Path-based matching

A path parameter in the URL of an HTTP GET request looks like this:

https://example.org/articles/books/123

Since it is passed after the base URL and API endpoint, in this case https://example.org/articles/, they are called path parameters. In the preceding URL, books and 123 are path parameters. Let us see an example of how to create routes that can consume data supplied as path parameters. Follow these steps: 

1. Create a new file for our program at the following path:

touch -p $GOPATH/src/github.com/git-user/chapter2/muxRouter/main.go

2. The idea is to create a new router, mux.NewRouter, and use it as a handler with in-built http.Server. We can attach URL endpoints to handler functions on this router object. The URL endpoints attached can also be regular expressions. The simple program to collect path parameters from a client HTTP request and return back the same looks like this:

package main

import (
  "fmt"
  "log"
  "net/http"
  "time"

  "github.com/gorilla/mux"
)

func ArticleHandler(w http.ResponseWriter, r *http.Request) {
  vars := mux.Vars(r)
  w.WriteHeader(http.StatusOK)
  fmt.Fprintf(w, "Category is: %v\n", vars["category"])
  fmt.Fprintf(w, "ID is: %v\n", vars["id"])
}

func main() {
  r := mux.NewRouter()
  r.HandleFunc("/articles/{category}/{id:[0-9]+}", ArticleHandler)
  srv := &http.Server{
    Handler: r,
    Addr: "127.0.0.1:8000",
    WriteTimeout: 15 * time.Second,
    ReadTimeout: 15 * time.Second,
  }
  log.Fatal(srv.ListenAndServe())
}

3. Now run the server using the following command in a shell:

go run $GOPATH/src/github.com/git-user/chapter2/muxRouter/main.go

4. Make a curl request from another shell and we can get the output as follows:

curl http://localhost:8000/articles/books/123

Category is: books ID is: 123

This example shows how to match and parse path parameters. There is one more popular way to collect variable information from an HTTP request and that is with query parameters. In the next section, we see how to create routes that match HTTP requests with query parameters.