fix(rpc): include write failure reason in log (#37959)

Also don't use LOGLVL_ERR on UV_EPIPE.

src/nvim/channel.c

@@ -617,7 +617,7 @@ size_t channel_send(uint64_t id, char *data, size_t len, bool data_owned, const
   // write can be delayed indefinitely, so always use an allocated buffer
   WBuffer *buf = wstream_new_buffer(data_owned ? data : xmemdup(data, len),
                                     len, 1, xfree);
-  return wstream_write(in, buf) ? len : 0;
+  return wstream_write(in, buf) == 0 ? len : 0;
 
 retfree:
   if (data_owned) {

src/nvim/event/wstream.c

@@ -63,8 +63,8 @@ void wstream_set_write_cb(Stream *stream, stream_write_cb cb, void *data)
 ///
 /// @param stream The `Stream` instance
 /// @param buffer The buffer which contains data to be written
-/// @return false if the write failed
+/// @return 0 on success, or libuv error code on failure
-bool wstream_write(Stream *stream, WBuffer *buffer)
+int wstream_write(Stream *stream, WBuffer *buffer)
   FUNC_ATTR_NONNULL_ALL
 {
   assert(stream->maxmem);
@@ -72,6 +72,7 @@ bool wstream_write(Stream *stream, WBuffer *buffer)
   // This should not be called after a stream was freed
   assert(!stream->closed);
 
+  int err = 0;
   uv_buf_t uvbuf;
   uvbuf.base = buffer->data;
   uvbuf.len = UV_BUF_LEN(buffer->size);
@@ -80,7 +81,7 @@ bool wstream_write(Stream *stream, WBuffer *buffer)
     uv_fs_t req;
 
     // Synchronous write
-    uv_fs_write(stream->uv.idle.loop, &req, stream->fd, &uvbuf, 1, stream->fpos, NULL);
+    err = uv_fs_write(stream->uv.idle.loop, &req, stream->fd, &uvbuf, 1, stream->fpos, NULL);
 
     uv_fs_req_cleanup(&req);
 
@@ -89,11 +90,12 @@ bool wstream_write(Stream *stream, WBuffer *buffer)
     assert(stream->write_cb == NULL);
 
     stream->fpos += MAX(req.result, 0);
-    return req.result > 0;
+    return req.result > 0 ? 0 : err != 0 ? err : UV_UNKNOWN;
   }
 
   if (stream->curmem > stream->maxmem) {
-    goto err;
+    err = UV_ENOMEM;
+    goto fail;
   }
 
   stream->curmem += buffer->size;
@@ -103,17 +105,19 @@ bool wstream_write(Stream *stream, WBuffer *buffer)
   data->buffer = buffer;
   data->uv_req.data = data;
 
-  if (uv_write(&data->uv_req, stream->uvstream, &uvbuf, 1, write_cb)) {
+  if ((err = uv_write(&data->uv_req, stream->uvstream, &uvbuf, 1, write_cb)) != 0) {
     xfree(data);
-    goto err;
+    goto fail;
   }
 
   stream->pending_reqs++;
-  return true;
+  assert(err == 0);
+  return 0;
 
-err:
+fail:
   wstream_release_wbuffer(buffer);
-  return false;
+  assert(err != 0);
+  return err;
 }
 
 /// Creates a WBuffer object for holding output data. Instances of this

src/nvim/msgpack_rpc/channel.c

@@ -393,7 +393,7 @@ bool rpc_write_raw(uint64_t id, WBuffer *buffer)
 
 static bool channel_write(Channel *channel, WBuffer *buffer)
 {
-  bool success;
+  int err = 0;
 
   if (channel->rpc.closed) {
     wstream_release_wbuffer(buffer);
@@ -403,24 +403,24 @@ static bool channel_write(Channel *channel, WBuffer *buffer)
   if (channel->streamtype == kChannelStreamInternal) {
     channel_incref(channel);
     CREATE_EVENT(channel->events, internal_read_event, channel, buffer);
-    success = true;
   } else {
     Stream *in = channel_instream(channel);
-    success = wstream_write(in, buffer);
+    err = wstream_write(in, buffer);
   }
 
-  if (!success) {
+  if (err != 0) {
     // If the write failed for any reason, close the channel
     char buf[256];
     snprintf(buf,
              sizeof(buf),
-             "ch %" PRIu64 ": stream write failed. "
+             "ch %" PRIu64 ": stream write failed: %s. "
              "RPC canceled; closing channel",
-             channel->id);
+             channel->id, os_strerror(err));
-    chan_close_on_err(channel, buf, LOGLVL_ERR);
+    // UV_EPIPE can happen if pipe is closed by peer and shouldn't be an error.
+    chan_close_on_err(channel, buf, err == UV_EPIPE ? LOGLVL_INF : LOGLVL_ERR);
   }
 
-  return success;
+  return err == 0;
 }
 
 static void internal_read_event(void **argv)

src/nvim/os/shell.c

@@ -923,7 +923,7 @@ static int do_os_system(char **argv, const char *input, size_t len, char **outpu
   if (has_input) {
     WBuffer *input_buffer = wstream_new_buffer((char *)input, len, 1, NULL);
 
-    if (!wstream_write(&proc->in, input_buffer)) {
+    if (wstream_write(&proc->in, input_buffer) != 0) {
       // couldn't write, stop the process and tell the user about it
       proc_stop(proc);
       goto end;