fix(sse): handle \r and \r\n line endings in writeSSE (#4644)

AprilNEA · web-flow · commit 2a9cd953b6e9 · 2026-01-26T23:42:07.000+09:00
According to the SSE specification, lines can end with `\r`, `\n`, or
`\r\n`.
diff --git a/src/helper/streaming/sse.test.tsx b/src/helper/streaming/sse.test.tsx
@@ -238,4 +238,81 @@ describe('SSE Streaming helper', () => {
     const decodedValue = decoder.decode(value)
     expect(decodedValue).toBe('data: <div>Error</div>\n\n')
   })
+
+  it('Check streamSSE handles \\r (CR) line ending correctly', async () => {
+    const res = streamSSE(c, async (stream) => {
+      await stream.writeSSE({
+        data: 'Line1\rLine2',
+        event: 'test-cr',
+      })
+    })
+
+    if (!res.body) {
+      throw new Error('Body is null')
+    }
+    const reader = res.body.getReader()
+    const decoder = new TextDecoder()
+    const { value } = await reader.read()
+    const decodedValue = decoder.decode(value)
+
+    expect(decodedValue).toBe('event: test-cr\ndata: Line1\ndata: Line2\n\n')
+  })
+
+  it('Check streamSSE handles \\r\\n (CRLF) line ending correctly', async () => {
+    const res = streamSSE(c, async (stream) => {
+      await stream.writeSSE({
+        data: 'Line1\r\nLine2',
+        event: 'test-crlf',
+      })
+    })
+
+    if (!res.body) {
+      throw new Error('Body is null')
+    }
+    const reader = res.body.getReader()
+    const decoder = new TextDecoder()
+    const { value } = await reader.read()
+    const decodedValue = decoder.decode(value)
+
+    expect(decodedValue).toBe('event: test-crlf\ndata: Line1\ndata: Line2\n\n')
+  })
+
+  it('Check streamSSE handles mixed line endings correctly', async () => {
+    const res = streamSSE(c, async (stream) => {
+      await stream.writeSSE({
+        data: 'A\nB\rC\r\nD',
+        event: 'test-mixed',
+      })
+    })
+
+    if (!res.body) {
+      throw new Error('Body is null')
+    }
+    const reader = res.body.getReader()
+    const decoder = new TextDecoder()
+    const { value } = await reader.read()
+    const decodedValue = decoder.decode(value)
+
+    expect(decodedValue).toBe('event: test-mixed\ndata: A\ndata: B\ndata: C\ndata: D\n\n')
+  })
+
+  it('Check streamSSE handles consecutive \\r correctly', async () => {
+    const res = streamSSE(c, async (stream) => {
+      await stream.writeSSE({
+        data: 'Left\r\rRight',
+        event: 'test-double-cr',
+      })
+    })
+
+    if (!res.body) {
+      throw new Error('Body is null')
+    }
+    const reader = res.body.getReader()
+    const decoder = new TextDecoder()
+    const { value } = await reader.read()
+    const decodedValue = decoder.decode(value)
+
+    // Two \r should produce an empty line in between
+    expect(decodedValue).toBe('event: test-double-cr\ndata: Left\ndata: \ndata: Right\n\n')
+  })
 })
diff --git a/src/helper/streaming/sse.ts b/src/helper/streaming/sse.ts
@@ -18,7 +18,7 @@ export class SSEStreamingApi extends StreamingApi {
   async writeSSE(message: SSEMessage) {
     const data = await resolveCallback(message.data, HtmlEscapedCallbackPhase.Stringify, false, {})
     const dataLines = (data as string)
-      .split('\n')
+      .split(/\r\n|\r|\n/)
       .map((line) => {
         return `data: ${line}`
       })
