git ssb

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var buffered = require('pull-buffered')
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var crypto = require('crypto')
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var pull = require('pull-stream')
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var toPull = require('stream-to-pull-stream')
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var Inflate = require('pako/lib/inflate').Inflate
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exports.decode = decodePack
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var objectTypes = [
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  'none', 'commit', 'tree', 'blob',
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  'tag', 'unused', 'ofs-delta', 'ref-delta'
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]
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function error(cb) {
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  return function (err) {
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    cb(err || true)
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  }
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}
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function createHash(type) {
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  var hash = crypto.createHash(type)
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  var hasher = pull.through(hash.update.bind(hash))
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  hasher.digest = hash.digest.bind(hash)
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  return hasher
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}
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function inflateBytes(read) {
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  var inflate = new Inflate()
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  var ended, dataOut
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  inflate.onData = function (data) {
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    dataOut = new Buffer(data)
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    // console.error('inflated data', data.length)
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  }
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  inflate.onEnd = function (status) {
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    ended = (status === 0) ? true : new Error(inflate.msg)
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    // console.error('inflated end', status, ended)
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  }
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  return function (abort, cb) {
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    if (ended) return cb(ended)
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    read(abort, function next(end, data) {
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      if (end === true) {
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        end = null
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        data = []
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      }
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      if (ended = end) return cb(end)
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      if (data.length > 1) return cb(new Error('got more than one byte'))
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      dataOut = null
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      inflate.push(data, end === true)
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      if (dataOut)
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        cb(null, dataOut)
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      else if (ended)
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        cb(ended)
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      else
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        read(null, next)
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    })
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  }
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}
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function decodePack(onEnd, read) {
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  if (read === undefined)
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    return decodePack.bind(this, onEnd)
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  var ended
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  var numObjects = -1
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  var checksum = createHash('sha1')
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  var b = buffered(read)
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  // TODO: optimize to pass through buffers to checksum
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  var readByte = checksum(b.chunks(1))
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  var readWord = checksum(b.chunks(4))
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  var readChecksum = b.chunks(20)
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  var expectChecksum = true
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  var opts = {
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    verbosity: 2
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  }
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  function readHeader(cb) {
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    readWord(null, function (end, header) {
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      if (ended = end) return cb(end)
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      if (!header.equals(header, new Buffer('PACK')))
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        read(new Error('Invalid packfile header'), error(cb))
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      else
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        readVersion(cb)
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    })
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  }
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  function readVersion(cb) {
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    readWord(null, function (end, word) {
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      if (ended = end) return cb(end)
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      var version = word.readUInt32BE()
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      if (version < 2 || version > 3)
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        read(new Error('Invalid packfile version ' + version), error(cb))
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      else
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        readNumObjects(cb)
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    })
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  }
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  function readNumObjects(cb) {
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    readWord(null, function (end, word) {
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      if (ended = end) return cb(end)
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      numObjects = word.readUInt32BE()
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      if (opts.verbosity >= 1)
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        console.error(numObjects + ' objects')
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      readObject(null, cb)
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    })
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  }
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  function readVarInt(cb) {
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    var type, value, shift
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    // https://codewords.recurse.com/images/three/varint.svg
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    readByte(null, function (end, buf) {
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      if (ended = end) return cb(end)
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      var firstByte = buf[0]
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      type = objectTypes[(firstByte >> 4) & 7]
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      value = firstByte & 15
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      // console.error('byte1', firstByte, firstByte.toString(2), value, value.toString(2))
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      shift = 4
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      checkByte(firstByte)
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    })
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    function checkByte(byte) {
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      if (byte & 0x80)
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        readByte(null, gotByte)
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      else
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        cb(null, type, value)
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    }
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    function gotByte(end, buf) {
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      if (ended = end) return cb(end)
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      var byte = buf[0]
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      value += (byte & 0x7f) << shift
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      shift += 7
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      // console.error('byte', byte, byte.toString(2), value, value.toString(2))
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      checkByte(byte)
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    }
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  }
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  function getObject(cb) {
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    readVarInt(function (end, type, length) {
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      if (opts.verbosity >= 2)
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        console.error('read var int', end, type, length)
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      numObjects--
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      if (end === true && expectChecksum)
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        onEnd(new Error('Missing checksum'))
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      if (ended = end) return cb(end)
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      // TODO: verify that the inflated data is the correct length
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      cb(null, type, inflateBytes(readByte))
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    })
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  }
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  function readTrailer(cb) {
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    // read the checksum before it updates to include the trailer
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    var expected = checksum.digest()
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    readChecksum(null, function (end, value) {
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      cb(true)
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      if (end === true && expectChecksum)
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        onEnd(new Error('Missing checksum'))
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      if (!value.equals(expected)) {
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        onEnd(new Error('Checksum mismatch: ' +
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          expected.hexSlice() + ' != ' + value.hexSlice()))
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      } else {
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        if (opts.verbosity >= 2)
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          console.error('checksum ok', expected.hexSlice())
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        onEnd(null)
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      }
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    })
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  }
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  function readObject(abort, cb) {
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    if (ended) cb(ended)
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    else if (abort) read(abort)
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    else if (numObjects < 0) readHeader(cb)
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    else if (numObjects > 0) getObject(cb)
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    else if (expectChecksum) readTrailer(cb)
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  }
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  return readObject
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}
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