parser.js

class RESPParser {
  constructor() {
    this.buffer = Buffer.alloc(0);
  }

  append(data) {
    this.buffer = Buffer.concat([this.buffer, data]);
  }

  *parse() {
    let offset = 0;

    while (offset < this.buffer.length) {
      const type = this.buffer[offset];
      if (type === 42) {
        // '*' Array
        const result = this.parseArray(offset);
        if (!result) break;
        offset = result.offset;
        yield result.value;
      } else {
        // Unknown or incomplete
        break;
      }
    }

    this.buffer = this.buffer.slice(offset);
  }

  parseArray(offset) {
    let currentOffset = offset + 1;
    const lineEnd = this.buffer.indexOf("\r\n", currentOffset);
    if (lineEnd === -1) return null;

    const countStr = this.buffer.toString("utf8", currentOffset, lineEnd);
    const count = parseInt(countStr, 10);
    currentOffset = lineEnd + 2;

    const array = [];
    for (let i = 0; i < count; i++) {
      const result = this.parseBulkString(currentOffset);
      if (!result) return null;
      array.push(result.value);
      currentOffset = result.offset;
    }

    return { value: array, offset: currentOffset };
  }

  parseBulkString(offset) {
    if (this.buffer[offset] !== 36) return null; // '$'

    let currentOffset = offset + 1;
    const lineEnd = this.buffer.indexOf("\r\n", currentOffset);
    if (lineEnd === -1) return null;

    const lengthStr = this.buffer.toString("utf8", currentOffset, lineEnd);
    const length = parseInt(lengthStr, 10);
    currentOffset = lineEnd + 2;

    if (length === -1) {
      return { value: null, offset: currentOffset };
    }

    if (this.buffer.length < currentOffset + length + 2) return null;

    const value = this.buffer.toString(
      "utf8",
      currentOffset,
      currentOffset + length,
    );
    currentOffset += length + 2;

    return { value, offset: currentOffset };
  }
}

module.exports = RESPParser;