Accept and ignore content-length: 0 in 204 response for now

lib/nghttp2_http.c

@@ -250,7 +250,21 @@ static int http_response_on_header(nghttp2_stream *stream, nghttp2_hd_nv *nv,
     break;
   }
   case NGHTTP2_TOKEN_CONTENT_LENGTH: {
-    if (stream->status_code == 204 || stream->status_code / 100 == 1 ||
+    if (stream->status_code == 204) {
+      /* content-length header field in 204 response is prohibited by
+         RFC 7230.  But some widely used servers send content-length:
+         0.  Until they get fixed, we ignore it. */
+      if (stream->content_length != -1) {
+        /* Found multiple content-length field */
+        return NGHTTP2_ERR_HTTP_HEADER;
+      }
+      if (!lstrieq("0", nv->value->base, nv->value->len)) {
+        return NGHTTP2_ERR_HTTP_HEADER;
+      }
+      stream->content_length = 0;
+      return NGHTTP2_ERR_REMOVE_HTTP_HEADER;
+    }
+    if (stream->status_code / 100 == 1 ||
         (stream->status_code == 200 &&
          (stream->http_flags & NGHTTP2_HTTP_FLAG_METH_CONNECT))) {
       return NGHTTP2_ERR_HTTP_HEADER;

lib/nghttp2_int.h

@@ -46,7 +46,13 @@ typedef enum {
    * Invalid HTTP header field was received but it can be treated as
    * if it was not received because of compatibility reasons.
    */
-  NGHTTP2_ERR_IGN_HTTP_HEADER = -105
+  NGHTTP2_ERR_IGN_HTTP_HEADER = -105,
+  /*
+   * Invalid HTTP header field was received, and it is ignored.
+   * Unlike NGHTTP2_ERR_IGN_HTTP_HEADER, this does not invoke
+   * nghttp2_on_invalid_header_callback.
+   */
+  NGHTTP2_ERR_REMOVE_HTTP_HEADER = -106
 } nghttp2_internal_error;
 
 #endif /* NGHTTP2_INT_H */

tests/nghttp2_session_test.c

@@ -10204,6 +10204,8 @@ void test_nghttp2_http_mandatory_headers(void) {
                                     MAKE_NV("content-length", "0")};
   const nghttp2_nv cl204_resnv[] = {MAKE_NV(":status", "204"),
                                     MAKE_NV("content-length", "0")};
+  const nghttp2_nv clnonzero204_resnv[] = {MAKE_NV(":status", "204"),
+                                           MAKE_NV("content-length", "100")};
 
   /* test case for request */
   const nghttp2_nv nopath_reqnv[] = {MAKE_NV(":scheme", "https"),
@@ -10307,10 +10309,16 @@ void test_nghttp2_http_mandatory_headers(void) {
                                        NGHTTP2_STREAM_OPENING, cl1xx_resnv,
                                        ARRLEN(cl1xx_resnv));
 
-  /* response header has content-length with 204 status code */
-  check_nghttp2_http_recv_headers_fail(session, &deflater, 19,
-                                       NGHTTP2_STREAM_OPENING, cl204_resnv,
-                                       ARRLEN(cl204_resnv));
+  /* response header has 0 content-length with 204 status code */
+  check_nghttp2_http_recv_headers_ok(session, &deflater, 19,
+                                     NGHTTP2_STREAM_OPENING, cl204_resnv,
+                                     ARRLEN(cl204_resnv));
+
+  /* response header has nonzero content-length with 204 status
+     code */
+  check_nghttp2_http_recv_headers_fail(
+      session, &deflater, 21, NGHTTP2_STREAM_OPENING, clnonzero204_resnv,
+      ARRLEN(clnonzero204_resnv));
 
   nghttp2_hd_deflate_free(&deflater);