git ssb

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const Buffer = require('safe-buffer').Buffer
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const TreeDAG = require('./datastore.js')
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const fetch = require('node-fetch')
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module.exports = class RemoteTreeDAG extends TreeDAG {
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  /**
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   * @param dag {object} a level db instance
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   * @param remoteOpts
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   * @param remoteOpts.uri {string} the HTTP uri which has an interface: GET /:key -> value
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   * @param remoteOpts.encoding {string} the encoding of the reponse
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   * @param opts.decoder {object} a cbor decoder
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   */
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  constructor (dag, remoteOpts, decoder) {
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    super(dag, decoder)
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    this.remoteOpts = Object.assign({
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      uri: null,
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      encoding: 'base64'
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    }, remoteOpts)
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  }
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  async get (link) {
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    try {
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      return await super.get(link)
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    } catch (e) {
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      if (this.remoteOpts.uri) {
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        await this.fetchRemote(link)
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        return super.get(link)
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      }
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    }
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  }
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  fetchRemote (key) {
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    if (!Buffer.isBuffer(key)) {
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      key = Buffer.from(key.buffer)
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    }
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    const route = `${this.remoteOpts.uri}/${key.toString('hex')}`
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    return fetch(route)
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      .then(res => res.text())
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      .then(text => {
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        const encoded = Buffer.from(text, this.remoteOpts.encoding)
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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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      .catch(err => {
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        console.warn(`error fetching ${route}:`, err.message)
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      })
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  }
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}
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