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Calling third party APIs

How to run

To run from the root of this repository;

go run lesson-third-party/main.go

then from a different terminal session (or program like postman)

curl localhost:8080/quotes/search/oneself
curl localhost:8080/quotes/random

Do it yourself

A few alternative APIs to challenge yourself;

Also, a meta list of APIs if non of those take your fancy.

Try implementing your own functionality, for example;

  • implement a 'random' functionality for an API that has a /list resource but no natural /random
  • combine multiple requests, i.e. take a quote and use a sentiment analysis on it
  • return a json object instead of plain text

How it works

This section aims to walkthrough what is happening in this API.

Handling input

In this particular example we only handle path parameters in our getSearchQuote, we can just as easily add query parameters, as well as handling URL forms with just the core library.

Making requests

In our main function, we create a http client, with a default timeout of 10 seconds. This is in case our downstream server is unresponsive, our server will at least return to the caller.

Within both of our handler functions, we make a GET request which returns both a *http.Response and an error. Perform an error check, if there is an error, return a 500 with a user friendly error message. If there's no error, we can continue. It's important to note the body of the response is a io.ReadCloser, so we should defer a Close() on the body once we're sure it's usable.

We can use io.Copy to copy the contents of our GET to our ResponseWriter if we want to return the response we get verbatim.

Serialization/Deserialization

The response we got from our GET request is a slice of bytes, to make this something useful within our own application it's important to serialize it into a struct we can use and manipulate. To do this, we create an instance of the response we're expecting Quote for a singular response, Quotes for our search query. We can then create a new decoder using the response body as it implements io.Reader.

For quickly creating the structs, mholt has a fantastic resource called json=to-go. Chuck in a json response example, and use the generated structs, this service can fall down on traditional map types though.

Responding to the caller

If all goes well, we can just use w.Write to write a slice of bytes out, in the example here we're created a String function that prints out the quote in a nice plain text format.