rust 46 lines · 8 steps

Content negotiation in an Axum handler

An Axum handler inspects the Accept header and returns JSON, HTML, or a 406 from the same route.

Explained by highlit
Axum Intermediate content-negotiation http-headers serialization request-handling
1use axum::{
2 extract::Path,
3 http::{header::ACCEPT, HeaderMap, StatusCode},
4 response::{Html, IntoResponse, Json, Response},
5};
6use serde::Serialize;
7 
8#[derive(Serialize)]
9struct Product {
10 id: u64,
11 name: String,
12 price_cents: u32,
13}
14 
15pub async fn show_product(
16 Path(id): Path<u64>,
17 headers: HeaderMap,
18) -> Response {
19 let product = Product {
20 id,
21 name: "Aeron Chair".into(),
22 price_cents: 149900,
23 };
24 
25 let accept = headers
26 .get(ACCEPT)
27 .and_then(|v| v.to_str().ok())
28 .unwrap_or("*/*");
29 
30 if accept.contains("application/json") {
31 Json(product).into_response()
32 } else if accept.contains("text/html") || accept.contains("*/*") {
33 let body = format!(
34 "<article>\n <h1>{}</h1>\n <p>${:.2}</p>\n</article>",
35 product.name,
36 product.price_cents as f64 / 100.0,
37 );
38 Html(body).into_response()
39 } else {
40 (
41 StatusCode::NOT_ACCEPTABLE,
42 "Supported types: application/json, text/html",
43 )
44 .into_response()
45 }
46}
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1A single handler can serve multiple representations by branching on the Accept header.
  2. 2Returning the erased Response type lets one function yield JSON, HTML, or an error uniformly.
  3. 3Always provide a fallback so an unmatched Accept value produces a clear 406 rather than a surprise.

Related explainers

rust 
use rand::distributions::{Alphanumeric, DistString};
use rand::rngs::OsRng;
 
#[derive(Debug, Clone, PartialEq, Eq)]

A newtype wrapper for API tokens in Rust

newtype-pattern randomness encapsulation
Intermediate 6 steps
rust 
pub fn normalize_path(input: &str) -> String {
    let is_absolute = input.starts_with('/');
    let has_trailing_slash = input.len() > 1 && input.ends_with('/');
    let mut stack: Vec<&str> = Vec::new();

Normalizing filesystem paths in Rust

string-processing stack path-manipulation
Intermediate 8 steps
rust 
use axum::{
    extract::Query,
    response::IntoResponse,
    Json,

Parsing query strings in Axum handlers

deserialization query-parameters defaults
Intermediate 7 steps
rust 
use axum::{
    body::{Body, Bytes},
    extract::Request,
    http::StatusCode,

Logging request and response sizes in Axum

middleware http streaming-bodies
Advanced 8 steps
rust 
use std::borrow::Cow;
 
pub fn escape_html(input: &str) -> Cow<'_, str> {
    let needs_escape = input

Zero-copy HTML escaping with Cow in Rust

clone-on-write zero-copy string-escaping
Intermediate 6 steps
rust 
use once_cell::sync::Lazy;
use regex::Regex;
 
static CREDIT_CARD: Lazy<Regex> = Lazy::new(|| {

Redacting sensitive data from logs in Rust

regex lazy-initialization checksum-validation
Intermediate 9 steps

Share this explainer

Here's the card — post it anywhere.

Content negotiation in an Axum handler — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code