from_fn_with_state does not compile #3353

harshRn · 2025-05-18T08:41:04Z

harshRn
May 18, 2025

Hi,
Picked up the guide from here:
https://docs.rs/axum/latest/axum/middleware/fn.from_fn_with_state.html

I want to understand why this does not work the way it has been described in the page:

My middleware

pub async fn middleware(
    State(state): State<AppState>,
    session: Session,
    mut request: Request,
    next: Next,
) -> Response {
   /* do something */
    next.run(request).await
}

my usage:

.layer(axum::middleware::from_fn_with_state(
    shared_state.clone(),
    middleware
))

AppState:

struct AppState {
    snippets: Model
}

#[derive(Clone)]
pub struct Model {
    pool: Pool<MySql>,
}

The error I get:

error[E0277]: the trait bound `axum::middleware::FromFn<fn(State<AppState>, tower_sessions::Session, axum::http::Request<Body>, Next) -> impl Future<Output = Response<Body>> {authenticate}, Arc<AppState>, Route, _>: tower_service::Service<axum::http::Request<Body>>` is not satisfied
   --> src/routes.rs:60:20
    |
60  |               .layer(axum::middleware::from_fn_with_state(
    |  ______________-----_^
    | |              |
    | |              required by a bound introduced by this call
61  | |                 shared_state.clone(),
62  | |                 authenticate,
63  | |             )) // since this uses session it needs to be work after the session layer
    | |_____________^ unsatisfied trait bound
    |
    = help: the trait `tower_service::Service<axum::http::Request<Body>>` is not implemented for `FromFn<fn(..., ..., ..., ...) -> ... {authenticate}, ..., ..., ...>`
    = help: the following other types implement trait `tower_service::Service<Request>`:
              axum::middleware::FromFn<F, S, I, (T1, T2)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5, T6)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5, T6, T7)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5, T6, T7, T8)>
              axum::middleware::FromFn<F, S, I, (T1, T2, T3, T4, T5, T6, T7, T8, T9)>
            and 8 others
note: required by a bound in `Router::<S>::layer`
  
    |
303 |     pub fn layer<L>(self, layer: L) -> Router<S>
    |            ----- required by a bound in this associated function
...
306 |         L::Service: Service<Request> + Clone + Send + Sync + 'static,
    |                     ^^^^^^^^^^^^^^^^ required by this bound in `Router::<S>::layer`

Answered by jplatte

May 18, 2025

Aha! I think with that hint (that removing the state parameter fixes the issue) I've found your problem: The error message above refers to the type that isn't a valid middleware as axum::middleware::FromFn<fn(State<AppState>, tower_sessions::Session, axum::http::Request<Body>, Next) -> impl Future<Output = Response<Body>> {middleware::middleware}, Arc<AppState>, Route, _>. The Arc<AppState> in there is a pretty clear sign that the second parameter you're passing to from_fn_with_state is actually an Arc<AppState>, not AppState.

You'll have to either change your function signature to use State<Arc<AppState>> (if AppState itself is not cheap to clone, I would recommend this), or pass a clone…

View full answer

jplatte · 2025-05-18T09:42:19Z

jplatte
May 18, 2025
Maintainer

Have you tried https://docs.rs/axum/latest/axum/attr.debug_middleware.html?

9 replies

jplatte May 18, 2025
Maintainer

Could you try adding #[warn(clippy::future_not_send)] to your middleware function, and comment out the usage of .layer(axum::middleware::from_fn(...)), then run cargo clippy?

I copied your stuff into a scratch project and could not reproduce the compile error, so the only reason I can think of this would fail is a non-Send future. I thought debug_middleware would catch this, but maybe not.

harshRn May 18, 2025
Author

Thanks for instant reply! I did as instructed. Unfortunately I don't see any errors about a non-Send future.
Not much to go on but removing State(state): State<AppState> from the param list of authenticate removes the error. But ultimately I do need it in order to use the MySQL pool. I am aware that there is a more 'complicated' way of writing middlewares, but ultimately I am just testing axum for micro web-apps that I can get up and running with the least amount of effort, so I decided to not go that way.

harshRn May 18, 2025
Author

My cargo clippy output if it's worth anything:

