src: error or NULL links they happen on close

Right after `uv_link_close()` all links will be unchained, meaning that
they `link->parent` is NULL. Instead of crashing on calls like:

`uv_link_try_write(link->parent, ...)`

Make them return `UV_EFAULT`, indicating that no parent is present
anymore. Alternatively, these checks could be done in user code, but it
will make it too cumbersome.

2 files changed, 16 insertions, 0 deletions

diff --git a/src/uv_link_t.c b/src/uv_link_t.c
index 32fa6c9..64ca70d 100644
--- a/src/uv_link_t.c
+++ b/src/uv_link_t.c
@@ -50,6 +50,8 @@ int uv_link_propagate_write(uv_link_t* link, uv_link_t* source,
                             const uv_buf_t bufs[], unsigned int nbufs,
                             uv_stream_t* send_handle,
                             uv_link_write_cb cb, void* arg) {
+  if (link == NULL)
+    return UV_EFAULT;
   CLOSE_WRAP(link->methods->write(link, source, bufs, nbufs, send_handle, cb,
                                   arg));
 }
@@ -59,16 +61,22 @@ int uv_link_propagate_shutdown(uv_link_t* link,
                                uv_link_t* source,
                                uv_link_shutdown_cb cb,
                                void* arg) {
+  if (link == NULL)
+    return UV_EFAULT;
   CLOSE_WRAP(link->methods->shutdown(link, source, cb, arg));
 }
 
 
 int uv_link_read_start(uv_link_t* link) {
+  if (link == NULL)
+    return UV_EFAULT;
   CLOSE_WRAP(link->methods->read_start(link));
 }
 
 
 int uv_link_read_stop(uv_link_t* link) {
+  if (link == NULL)
+    return UV_EFAULT;
   CLOSE_WRAP(link->methods->read_stop(link));
 }
 
@@ -76,6 +84,8 @@ int uv_link_read_stop(uv_link_t* link) {
 int uv_link_try_write(uv_link_t* link,
                       const uv_buf_t bufs[],
                       unsigned int nbufs) {
+  if (link == NULL)
+    return UV_EFAULT;
   CLOSE_WRAP(link->methods->try_write(link, bufs, nbufs));
 }
 
diff --git a/test/src/test-close.c b/test/src/test-close.c
index bbbaf26..4f10630 100644
--- a/test/src/test-close.c
+++ b/test/src/test-close.c
@@ -19,10 +19,16 @@ static void c_close_cb(uv_link_t* l) {
 static void b_read_cb(uv_link_observer_t* o, ssize_t nread, const uv_buf_t* d) {
   b_reads |= 1 << nread;
   if (nread == 2) {
+    uv_buf_t tmp;
+
     CHECK_EQ(a.close_depth, 0, "depth check");
     CHECK_EQ(b.close_depth, 2, "depth check");
     CHECK_EQ(c.close_depth, 1, "depth check");
     uv_link_close((uv_link_t*) &c, c_close_cb);
+
+    CHECK_EQ(o->parent, NULL, "parent should be zeroed");
+    CHECK_EQ(uv_link_try_write(o->parent, &tmp, 0), UV_EFAULT,
+             "write should fail");
   } else {
     CHECK_EQ(a.close_depth, 0, "depth check");
     CHECK_EQ(b.close_depth, 1, "depth check");