add support for multiline data messages.

Currently, the `data` passed to `Sender::send()` is prepended with
`data:` and written as-is. If the data string contains newlines, that
causes any data beyond the newline(s) to end up on a line that does not
begin with `data:`, which the spec dictates should be ignored. This
change splits the message on newlines and writes each line with its own
`data:` prefix.

Author: igowen

src/encoder.rs

@@ -117,8 +117,11 @@ impl Sender {
         }
 
         // Write the data section, and end.
-        let msg = format!("data:{}\n\n", data);
-        self.inner_send(msg).await?;
+        for line in data.lines() {
+            let msg = format!("data:{}\n", line);
+            self.inner_send(msg).await?;
+        }
+        self.inner_send("\n").await?;
 
         Ok(())
     }

tests/encode.rs

@@ -95,6 +95,17 @@ async fn encode_retry() -> http_types::Result<()> {
     Ok(())
 }
 
+#[async_std::test]
+async fn encode_multiline_message() -> http_types::Result<()> {
+    let (sender, encoder) = encode();
+    task::spawn(async move { sender.send("cats", "chashu\nnori", None).await });
+
+    let mut reader = decode(BufReader::new(encoder));
+    let event = reader.next().await.unwrap()?;
+    assert_message(&event, "cats", "chashu\nnori", None);
+    Ok(())
+}
+
 #[async_std::test]
 async fn dropping_encoder() -> http_types::Result<()> {
     let (sender, encoder) = encode();