    Checking snippetbox-rs v0.1.0 (/Users/harshranjan/snippetbox-rs)
warning: unused import: `error::DatabaseError`
  --> src/handlers.rs:20:12
   |
20 | use sqlx::{error::DatabaseError, mysql::MySqlDatabaseError};
   |            ^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` on by default

warning: redundant field names in struct initialization
  --> src/handlers.rs:50:13
   |
50 |             is_authenticated: is_authenticated,
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `is_authenticated`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_field_names
   = note: `#[warn(clippy::redundant_field_names)]` on by default

warning: redundant field names in struct initialization
   --> src/handlers.rs:105:9
    |
105 |         is_authenticated: is_authenticated,
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace it with: `is_authenticated`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_field_names

warning: unused import: `f64::consts::E`
 --> src/models/users.rs:6:25
  |
6 | use std::{error::Error, f64::consts::E};
  |                         ^^^^^^^^^^^^^^

warning: unused import: `askama::Template`
 --> src/middleware.rs:3:5
  |
3 | use askama::Template;
  |     ^^^^^^^^^^^^^^^^

warning: unused import: `self`
 --> src/middleware.rs:8:18
  |
8 |     middleware::{self, Next},
  |                  ^^^^

warning: unused import: `tower_http::auth`
  --> src/middleware.rs:11:5
   |
11 | use tower_http::auth;
   |     ^^^^^^^^^^^^^^^^

warning: unused import: `utils::login_form_validation::LoginTemplate`
  --> src/middleware.rs:14:38
   |
14 | use crate::{AppState, Authenticated, utils::login_form_validation::LoginTemplate};
   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: unused import: `authenticate`
 --> src/routes.rs:4:25
  |
4 | use crate::middleware::{authenticate, common_headers, request_ip, require_auth};
  |                         ^^^^^^^^^^^^

warning: unused import: `axum::middleware::from_fn`
 --> src/routes.rs:9:5
  |
9 | use axum::middleware::from_fn;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^

warning: unused import: `tower_sessions::Session`
  --> src/main.rs:24:5
   |
24 | use tower_sessions::Session;
   |     ^^^^^^^^^^^^^^^^^^^^^^^

warning: unused variable: `session_layer`
  --> src/routes.rs:34:13
   |
34 |         let session_layer = SessionManagerLayer::new(session_store)
   |             ^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_session_layer`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: struct `User` is never constructed
  --> src/models/users.rs:12:8
   |
12 | struct User {
   |        ^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: field `flag` is never read
  --> src/models/users.rs:28:5
   |
27 | struct Exists {
   |        ------ field in this struct
28 |     flag: i32,
   |     ^^^^
   |
   = note: `Exists` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis

warning: method `exists` is never used
   --> src/models/users.rs:120:18
    |
36  | impl UserModel {
    | -------------- method in this implementation
...
120 |     pub async fn exists(&self, id: i32) -> Result<bool, sqlx::Error> {
    |                  ^^^^^^

warning: function `authenticate` is never used
  --> src/middleware.rs:73:14
   |
73 | pub async fn authenticate(
   |              ^^^^^^^^^^^^

warning: field `password` is never read
  --> src/utils/login_form_validation.rs:25:5
   |
23 | pub struct LoginTemplate {
   |            ------------- field in this struct
24 |     email: String,
25 |     password: String,
   |     ^^^^^^^^

warning: field `password` is never read
  --> src/utils/signup_form_validation.rs:26:9
   |
22 | pub struct SignupTemplate {
   |            -------------- field in this struct
...
26 |     pub password: String,
   |         ^^^^^^^^
   |
   = note: `SignupTemplate` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis

warning: this boolean expression can be simplified
  --> src/handlers.rs:34:8
   |
34 |     if !snippets.is_err() {
   |        ^^^^^^^^^^^^^^^^^^ help: try: `snippets.is_ok()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#nonminimal_bool
   = note: `#[warn(clippy::nonminimal_bool)]` on by default

warning: length comparison to zero
  --> src/handlers.rs:43:16
   |
43 |             if flash.len() > 0 {
   |                ^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!flash.is_empty()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#len_zero
   = note: `#[warn(clippy::len_zero)]` on by default

warning: this boolean expression can be simplified
  --> src/handlers.rs:68:8
   |
68 |     if !result.is_err() {
   |        ^^^^^^^^^^^^^^^^ help: try: `result.is_ok()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#nonminimal_bool

warning: length comparison to zero
  --> src/handlers.rs:81:16
   |
81 |             if flash.len() > 0 {
   |                ^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!flash.is_empty()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#len_zero

