view src/http/ngx_http_header_filter_module.c @ 8122:106328a70f4e

Added warning about redefinition of listen socket protocol options. The "listen" directive in the http module can be used multiple times in different server blocks. Originally, it was supposed to be specified once with various socket options, and without any parameters in virtual server blocks. For example: server { listen 80 backlog=1024; server_name foo; ... } server { listen 80; server_name bar; ... } server { listen 80; server_name bazz; ... } The address part of the syntax ("address[:port]" / "port" / "unix:path") uniquely identifies the listening socket, and therefore is enough for name-based virtual servers (to let nginx know that the virtual server accepts requests on the listening socket in question). To ensure that listening options do not conflict between virtual servers, they were allowed only once. For example, the following configuration will be rejected ("duplicate listen options for 0.0.0.0:80 in ..."): server { listen 80 backlog=1024; server_name foo; ... } server { listen 80 backlog=512; server_name bar; ... } At some point it was, however, noticed, that it is sometimes convenient to repeat some options for clarity. In nginx 0.8.51 the "ssl" parameter was allowed to be specified multiple times, e.g.: server { listen 443 ssl backlog=1024; server_name foo; ... } server { listen 443 ssl; server_name bar; ... } server { listen 443 ssl; server_name bazz; ... } This approach makes configuration more readable, since SSL sockets are immediately visible in the configuration. If this is not needed, just the address can still be used. Later, additional protocol-specific options similar to "ssl" were introduced, notably "http2" and "proxy_protocol". With these options, one can write: server { listen 443 ssl backlog=1024; server_name foo; ... } server { listen 443 http2; server_name bar; ... } server { listen 443 proxy_protocol; server_name bazz; ... } The resulting socket will use ssl, http2, and proxy_protocol, but this is not really obvious from the configuration. To emphasize such misleading configurations are discouraged, nginx now warns as long as the "listen" directive is used with options different from the options previously used if this is potentially confusing. In particular, the following configurations are allowed: server { listen 8401 ssl backlog=1024; server_name foo; } server { listen 8401 ssl; server_name bar; } server { listen 8401 ssl; server_name bazz; } server { listen 8402 ssl http2 backlog=1024; server_name foo; } server { listen 8402 ssl; server_name bar; } server { listen 8402 ssl; server_name bazz; } server { listen 8403 ssl; server_name bar; } server { listen 8403 ssl; server_name bazz; } server { listen 8403 ssl http2; server_name foo; } server { listen 8404 ssl http2 backlog=1024; server_name foo; } server { listen 8404 http2; server_name bar; } server { listen 8404 http2; server_name bazz; } server { listen 8405 ssl http2 backlog=1024; server_name foo; } server { listen 8405 ssl http2; server_name bar; } server { listen 8405 ssl http2; server_name bazz; } server { listen 8406 ssl; server_name foo; } server { listen 8406; server_name bar; } server { listen 8406; server_name bazz; } And the following configurations will generate warnings: server { listen 8501 ssl http2 backlog=1024; server_name foo; } server { listen 8501 http2; server_name bar; } server { listen 8501 ssl; server_name bazz; } server { listen 8502 backlog=1024; server_name foo; } server { listen 8502 ssl; server_name bar; } server { listen 8503 ssl; server_name foo; } server { listen 8503 http2; server_name bar; } server { listen 8504 ssl; server_name foo; } server { listen 8504 http2; server_name bar; } server { listen 8504 proxy_protocol; server_name bazz; } server { listen 8505 ssl http2 proxy_protocol; server_name foo; } server { listen 8505 ssl http2; server_name bar; } server { listen 8505 ssl; server_name bazz; } server { listen 8506 ssl http2; server_name foo; } server { listen 8506 ssl; server_name bar; } server { listen 8506; server_name bazz; } server { listen 8507 ssl; server_name bar; } server { listen 8507; server_name bazz; } server { listen 8507 ssl http2; server_name foo; } server { listen 8508 ssl; server_name bar; } server { listen 8508; server_name bazz; } server { listen 8508 ssl backlog=1024; server_name foo; } server { listen 8509; server_name bazz; } server { listen 8509 ssl; server_name bar; } server { listen 8509 ssl backlog=1024; server_name foo; } The basic idea is that at most two sets of protocol options are allowed: the main one (with socket options, if any), and a shorter one, with options being a subset of the main options, repeated for clarity. As long as the shorter set of protocol options is used, all listen directives except the main one should use it.
author Maxim Dounin <mdounin@mdounin.ru>
date Sat, 28 Jan 2023 01:29:45 +0300
parents 96ae8e57b3dd
children 7c2adf237091
line wrap: on
line source


