Added support for trailers in HTTP responses.

Example:

   ngx_table_elt_t  *h;

   h = ngx_list_push(&r->headers_out.trailers);
   if (h == NULL) {
       return NGX_ERROR;
   }

   ngx_str_set(&h->key, "Fun");
   ngx_str_set(&h->value, "with trailers");
   h->hash = ngx_hash_key_lc(h->key.data, h->key.len);

The code above adds "Fun: with trailers" trailer to the response.

Modules that want to emit trailers must set r->expect_trailers = 1
in header filter, otherwise they might not be emitted for HTTP/1.1
responses that aren't already chunked.

This change also adds $sent_trailer_* variables.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

5 files changed, 157 insertions, 27 deletions

diff --git a/src/http/modules/ngx_http_chunked_filter_module.c b/src/http/modules/ngx_http_chunked_filter_module.c
index ac2e3e8f9..4d6fd3eed 100644
--- a/src/http/modules/ngx_http_chunked_filter_module.c
+++ b/src/http/modules/ngx_http_chunked_filter_module.c
@@ -17,6 +17,8 @@ typedef struct {
 
 
 static ngx_int_t ngx_http_chunked_filter_init(ngx_conf_t *cf);
+static ngx_chain_t *ngx_http_chunked_create_trailers(ngx_http_request_t *r,
+    ngx_http_chunked_filter_ctx_t *ctx);
 
 
 static ngx_http_module_t  ngx_http_chunked_filter_module_ctx = {
@@ -69,27 +71,29 @@ ngx_http_chunked_header_filter(ngx_http_request_t *r)
         return ngx_http_next_header_filter(r);
     }
 
-    if (r->headers_out.content_length_n == -1) {
-        if (r->http_version < NGX_HTTP_VERSION_11) {
-            r->keepalive = 0;
+    if (r->headers_out.content_length_n == -1
+        || r->expect_trailers)
+    {
+        clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
 
-        } else {
-            clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
+        if (r->http_version >= NGX_HTTP_VERSION_11
+            && clcf->chunked_transfer_encoding)
+        {
+            if (r->expect_trailers) {
+                ngx_http_clear_content_length(r);
+            }
 
-            if (clcf->chunked_transfer_encoding) {
-                r->chunked = 1;
+            r->chunked = 1;
 
-                ctx = ngx_pcalloc(r->pool,
-                                  sizeof(ngx_http_chunked_filter_ctx_t));
-                if (ctx == NULL) {
-                    return NGX_ERROR;
-                }
+            ctx = ngx_pcalloc(r->pool, sizeof(ngx_http_chunked_filter_ctx_t));
+            if (ctx == NULL) {
+                return NGX_ERROR;
+            }
 
-                ngx_http_set_ctx(r, ctx, ngx_http_chunked_filter_module);
+            ngx_http_set_ctx(r, ctx, ngx_http_chunked_filter_module);
 
-            } else {
-                r->keepalive = 0;
-            }
+        } else if (r->headers_out.content_length_n == -1) {
+            r->keepalive = 0;
         }
     }
 
@@ -179,26 +183,17 @@ ngx_http_chunked_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
     }
 
     if (cl->buf->last_buf) {
-        tl = ngx_chain_get_free_buf(r->pool, &ctx->free);
+        tl = ngx_http_chunked_create_trailers(r, ctx);
         if (tl == NULL) {
             return NGX_ERROR;
         }
 
-        b = tl->buf;
-
-        b->tag = (ngx_buf_tag_t) &ngx_http_chunked_filter_module;
-        b->temporary = 0;
-        b->memory = 1;
-        b->last_buf = 1;
-        b->pos = (u_char *) CRLF "0" CRLF CRLF;
-        b->last = b->pos + 7;
-
         cl->buf->last_buf = 0;
 
         *ll = tl;
 
         if (size == 0) {
-            b->pos += 2;
+            tl->buf->pos += 2;
         }
 
     } else if (size > 0) {
@@ -230,6 +225,109 @@ ngx_http_chunked_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
 }
 
 
+static ngx_chain_t *
+ngx_http_chunked_create_trailers(ngx_http_request_t *r,
+    ngx_http_chunked_filter_ctx_t *ctx)
+{
+    size_t            len;
+    ngx_buf_t        *b;
+    ngx_uint_t        i;
+    ngx_chain_t      *cl;
+    ngx_list_part_t  *part;
+    ngx_table_elt_t  *header;
+
+    len = 0;
+
+    part = &r->headers_out.trailers.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;
+    }
+
+    cl = ngx_chain_get_free_buf(r->pool, &ctx->free);
+    if (cl == NULL) {
+        return NULL;
+    }
+
+    b = cl->buf;
+
+    b->tag = (ngx_buf_tag_t) &ngx_http_chunked_filter_module;
+    b->temporary = 0;
+    b->memory = 1;
+    b->last_buf = 1;
+
+    if (len == 0) {
+        b->pos = (u_char *) CRLF "0" CRLF CRLF;
+        b->last = b->pos + sizeof(CRLF "0" CRLF CRLF) - 1;
+        return cl;
+    }
+
+    len += sizeof(CRLF "0" CRLF CRLF) - 1;
+
+    b->pos = ngx_palloc(r->pool, len);
+    if (b->pos == NULL) {
+        return NULL;
+    }
+
+    b->last = b->pos;
+
+    *b->last++ = CR; *b->last++ = LF;
+    *b->last++ = '0';
+    *b->last++ = CR; *b->last++ = LF;
+
+    part = &r->headers_out.trailers.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;
+        }
+
+        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                       "http trailer: \"%V: %V\"",
+                       &header[i].key, &header[i].value);
+
+        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;
+    }
+
+    *b->last++ = CR; *b->last++ = LF;
+
+    return cl;
+}
+
+
 static ngx_int_t
 ngx_http_chunked_filter_init(ngx_conf_t *cf)
 {
diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index b5be1ffeb..02059efd8 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -2485,6 +2485,13 @@ ngx_http_subrequest(ngx_http_request_t *r,
         return NGX_ERROR;
     }
 
