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HTTP & Routing

HTTP Overview

HTTP is a textual protocol over TCP/IP. An HTTP call looks like:

POST /x?ttl=10 HTTP/1.1
Host: httpbin.org
Connection: close
Content-Length: 5

hello

The first line (request line) states the request:

  • POST is the method (or verb)
  • /x?ttl=10 is the path
  • HTTP/1.1 is the protocol

After that we have a bunch of headers in key: value format. Then an empty line and an optional body.

URLs

Let's assume we call https://httpbin.org/get?x=1?y=2, then

  • https is the protocol
  • httpbin.org is the host
  • /get is the path
  • x=1?y=2 are the query (or parameters)

REST Overview

Most operations on data can be summed with CRUD - Create, Retrieve, Update and Delete.

In REST we make HTTP calls to a server and use HTTP methods to describe which operation we'd like to do. The mapping of CRUD to REST is

  • Create -> POST
  • Retrieve -> GET
  • Update -> PUT/PATCH
  • Delete -> DELETE

We can find out the HTTP method from the request object Method field.

When we make an HTTP call with curl we can use the -X switch to define the method.

 curl -XPOST https://httpbin.org/post

We can pass data in the request body. The request data is available in the Body field of the request and it's an io.Reader (since request body can be very large).

When we make an HTTP call with curl we can either pass the data using the -d switch or pass a file if the data starts with @.

 curl -XPOST -d hello https://httpbin.org/post
 curl -XPOST [email protected] https://httpbin.org/post

The resource we're accessing is defined by the path after the host name. For example in http://localhost:8080/a/b the path will be /a/b.

In our handler we can get the path from r.URL.Path

We can also pass parameters in HTTP calls. We pass them after ? in the URL and by name separated by &, for example

curl "https://httpbin.org/get?x=1&y=2"

In our handler we can access these parameters via r.URL.Query

HTTP Errors

When we return an HTTP response, we return an HTTP status code with the response. There are many status codes codes available. Basically 200s means OK, 300s means redirect, 400s means the request was bad and 500s mean there was some error in the server.

In our handlers, we can use w.WriteHeader to set the status. There also http.Error to set the status and return an answer.

Exercise

Add two HTTP end points to our server.

  • /ping should accept GET request and return PONG
    • If ping gets a msg parameter it should return it instead of PONG
  • /time should accept a GET request and return the current time in RFC3339 format

Hint: The time package

Testing

Normal ping

curl http://localhost:8080/ping

Ping with parameters

curl "http://localhost:8080/ping?msg=hi"

Time

curl http://localhost:8080/time

Solution