/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>
#include <nginx.h>


static ngx_int_t ngx_http_header_filter_init(ngx_conf_t *cf);
static ngx_int_t ngx_http_header_filter(ngx_http_request_t *r);


static ngx_http_module_t  ngx_http_header_filter_module_ctx = {
    NULL,                                  /* preconfiguration */
    ngx_http_header_filter_init,           /* postconfiguration */

    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

    NULL,                                  /* create server configuration */
    NULL,                                  /* merge server configuration */

    NULL,                                  /* create location configuration */
    NULL,                                  /* merge location configuration */
};


ngx_module_t  ngx_http_header_filter_module = {
    NGX_MODULE_V1,
    &ngx_http_header_filter_module_ctx,    /* module context */
    NULL,                                  /* module directives */
    NGX_HTTP_MODULE,                       /* module type */
    NULL,                                  /* init master */
    NULL,                                  /* init module */
    NULL,                                  /* init process */
    NULL,                                  /* init thread */
    NULL,                                  /* exit thread */
    NULL,                                  /* exit process */
    NULL,                                  /* exit master */
    NGX_MODULE_V1_PADDING
};


static u_char ngx_http_server_string[] = "Server: nginx" CRLF;
static u_char ngx_http_server_full_string[] = "Server: " NGINX_VER CRLF;
static u_char ngx_http_server_build_string[] = "Server: " NGINX_VER_BUILD CRLF;


static ngx_str_t ngx_http_status_lines[] = {

    ngx_string("200 OK"),
    ngx_string("201 Created"),
    ngx_string("202 Accepted"),
    ngx_null_string,  /* "203 Non-Authoritative Information" */
    ngx_string("204 No Content"),
    ngx_null_string,  /* "205 Reset Content" */
    ngx_string("206 Partial Content"),

    /* ngx_null_string, */  /* "207 Multi-Status" */

#define NGX_HTTP_LAST_2XX  207
#define NGX_HTTP_OFF_3XX   (NGX_HTTP_LAST_2XX - 200)

    /* ngx_null_string, */  /* "300 Multiple Choices" */

    ngx_string("301 Moved Permanently"),
    ngx_string("302 Moved Temporarily"),
    ngx_string("303 See Other"),
    ngx_string("304 Not Modified"),
    ngx_null_string,  /* "305 Use Proxy" */
    ngx_null_string,  /* "306 unused" */
    ngx_string("307 Temporary Redirect"),
    ngx_string("308 Permanent Redirect"),

#define NGX_HTTP_LAST_3XX  309
#define NGX_HTTP_OFF_4XX   (NGX_HTTP_LAST_3XX - 301 + NGX_HTTP_OFF_3XX)

    ngx_string("400 Bad Request"),
    ngx_string("401 Unauthorized"),
    ngx_string("402 Payment Required"),
    ngx_string("403 Forbidden"),
    ngx_string("404 Not Found"),
    ngx_string("405 Not Allowed"),
    ngx_string("406 Not Acceptable"),
    ngx_null_string,  /* "407 Proxy Authentication Required" */
    ngx_string("408 Request Time-out"),
    ngx_string("409 Conflict"),
    ngx_string("410 Gone"),
    ngx_string("411 Length Required"),
    ngx_string("412 Precondition Failed"),
    ngx_string("413 Request Entity Too Large"),
    ngx_string("414 Request-URI Too Large"),
    ngx_string("415 Unsupported Media Type"),
    ngx_string("416 Requested Range Not Satisfiable"),
    ngx_null_string,  /* "417 Expectation Failed" */
    ngx_null_string,  /* "418 unused" */
    ngx_null_string,  /* "419 unused" */
    ngx_null_string,  /* "420 unused" */
    ngx_string("421 Misdirected Request"),
    ngx_null_string,  /* "422 Unprocessable Entity" */
    ngx_null_string,  /* "423 Locked" */
    ngx_null_string,  /* "424 Failed Dependency" */
    ngx_null_string,  /* "425 unused" */
    ngx_null_string,  /* "426 Upgrade Required" */
    ngx_null_string,  /* "427 unused" */
    ngx_null_string,  /* "428 Precondition Required" */
    ngx_string("429 Too Many Requests"),

