unix,win: harmonize buffer checking

For any API that takes a buffer and size pointer, check both pointers
and the pointed-to size and return UV_EINVAL in case of error.

Example:

```
int uv_foo(char* buffer, size_t* size) {
  if (buffer == NULL || size == NULL || *size == 0)
    return UV_EINVAL;
  ...
}
```

In order to "peek" the necessary size for dynamic allocation, the
following pattern can be used:

```
char *buf;
char scratch[1];
size_t len = sizeof(scratch);
int r;
r = uv_foo(scratch, &len);
assert(r == UV_ENOBUFS);
buf = malloc(len);
r = uv_foo(buf, &len);
...
```

src/fs-poll.c

@@ -139,6 +139,9 @@ int uv_fs_poll_getpath(uv_fs_poll_t* handle, char* buffer, size_t* size) {
   struct poll_ctx* ctx;
   size_t required_len;
 
+  if (buffer == NULL || size == NULL || *size == 0)
+    return UV_EINVAL;
+
   if (!uv_is_active((uv_handle_t*)handle)) {
     *size = 0;
     return UV_EINVAL;

src/unix/core.c

@@ -751,7 +751,7 @@ ssize_t uv__recvmsg(int fd, struct msghdr* msg, int flags) {
 int uv_cwd(char* buffer, size_t* size) {
   char scratch[1 + UV__PATH_MAX];
 
-  if (buffer == NULL || size == NULL)
+  if (buffer == NULL || size == NULL || *size == 0)
     return UV_EINVAL;
 
   /* Try to read directly into the user's buffer first... */

src/uv-common.c

@@ -644,6 +644,9 @@ int uv_send_buffer_size(uv_handle_t* handle, int *value) {
 int uv_fs_event_getpath(uv_fs_event_t* handle, char* buffer, size_t* size) {
   size_t required_len;
 
+  if (buffer == NULL || size == NULL || *size == 0)
+    return UV_EINVAL;
+
   if (!uv__is_active(handle)) {
     *size = 0;
     return UV_EINVAL;

src/win/pipe.c

@@ -1161,9 +1161,9 @@ int uv__pipe_accept(uv_pipe_t* server, uv_stream_t* client) {
 
     err = uv__tcp_xfer_import(
         (uv_tcp_t*) client, item->xfer_type, &item->xfer_info);
-    
+
     uv__free(item);
-    
+
     if (err != 0)
       return err;
 
@@ -1738,7 +1738,7 @@ static DWORD uv__pipe_get_ipc_remote_pid(uv_pipe_t* handle) {
       GetNamedPipeServerProcessId(handle->handle, pid);
     }
   }
-  
+
   return *pid;
 }
 
@@ -2602,6 +2602,9 @@ int uv_pipe_pending_count(uv_pipe_t* handle) {
 
 
 int uv_pipe_getsockname(const uv_pipe_t* handle, char* buffer, size_t* size) {
+  if (buffer == NULL || size == NULL || *size == 0)
+    return UV_EINVAL;
+
   if (handle->flags & UV_HANDLE_BOUND)
     return uv__pipe_getname(handle, buffer, size);
 
@@ -2616,6 +2619,9 @@ int uv_pipe_getsockname(const uv_pipe_t* handle, char* buffer, size_t* size) {
 
 
 int uv_pipe_getpeername(const uv_pipe_t* handle, char* buffer, size_t* size) {
+  if (buffer == NULL || size == NULL || *size == 0)
+    return UV_EINVAL;
+
   /* emulate unix behaviour */
   if (handle->flags & UV_HANDLE_BOUND)
     return UV_ENOTCONN;

src/win/util.c

@@ -191,7 +191,7 @@ int uv_cwd(char* buffer, size_t* size) {
   WCHAR *utf16_buffer;
   int r;
 
-  if (buffer == NULL || size == NULL) {
+  if (buffer == NULL || size == NULL || *size == 0) {
     return UV_EINVAL;
   }
 
@@ -1589,7 +1589,7 @@ int uv_os_uname(uv_utsname_t* buffer) {
     version_size = sizeof(buffer->version) - version_size;
     r = uv__copy_utf16_to_utf8(os_info.szCSDVersion,
                                -1,
-                               buffer->version + 
+                               buffer->version +
                                  sizeof(buffer->version) - version_size,
                                &version_size);
     if (r)

test/test-fs-event.c

@@ -1121,7 +1121,7 @@ TEST_IMPL(fs_event_getpath) {
     ASSERT_EQ(r, UV_EINVAL);
     r = uv_fs_event_start(&fs_event, fail_cb, watch_dir[i], 0);
     ASSERT_OK(r);
-    len = 0;
+    len = 1;
     r = uv_fs_event_getpath(&fs_event, buf, &len);
     ASSERT_EQ(r, UV_ENOBUFS);
     ASSERT_LT(len, sizeof buf); /* sanity check */