Technical Considerations

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Deep dive in to setting up micro-services to facilitate ledger interactions.
Proxy Signing Service
​Sawtooth is built for enterprises and has some limitations that need to be considered when allowing public write access to a database. To interact with Transaction Processors(TPs) memory must be managed in the signed batch of transactions. These complexities have lead to building a simple Relay Process Command(RPC) which is described below. This is built with Node.js and happens inside an express.js server instance 'app':
index.js { transaction proxying }
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app.get('/adv-build', (req, res, next) => {
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  var auth = false
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  if (req.session) auth = authed(req.session.user)
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  if (!auth) {
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    delete req.session
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    res.redirect('/login')
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  } else {
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  //[1-4Now all the memory access has been permission by Batch Processor (BP) signature (authorization is important). The transactions have been listed, that batch has been built and signed and "finished" into a package.]
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  }
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});
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 This authorization check should happen in middleware; here for linearity.
Here a JSON web token is verified against our secret key. This token could be delivered by magic link.
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function authed(user) {
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  var auth = false
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  try {
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    if (user && localUsers[jwt.verify(user.token, sessionSecretKey).sub] != null) {
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      auth = true    //If session exists, proceed to page
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    }
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  } catch (e) { console.log('JWT Error: ' + e)}
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  return auth
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}
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Once the user is verified a method to hand form data over is used; here in url query:
index.js [1]
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var payload = {
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      [req.query.vt || 'Verb']: req.query.verb || 'inc',
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      [req.query.nt || 'Name']: req.query.action || 'test',
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      [req.query.at || 'Value']: req.query.desc || parseInt(req.query.num) || 1
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    }
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    if (req.query.addr || req.query.rt) {
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      payload[req.query.rt || 'addr'] = req.query.addr || null
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    }
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    if (req.query.family === 'emre') {
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      payload = `${
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        req.query.verb || '0002019CO2T8642'},${
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        req.query.action || 'create'},${
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        req.query.desc || '000_2019_CO2_T_8642_test_Qmtest'}`
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    }
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This supports building any type of transaction. It was modeled off the intKey transaction family but includes methods to change to any transaction payload with three strings. More complex transactions will need more work here and refinement is suggested. By default this will generate a transaction that will increment an intKey at the 'test' address. If emission records(emre) are requested a test transaction is also built there. From here we will be talking through selecting both of these types.
index.js [2]
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let payloadBytes
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    var inputs = [], //addresses to read
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      outputs = [] //addresses to write
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    const _hash = (x) => // crypto = require('crypto')
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      crypto.createHash('sha512').update(x).digest('hex').toLowerCase()
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    const _hash64 = (x) =>
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      crypto.createHash('sha512').update(x).digest('hex').toLowerCase().substring(0, 64)
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    const INT_KEY_FAMILY = 'intkey'
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    const INT_KEY_NAMESPACE = _hash(INT_KEY_FAMILY).substring(0, 6)
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​
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    const EMSSIONS_KEY_FAMILY = 'emre'
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    const EMSSIONS_KEY_NAMESPACE = _hash(EMSSIONS_KEY_FAMILY).substring(0, 6)
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    switch (req.query.family) {
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      case 'emre':
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        inputs.push(EMSSIONS_KEY_NAMESPACE + _hash64(payload.split(',')[0])) //test for allowed names?
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        outputs.push(EMSSIONS_KEY_NAMESPACE + _hash64(payload.split(',')[0]))
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        payloadBytes = Buffer.from(payload, 'utf-8')
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        break;
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      case 'intkey'://intkey
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      default: //intkey
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        inputs.push(INT_KEY_NAMESPACE + _hash(payload.Name).slice(-64))
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        outputs.push(INT_KEY_NAMESPACE + _hash(payload.Name).slice(-64))
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        payloadBytes = cbor.encode(payload)
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    }
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TPs are expecting properly formatted payloads in properly signed and addressed batches. Depending on how the TP is made will determine the type of payload it is expecting. IntKey expects a concise binary object representation (cbor) while emission records uses a standard utf-8 buffer available in node.
Depending on which TP is intended will determine the addressing scheme. Both of these transactions only take the same input and write to the same output. To build reference tables and utilize internal data dependencies for these addressing schemes will also require more addresses to be added to these input and output arrays. 
Now that we have out payload encoded for each of their possible TPs let's look at how signing occurs.
index.js [3]
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const transactionHeaderBytes = protobuf.TransactionHeader.encode({
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      familyName: req.query.family || 'intkey', //can these be arrays? this could be a goverenace limitation
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      familyVersion: req.query.version || '1.0',
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      inputs: inputs,
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      outputs: outputs,
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      signerPublicKey: signer.getPublicKey().asHex(),//public keys for signers
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      batcherPublicKey: signer.getPublicKey().asHex(),//'signer' is batch processor key
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      dependencies: [],
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      payloadSha512: createHash('sha512').update(payloadBytes).digest('hex')
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    }).finish()
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    const signature = signer.sign(transactionHeaderBytes)//sign header bytes
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​
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    const transaction = protobuf.Transaction.create({
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      header: transactionHeaderBytes,
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      headerSignature: signature,
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      payload: payloadBytes
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    }) //
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    const transactions = [transaction] //can include multiple in batch
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    const batchHeaderBytes = protobuf.BatchHeader.encode({
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      signerPublicKey: signer.getPublicKey().asHex(),
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      transactionIds: transactions.map((txn) => txn.headerSignature),
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    }).finish()
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​
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    const bsignature = signer.sign(batchHeaderBytes)
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​
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    const batch = protobuf.Batch.create({
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      header: batchHeaderBytes,
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      headerSignature: bsignature,
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      transactions: transactions
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    })
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​
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    const batchListBytes = protobuf.BatchList.encode({
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      batches: [batch]
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    }).finish()
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All that's left to do is send off the batch to our sawtooth api running normally at port 8008
index.js [4]
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request.post({
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      url: 'http://127.0.0.1:8008/batches',
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      body: batchListBytes,
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      headers: { 'Content-Type': 'application/octet-stream' }
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    }, (err, response) => {
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      var link = JSON.parse(response.body).link
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      if (err) {
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        res.setHeader('Content-Type', 'application/json');
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        res.send(JSON.stringify({ payload, err, res: response.body }, null, 3))
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        console.log(err)
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      } else {
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        if (link) {
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          console.log('Followed: ' + link)
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          request.get({
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            url: link
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          }, (e, r) => {
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            if (e) return console.log(e)
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            res.setHeader('Content-Type', 'application/json');
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            var body = JSON.parse(r.body)
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            var link = body.link.replace(/127.0.0.1:8008/g, req.headers.host)
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            res.send(JSON.stringify({ payload, inputs, outputs, data: body.data, link }, null, 3))
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          })
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        } else {
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          res.setHeader('Content-Type', 'application/json');
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          res.send(JSON.stringify({ payload, inputs, outputs, body: JSON.parse(response.body) }, null, 3))
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        }
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      }
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    })
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Following which the confirmation/status link is re-wrapped and returned to the user. 
​
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Proxy Signing Service
Proxy Signing Service

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