wstream: Refactor wstream_new_buffer/wstream_write

- Removed 'copy' parameter from `wstream_new_buffer`. Callers simply pass a
  copy of the buffer if required.
- Added a callback parameter, which is used to notify callers when the data is
  successfully written. The callback is also used to free the buffer(if
  required) and is compatible with `free` from the standard library.

src/nvim/os/channel.c

@@ -194,9 +194,10 @@ static void parse_msgpack(RStream *rstream, void *data, bool eof)
     // Perform the call
     msgpack_rpc_call(channel->id, &unpacked.data, &response);
     wstream_write(channel->data.streams.write,
-                  wstream_new_buffer(channel->sbuffer->data,
+                  wstream_new_buffer(xmemdup(channel->sbuffer->data,
+                                             channel->sbuffer->size),
                                      channel->sbuffer->size,
-                                     true));
+                                     free));
 
     // Clear the buffer for future calls
     msgpack_sbuffer_clear(channel->sbuffer);
@@ -218,9 +219,10 @@ static void parse_msgpack(RStream *rstream, void *data, bool eof)
                       "an object with high level of nesting",
                       &response);
     wstream_write(channel->data.streams.write,
-                  wstream_new_buffer(channel->sbuffer->data,
+                  wstream_new_buffer(xmemdup(channel->sbuffer->data,
+                                             channel->sbuffer->size),
                                      channel->sbuffer->size,
-                                     true));
+                                     free));
     // Clear the buffer for future calls
     msgpack_sbuffer_clear(channel->sbuffer);
   }
@@ -310,9 +312,10 @@ static WBuffer *serialize_event(char *type, typval_T *data)
   msgpack_packer packer;
   msgpack_packer_init(&packer, &msgpack_event_buffer, msgpack_sbuffer_write);
   msgpack_rpc_notification(event_type, event_data, &packer);
-  WBuffer *rv = wstream_new_buffer(msgpack_event_buffer.data,
+  WBuffer *rv = wstream_new_buffer(xmemdup(msgpack_event_buffer.data,
+                                           msgpack_event_buffer.size),
                                    msgpack_event_buffer.size,
-                                   true);
+                                   free);
   msgpack_rpc_free_object(event_data);
   msgpack_sbuffer_clear(&msgpack_event_buffer);
 

src/nvim/os/job.c

@@ -258,7 +258,7 @@ bool job_write(int id, char *data, uint32_t len)
     return false;
   }
 
-  if (!wstream_write(job->in, wstream_new_buffer(data, len, false))) {
+  if (!wstream_write(job->in, wstream_new_buffer(data, len, free))) {
     job_stop(job->id);
     return false;
   }

src/nvim/os/wstream.c

@@ -21,8 +21,9 @@ struct wstream {
 };
 
 struct wbuffer {
-  size_t refcount, size;
+  size_t size, refcount;
   char *data;
+  wbuffer_data_finalizer cb;
 };
 
 typedef struct {
@@ -116,19 +117,16 @@ bool wstream_write(WStream *wstream, WBuffer *buffer)
 ///
 /// @param data Data stored by the WBuffer
 /// @param size The size of the data array
-/// @param copy If true, the data will be copied into the WBuffer
+/// @param cb Pointer to function that will be responsible for freeing
+///        the buffer data(passing 'free' will work as expected).
 /// @return The allocated WBuffer instance
-WBuffer *wstream_new_buffer(char *data, size_t size, bool copy)
+WBuffer *wstream_new_buffer(char *data, size_t size, wbuffer_data_finalizer cb)
 {
   WBuffer *rv = xmalloc(sizeof(WBuffer));
   rv->size = size;
   rv->refcount = 0;
-
-  if (copy) {
-    rv->data = xmemdup(data, size);
-  } else {
-    rv->data = data;
-  }
+  rv->cb = cb;
+  rv->data = data;
 
   return rv;
 }
@@ -141,8 +139,7 @@ static void write_cb(uv_write_t *req, int status)
   data->wstream->curmem -= data->buffer->size;
 
   if (!--data->buffer->refcount) {
-    // Free the data written to the stream
-    free(data->buffer->data);
+    data->buffer->cb(data->buffer->data);
     free(data->buffer);
   }
 

src/nvim/os/wstream_defs.h

@@ -3,6 +3,7 @@
 
 typedef struct wbuffer WBuffer;
 typedef struct wstream WStream;
+typedef void (*wbuffer_data_finalizer)(void *data);
 
 #endif  // NVIM_OS_WSTREAM_DEFS_H