Function iterLines

packages/client-common/src/sse.ts:83–174

* Yields individual lines from a byte stream. * * Handles \r, \n, and \r\n line endings, including \r\n split across chunks. * Uses offset tracking within each decoded chunk to avoid O(n²) buffer growth. * Strips BOM (U+FEFF) from the very first line. * Throws if the internal line buffer exceed

(stream: ReadableStream<Uint8Array> | AsyncIterable<Uint8Array>)

 * Throws if the internal line buffer exceeds 10MB.
 */
async function* iterLines(stream: ReadableStream<Uint8Array> | AsyncIterable<Uint8Array>): AsyncGenerator<string> {
  const decoder = new TextDecoder('utf-8');
  const buffer: string[] = [];
  let bufferSize = 0;
  let trailingCR = false;
  let isFirstLine = true;

  for await (const chunk of toAsyncIterable(stream)) {
    const text = decoder.decode(chunk, { stream: true });
    let offset = 0;

    // Handle \r\n split across chunks: if the previous chunk ended with \r
    // and this one starts with \n, skip the \n (it's the second half of \r\n)
    if (trailingCR) {
      trailingCR = false;
      if (text.length > 0 && text[0] === '\n') {
        offset = 1;
      }
    }

    while (offset < text.length) {
      const crIdx = text.indexOf('\r', offset);
      const lfIdx = text.indexOf('\n', offset);

      // No more line endings in this chunk — buffer the rest
      if (crIdx === -1 && lfIdx === -1) {
        const remaining = text.slice(offset);
        buffer.push(remaining);
        bufferSize += remaining.length;
        if (bufferSize > MAX_LINE_BUFFER_SIZE) {
          throw new Error('SSE line buffer exceeded 10MB');
        }
        break;
      }

      let endIdx: number;
      let skipLen: number;

      if (crIdx !== -1 && (lfIdx === -1 || crIdx < lfIdx)) {
        // \r found before \n (or no \n at all)
        endIdx = crIdx;
        if (crIdx + 1 < text.length) {
          // Peek ahead: \r\n or bare \r
          skipLen = text[crIdx + 1] === '\n' ? 2 : 1;
        } else {
          // \r at end of chunk — might be \r\n split across chunks
          trailingCR = true;
          skipLen = 1;
        }
      } else {
        // \n found before \r (or no \r at all)
        // Safe: at least one of crIdx/lfIdx is != -1, and we're in the else
        // branch, so lfIdx must be != -1
        endIdx = lfIdx;
        skipLen = 1;
      }

      const segment = text.slice(offset, endIdx);