Class SSEDecoder

packages/client-common/src/sse.ts:190–273

* Stateful SSE event decoder. Feed lines one at a time via decode(). * Returns a ServerSentEvent on blank lines (dispatch), null otherwise. * * Per WHATWG spec §9.2.6: * - lastEventId persists across dispatches * - retry persists across dispatches (global reconnection setting) * - eventType re

 * - retry field must be ASCII digits only
 */
class SSEDecoder {
  private data: string[] = [];
  private eventType = '';
  private lastEventId: string | null = null;
  private retry: number | null = null;

  decode(line: string): ServerSentEvent | null {
    // Blank line → dispatch event or reset
    if (line === '') {
      return this.dispatch();
    }

    // Comment line (starts with ':')
    if (line[0] === ':') {
      return null;
    }

    // Parse field:value
    const colonIdx = line.indexOf(':');
    let field: string;
    let value: string;

    if (colonIdx === -1) {
      // No colon → field is entire line, value is empty
      field = line;
      value = '';
    } else {
      field = line.slice(0, colonIdx);
      value = line.slice(colonIdx + 1);
      // Strip exactly ONE leading space (if present)
      if (value[0] === ' ') {
        value = value.slice(1);
      }
    }

    switch (field) {
      case 'data':
        this.data.push(value);
        break;
      case 'event':
        this.eventType = value;
        break;
      case 'id':
        // Ignore if value contains NULL character (security: WHATWG spec)
        if (!value.includes('\0')) {
          this.lastEventId = value;
        }
        break;
      case 'retry':
        // Must consist of ASCII digits only (no negatives, no whitespace)
        if (/^[0-9]+$/.test(value)) {
          this.retry = parseInt(value, 10);
        }
        break;
      // Unknown fields: ignore silently
    }

    return null;