#define NGX_HTTP_LAST_4XX  430
#define NGX_HTTP_OFF_5XX   (NGX_HTTP_LAST_4XX - 400 + NGX_HTTP_OFF_4XX)

    ngx_string("500 Internal Server Error"),
    ngx_string("501 Not Implemented"),
    ngx_string("502 Bad Gateway"),
    ngx_string("503 Service Temporarily Unavailable"),
    ngx_string("504 Gateway Time-out"),
    ngx_string("505 HTTP Version Not Supported"),
    ngx_null_string,        /* "506 Variant Also Negotiates" */
    ngx_string("507 Insufficient Storage"),

    /* ngx_null_string, */  /* "508 unused" */
    /* ngx_null_string, */  /* "509 unused" */
    /* ngx_null_string, */  /* "510 Not Extended" */

#define NGX_HTTP_LAST_5XX  508

};


ngx_http_header_out_t  ngx_http_headers_out[] = {
    { ngx_string("Server"), offsetof(ngx_http_headers_out_t, server) },
    { ngx_string("Date"), offsetof(ngx_http_headers_out_t, date) },
    { ngx_string("Content-Length"),
                 offsetof(ngx_http_headers_out_t, content_length) },
    { ngx_string("Content-Encoding"),
                 offsetof(ngx_http_headers_out_t, content_encoding) },
    { ngx_string("Location"), offsetof(ngx_http_headers_out_t, location) },
    { ngx_string("Last-Modified"),
                 offsetof(ngx_http_headers_out_t, last_modified) },
    { ngx_string("Accept-Ranges"),
                 offsetof(ngx_http_headers_out_t, accept_ranges) },
    { ngx_string("Expires"), offsetof(ngx_http_headers_out_t, expires) },
    { ngx_string("Cache-Control"),
                 offsetof(ngx_http_headers_out_t, cache_control) },
    { ngx_string("ETag"), offsetof(ngx_http_headers_out_t, etag) },

    { ngx_null_string, 0 }
};


static ngx_int_t
ngx_http_header_filter(ngx_http_request_t *r)
{
    u_char                    *p;
    size_t                     len;
    ngx_str_t                  host, *status_line;
    ngx_buf_t                 *b;
    ngx_uint_t                 status, i, port;
    ngx_chain_t                out;
    ngx_list_part_t           *part;
    ngx_table_elt_t           *header;
    ngx_connection_t          *c;
    ngx_http_core_loc_conf_t  *clcf;
    ngx_http_core_srv_conf_t  *cscf;
    u_char                     addr[NGX_SOCKADDR_STRLEN];

    if (r->header_sent) {
        return NGX_OK;
    }

    r->header_sent = 1;

    if (r != r->main) {
        return NGX_OK;
    }

    if (r->http_version < NGX_HTTP_VERSION_10) {
        return NGX_OK;
    }

    if (r->method == NGX_HTTP_HEAD) {
        r->header_only = 1;
    }

    if (r->headers_out.last_modified_time != -1) {
        if (r->headers_out.status != NGX_HTTP_OK
            && r->headers_out.status != NGX_HTTP_PARTIAL_CONTENT
            && r->headers_out.status != NGX_HTTP_NOT_MODIFIED)
        {
            r->headers_out.last_modified_time = -1;
            r->headers_out.last_modified = NULL;
        }
    }

    if (r->keepalive && (ngx_terminate || ngx_exiting)) {
        r->keepalive = 0;
    }

    len = sizeof("HTTP/1.x ") - 1 + sizeof(CRLF) - 1
          /* the end of the header */
          + sizeof(CRLF) - 1;

    /* status line */

    if (r->headers_out.status_line.len) {
        len += r->headers_out.status_line.len;
        status_line = &r->headers_out.status_line;
#if (NGX_SUPPRESS_WARN)
        status = 0;
#endif

