fix(stream-text): ensure SSE handling conforms to the spec

packages/stream-text/src/index.ts

@@ -44,8 +44,7 @@ export interface StreamTextResult {
   usage?: Usage
 }
 
-const chunkHeaderPrefix = 'data: '
-const chunkErrorPrefix = `{"error":`
+const chunkHeaderPrefix = 'data:'
 
 /**
  * @experimental WIP, does not support function calling (tools).
@@ -64,30 +63,51 @@ export const streamText = async (options: StreamTextOptions): Promise<StreamText
   const rawChunkStream = res.body!.pipeThrough(new TransformStream({
     transform: async (chunk, controller) => {
       buffer += decoder.decode(chunk, { stream: true })
-      const lines = buffer.split('\n\n')
-      buffer = lines.pop() || ''
-
-      for (const line of lines) {
-        // Some cases:
-        // - Empty chunk
-        // - :ROUTER PROCESSING from OpenRouter
-        if (!line || !line.startsWith(chunkHeaderPrefix)) {
-          continue
+      const events = buffer.split('\n\n')
+      // Since the stream must ended with '\n\n', so it's safe to pop the last "event"(it should be empty)
+      buffer = events.pop() || ''
+
+      for (const event of events) {
+        // Handle multi-line data
+        const lines = event.split('\n')
+        const dataLines: string[] = []
+
+        for (const line of lines) {
+          // Skip empty lines
+          if (!line)
+            continue
+          // Check for comments
+          if (line.startsWith(':'))
+            continue
+          // Check if line starts with data: (allowing spaces)
+          if (line.startsWith(chunkHeaderPrefix)) {
+            // Extract content after data: (remove leading single space if present)
+            const content = line.slice(chunkHeaderPrefix.length)
+            dataLines.push(content.length > 0 && content[0] === ' ' ? content.slice(1) : content)
+          }
+          else {
+            break // event ended, dispatch
+          }
         }
 
-        const lineWithoutPrefix = line.slice(chunkHeaderPrefix.length)
-        if (lineWithoutPrefix.startsWith(chunkErrorPrefix)) {
-          // About controller error: https://developer.mozilla.org/en-US/docs/Web/API/TransformStreamDefaultController/error
-          controller.error(new Error(`Error from server: ${lineWithoutPrefix}`))
+        // Skip this event if no data lines found
+        if (dataLines.length === 0)
+          continue
+
+        const data = dataLines.join('\n')
+
+        if (data === '[DONE]') {
+          controller.terminate()
           break
         }
 
-        if (lineWithoutPrefix === '[DONE]') {
-          controller.terminate()
+        // Maybe we should use `JSON.parse` to check if it's a valid JSON
+        if (data.startsWith('{') && data.includes('"error"')) {
+          controller.error(new Error(`Error from server: ${data}`))
           break
         }
 
-        const chunk: ChunkResult = JSON.parse(lineWithoutPrefix)
+        const chunk: ChunkResult = JSON.parse(data)
         controller.enqueue(chunk)
 
         if (options.onChunk)