warning: useless use of `format!`
   --> src/handlers.rs:201:27
    |
201 |         redirection_uri = format!("/user/login")
    |                           ^^^^^^^^^^^^^^^^^^^^^^ help: consider using `.to_string()`: `"/user/login".to_string()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format
    = note: `#[warn(clippy::useless_format)]` on by default

warning: length comparison to zero
   --> src/handlers.rs:214:12
    |
214 |         if flash.len() > 0 {
    |            ^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!flash.is_empty()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#len_zero

warning: this expression creates a reference which is immediately dereferenced by the compiler
   --> src/handlers.rs:244:34
    |
244 |                     Redirect::to(&redirection_uri).into_response()
    |                                  ^^^^^^^^^^^^^^^^ help: change this to: `redirection_uri`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
    = note: `#[warn(clippy::needless_borrow)]` on by default

warning: unneeded `return` statement
  --> src/models/snippet.rs:44:17
   |
44 |                 return Err(e);
   |                 ^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_return
   = note: `#[warn(clippy::needless_return)]` on by default
help: remove `return`
   |
44 -                 return Err(e);
44 +                 Err(e)
   |

warning: unneeded `return` statement
  --> src/models/users.rs:95:29
   |
95 | ...                   return Ok(res.id);
   |                       ^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_return
help: remove `return`
   |
95 -                             return Ok(res.id);
95 +                             Ok(res.id)
   |

warning: unneeded `return` statement
   --> src/models/users.rs:112:25
    |
112 |                         return Err(Box::new(e));
    |                         ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_return
help: remove `return`
    |
112 -                         return Err(Box::new(e));
112 +                         Err(Box::new(e))
    |

warning: unneeded `return` statement
   --> src/models/users.rs:116:23
    |
116 |             Err(e) => return Err(Box::new(e)),
    |                       ^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_return
help: remove `return`
    |
116 |             Err(e) => Err(Box::new(e)),
    |                       ~~~~~~~~~~~~~~~~

warning: this `if let` can be collapsed into the outer `if let`
  --> src/middleware.rs:83:9
   |
83 | /         if let Some(rid) = id_opt {
84 | |             id = rid;
85 | |         } else {
86 | |             return next.run(request).await;
87 | |         }
   | |_________^
   |
help: the outer pattern can be modified to include the inner pattern
  --> src/middleware.rs:82:15
   |
82 |     if let Ok(id_opt) = auth_res {
   |               ^^^^^^ replace this binding
83 |         if let Some(rid) = id_opt {
   |                ^^^^^^^^^ with this pattern
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match
   = note: `#[warn(clippy::collapsible_match)]` on by default

warning: this `.into_iter()` call is equivalent to `.iter()` and will not consume the `Vec`
   --> src/utils/form_validation.rs:114:27
    |
114 |                         e.into_iter().for_each(|err| {
    |                           ^^^^^^^^^ help: call directly: `iter`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#into_iter_on_ref
    = note: `#[warn(clippy::into_iter_on_ref)]` on by default

warning: unnecessary use of `to_string`
   --> src/utils/form_validation.rs:115:45
    |
115 | ...                   error_string += &err.message.as_ref().unwrap().to_string()
    |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `err.message.as_ref().unwrap().as_ref()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_to_owned
    = note: `#[warn(clippy::unnecessary_to_owned)]` on by default

warning: writing `&String` instead of `&str` involves a new object where a slice will do
  --> src/utils/login_form_validation.rs:60:26
   |
60 | fn validate_email(email: &String) -> Result<(), ValidationError> {
   |                          ^^^^^^^ help: change this to: `&str`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg
   = note: `#[warn(clippy::ptr_arg)]` on by default

warning: redundant pattern matching, consider using `is_none()`
  --> src/utils/login_form_validation.rs:63:12
   |
63 |     if let None = caps {
   |     -------^^^^------- help: try: `if caps.is_none()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_pattern_matching
   = note: `#[warn(clippy::redundant_pattern_matching)]` on by default

warning: this `.into_iter()` call is equivalent to `.iter()` and will not consume the `Vec`
   --> src/utils/login_form_validation.rs:115:27
    |
115 |                         e.into_iter().for_each(|err| {
    |                           ^^^^^^^^^ help: call directly: `iter`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#into_iter_on_ref