    } else {

        status = r->headers_out.status;

        if (status >= NGX_HTTP_OK
            && status < NGX_HTTP_LAST_2XX)
        {
            /* 2XX */

            if (status == NGX_HTTP_NO_CONTENT) {
                r->header_only = 1;
                ngx_str_null(&r->headers_out.content_type);
                r->headers_out.last_modified_time = -1;
                r->headers_out.last_modified = NULL;
                r->headers_out.content_length = NULL;
                r->headers_out.content_length_n = -1;
            }

            status -= NGX_HTTP_OK;
            status_line = &ngx_http_status_lines[status];
            len += ngx_http_status_lines[status].len;

        } else if (status >= NGX_HTTP_MOVED_PERMANENTLY
                   && status < NGX_HTTP_LAST_3XX)
        {
            /* 3XX */

            if (status == NGX_HTTP_NOT_MODIFIED) {
                r->header_only = 1;
            }

            status = status - NGX_HTTP_MOVED_PERMANENTLY + NGX_HTTP_OFF_3XX;
            status_line = &ngx_http_status_lines[status];
            len += ngx_http_status_lines[status].len;

        } else if (status >= NGX_HTTP_BAD_REQUEST
                   && status < NGX_HTTP_LAST_4XX)
        {
            /* 4XX */
            status = status - NGX_HTTP_BAD_REQUEST
                            + NGX_HTTP_OFF_4XX;

            status_line = &ngx_http_status_lines[status];
            len += ngx_http_status_lines[status].len;

        } else if (status >= NGX_HTTP_INTERNAL_SERVER_ERROR
                   && status < NGX_HTTP_LAST_5XX)
        {
            /* 5XX */
            status = status - NGX_HTTP_INTERNAL_SERVER_ERROR
                            + NGX_HTTP_OFF_5XX;

            status_line = &ngx_http_status_lines[status];
            len += ngx_http_status_lines[status].len;

        } else {
            len += NGX_INT_T_LEN + 1 /* SP */;
            status_line = NULL;
        }

        if (status_line && status_line->len == 0) {
            status = r->headers_out.status;
            len += NGX_INT_T_LEN + 1 /* SP */;
            status_line = NULL;
        }
    }

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    if (r->headers_out.server == NULL) {
        if (clcf->server_tokens == NGX_HTTP_SERVER_TOKENS_ON) {
            len += sizeof(ngx_http_server_full_string) - 1;

        } else if (clcf->server_tokens == NGX_HTTP_SERVER_TOKENS_BUILD) {
            len += sizeof(ngx_http_server_build_string) - 1;

        } else {
            len += sizeof(ngx_http_server_string) - 1;
        }
    }

    if (r->headers_out.date == NULL) {
        len += sizeof("Date: Mon, 28 Sep 1970 06:00:00 GMT" CRLF) - 1;
    }

    if (r->headers_out.content_type.len) {
        len += sizeof("Content-Type: ") - 1
               + r->headers_out.content_type.len + 2;

        if (r->headers_out.content_type_len == r->headers_out.content_type.len
            && r->headers_out.charset.len)
        {
            len += sizeof("; charset=") - 1 + r->headers_out.charset.len;
        }
    }

    if (r->headers_out.content_length == NULL
        && r->headers_out.content_length_n >= 0)
    {
        len += sizeof("Content-Length: ") - 1 + NGX_OFF_T_LEN + 2;
    }

    if (r->headers_out.last_modified == NULL
        && r->headers_out.last_modified_time != -1)
    {
        len += sizeof("Last-Modified: Mon, 28 Sep 1970 06:00:00 GMT" CRLF) - 1;
    }

    c = r->connection;

    if (r->headers_out.location
        && r->headers_out.location->value.len
        && r->headers_out.location->value.data[0] == '/'
        && clcf->absolute_redirect)
    {
        r->headers_out.location->hash = 0;

        if (clcf->server_name_in_redirect) {
            cscf = ngx_http_get_module_srv_conf(r, ngx_http_core_module);
            host = cscf->server_name;

        } else if (r->headers_in.server.len) {
            host = r->headers_in.server;

