Merging r4147, r4148, r4149, r4150, r4207:

Fixes of combination of error_page and return directives:

*) Fix for incorrect 201 replies from dav module.

   Replies with 201 code contain body, and we should clearly indicate it's
   empty if it's empty.  Before 0.8.32 chunked was explicitly disabled for
   201 replies and as a result empty body was indicated by connection close
   (not perfect, but worked).  Since 0.8.32 chunked is enabled, and this
   causes incorrect responses from dav module when HTTP/1.1 is used: with
   "Transfer-Encoding: chunked" but no chunks at all.

   Fix is to actually return empty body in special response handler instead
   of abusing r->header_only flag.

   See here for initial report:
   http://mailman.nginx.org/pipermail/nginx-ru/2010-October/037535.html

*) Fix for double content when return is used in error_page handler.

   Test case:

      location / {
          error_page 405 /nope;
          return 405;
      }

      location /nope {
          return 200;
      }

   This is expected to return 405 with empty body, but in 0.8.42+ will return
   builtin 405 error page as well (though not counted in Content-Length, thus
   breaking protocol).

   Fix is to use status provided by rewrite script execution in case
   it's less than NGX_HTTP_BAD_REQUEST even if r->error_status set.  This
   check is in line with one in ngx_http_script_return_code().

   Note that this patch also changes behaviour for "return 302 ..." and
   "rewrite ... redirect" used as error handler.  E.g.

       location / {
           error_page 405 /redirect;
           return 405;
       }

       location /redirect {
           rewrite ^ http://example.com/;
       }

   will actually return redirect to "http://example.com/" instead of builtin
   405 error page with meaningless Location header.  This looks like correct
   change and it's in line with what happens on e.g. directory redirects
   in error handlers.

*) Fix for "return 202" not discarding body.

   Big POST (not fully preread) to a

       location / {
           return 202;
       }

   resulted in incorrect behaviour due to "return" code path not calling
   ngx_http_discard_request_body().  The same applies to all "return" used
   with 2xx/3xx codes except 201 and 204, and to all "return ... text" uses.

   Fix is to add ngx_http_discard_request_body() call to
   ngx_http_send_response() function where it looks appropriate.
   Discard body call from emtpy gif module removed as it's now redundant.

   Reported by Pyry Hakulinen, see
   http://mailman.nginx.org/pipermail/nginx/2011-August/028503.html

*) Incorrect special case for "return 204" removed.

   The special case in question leads to replies without body in
   configuration like

       location / { error_page 404 /zero; return 404; }
       location /zero { return 204; }

   while replies with empty body are expected per protocol specs.

   Correct one will look like

       if (status == NGX_HTTP_NO_CONTENT) {

           rc = ngx_http_send_header(r);

           if (rc == NGX_ERROR || r->header_only) {
               return rc;
           }

           return ngx_http_send_special(r, NGX_HTTP_LAST);
       }

   though it looks like it's better to drop this special case at all.

*) Clear old Location header (if any) while adding a new one.

   This prevents incorrect behaviour when another redirect is issued within
   error_page 302 handler.

src/http/modules/ngx_http_empty_gif_module.c

@@ -111,19 +111,12 @@ static ngx_str_t  ngx_http_gif_type = ngx_string("image/gif");
 static ngx_int_t
 ngx_http_empty_gif_handler(ngx_http_request_t *r)
 {
-    ngx_int_t                 rc;
     ngx_http_complex_value_t  cv;
 
     if (!(r->method & (NGX_HTTP_GET|NGX_HTTP_HEAD))) {
         return NGX_HTTP_NOT_ALLOWED;
     }
 
-    rc = ngx_http_discard_request_body(r);
-
-    if (rc != NGX_OK) {
-        return rc;
-    }
-
     ngx_memzero(&cv, sizeof(ngx_http_complex_value_t));
 
     cv.value.len = sizeof(ngx_empty_gif);

src/http/modules/ngx_http_rewrite_module.c

@@ -167,8 +167,8 @@ ngx_http_rewrite_handler(ngx_http_request_t *r)
         code(e);
     }
 
-    if (e->status == NGX_DECLINED) {
-        return NGX_DECLINED;
+    if (e->status < NGX_HTTP_BAD_REQUEST) {
+        return e->status;
     }
 
     if (r->err_status == 0) {

src/http/modules/ngx_http_static_module.c

@@ -139,6 +139,8 @@ ngx_http_static_handler(ngx_http_request_t *r)
 
         ngx_log_debug0(NGX_LOG_DEBUG_HTTP, log, 0, "http dir");
 