+    if (ngx_list_init(&sr->headers_out.trailers, r->pool, 4,
+                      sizeof(ngx_table_elt_t))
+        != NGX_OK)
+    {
+        return NGX_ERROR;
+    }
+
     cscf = ngx_http_get_module_srv_conf(r, ngx_http_core_module);
     sr->main_conf = cscf->ctx->main_conf;
     sr->srv_conf = cscf->ctx->srv_conf;
diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index cc3722fb3..de1b20270 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -562,6 +562,14 @@ ngx_http_create_request(ngx_connection_t *c)
         return NULL;
     }
 
+    if (ngx_list_init(&r->headers_out.trailers, r->pool, 4,
+                      sizeof(ngx_table_elt_t))
+        != NGX_OK)
+    {
+        ngx_destroy_pool(r->pool);
+        return NULL;
+    }
+
     r->ctx = ngx_pcalloc(r->pool, sizeof(void *) * ngx_http_max_module);
     if (r->ctx == NULL) {
         ngx_destroy_pool(r->pool);
diff --git a/src/http/ngx_http_request.h b/src/http/ngx_http_request.h
index 283c58294..f7f3e97f4 100644
--- a/src/http/ngx_http_request.h
+++ b/src/http/ngx_http_request.h
@@ -252,6 +252,7 @@ typedef struct {
 
 typedef struct {
     ngx_list_t                        headers;
+    ngx_list_t                        trailers;
 
     ngx_uint_t                        status;
     ngx_str_t                         status_line;
@@ -514,6 +515,7 @@ struct ngx_http_request_s {
     unsigned                          pipeline:1;
     unsigned                          chunked:1;
     unsigned                          header_only:1;
+    unsigned                          expect_trailers:1;
     unsigned                          keepalive:1;
     unsigned                          lingering_close:1;
     unsigned                          discard_body:1;
diff --git a/src/http/ngx_http_variables.c b/src/http/ngx_http_variables.c
index 6138819dd..cfb538a69 100644
--- a/src/http/ngx_http_variables.c
+++ b/src/http/ngx_http_variables.c
@@ -38,6 +38,8 @@ static ngx_int_t ngx_http_variable_unknown_header_in(ngx_http_request_t *r,
     ngx_http_variable_value_t *v, uintptr_t data);
 static ngx_int_t ngx_http_variable_unknown_header_out(ngx_http_request_t *r,
     ngx_http_variable_value_t *v, uintptr_t data);
+static ngx_int_t ngx_http_variable_unknown_trailer_out(ngx_http_request_t *r,
+    ngx_http_variable_value_t *v, uintptr_t data);
 static ngx_int_t ngx_http_variable_request_line(ngx_http_request_t *r,
     ngx_http_variable_value_t *v, uintptr_t data);
 static ngx_int_t ngx_http_variable_cookie(ngx_http_request_t *r,
@@ -365,6 +367,9 @@ static ngx_http_variable_t  ngx_http_core_variables[] = {
     { ngx_string("sent_http_"), NULL, ngx_http_variable_unknown_header_out,
       0, NGX_HTTP_VAR_PREFIX, 0 },
 
+    { ngx_string("sent_trailer_"), NULL, ngx_http_variable_unknown_trailer_out,
+      0, NGX_HTTP_VAR_PREFIX, 0 },
+
     { ngx_string("cookie_"), NULL, ngx_http_variable_cookie,
       0, NGX_HTTP_VAR_PREFIX, 0 },
 
@@ -934,6 +939,16 @@ ngx_http_variable_unknown_header_out(ngx_http_request_t *r,
 }
 
 
+static ngx_int_t
+ngx_http_variable_unknown_trailer_out(ngx_http_request_t *r,
+    ngx_http_variable_value_t *v, uintptr_t data)
+{
+    return ngx_http_variable_unknown_header(v, (ngx_str_t *) data,
+                                            &r->headers_out.trailers.part,
+                                            sizeof("sent_trailer_") - 1);
+}
+
+
 ngx_int_t
 ngx_http_variable_unknown_header(ngx_http_variable_value_t *v, ngx_str_t *var,
     ngx_list_part_t *part, size_t prefix)