        } else {
            host.len = NGX_SOCKADDR_STRLEN;
            host.data = addr;

            if (ngx_connection_local_sockaddr(c, &host, 0) != NGX_OK) {
                return NGX_ERROR;
            }
        }

        port = ngx_inet_get_port(c->local_sockaddr);

        len += sizeof("Location: https://") - 1
               + host.len
               + r->headers_out.location->value.len + 2;

        if (clcf->port_in_redirect) {

#if (NGX_HTTP_SSL)
            if (c->ssl)
                port = (port == 443) ? 0 : port;
            else
#endif
                port = (port == 80) ? 0 : port;

        } else {
            port = 0;
        }

        if (port) {
            len += sizeof(":65535") - 1;
        }

    } else {
        ngx_str_null(&host);
        port = 0;
    }

    if (r->chunked) {
        len += sizeof("Transfer-Encoding: chunked" CRLF) - 1;
    }

    if (r->headers_out.status == NGX_HTTP_SWITCHING_PROTOCOLS) {
        len += sizeof("Connection: upgrade" CRLF) - 1;

    } else if (r->keepalive) {
        len += sizeof("Connection: keep-alive" CRLF) - 1;

        /*
         * MSIE and Opera ignore the "Keep-Alive: timeout=<N>" header.
         * MSIE keeps the connection alive for about 60-65 seconds.
         * Opera keeps the connection alive very long.
         * Mozilla keeps the connection alive for N plus about 1-10 seconds.
         * Konqueror keeps the connection alive for about N seconds.
         */

        if (clcf->keepalive_header) {
            len += sizeof("Keep-Alive: timeout=") - 1 + NGX_TIME_T_LEN + 2;
        }

    } else {
        len += sizeof("Connection: close" CRLF) - 1;
    }

#if (NGX_HTTP_GZIP)
    if (r->gzip_vary) {
        if (clcf->gzip_vary) {
            len += sizeof("Vary: Accept-Encoding" CRLF) - 1;

        } else {
            r->gzip_vary = 0;
        }
    }
#endif

    part = &r->headers_out.headers.part;
    header = part->elts;

    for (i = 0; /* void */; i++) {

        if (i >= part->nelts) {
            if (part->next == NULL) {
                break;
            }

            part = part->next;
            header = part->elts;
            i = 0;
        }

        if (header[i].hash == 0) {
            continue;
        }

        len += header[i].key.len + sizeof(": ") - 1 + header[i].value.len
               + sizeof(CRLF) - 1;
    }

    b = ngx_create_temp_buf(r->pool, len);
    if (b == NULL) {
        return NGX_ERROR;
    }

    /* "HTTP/1.x " */
    b->last = ngx_cpymem(b->last, "HTTP/1.1 ", sizeof("HTTP/1.x ") - 1);

    /* status line */
    if (status_line) {
        b->last = ngx_copy(b->last, status_line->data, status_line->len);

    } else {
        b->last = ngx_sprintf(b->last, "%03ui ", status);
    }
    *b->last++ = CR; *b->last++ = LF;

    if (r->headers_out.server == NULL) {
        if (clcf->server_tokens == NGX_HTTP_SERVER_TOKENS_ON) {
            p = ngx_http_server_full_string;
            len = sizeof(ngx_http_server_full_string) - 1;

        } else if (clcf->server_tokens == NGX_HTTP_SERVER_TOKENS_BUILD) {
            p = ngx_http_server_build_string;
            len = sizeof(ngx_http_server_build_string) - 1;

        } else {
            p = ngx_http_server_string;
            len = sizeof(ngx_http_server_string) - 1;
        }

        b->last = ngx_cpymem(b->last, p, len);
    }

    if (r->headers_out.date == NULL) {
        b->last = ngx_cpymem(b->last, "Date: ", sizeof("Date: ") - 1);
        b->last = ngx_cpymem(b->last, ngx_cached_http_time.data,
                             ngx_cached_http_time.len);

        *b->last++ = CR; *b->last++ = LF;
    }

    if (r->headers_out.content_type.len) {
        b->last = ngx_cpymem(b->last, "Content-Type: ",
                             sizeof("Content-Type: ") - 1);
        p = b->last;
        b->last = ngx_copy(b->last, r->headers_out.content_type.data,
                           r->headers_out.content_type.len);

        if (r->headers_out.content_type_len == r->headers_out.content_type.len
            && r->headers_out.charset.len)
        {
            b->last = ngx_cpymem(b->last, "; charset=",
                                 sizeof("; charset=") - 1);
            b->last = ngx_copy(b->last, r->headers_out.charset.data,
                               r->headers_out.charset.len);

