protobuf-codec/decode/wire-types.js

Minimal Protocol Buffers wire encoding/decoding

const assert = require('nanoassert')

/**
 * Wire type decoders mapping the `type` integer to the basic decoder.
 * Groups are not supported, and the higher-level types are done in a 2nd pass
 * @type {Object}
 */
const decoders = {
  0: varint,
  1: fixed64bit,
  2: bytes,
  5: fixed32bit
}

function tag (buf, byteOffset = 0) {
  const int = Number(varint(buf, byteOffset)) // Safe as protoc only allows fieldNumber up to int32 + 3 bits for wireType
  const wireType = int & 0b111
  const fieldNumber = int >> 3

  tag.bytes = varint.bytes

  return { wireType, fieldNumber }
}

function varint (buf, byteOffset = 0) {
  let o = byteOffset
  let acc = 0n
  let shift = 0n
  while (buf[o] & 0b1000_0000) {
    acc |= BigInt(buf[o++] & 0b0111_1111) << shift
    shift += 7n
  }

  assert((buf[o] & 0b1000_0000) === 0, 'Malformed varint')

  acc |= BigInt(buf[o++] & 0b0111_1111) << shift

  varint.bytes = o - byteOffset
  return acc
}

function bytes (buf, byteOffset = 0) {
  const len = varint(buf, byteOffset)

  assert(buf.byteLength - byteOffset - varint.bytes >= len, 'Malformed bytes')
  const b = buf.subarray(byteOffset + varint.bytes, byteOffset + varint.bytes + Number(len))

  bytes.bytes = varint.bytes + Number(len)
  return b
}

function fixed64bit (buf, byteOffset = 0) {
  assert(buf.byteLength - byteOffset >= 8, 'Malformed 64-bit')
  fixed64bit.bytes = 8
  return buf.subarray(byteOffset, byteOffset + 8)
}

function fixed32bit (buf, byteOffset = 0) {
  assert(buf.byteLength - byteOffset >= 4, 'Malformed 64-bit')
  fixed32bit.bytes = 4
  return buf.subarray(byteOffset, byteOffset + 4)
}

module.exports = {
  decoders,
  tag,
  varint,
  bytes,
  fixed64bit,
  fixed32bit
}