git ssb

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const Buffer = require('safe-buffer').Buffer
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const crypto = require('crypto')
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const DAG = require('ipld-graph-builder/datastore.js')
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const cbor = require('borc')
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const HASH_LEN = 20
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const LINK_TAG = 42
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module.exports = class TreeDAG extends DAG {
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  async put (val) {
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    if (val[1]) {
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      val[1] = new cbor.Tagged(LINK_TAG, val[1]['/'])
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    }
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    if (val[2]) {
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      val[2] = new cbor.Tagged(LINK_TAG, val[2]['/'])
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    }
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    const encoded = cbor.encode(val)
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    const key = await TreeDAG.getMerkleLink(encoded)
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    return new Promise((resolve, reject) => {
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      this._dag.put(key, encoded.toString('hex'), () => {
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        resolve(key)
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      })
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    })
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  }
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  get (link) {
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    return new Promise((resolve, reject) => {
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      this._dag.get(link, (err, val) => {
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        if (err) {
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          reject(err)
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        } else {
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          val = Buffer.from(val, 'hex')
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          const decoded = cbor.decode(val)
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          if (decoded[1]) {
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            decoded[1]['/'] = decoded[1].value
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          }
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          if (decoded[2]) {
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            decoded[2]['/'] = decoded[2].value
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          }
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          resolve(decoded)
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        }
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      })
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    })
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  }
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  static isValidLink (link) {
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    return Buffer.isBuffer(link) && link.length === HASH_LEN
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  }
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  static getMerkleLink (buf) {
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    const hash = crypto.createHash('sha256')
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    hash.update(buf)
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    return hash.digest().slice(0, HASH_LEN)
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  }
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}
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