Use when a handler must return a status code, headers, JSON, HTML, raw bytes, a redirect, or a cookie in Axum, or when a handler return value fails the Handler trait bound because the returned type does not implement IntoResponse. Prevents returning a bare domain struct or a bare integer that does not implement IntoResponse, prevents the wrong tuple order where the body is not the final element, prevents using 301 for a permanent redirect when Axum emits 308, and prevents a CookieJar silently dropping changes when the jar is not returned from the handler. Covers IntoResponse and IntoResponseParts, status and header and body tuple combining, Json and Html and raw byte bodies, Redirect (303, 307, 308), AppendHeaders, raw Set-Cookie headers, the axum-extra CookieJar family, and the Axum 0.8 axum::body::Body requirement. Keywords: axum IntoResponse, IntoResponseParts, ResponseParts, Json, Html, Form, Redirect, Redirect::to, Redirect::permanent, Redirect::temporary, AppendHeaders, NoContent, StatusCode, HeaderMap,
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Use when a handler must return a status code, headers, JSON, HTML, raw bytes, a redirect, or a cookie in Axum, or when a handler return value fails the Handler trait bound because the returned type does not implement IntoResponse. Prevents returning a bare domain struct or a bare integer that does not implement IntoResponse, prevents the wrong tuple order where the body is not the final element, prevents using 301 for a permanent redirect when Axum emits 308, and prevents a CookieJar silently dropping changes when the jar is not returned from the handler. Covers IntoResponse and IntoResponseParts, status and header and body tuple combining, Json and Html and raw byte bodies, Redirect (303, 307, 308), AppendHeaders, raw Set-Cookie headers, the axum-extra CookieJar family, and the Axum 0.8 axum::body::Body requirement. Keywords: axum IntoResponse, IntoResponseParts, ResponseParts, Json, Html, Form, Redirect, Redirect::to, Redirect::permanent, Redirect::temporary, AppendHeaders, NoContent, StatusCode, HeaderMap, Set-Cookie, CookieJar, SignedCookieJar, PrivateCookieJar, the trait bound Handler is not satisfied, handler return type does not implement IntoResponse, my cookie is not set, redirect returns the wrong status, 301 vs 308, how do I return JSON, how do I set a response header, how do I redirect, what status does Redirect use.
license
MIT
compatibility
Designed for Claude Code. Requires Axum 0.7,0.8.
metadata
{"author":"OpenAEC-Foundation","version":"1.0"}
axum-syntax-responses
Overview
A handler's return value becomes an http::Response through one trait:
IntoResponse. Its single method is fn into_response(self) -> Response<Body>,
where Body is axum::body::Body. Axum calls this method automatically on
whatever a handler returns, so the return type MUST implement IntoResponse or
the handler fails the Handler trait bound.
A companion trait, IntoResponseParts, modifies response parts (headers and
extensions) WITHOUT setting the status code or body. Tuples combine one
IntoResponse body with one or more IntoResponseParts elements and an
optional leading StatusCode, which is how a single return statement sets
status, headers, and body together.
Axum 0.8 removed the generic body type parameter. Every response body MUST be
axum::body::Body; hyper::Body is no longer re-exported.
Quick Reference
Return type
Status
Content-Type
()
200 OK
none, empty body
&'static str, String, Cow<str>
200 OK
text/plain; charset=utf-8
Vec<u8>, Bytes, &'static [u8]
200 OK
application/octet-stream
StatusCode
that status
none, empty body
HeaderMap, [(K, V); N]
200 OK
none, headers only
Json<T> (T: Serialize)
200 OK
application/json
Html<T> (T: Into<Body>)
200 OK
text/html; charset=utf-8
Form<T> (T: Serialize)
200 OK
application/x-www-form-urlencoded
NoContent
204 No Content
none, empty body
Redirect
303 / 307 / 308
none, Location header
Response
unchanged
unchanged
(StatusCode, R)
leading status
from R
(StatusCode, parts..., R)
leading status
from R, plus parts
Result<T, E> (both IntoResponse)
from the variant
from the variant
Core rules:
ALWAYS return a type that implements IntoResponse. A bare domain struct or
a bare integer does NOT implement it; wrap it in Json(...) or implement
IntoResponse for it.
ALWAYS make the body the LAST element of a response tuple. Every element
before it MUST implement IntoResponseParts.
ALWAYS place StatusCode first when a tuple sets the status.
NEVER assume Redirect::permanent emits 301. It emits 308. Redirect::to
emits 303, Redirect::temporary emits 307.
ALWAYS return the CookieJar from the handler. add and remove consume the
jar and return a new one; an unreturned jar silently loses every change.
ALWAYS use axum::body::Body for a manually built Response on Axum 0.8.