            /* update r->headers_out.content_type for possible logging */

            r->headers_out.content_type.len = b->last - p;
            r->headers_out.content_type.data = p;
        }

        *b->last++ = CR; *b->last++ = LF;
    }

    if (r->headers_out.content_length == NULL
        && r->headers_out.content_length_n >= 0)
    {
        b->last = ngx_sprintf(b->last, "Content-Length: %O" CRLF,
                              r->headers_out.content_length_n);
    }

    if (r->headers_out.last_modified == NULL
        && r->headers_out.last_modified_time != -1)
    {
        b->last = ngx_cpymem(b->last, "Last-Modified: ",
                             sizeof("Last-Modified: ") - 1);
        b->last = ngx_http_time(b->last, r->headers_out.last_modified_time);

        *b->last++ = CR; *b->last++ = LF;
    }

    if (host.data) {

        p = b->last + sizeof("Location: ") - 1;

        b->last = ngx_cpymem(b->last, "Location: http",
                             sizeof("Location: http") - 1);

#if (NGX_HTTP_SSL)
        if (c->ssl) {
            *b->last++ ='s';
        }
#endif

        *b->last++ = ':'; *b->last++ = '/'; *b->last++ = '/';
        b->last = ngx_copy(b->last, host.data, host.len);

        if (port) {
            b->last = ngx_sprintf(b->last, ":%ui", port);
        }

        b->last = ngx_copy(b->last, r->headers_out.location->value.data,
                           r->headers_out.location->value.len);

        /* update r->headers_out.location->value for possible logging */

        r->headers_out.location->value.len = b->last - p;
        r->headers_out.location->value.data = p;
        ngx_str_set(&r->headers_out.location->key, "Location");

        *b->last++ = CR; *b->last++ = LF;
    }

    if (r->chunked) {
        b->last = ngx_cpymem(b->last, "Transfer-Encoding: chunked" CRLF,
                             sizeof("Transfer-Encoding: chunked" CRLF) - 1);
    }

    if (r->headers_out.status == NGX_HTTP_SWITCHING_PROTOCOLS) {
        b->last = ngx_cpymem(b->last, "Connection: upgrade" CRLF,
                             sizeof("Connection: upgrade" CRLF) - 1);

    } else if (r->keepalive) {
        b->last = ngx_cpymem(b->last, "Connection: keep-alive" CRLF,
                             sizeof("Connection: keep-alive" CRLF) - 1);

        if (clcf->keepalive_header) {
            b->last = ngx_sprintf(b->last, "Keep-Alive: timeout=%T" CRLF,
                                  clcf->keepalive_header);
        }

    } else {
        b->last = ngx_cpymem(b->last, "Connection: close" CRLF,
                             sizeof("Connection: close" CRLF) - 1);
    }

#if (NGX_HTTP_GZIP)
    if (r->gzip_vary) {
        b->last = ngx_cpymem(b->last, "Vary: Accept-Encoding" CRLF,
                             sizeof("Vary: Accept-Encoding" CRLF) - 1);
    }
#endif

    part = &r->headers_out.headers.part;
    header = part->elts;

    for (i = 0; /* void */; i++) {

        if (i >= part->nelts) {
            if (part->next == NULL) {
                break;
            }

            part = part->next;
            header = part->elts;
            i = 0;
        }

        if (header[i].hash == 0) {
            continue;
        }

        b->last = ngx_copy(b->last, header[i].key.data, header[i].key.len);
        *b->last++ = ':'; *b->last++ = ' ';

        b->last = ngx_copy(b->last, header[i].value.data, header[i].value.len);
        *b->last++ = CR; *b->last++ = LF;
    }

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "%*s", (size_t) (b->last - b->pos), b->pos);

    /* the end of HTTP header */
    *b->last++ = CR; *b->last++ = LF;

    r->header_size = b->last - b->pos;

    if (r->header_only) {
        b->last_buf = 1;
    }

    out.buf = b;
    out.next = NULL;

    return ngx_http_write_filter(r, &out);
}


static ngx_int_t
ngx_http_header_filter_init(ngx_conf_t *cf)
{
    ngx_http_top_header_filter = ngx_http_header_filter;

    return NGX_OK;
}