git ssb

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const leb128 = require('leb128').unsigned
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const LebStream = require('leb128/stream')
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const Uint1Array = require('uint1array')
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const HASH_LEN = 20
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function toTypedArray (array) {
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  return new Uint1Array(new Uint8Array(array).buffer)
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}
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// helper functions for nodes
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const EXTENSION = exports.EXTENSION = 0
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const LBRANCH = exports.LBRANCH = 1
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const RBRANCH = exports.RBRANCH = 2
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const VALUE = exports.VALUE = 3
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exports.setBranch = function (node, branch) {
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  node['/'][LBRANCH] = branch[0]
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  node['/'][RBRANCH] = branch[1]
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}
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exports.getBranch = function (node) {
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  return node['/'].slice(LBRANCH, LBRANCH + 2)
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}
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exports.getValue = function (node) {
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  return node['/'][VALUE]
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}
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exports.deleteValue = function (node) {
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  delete node['/'][VALUE]
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}
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exports.getExtension = function (node) {
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  if (node['/'][EXTENSION]) {
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    const len = node['/'][EXTENSION][0]
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    const extension = toTypedArray(node['/'][EXTENSION][1])
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    return extension.subarray(0, len)
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  } else {
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    return []
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  }
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}
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exports.setExtension = function (node, ex) {
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  if (ex && ex.length) {
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    node['/'][EXTENSION] = [ex.length, Buffer.from(ex.buffer)]
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  } else {
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    delete node['/'][EXTENSION]
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  }
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}
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exports.setValue = function (node, val) {
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  node['/'][VALUE] = val
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}
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exports.isEmpty = function (node) {
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  const branch = exports.getBranch(node)
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  return !node['/'][EXTENSION] && !branch[0] && !branch[1] && node['/'][VALUE] === undefined
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}
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// PREFIX :=  | LBP | RBP | EXT | LB | RB | VALUE |
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// NODE := | PREFIX | LEN | PAYLOAD
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const MASK = {
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  EXTENSION: 8,
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  LBRANCH: 4,
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  RBRANCH: 2,
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  VALUE: 1
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}
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exports.encode = function (node, prefix = 0, encodeLen = false) {
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  let encoded = []
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  const ext = node[EXTENSION]
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  if (ext) {
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    const len = leb128.encode(ext[0])
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    encoded.push(len)
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    encoded.push(ext[1])
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    prefix += MASK.EXTENSION
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  }
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  const lb = node[LBRANCH]
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  if (lb) {
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    encoded.push(lb['/'])
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    prefix += MASK.LBRANCH
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  }
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  const rb = node[RBRANCH]
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  if (rb) {
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    encoded.push(rb['/'])
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    prefix += MASK.RBRANCH
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  }
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  const val = node[VALUE]
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  if (val !== undefined) {
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    encoded.push(val)
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    prefix += MASK.VALUE
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  }
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  encoded.unshift(Buffer.from([prefix]))
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  encoded = Buffer.concat(encoded)
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  if (encodeLen) {
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    const len = leb128.encode(encoded.length)
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    encoded = Buffer.concat([len, encoded])
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  }
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  return encoded
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}
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exports.decode = function (val) {
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  const node = [null, null, null]
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  const prefix = val[0]
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  const lebStream = new LebStream(val.slice(1))
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  if (prefix & MASK.EXTENSION) {
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    const len = Number(leb128.read(lebStream))
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    const ext = lebStream.read(Math.ceil(len / 8))
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    node[EXTENSION] = [len, ext]
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  }
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  if (prefix & MASK.LBRANCH) {
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    node[LBRANCH] = {
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      '/': lebStream.read(HASH_LEN)
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    }
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  }
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  if (prefix & MASK.RBRANCH) {
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    node[RBRANCH] = {
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      '/': lebStream.read(HASH_LEN)
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    }
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  }
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  if (prefix & MASK.VALUE) {
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    node[VALUE] = lebStream.buffer
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  }
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  return node
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}
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