http/2: simplify eos/blocked handling

- rely on the new flush to handle blocked sends. No longer
  do simulated EAGAIN on (partially) blocked sends with their
  need to handle repeats.
- fix some debug handling CURL_SMALLREQSEND env var
- add some assertings in request.c for affirming we do it right
- enhance assertion output in test_16 for easier analysis

Closes #14435

lib/http2.c

@@ -207,8 +207,6 @@ struct h2_stream_ctx {
   BIT(reset);  /* TRUE on stream reset */
   BIT(close_handled); /* TRUE if stream closure is handled by libcurl */
   BIT(bodystarted);
-  BIT(send_closed); /* transfer is done sending, we might have still
-                       buffered data in stream->sendbuf to upload. */
   BIT(body_eos);    /* the complete body has been added to `sendbuf` and
                      * is being/has been processed from there. */
 };
@@ -347,10 +345,10 @@ static void drain_stream(struct Curl_cfilter *cf,
 
   (void)cf;
   bits = CURL_CSELECT_IN;
-  if(!stream->send_closed &&
+  if(!stream->closed &&
      (!stream->body_eos || !Curl_bufq_is_empty(&stream->sendbuf)))
     bits |= CURL_CSELECT_OUT;
-  if(data->state.select_bits != bits) {
+  if(stream->closed || (data->state.select_bits != bits)) {
     CURL_TRC_CF(data, cf, "[%d] DRAIN select_bits=%x",
                 stream->id, bits);
     data->state.select_bits = bits;
@@ -406,7 +404,6 @@ static void http2_data_done(struct Curl_cfilter *cf, struct Curl_easy *data)
                   stream->id);
       stream->closed = TRUE;
       stream->reset = TRUE;
-      stream->send_closed = TRUE;
       nghttp2_submit_rst_stream(ctx->h2, NGHTTP2_FLAG_NONE,
                                 stream->id, NGHTTP2_STREAM_CLOSED);
       flush_egress = TRUE;
@@ -1164,7 +1161,6 @@ static CURLcode on_stream_frame(struct Curl_cfilter *cf,
     if(frame->rst_stream.error_code) {
       stream->reset = TRUE;
     }
-    stream->send_closed = TRUE;
     drain_stream(cf, data, stream);
     break;
   case NGHTTP2_WINDOW_UPDATE:
@@ -1430,7 +1426,6 @@ static int on_stream_close(nghttp2_session *session, int32_t stream_id,
   stream->error = error_code;
   if(stream->error) {
     stream->reset = TRUE;
-    stream->send_closed = TRUE;
   }
 
   if(stream->error)
@@ -1742,35 +1737,6 @@ CURLcode Curl_http2_request_upgrade(struct dynbuf *req,
   return result;
 }
 
-static CURLcode http2_data_done_send(struct Curl_cfilter *cf,
-                                     struct Curl_easy *data)
-{
-  struct cf_h2_ctx *ctx = cf->ctx;
-  CURLcode result = CURLE_OK;
-  struct h2_stream_ctx *stream = H2_STREAM_CTX(ctx, data);
-
-  if(!ctx || !ctx->h2 || !stream)
-    goto out;
-
-  CURL_TRC_CF(data, cf, "[%d] data done send", stream->id);
-  if(!stream->send_closed) {
-    stream->send_closed = TRUE;
-    if(!Curl_bufq_is_empty(&stream->sendbuf)) {
-      /* TODO: if we had not seen EOS on send(), it seems the request
-       * is now aborted? */
-      /* we now know that everything that is buffered is all there is. */
-      stream->body_eos = TRUE;
-      /* resume sending here to trigger the callback to get called again so
-         that it can signal EOF to nghttp2 */
-      (void)nghttp2_session_resume_data(ctx->h2, stream->id);
-      drain_stream(cf, data, stream);
-    }
-  }
-
-out:
-  return result;
-}
-
 static ssize_t http2_handle_stream_close(struct Curl_cfilter *cf,
                                          struct Curl_easy *data,
                                          struct h2_stream_ctx *stream,
@@ -2339,18 +2305,6 @@ static ssize_t cf_h2_send(struct Curl_cfilter *cf, struct Curl_easy *data,
     nwritten = -1;
     goto out;
   }
-  else if(stream && stream->body_eos &&
-          (!Curl_bufq_is_empty(&stream->sendbuf) ||
-           !Curl_bufq_is_empty(&ctx->outbufq))) {
-    /* We added the last send chunk to stream->sendbuf, but were unable
-     * to send it all off. Either the socket EAGAINed or the HTTP/2 flow
-     * control prevents it. This should be a call with `eos` set and
-     * we CURLE_AGAIN it until we flushed everything. */
-    CURL_TRC_CF(data, cf, "[%d] could not flush last send chunk -> EAGAIN",
-                stream->id);
-    *err = CURLE_AGAIN;
-    nwritten = -1;
-  }
 
