Upstream: added check if a response is complete.

Checks were added to both buffered and unbuffered code paths to detect
and complain if a response is incomplete.  Appropriate error codes are
now passed to ngx_http_upstream_finalize_request().

With this change in unbuffered mode we now use u->length set to -1 as an
indicator that EOF is allowed per protocol and used to indicate response
end (much like its with p->length in buffered mode).  Proxy module was
changed to set u->length to 1 (instead of previously used -1) in case of
chunked transfer encoding used to comply with the above.

src/http/modules/ngx_http_proxy_module.c

@@ -1542,7 +1542,7 @@ ngx_http_proxy_input_filter_init(void *data)
         u->pipe->length = 3; /* "0" LF LF */
 
         u->input_filter = ngx_http_proxy_non_buffered_chunked_filter;
-        u->length = -1;
+        u->length = 1;
 
     } else if (u->headers_in.content_length_n == 0) {
         /* empty body: special case as filter won't be called */

src/http/ngx_http_upstream.c

@@ -2748,13 +2748,27 @@ ngx_http_upstream_process_non_buffered_request(ngx_http_request_t *r,
             if (u->busy_bufs == NULL) {
 
                 if (u->length == 0
-                    || upstream->read->eof
-                    || upstream->read->error)
+                    || (upstream->read->eof && u->length == -1))
                 {
                     ngx_http_upstream_finalize_request(r, u, 0);
                     return;
                 }
 
+                if (upstream->read->eof) {
+                    ngx_log_error(NGX_LOG_ERR, upstream->log, 0,
+                                  "upstream prematurely closed connection");
+
+                    ngx_http_upstream_finalize_request(r, u,
+                                                       NGX_HTTP_BAD_GATEWAY);
+                    return;
+                }
+
+                if (upstream->read->error) {
+                    ngx_http_upstream_finalize_request(r, u,
+                                                       NGX_HTTP_BAD_GATEWAY);
+                    return;
+                }
+
                 b->pos = b->start;
                 b->last = b->start;
             }
@@ -3027,7 +3041,20 @@ ngx_http_upstream_process_request(ngx_http_request_t *r)
         if (p->upstream_done || p->upstream_eof || p->upstream_error) {
             ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                            "http upstream exit: %p", p->out);
-            ngx_http_upstream_finalize_request(r, u, 0);
+
+            if (p->upstream_done
+                || (p->upstream_eof && p->length == -1))
+            {
+                ngx_http_upstream_finalize_request(r, u, 0);
+                return;
+            }
+
+            if (p->upstream_eof) {
+                ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
+                              "upstream prematurely closed connection");
+            }
+
+            ngx_http_upstream_finalize_request(r, u, NGX_HTTP_BAD_GATEWAY);
             return;
         }
     }