translation explicitly (if needed)
         */

        ap_rvputs_proto_in_ascii(r,
                  DOCTYPE_HTML_2_0
                  "<html><head>\n<title>", title,
                  "</title>\n</head><body>\n<h1>", h1, "</h1>\n",
                  NULL);

        ap_rvputs_proto_in_ascii(r,
                                 get_canned_error_string(status, r, location),
                                 NULL);

        if (recursive_error) {
            ap_rvputs_proto_in_ascii(r, "<p>Additionally, a ",
                      status_lines[ap_index_of_response(recursive_error)],
                      "\nerror was encountered while trying to use an "
                      "ErrorDocument to handle the request.</p>\n", NULL);
        }
        ap_rvputs_proto_in_ascii(r, ap_psignature("<hr>\n", r), NULL);
        ap_rvputs_proto_in_ascii(r, "</body></html>\n", NULL);
    }
    ap_finalize_request_protocol(r);
}

/*
 * Create a new method list with the specified number of preallocated
 * extension slots.
 */
AP_DECLARE(ap_method_list_t *) ap_make_method_list(apr_pool_t *p, int nelts)
{
    ap_method_list_t *ml;

    ml = (ap_method_list_t *) apr_palloc(p, sizeof(ap_method_list_t));
    ml->method_mask = 0;
    ml->method_list = apr_array_make(p, nelts, sizeof(char *));
    return ml;
}

/*
 * Make a copy of a method list (primarily for subrequests that may
 * subsequently change it; don't want them changing the parent's, too!).
 */
AP_DECLARE(void) ap_copy_method_list(ap_method_list_t *dest,
                                     ap_method_list_t *src)
{
    int i;
    char **imethods;
    char **omethods;

    dest->method_mask = src->method_mask;
    imethods = (char **) src->method_list->elts;
    for (i = 0; i < src->method_list->nelts; ++i) {
        omethods = (char **) apr_array_push(dest->method_list);
        *omethods = apr_pstrdup(dest->method_list->pool, imethods[i]);
    }
}

/*
 * Return true if the specified HTTP method is in the provided
 * method list.
 */
AP_DECLARE(int) ap_method_in_list(ap_method_list_t *l, const char *method)
{
    int methnum;

    /*
     * If it's one of our known methods, use the shortcut and check the
     * bitmask.
     */
    methnum = ap_method_number_of(method);
    if (methnum != M_INVALID) {
        return !!(l->method_mask & (AP_METHOD_BIT << methnum));
    }
    /*
     * Otherwise, see if the method name is in the array of string names.
     */
    if ((l->method_list == NULL) || (l->method_list->nelts == 0)) {
        return 0;
    }

    return ap_array_str_contains(l->method_list, method);
}

/*
 * Add the specified method to a method list (if it isn't already there).
 */
AP_DECLARE(void) ap_method_list_add(ap_method_list_t *l, const char *method)
{
    int methnum;
    const char **xmethod;

    /*
     * If it's one of our known methods, use the shortcut and use the
     * bitmask.
     */
    methnum = ap_method_number_of(method);
    if (methnum != M_INVALID) {
        l->method_mask |= (AP_METHOD_BIT << methnum);
        return;
    }
    /*
     * Otherwise, see if the method name is in the array of string names.
     */
    if (ap_array_str_contains(l->method_list, method)) {
        return;
    }

    xmethod = (const char **) apr_array_push(l->method_list);
    *xmethod = method;
}

/*
 * Remove the specified method from a method list.
 */
AP_DECLARE(void) ap_method_list_remove(ap_method_list_t *l,
                                       const char *method)
{
    int methnum;
    char **methods;

    /*
     * If it's a known methods, either builtin or registered
     * by a module, use the bitmask.
     */
    methnum = ap_method_number_of(method);
    if (methnum != M_INVALID) {
        l->method_mask &= ~(AP_METHOD_BIT << methnum);
        return;
    }
    /*
     * Otherwise, see if the method name is in the array of string names.
     */
    if (l->method_list->nelts != 0) {
        int i, j, k;
        methods = (char **)l->method_list->elts;
        for (i = 0; i < l->method_list->nelts; ) {
            if (strcmp(method, methods[i]) == 0) {
                for (j = i, k = i + 1; k < l->method_list->nelts; ++j, ++k) {
                    methods[j] = methods[k];
                }
                --l->method_list->nelts;
            }
            else {
                ++i;
            }
        }
    }
}

/*
 * Reset a method list to be completely empty.
 */
AP_DECLARE(void) ap_clear_method_list(ap_method_list_t *l)
{
    l->method_mask = 0;
    l->method_list->nelts = 0;
}