fix(streaming): correctly handle trailing new lines in byte chunks (#708)

Author: stainless-bot

src/streaming.ts

@@ -267,7 +267,7 @@ class SSEDecoder {
  *
  * https://github.com/encode/httpx/blob/920333ea98118e9cf617f246905d7b202510941c/httpx/_decoders.py#L258
  */
-class LineDecoder {
+export class LineDecoder {
   // prettier-ignore
   static NEWLINE_CHARS = new Set(['\n', '\r', '\x0b', '\x0c', '\x1c', '\x1d', '\x1e', '\x85', '\u2028', '\u2029']);
   static NEWLINE_REGEXP = /\r\n|[\n\r\x0b\x0c\x1c\x1d\x1e\x85\u2028\u2029]/g;
@@ -300,6 +300,12 @@ class LineDecoder {
     const trailingNewline = LineDecoder.NEWLINE_CHARS.has(text[text.length - 1] || '');
     let lines = text.split(LineDecoder.NEWLINE_REGEXP);
 
+    // if there is a trailing new line then the last entry will be an empty
+    // string which we don't care about
+    if (trailingNewline) {
+      lines.pop();
+    }
+
     if (lines.length === 1 && !trailingNewline) {
       this.buffer.push(lines[0]!);
       return [];

tests/streaming.test.ts

@@ -0,0 +1,42 @@
+import { LineDecoder } from 'openai/streaming';
+
+function decodeChunks(chunks: string[], decoder?: LineDecoder): string[] {
+  if (!decoder) {
+    decoder = new LineDecoder();
+  }
+
+  const lines = [];
+  for (const chunk of chunks) {
+    lines.push(...decoder.decode(chunk));
+  }
+
+  return lines;
+}
+
+describe('line decoder', () => {
+  test('basic', () => {
+    // baz is not included because the line hasn't ended yet
+    expect(decodeChunks(['foo', ' bar\nbaz'])).toEqual(['foo bar']);
+  });
+
+  test('basic with \\r', () => {
+    // baz is not included because the line hasn't ended yet
+    expect(decodeChunks(['foo', ' bar\r\nbaz'])).toEqual(['foo bar']);
+  });
+
+  test('trailing new lines', () => {
+    expect(decodeChunks(['foo', ' bar', 'baz\n', 'thing\n'])).toEqual(['foo barbaz', 'thing']);
+  });
+
+  test('trailing new lines with \\r', () => {
+    expect(decodeChunks(['foo', ' bar', 'baz\r\n', 'thing\r\n'])).toEqual(['foo barbaz', 'thing']);
+  });
+
+  test('escaped new lines', () => {
+    expect(decodeChunks(['foo', ' bar\\nbaz\n'])).toEqual(['foo bar\\nbaz']);
+  });
+
+  test('escaped new lines with \\r', () => {
+    expect(decodeChunks(['foo', ' bar\\r\\nbaz\n'])).toEqual(['foo bar\\r\\nbaz']);
+  });
+});