unix,stream: fix zero byte writes

Fixes a regression where a write request to write a zero byte buffer
would never complete.

Refs: https://github.com/libuv/libuv/pull/2097
Refs: https://github.com/libuv/libuv/issues/2134
PR-URL: https://github.com/libuv/libuv/pull/2149
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/unix/stream.c

@@ -745,13 +745,13 @@ static int uv__write_req_update(uv_stream_t* stream,
 
   buf = req->bufs + req->write_index;
 
-  while (n > 0) {
+  do {
     len = n < buf->len ? n : buf->len;
     buf->base += len;
     buf->len -= len;
     buf += (buf->len == 0);  /* Advance to next buffer if this one is empty. */
     n -= len;
-  }
+  } while (n > 0);
 
   req->write_index = buf - req->bufs;
 
@@ -897,7 +897,7 @@ start:
     goto error;
   }
 
-  if (n > 0 && uv__write_req_update(stream, req, n)) {
+  if (n >= 0 && uv__write_req_update(stream, req, n)) {
     uv__write_req_finish(req);
     return;  /* TODO(bnoordhuis) Start trying to write the next request. */
   }

test/run-tests.c

@@ -42,6 +42,7 @@ int ipc_helper_tcp_connection(void);
 int ipc_helper_closed_handle(void);
 int ipc_send_recv_helper(void);
 int ipc_helper_bind_twice(void);
+int ipc_helper_send_zero(void);
 int stdio_over_pipes_helper(void);
 int spawn_stdin_stdout(void);
 int spawn_tcp_server_helper(void);
@@ -104,6 +105,10 @@ static int maybe_run_test(int argc, char **argv) {
     return ipc_helper_bind_twice();
   }
 
+  if (strcmp(argv[1], "ipc_helper_send_zero") == 0) {
+    return ipc_helper_send_zero();
+  }
+
   if (strcmp(argv[1], "stdio_over_pipes_helper") == 0) {
     return stdio_over_pipes_helper();
   }

test/test-ipc.c

@@ -47,6 +47,7 @@ static int tcp_conn_read_cb_called;
 static int tcp_conn_write_cb_called;
 static int closed_handle_data_read;
 static int closed_handle_write;
+static int send_zero_write;
 
 typedef struct {
   uv_connect_t conn_req;
@@ -431,6 +432,14 @@ static void on_read_closed_handle(uv_stream_t* handle,
 #endif
 
 
+static void on_read_send_zero(uv_stream_t* handle,
+                              ssize_t nread,
+                              const uv_buf_t* buf) {
+  ASSERT(nread == 0 || nread == UV_EOF);
+  free(buf->base);
+}
+
+
 static int run_ipc_test(const char* helper, uv_read_cb read_cb) {
   uv_process_t process;
   int r;
@@ -555,6 +564,13 @@ TEST_IMPL(ipc_listen_after_bind_twice) {
 }
 #endif
 
+TEST_IMPL(ipc_send_zero) {
+  int r;
+  r = run_ipc_test("ipc_helper_send_zero", on_read_send_zero);
+  ASSERT(r == 0);
+  return 0;
+}
+
 
 /* Everything here runs in a child process. */
 
@@ -598,6 +614,11 @@ static void closed_handle_write_cb(uv_write_t* req, int status) {
 }
 
 
+static void send_zero_write_cb(uv_write_t* req, int status) {
+  ASSERT(status == 0);
+  send_zero_write++;
+}
+
 static void on_tcp_child_process_read(uv_stream_t* tcp,
                                       ssize_t nread,
                                       const uv_buf_t* buf) {
@@ -919,3 +940,35 @@ int ipc_helper_bind_twice(void) {
   MAKE_VALGRIND_HAPPY();
   return 0;
 }
+
+int ipc_helper_send_zero(void) {
+  int r;
+  uv_buf_t zero_buf;
+
+  zero_buf = uv_buf_init(0, 0);
+
+  r = uv_pipe_init(uv_default_loop(), &channel, 0);
+  ASSERT(r == 0);
+
+  uv_pipe_open(&channel, 0);
+
+  ASSERT(1 == uv_is_readable((uv_stream_t*) &channel));
+  ASSERT(1 == uv_is_writable((uv_stream_t*) &channel));
+  ASSERT(0 == uv_is_closing((uv_handle_t*) &channel));
+
+  r = uv_write(&write_req,
+               (uv_stream_t*)&channel,
+               &zero_buf,
+               1,
+               send_zero_write_cb);
+
+  ASSERT(r == 0);
+
+  r = uv_run(uv_default_loop(), UV_RUN_DEFAULT);
+  ASSERT(r == 0);
+
+  ASSERT(send_zero_write == 1);
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}

test/test-list.h

@@ -69,6 +69,7 @@ TEST_DECLARE   (ipc_send_recv_pipe_inprocess)
 TEST_DECLARE   (ipc_send_recv_tcp)
 TEST_DECLARE   (ipc_send_recv_tcp_inprocess)
 TEST_DECLARE   (ipc_tcp_connection)
+TEST_DECLARE   (ipc_send_zero)
 #ifndef _WIN32
 TEST_DECLARE   (ipc_closed_handle)
 #endif
@@ -515,6 +516,7 @@ TASK_LIST_START
   TEST_ENTRY  (ipc_send_recv_tcp)
   TEST_ENTRY  (ipc_send_recv_tcp_inprocess)
   TEST_ENTRY  (ipc_tcp_connection)
+  TEST_ENTRY  (ipc_send_zero)
 #ifndef _WIN32
   TEST_ENTRY  (ipc_closed_handle)
 #endif