Decision Trees
What return type for which response
What does the handler produce?
a serializable struct as JSON -> Json<T>
an HTML page -> Html<T>
only a status, no body -> StatusCode (204 -> NoContent)
a file or binary payload -> (headers, Vec<u8>) or (headers, Bytes)
plain text -> String or &'static str
a redirect to another URL -> Redirect (see next tree)
status + headers + body together -> (StatusCode, [(HeaderName, _); N], body)
a fallible operation with ? operator -> Result<T, E> where E: IntoResponse
total control over the Response -> Response (build with Response::builder)
Which Redirect constructor
Why are you redirecting?
after a successful POST or PUT form submission
-> Redirect::to (303 See Other, client switches to GET, no resubmit)
the resource moved permanently, keep the method and body
-> Redirect::permanent (308 Permanent Redirect)
the resource moved temporarily, keep the method and body
-> Redirect::temporary (307 Temporary Redirect)
Axum exposes NO constructor for 301 or 302. 301 and 302 rewrite a
non-GET method to GET in many clients; Axum deliberately offers only the
method-explicit codes 303, 307, and 308.
Which cookie mechanism
What kind of cookie value?
non-sensitive, readable by the client (theme, locale)
-> CookieJar (axum-extra feature "cookie")
client must not tamper with it, but may read it
-> SignedCookieJar (axum-extra feature "cookie-signed", needs Key)
client must neither read nor tamper (session id, user id)
-> PrivateCookieJar (axum-extra feature "cookie-private", needs Key)
no axum-extra dependency wanted, one simple cookie
-> raw [(header::SET_COOKIE, "name=value; HttpOnly; Path=/")]
Patterns
Pattern: return JSON
Json<T> wraps any T: Serialize. A serialization failure produces
500 Internal Server Error automatically.
A bare User does NOT implement IntoResponse. Returning it fails the
Handler trait bound. The wrap in Json(...) is mandatory.
Pattern: status, headers, and body in one tuple
Axum implements IntoResponse for (StatusCode, T1, ..., Tn, R) where every
Ti implements IntoResponseParts and the final R implements
IntoResponse. The leading StatusCode overrides the status; the final
element is the body.
// axum 0.7 / 0.8 - identicaluse axum::{http::{StatusCode, header}, response::IntoResponse, Json};
asyncfncreate() ->implIntoResponse {
(
StatusCode::CREATED, // status, must be first
[(header::CACHE_CONTROL, "no-store")], // IntoResponsePartsJson(serde_json::json!({ "id": 7 })), // body, must be last
)
}
The body is the LAST element. Putting it anywhere else, or putting two
body-typed elements in one tuple, fails to compile.
Pattern: raw bytes with an explicit content type
A Vec<u8> body defaults to application/octet-stream. Override it by
prepending a header array.
A HeaderMap or header array in a tuple REPLACES matching headers.
AppendHeaders APPENDS, which is required for emitting multiple Set-Cookie
headers in one response.
Axum core has no cookie API. axum-extra provides CookieJar,
SignedCookieJar, and PrivateCookieJar. A jar is extracted as a handler
argument and the MODIFIED jar MUST be returned, because add and remove
consume the jar and return a new one.
// axum 0.7 / 0.8 - identical. Cargo.toml: axum-extra with feature "cookie".use axum::response::Redirect;
use axum_extra::extract::cookie::{Cookie, CookieJar};
asyncfnlogin(jar: CookieJar) -> (CookieJar, Redirect) {
letjar = jar.add(
Cookie::build(("session", "abc123"))
.http_only(true)
.secure(true)
.path("/")
.build(),
);
(jar, Redirect::to("/dashboard")) // jar first (parts), Redirect last (body)
}
The jar implements IntoResponseParts, so it goes BEFORE the body in a tuple.
SignedCookieJar and PrivateCookieJar need a Key in application state,
reached via FromRef; see references/examples.md.
Reference Links
references/methods.md: the IntoResponse and IntoResponseParts trait
definitions, the complete built-in implementation table, every tuple impl
form, Redirect constructors and accessors, Json / Html / Form /
NoContent / AppendHeaders signatures, and the CookieJar method set.
references/examples.md: full version-annotated working code for every
response type, the tuple combining rule, SignedCookieJar and
PrivateCookieJar with a Key, and the Axum 0.8 axum::body::Body change.
references/anti-patterns.md: real mistakes with root-cause analysis,
including the bare-struct return, the wrong tuple order, the 301 redirect
myth, and the unreturned cookie jar.
Related skills: axum-syntax-handlers (the Handler trait and what makes a
return type valid), axum-errors-handling (mapping domain errors to responses
through IntoResponse), axum-syntax-extractors (reading data from a request).
