Start your 2019 journey learning the right skills to become a Blockchain programmer with this tutorial on how to create a backend for Hyperledger Fabric. 2018 was a great year for Blockchain in the enterprise, one of my favorites projects is , from the . Fabric Hyperledger Project is a framework to create permissioned Blockchain/DLT networks. It provides the tools to install and configure the protocol which on top of it can host smart contracts (called chaincodes). Fabric This is a continuation post from , in which I show cased how to create a smart contract using (Open source JavaScript Framework). Hyperledger Fabric + Convector + Convector CLI (JavaScript only) Convector In this post, I will show how to create a backend in NodeJS for a blockchain application. Basically what a backend does is call the blockchain nodes to submit requests or make queries. With Fabric we also have a CouchDB or a LevelDB database that allows for complex queries. Fabric’s nodes have some APIs and we can use the Fabric Node SDK to make those calls. I assume that you already followed to set up your Convector project or downloaded this code: this previous tutorial https://github.com/worldsibu/convector-example-fabcar # Download the source code from githubgit clone cd convector-example-fabcar/ https://github.com/worldsibu/convector-example-fabcar.git # The repo already has a backend so for you to be able to create it from scratch, switch to a branch with not backendgit checkout learning/just-cc This project has a smart contract ready to be installed with a JavaScript version of the FabCar official example from Fabric Samples repo. Launch the project to create a blockchain network and install the smart contract: npm i# Wake yourself up a dev blockchain - run this at any time to destroy and recreate a new blockchain for you!npm run env:restart# Now install the chaincode!npm run cc:start -- car 1 Congratulations! 🎊 You have installed a whole blockchain network on your computer. If you are curious about what was created, with just that command line. check here the details of what the Dev Env created for you Backend with Node JS Now that you have a protocol running plus an easy smart contract it is time to make a backend exposing the data. The reason you need a backend is that something has to hold the identity querying the blockchain. Yes, an end user will make the request, but for the communication, you need some certificates so usually, the pattern is to have an making the call on behalf of the user. Also, the backend will return data from CouchDB for complex queries ( ) and also send transactions to the blockchain. Application this I will keep it out of the tutorial, for now, everything will come and go directly from the smart contract Create a new folder for your backend code. Let’s use a to avoid wasting time on the basic plumbing. Outside the blockchain project create a new project like this: Yeoman generator # make sure to be in the root ./convector-example/fabcarcd packages npm install generator-express-no-stress-typescriptyo express-no-stress-typescript myapp # type ENTER a few times cd myapp Compile and run the backend project. npx lerna run compile --scope myappnpx lerna run dev:debug --scope myapp Open in your browser to see the project running. We won’t create an UI but it will let you see if everything works so far. http://localhost:3000/ If you have this, your backend is running well. A few details about the folders and files: : this contains all the cryptographic materials (crypto materials) for you to communicate and run the blockchain network. FOLDER ./.convector-dev-env : this folder mainly files, which are files ConvectorCLI includes so that you don’t have to create them from scratch, however you need to adapt its paths to match your project structure, I will detail later about this. FOLDER ./convector-dev-env/examples *.network-profile.yaml : includes your smart contract compiled to JavaScript. FOLDER./chaincode : is the smart contract configuration file. It includes the network topology for the Fabric SDK to resolve the nodes of the network. It is used to install and upgrade the chaincode as you need it. FILE ./org1.car.config.json : includes all your source code. We use to be able to have multiple projects on a same folder so it is easier to make dependencies without uploading code during development to NPM for example. FOLDER ./packages Lerna Next step is to setup the Node JS project dependencies for Fabric communication. # To send transactions to the blockchainnpx lerna add --scope myapp @worldsibu/convector-adapter-fabric # To query the couchdb laternpx lerna add --scope myapp @worldsibu/convector-storage-couchdb npx lerna add fabric-client --scope myappnpx lerna add fabric-ca-client --scope myapp npx lerna add @types/bytebuffer --scope myapp Also add flag to the server file, inside . experimentaDecorators ./packages/myapp/tsconfig.json compilerOptions "experimentalDecorators": true, Since we are using you can import the models and controllers to reuse code made for the smart contract. For your backend to recognize your Smart Contract files, simply run: Convector # now you won't have to replicate the model or the functions (interface) in your backendnpx lerna add car-cc --scope myapp We use a lot of environment variables to setup our project, so we need to make sure to have the right variables for our project. In your file be sure to have the following: ./packages/myapp/.env Import and reuse the controller and model from the smart contract to NodeJS Create a file to pass the network configuration to the SDK at server create a file and include the following. ./packages/myapp/server selfgenfabriccontext.ts To call the blockchain we will reuse the created in the smart contract, so create a file called and paste this contents at . CarController smartContractControllers.ts ./packages/myapp/server Now we need to configure the model file from the smart contract to understand that it is in another layer, in this case in nodejs rather than Hyperledger Fabric. Create a file at and paste the following. smartContractModels.ts ./packages/myapp/server Last but not least, make the Swagger API recognize our structure. Car model Go to and replace from line with the following contents: ./packages/myapp/server/common/swagger/Api.yaml 19 All setup! Call the blockchain At this point you have a running blockchain network, a smart contract installed and working, and a backend almost ready to query and send transaction to the blockchain. What we need next is to tell your node backend to the blockchain and . call how to communicate with it Locate the existing API called from the Yeoman generator and replace its contents examples ./packages/myapp/server/api/controllers/examples/controller.ts Change its contents for this: Finally, we need to tell the SDK and send transactions. For that matter, Fabric requires a yaml file. In your path create a new folder called , create a file called and paste the following. how to communicate Network Profile ./packages/myapp/server config org1.network-profile.yaml At this point, you need to be sure you have your NodeJS Application running as well your blockchain network. During this post, we already ran this commands, but just in case I’m adding them here again: # Start the backend NodeJsnpx lerna run dev:debug --scope myapp # Wake yourself up a dev blockchain - run this at any time to destroy and recreate a new blockchain for you!npm run env:restart# Now install the chaincode!npm run cc:start -- car 1 API Calls Start and try it yourself. You can make calls which can very well come from an Angular or React front end as well. All the available endpoints from the Nodejs app are: Postman GET localhost:3000/api/v1/examples GET localhost:3000/api/v1/examples/1 POST localhost:3000/api/v1/examples/Body{"make":"Volkswagen","model":"Jetta","colour":"gray","owner":"Walter Montes","id":"1"} You now have a way to add items to the blockchain, as well to make the necessary calls to retrieve the data. That is all for now. For my next post, I will show how to easily integrate calls to your CouchDB. Part 1 of this post here. 💻 The source code for this project is here. Contributors We constantly look for Convector contributors. We do know a lot of people are using Convector to build their innovations and businesses, so it would be great to have feedback from you and why not a PR adding a feature you’d love to see live in Convector. Join the community here! Look into Convector here — Source code. Knowledge base for more info — Knowledgebase. WorldSibu — Developers behind the project.

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Walter Montes

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