Avoid sending a new chunk when the body is already done

As discussed in servo#26807 (comment), we'd like to
add a new flag, `in_memory_done`, to `TransmitBodyConnectHandler` so
that we can correctly finish and drop the sender correctly.

When we send the bytes, we will mark the body as done and we can
recognize it's already done in next tick so that we can send a Done
request to finish the sender.

components/script/body.rs

@@ -42,6 +42,7 @@ use js::typedarray::{ArrayBuffer, CreateWith};
 use mime::{self, Mime};
 use net_traits::request::{BodyChunkRequest, BodySource as NetBodySource, RequestBody};
 use script_traits::serializable::BlobImpl;
+use std::cell::Cell;
 use std::ptr;
 use std::rc::Rc;
 use std::str;
@@ -72,6 +73,7 @@ struct TransmitBodyConnectHandler {
     bytes_sender: Option<IpcSender<Vec<u8>>>,
     control_sender: IpcSender<BodyChunkRequest>,
     in_memory: Option<Vec<u8>>,
+    in_memory_done: Cell<bool>,
     source: BodySource,
 }
 
@@ -91,6 +93,7 @@ impl TransmitBodyConnectHandler {
             bytes_sender: None,
             control_sender,
             in_memory,
+            in_memory_done: Cell::new(false),
             source,
         }
     }
@@ -155,6 +158,12 @@ impl TransmitBodyConnectHandler {
 
     /// The entry point to <https://fetch.spec.whatwg.org/#concept-request-transmit-body>
     fn transmit_body_chunk(&mut self) {
+        if self.in_memory_done.get() {
+            // Step 5.1.3
+            let _ = self.control_sender.send(BodyChunkRequest::Done);
+            return;
+        }
+
         let stream = self.stream.clone();
         let control_sender = self.control_sender.clone();
         let bytes_sender = self
@@ -165,7 +174,9 @@ impl TransmitBodyConnectHandler {
         // In case of the data being in-memory, send everything in one chunk, by-passing SpiderMonkey.
         if let Some(bytes) = self.in_memory.clone() {
             let _ = bytes_sender.send(bytes);
-            let _ = control_sender.send(BodyChunkRequest::Done);
+            // Mark this body as `done` so that we can correctly make it as Done in next tick
+            // and we won't leave this stream too early
+            self.in_memory_done.set(true);
             return;
         }