Fix Wyoming protocol: read data as separate chunk after header

The Wyoming wire format sends data as a separate byte chunk after the
header JSON line, not inline. The header's data_length field indicates
how many bytes to read for the data JSON, followed by payload_length
bytes of binary payload.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

wyoming-whisper-rs/src/protocol.rs

@@ -6,26 +6,24 @@ use crate::error::Error;
 
 const MAX_PAYLOAD: usize = 100 * 1024 * 1024; // 100 MB
 
+/// Wire header: the JSON line sent before data/payload bytes.
 #[derive(Debug, Clone, Serialize, Deserialize)]
-pub struct Event {
+struct Header {
     #[serde(rename = "type")]
-    pub event_type: String,
+    event_type: String,
 
-    #[serde(default, skip_serializing_if = "Option::is_none")]
-    pub data: Option<Value>,
+    #[serde(default)]
+    data_length: usize,
 
-    #[serde(default, skip_serializing_if = "is_zero")]
-    pub data_length: usize,
-
-    #[serde(default, skip_serializing_if = "is_zero")]
-    pub payload_length: usize,
-
-    #[serde(skip)]
-    pub payload: Option<Vec<u8>>,
+    #[serde(default)]
+    payload_length: usize,
 }
 
-fn is_zero(v: &usize) -> bool {
-    *v == 0
+#[derive(Debug, Clone)]
+pub struct Event {
+    pub event_type: String,
+    pub data: Option<Value>,
+    pub payload: Option<Vec<u8>>,
 }
 
 impl Event {
@@ -33,15 +31,11 @@ impl Event {
         Self {
             event_type: event_type.into(),
             data: None,
-            data_length: 0,
-            payload_length: 0,
             payload: None,
         }
     }
 
     pub fn with_data(mut self, data: Value) -> Self {
-        let serialized = serde_json::to_string(&data).unwrap_or_default();
-        self.data_length = serialized.len();
         self.data = Some(data);
         self
     }
@@ -56,31 +50,67 @@ pub async fn read_event<R: tokio::io::AsyncRead + Unpin>(
         return Ok(None);
     }
 
-    let mut event: Event = serde_json::from_str(line.trim())?;
+    let header: Header = serde_json::from_str(line.trim())?;
 
-    if event.payload_length > 0 {
-        if event.payload_length > MAX_PAYLOAD {
+    let data = if header.data_length > 0 {
+        if header.data_length > MAX_PAYLOAD {
             return Err(Error::PayloadTooLarge {
-                size: event.payload_length,
+                size: header.data_length,
                 max: MAX_PAYLOAD,
             });
         }
-        let mut buf = vec![0u8; event.payload_length];
+        let mut buf = vec![0u8; header.data_length];
         reader.read_exact(&mut buf).await?;
-        event.payload = Some(buf);
-    }
+        Some(serde_json::from_slice(&buf)?)
+    } else {
+        None
+    };
 
-    Ok(Some(event))
+    let payload = if header.payload_length > 0 {
+        if header.payload_length > MAX_PAYLOAD {
+            return Err(Error::PayloadTooLarge {
+                size: header.payload_length,
+                max: MAX_PAYLOAD,
+            });
+        }
+        let mut buf = vec![0u8; header.payload_length];
+        reader.read_exact(&mut buf).await?;
+        Some(buf)
+    } else {
+        None
+    };
+
+    Ok(Some(Event {
+        event_type: header.event_type,
+        data,
+        payload,
+    }))
 }
 
 pub async fn write_event<W: tokio::io::AsyncWrite + Unpin>(
     writer: &mut W,
     event: &Event,
 ) -> Result<(), Error> {
-    let json = serde_json::to_string(event)?;
-    writer.write_all(json.as_bytes()).await?;
+    let data_bytes = event
+        .data
+        .as_ref()
+        .map(|d| serde_json::to_vec(d))
+        .transpose()?;
+
+    let header = Header {
+        event_type: event.event_type.clone(),
+        data_length: data_bytes.as_ref().map_or(0, |b| b.len()),
+        payload_length: event.payload.as_ref().map_or(0, |b| b.len()),
+    };
+
+    let header_json = serde_json::to_string(&header)?;
+    writer.write_all(header_json.as_bytes()).await?;
     writer.write_all(b"\n").await?;
 
+    if let Some(ref data) = data_bytes {
+        writer.write_all(data).await?;
+    }
+
     if let Some(ref payload) = event.payload {
         writer.write_all(payload).await?;
     }