accept

A lightweight Go library for parsing HTTP Accept headers and selecting the most suitable Content-Type.

Documents followed for Accept http request header:

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept
• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Type
• https://developer.mozilla.org/en-US/docs/Web/HTTP/MIME_types
• https://www.iana.org/assignments/media-types/media-types.xhtml#application
• https://developer.mozilla.org/en-US/docs/Glossary/Quality_values

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Installation

go get -u github.com/vigo/accept

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Usage

By default, unless otherwise specified, the fallback content type is always set to application/json. If desired, you can customize the fallback value using WithDefaultMediaType method. Also, if request Accept header is */*, library matches first supported media type too.

// your server supports: application/json and text/html
contentNegotiator := accept.New(
    accept.WithSupportedMediaTypes("application/json", "text/html"),
)

contentNegotiator := accept.New(
    accept.WithSupportedMediaTypes("application/json", "text/html"),
    accept.WithDefaultMediaType("text/plain"),
)

// in your http handler
acceptHeader := r.Header.Get("Accept")
contentType := cn.Negotiate(acceptHeader)

Full example, your server supports: application/json, text/html and text/plain and for unmatched Accept header, will use text/plain as default fallback value.

# main.go
package main

import (
	"encoding/json"
	"log"
	"net/http"

	"github.com/vigo/accept"
)

func handlerFunc(cn *accept.ContentNegotiation) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		acceptHeader := r.Header.Get("Accept")

		contentType := cn.Negotiate(acceptHeader)
		w.Header().Set("Content-Type", contentType)

		switch contentType {
		case "application/json":
			response := map[string]string{"message": "OK"}
			if err := json.NewEncoder(w).Encode(response); err != nil {
				http.Error(w, "failed to encode JSON", http.StatusInternalServerError)
			}
		case "text/html":
			_, _ = w.Write([]byte("<p>\n\t<span>message<span>\n\t<pre>OK</pre>\n</p>\n"))
		default:
			_, _ = w.Write([]byte("message: OK\n"))
		}
	}
}

func main() {
	contentNegotiator := accept.New(
		accept.WithSupportedMediaTypes("application/json", "text/html", "text/plain"),
		accept.WithDefaultMediaType("text/plain"),
	)

	log.Println("starting server at :8080")
	http.HandleFunc("/", handlerFunc(contentNegotiator))
	log.Fatal(http.ListenAndServe(":8080", nil))
}

Run the server:

go run main.go

Test the requests:

curl localhost:8080 -H 'Accept: text/html'
curl localhost:8080 -H 'Accept: text/plain'
curl localhost:8080 -H 'Accept: text/markdown'     # fallback to "text/plain"
curl localhost:8080 -H 'Accept: application/json'
curl localhost:8080                                # curl sends */*, first match is "application/json"

---

Rake Tasks

rake -T

rake coverage  # show test coverage
rake test      # run test

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License

This project is licensed under MIT (MIT)

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This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.