warning: unnecessary use of `to_string`
   --> src/utils/login_form_validation.rs:116:45
    |
116 | ...                   error_string += &err.message.as_ref().unwrap().to_string()
    |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `err.message.as_ref().unwrap().as_ref()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_to_owned

warning: writing `&String` instead of `&str` involves a new object where a slice will do
  --> src/utils/signup_form_validation.rs:51:26
   |
51 | fn validate_email(email: &String) -> Result<(), ValidationError> {
   |                          ^^^^^^^ help: change this to: `&str`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg

warning: redundant pattern matching, consider using `is_none()`
  --> src/utils/signup_form_validation.rs:54:12
   |
54 |     if let None = caps {
   |     -------^^^^------- help: try: `if caps.is_none()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_pattern_matching

warning: this `.into_iter()` call is equivalent to `.iter()` and will not consume the `Vec`
   --> src/utils/signup_form_validation.rs:112:27
    |
112 |                         e.into_iter().for_each(|err| {
    |                           ^^^^^^^^^ help: call directly: `iter`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#into_iter_on_ref

warning: unnecessary use of `to_string`
   --> src/utils/signup_form_validation.rs:113:45
    |
113 | ...                   error_string += &err.message.as_ref().unwrap().to_string()
    |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `err.message.as_ref().unwrap().as_ref()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_to_owned

warning: this if-then-else expression returns a bool literal
  --> src/main.rs:96:9
   |
96 |         if auth { true } else { false }
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: you can reduce it to: `auth`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_bool
   = note: `#[warn(clippy::needless_bool)]` on by default

warning: returning the result of a `let` binding from a block
   --> src/main.rs:312:5
    |
305 | /     let pool = match MySqlPool::connect_with(dsn).await {
306 | |         Ok(p) => p,
307 | |         Err(e) => {
308 | |             println!("{}", e);
...   |
311 | |     };
    | |______- unnecessary `let` binding
312 |       pool
    |       ^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_and_return
    = note: `#[warn(clippy::let_and_return)]` on by default
help: return the expression directly
    |
305 ~     
306 ~     match MySqlPool::connect_with(dsn).await {
307 +         Ok(p) => p,
308 +         Err(e) => {
309 +             println!("{}", e);
310 +             panic!("");
311 +         }
312 +     }
    |

warning: `snippetbox-rs` (bin "snippetbox-rs") generated 42 warnings (run `cargo clippy --fix --bin "snippetbox-rs"` to apply 32 suggestions)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.12s
    ```

jplatte May 18, 2025
Maintainer

Aha! I think with that hint (that removing the state parameter fixes the issue) I've found your problem: The error message above refers to the type that isn't a valid middleware as axum::middleware::FromFn<fn(State<AppState>, tower_sessions::Session, axum::http::Request<Body>, Next) -> impl Future<Output = Response<Body>> {middleware::middleware}, Arc<AppState>, Route, _>. The Arc<AppState> in there is a pretty clear sign that the second parameter you're passing to from_fn_with_state is actually an Arc<AppState>, not AppState.

You'll have to either change your function signature to use State<Arc<AppState>> (if AppState itself is not cheap to clone, I would recommend this), or pass a clone of the actual app state as the second parameter to from_fn_with_state.

Answer selected by harshRn

harshRn May 18, 2025
Author

That was very stupid on my part! thank you for your patience and effort! That did solve it! I went with
State<Arc<AppState>> in the function signature

jplatte May 18, 2025
Maintainer

You're welcome!

from_fn_with_state does not compile #3353

Uh oh!

Uh oh!

harshRn May 18, 2025

Replies: 1 comment · 9 replies

Uh oh!

jplatte May 18, 2025 Maintainer

Uh oh!

Uh oh!

jplatte May 18, 2025 Maintainer

Uh oh!

harshRn May 18, 2025 Author

Uh oh!

harshRn May 18, 2025 Author

Uh oh!

Uh oh!

jplatte May 18, 2025 Maintainer

Uh oh!

harshRn May 18, 2025 Author

Uh oh!

jplatte May 18, 2025 Maintainer

harshRn
May 18, 2025

Replies: 1 comment 9 replies

jplatte
May 18, 2025
Maintainer

jplatte May 18, 2025
Maintainer

harshRn May 18, 2025
Author

harshRn May 18, 2025
Author

jplatte May 18, 2025
Maintainer

harshRn May 18, 2025
Author

jplatte May 18, 2025
Maintainer