Async / Await in ReasonML

Automatically decode JSON into records in ReasonML using Decco

Write a simple custom JSON decoder for Decco in ReasonML

Working with cryptic error messages from ReasonML when writing custom Decco decoders.

Make a basic server with ReasonML and Node.js

Handle JSON request bodies and send JSON responses from a Node.js server using ReasonML

Making an HTTP server in ReasonML on top of Node.js

This lesson shows how the Serbet server library for ReasonML and Node.js makes handling JSON request bodies, and responding with JSON request bodies a simple task.

Instructor: [0:00] Here I've got a basic server that responds to a get request with a "Hello World!" message, but let's say I want to do something a little more complex and actually deal with JSON. Module json endpoint, this is just the name of my module, it's there for me to remember what this does, = app.handle.

[0:19] Now we're going to use a fancy little shortcut called HandleJson. This is nice if you're doing a brand-new server and you don't have to conform to old APIs and do stuff in weird ways. If you're just starting out with a server that can take json and respond with json, this is a really nifty way to go.

[0:36] Let's add our verb, let verb equal, and let's do a post, and let's let the path be "/hello/json". Now I've got to specify a body type, so @decco.decode type body =, now let's have the body have the name in it, name: strong, and we also need to specify a response type.

@[0:58] decco.encode, because we're going to be encoding the response, type response =, and let's say there's a message on the response, and that's a string. Now we need to add the handler. Let handler =, now instead of just the request, I'm actually going to take in the body and then the request, and then respond.

[1:20] The funny thing is now that I have the body, I don't actually need the request. I'm going to put an underscore in front of it so the compiler doesn't get angry with me. All right, so now let's respond. This is a little different than the above, where I said OK string, because since this endpoint knows that I'm going to be handing back JSON and that I've specified a response type, I can just return a promise of the response type.

[1:40] I'm going to initialize a record with a field message, and that's going to be "Hello there, " ++ body.name and then I'm going to make it async, and all of our compiler warnings go away. Now you can rerun the server and try it out. I've got a handy little utility called HTTPie installed for doing http request from the command list.

[2:01] Let's try that now. http POST locahost:1337/hello/json and you can specify a JSON body using this tool, just by passing name=superface it's going to take care of actually building that into a JSON body for me. Let's see what happens.

[2:20] All right, so you see the server took that JSON body in, parsed it, and then responded with more JSON, "message": "Hello there, superface". This is how you very quickly make an endpoint that can take in, validate, parse JSON, and return other JSON.

Course

Making an HTTP server in ReasonML on top of Node.js

Handle JSON request bodies and send JSON responses from a Node.js server using ReasonML

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