   if(should_close_session(ctx)) {
     /* nghttp2 thinks this session is done. If the stream has not been
@@ -2650,9 +2604,6 @@ static CURLcode cf_h2_cntrl(struct Curl_cfilter *cf,
   case CF_CTRL_FLUSH:
     result = cf_h2_flush(cf, data);
     break;
-  case CF_CTRL_DATA_DONE_SEND:
-    result = http2_data_done_send(cf, data);
-    break;
   case CF_CTRL_DATA_DETACH:
     http2_data_done(cf, data);
     break;

lib/request.c

@@ -182,16 +182,17 @@ static CURLcode xfer_send(struct Curl_easy *data,
   bool eos = FALSE;
 
   *pnwritten = 0;
+  DEBUGASSERT(hds_len <= blen);
 #ifdef DEBUGBUILD
   {
     /* Allow debug builds to override this logic to force short initial
-       sends
-     */
+       sends */
+    size_t body_len = blen - hds_len;
     char *p = getenv("CURL_SMALLREQSEND");
     if(p) {
-      size_t altsize = (size_t)strtoul(p, NULL, 10);
-      if(altsize && altsize < blen)
-        blen = altsize;
+      size_t body_small = (size_t)strtoul(p, NULL, 10);
+      if(body_small && body_small < body_len)
+        blen = hds_len + body_small;
     }
   }
 #endif
@@ -267,10 +268,12 @@ static CURLcode req_set_upload_done(struct Curl_easy *data)
   else if(data->req.writebytecount)
     infof(data, "upload completely sent off: %" CURL_FORMAT_CURL_OFF_T
           " bytes", data->req.writebytecount);
-  else if(!data->req.download_done)
+  else if(!data->req.download_done) {
+    DEBUGASSERT(Curl_bufq_is_empty(&data->req.sendbuf));
     infof(data, Curl_creader_total_length(data)?
                 "We are completely uploaded and fine" :
                 "Request completely sent off");
+  }
 
   return Curl_xfer_send_close(data);
 }

tests/http/test_16_info.py

@@ -111,11 +111,11 @@ class TestInfo:
             self.check_stat(idx, s, r, dl_size=30, ul_size=0)
 
     def check_stat(self, idx, s, r, dl_size=None, ul_size=None):
-        self.check_stat_times(s)
+        self.check_stat_times(s, idx)
         # we always send something
-        self.check_stat_positive(s, 'size_request')
+        self.check_stat_positive(s, idx, 'size_request')
         # we always receive response headers
-        self.check_stat_positive(s, 'size_header')
+        self.check_stat_positive(s, idx, 'size_header')
         if ul_size is not None:
             assert s['size_upload'] == ul_size, f'stat #{idx}\n{r.dump_logs()}'  # the file we sent
         assert s['size_request'] >= s['size_upload'], \
@@ -123,15 +123,15 @@ class TestInfo:
         if dl_size is not None:
             assert s['size_download'] == dl_size, f'stat #{idx}\n{r.dump_logs()}'  # the file we received
 
-    def check_stat_positive(self, s, key):
-        assert key in s, f'stat "{key}" missing: {s}'
-        assert s[key] > 0, f'stat "{key}" not positive: {s}'
+    def check_stat_positive(self, s, idx, key):
+        assert key in s, f'stat #{idx} "{key}" missing: {s}'
+        assert s[key] > 0, f'stat #{idx} "{key}" not positive: {s}'
 
     def check_stat_zero(self, s, key):
         assert key in s, f'stat "{key}" missing: {s}'
         assert s[key] == 0, f'stat "{key}" not zero: {s}'
 
-    def check_stat_times(self, s):
+    def check_stat_times(self, s, idx):
         # check timings reported on a transfer for consistency
         url = s['url_effective']
         # all stat keys which reporting timings
@@ -152,7 +152,7 @@ class TestInfo:
         for key in zero_keys:
             self.check_stat_zero(s, key)
         for key in pos_keys:
-            self.check_stat_positive(s, key)
+            self.check_stat_positive(s, idx, key)
         # assert that all timers before "time_pretransfer" are less or equal
         for key in ['time_appconnect', 'time_connect', 'time_namelookup']:
             assert s[key] < s['time_pretransfer'], f'time "{key}" larger than' \