From be35be8d381449149040938f24c124861da9860e Mon Sep 17 00:00:00 2001
From: Sebastien Bourdeauducq <sb@m-labs.hk>
Date: Wed, 15 Apr 2020 09:16:25 +0800
Subject: [PATCH] Revert "Revert "libasync: don't let TcpStream::read() call
 back for empty buffers""

Zero-length buffer is really a special case, as one must return Poll::Pending in this case.

This reverts commit 1ac10ba0d4bb625c67fd897c22462608a4c24fba.
---
 libasync/src/smoltcp/tcp_stream.rs | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/libasync/src/smoltcp/tcp_stream.rs b/libasync/src/smoltcp/tcp_stream.rs
index 4fed9ef..7fa176f 100644
--- a/libasync/src/smoltcp/tcp_stream.rs
+++ b/libasync/src/smoltcp/tcp_stream.rs
@@ -141,12 +141,18 @@ impl TcpStream {
 
             fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
                 let result = self.stream.with_socket(|mut socket| {
-                    socket.recv(|buf| match (self.f)(buf) {
-                        Poll::Ready((amount, result)) =>
-                            (amount, Poll::Ready(Ok(result))),
-                        Poll::Pending =>
-                            // 0 bytes consumed
-                            (0, Poll::Pending),
+                    socket.recv(|buf| {
+                        if buf.len() > 0 {
+                            match (self.f)(buf) {
+                                Poll::Ready((amount, result)) =>
+                                    (amount, Poll::Ready(Ok(result))),
+                                Poll::Pending =>
+                                    // 0 bytes consumed
+                                    (0, Poll::Pending),
+                            }
+                        } else {
+                            (0, Poll::Pending)
+                        }
                     })
                 });
                 match result {