+        ngx_http_clear_location(r);
+
         r->headers_out.location = ngx_palloc(r->pool, sizeof(ngx_table_elt_t));
         if (r->headers_out.location == NULL) {
             return NGX_HTTP_INTERNAL_SERVER_ERROR;

src/http/ngx_http_core_module.c

@@ -983,6 +983,8 @@ ngx_http_core_find_config_phase(ngx_http_request_t *r,
     }
 
     if (rc == NGX_DONE) {
+        ngx_http_clear_location(r);
+
         r->headers_out.location = ngx_list_push(&r->headers_out.headers);
         if (r->headers_out.location == NULL) {
             ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
@@ -1784,19 +1786,20 @@ ngx_http_send_response(ngx_http_request_t *r, ngx_uint_t status,
     ngx_buf_t    *b;
     ngx_chain_t   out;
 
-    r->headers_out.status = status;
-
-    if (status == NGX_HTTP_NO_CONTENT) {
-        r->header_only = 1;
-        return ngx_http_send_header(r);
+    if (ngx_http_discard_request_body(r) != NGX_OK) {
+        return NGX_HTTP_INTERNAL_SERVER_ERROR;
     }
 
+    r->headers_out.status = status;
+
     if (ngx_http_complex_value(r, cv, &val) != NGX_OK) {
         return NGX_HTTP_INTERNAL_SERVER_ERROR;
     }
 
     if (status >= NGX_HTTP_MOVED_PERMANENTLY && status <= NGX_HTTP_SEE_OTHER) {
 
+        ngx_http_clear_location(r);
+
         r->headers_out.location = ngx_list_push(&r->headers_out.headers);
         if (r->headers_out.location == NULL) {
             return NGX_HTTP_INTERNAL_SERVER_ERROR;

src/http/ngx_http_core_module.h

@@ -529,5 +529,12 @@ extern ngx_str_t  ngx_http_core_get_method;
         r->headers_out.last_modified = NULL;                                  \
     }
 
+#define ngx_http_clear_location(r)                                            \
+                                                                              \
+    if (r->headers_out.location) {                                            \
+        r->headers_out.location->hash = 0;                                    \
+        r->headers_out.location = NULL;                                       \
+    }
+
 
 #endif /* _NGX_HTTP_CORE_H_INCLUDED_ */

src/http/ngx_http_script.c

@@ -1106,6 +1106,8 @@ ngx_http_script_regex_end_code(ngx_http_script_engine_t *e)
                           "rewritten redirect: \"%V\"", &e->buf);
         }
 
+        ngx_http_clear_location(r);
+
         r->headers_out.location = ngx_list_push(&r->headers_out.headers);
         if (r->headers_out.location == NULL) {
             e->ip = ngx_http_script_exit;

src/http/ngx_http_special_response.c

@@ -421,7 +421,6 @@ ngx_http_special_response_handler(ngx_http_request_t *r, ngx_int_t error)
     if (error == NGX_HTTP_CREATED) {
         /* 201 */
         err = 0;
-        r->header_only = 1;
 
     } else if (error == NGX_HTTP_NO_CONTENT) {
         /* 204 */
@@ -583,6 +582,8 @@ ngx_http_send_error_page(ngx_http_request_t *r, ngx_http_err_page_t *err_page)
     ngx_str_set(&location->key, "Location");
     location->value = uri;
 
+    ngx_http_clear_location(r);
+
     r->headers_out.location = location;
 
     clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
@@ -636,7 +637,7 @@ ngx_http_send_special_response(ngx_http_request_t *r,
         r->headers_out.content_type_lowcase = NULL;
 
     } else {
-        r->headers_out.content_length_n = -1;
+        r->headers_out.content_length_n = 0;
     }
 
     if (r->headers_out.content_length) {
@@ -654,7 +655,7 @@ ngx_http_send_special_response(ngx_http_request_t *r,
     }
 
     if (ngx_http_error_pages[err].len == 0) {
-        return NGX_OK;
+        return ngx_http_send_special(r, NGX_HTTP_LAST);
     }
 
     b = ngx_calloc_buf(r->pool);