Rust SDK: Agent Feedback Tower Layer for Axum Apps

The agent-feedback crate provides a cloneable Tower Layer and Service for Axum. Finite JSON object and HTML responses are instrumented in-place; responses without an exact bounded Content-Length — including streams — are left completely untouched. Telemetry is dispatched through a bounded Tokio mpsc channel and never blocks the product response.

Requirements

Rust 1.88 or later
Axum 0.8
Tower 0.5
A Tokio async runtime

Installation

Add the crate

# Cargo.toml
[dependencies]
agent-feedback = "0.1"

Create a product key

Open the Agent Feedback dashboard, create a product, and copy the API key. Store it as AGENT_FEEDBACK_KEY in your environment.

Creating the layer

Call AgentFeedbackLayer::new with an Options value built using the builder API. Clone the layer freely — all clones share the same telemetry queue.

use agent_feedback::{AgentFeedbackLayer, Options};
use axum::{Router, routing::get};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let feedback = AgentFeedbackLayer::new(
        Options::new(std::env::var("AGENT_FEEDBACK_KEY")?)
            .include(["/search", "/docs/**"])
            .customer_ref(|request| {
                request
                    .headers()
                    .get("x-account-id")?
                    .to_str()
                    .ok()
                    .map(str::to_owned)
            }),
    )?;

    let app = Router::new()
        .route("/search", get(search))
        .layer(feedback.clone());

    let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await?;
    axum::serve(listener, app)
        .with_graceful_shutdown(async {
            tokio::signal::ctrl_c().await.ok();
            feedback.shutdown().await;
        })
        .await?;

    Ok(())
}

Options builder methods

Construct an Options value using Options::new(api_key) and chain the builder methods below. Only the API key is required.

impl Into<String>

required

Constructs a new Options value with the given API key. The key must match the pattern af_live_<keyId>_<secret>. AgentFeedbackLayer::new returns an error if the key format is invalid.

impl Into<String>

Override the Agent Feedback API endpoint. Trailing slashes are trimmed. Defaults to https://agent-feedback-api-production.up.railway.app.

impl IntoIterator<Item = impl Into<String>>

Glob-style path patterns that opt routes in. When empty, all routes are instrumented (subject to default and custom excludes). Supports * (single segment) and ** (any path). Example: .include(["/search", "/docs/**"]).

impl IntoIterator<Item = impl Into<String>>

Glob-style patterns to skip. The default exclusion list (/health, /healthz, /metrics, /favicon.ico, /robots.txt, /_agent-feedback/*, /api/v2/outcomes) is always applied. Patterns you provide here extend that list.

impl Fn(&Request<Body>) -> Option<String> + Send + Sync + 'static

Closure that extracts an opaque customer identifier from the request. Used to group interactions by account in the dashboard.

impl Fn(&Request<Body>) -> Option<String> + Send + Sync + 'static

Closure that extracts a session identifier from the request. Links a sequence of interactions for session-level analytics.

impl Fn(&Request<Body>) -> Option<String> + Send + Sync + 'static

Closure that returns a hint about the agent runtime. Used for runtime-level breakdown in the dashboard.

`FeedbackMode`

Set feedback_mode directly on the Options struct (it is a public field). The enum has three variants:

Variant	Behaviour
`FeedbackMode::Auto` (default)	Instructs the agent to submit a review autonomously, without asking the user.
`FeedbackMode::Ask`	Instructs the agent to submit only when the outcome is unambiguous.
`FeedbackMode::Off`	Disables instrumentation entirely.

use agent_feedback::{FeedbackMode, Options};

let options = Options::new(api_key);
// options.feedback_mode is FeedbackMode::Auto by default

Stream detection

The layer reads the response body size hint from the http_body::Body trait before buffering. Responses without an exact bounded size — including streams — bypass instrumentation entirely and are forwarded untouched to the client. The body size cap is 1 MiB; responses larger than this limit are also forwarded without modification.

Graceful shutdown

Call feedback.shutdown().await at application shutdown. The method sends a shutdown signal to the Tokio telemetry worker and waits up to 2 seconds for in-flight events to flush.

axum::serve(listener, app)
    .with_graceful_shutdown(async {
        tokio::signal::ctrl_c().await.ok();
        feedback.shutdown().await;
    })
    .await?;

Agent helper functions

The crate exports feedback_from_response and submit_product_outcome for building feedback-aware agent runtimes.

`feedback_from_response`

Extracts the Envelope from a response’s HeaderMap and body bytes. Checks the JSON body for _agentFeedback, then the HTML body for <script id="agent-feedback">, then the agent-feedback response header.

use agent_feedback::feedback_from_response;

let response = client.get("https://api.example.com/search?q=logs").send().await?;
let headers = response.headers().clone();
let body = response.bytes().await?;

if let Some(envelope) = feedback_from_response(&headers, &body) {
    // envelope is agent_feedback::Envelope
}

`submit_product_outcome`

Submits a compact outcome review to the URL embedded in the envelope. Validates the contract, enforces the allowed-origin allow-list, and returns a serde_json::Value with the API response.

use agent_feedback::{OutcomeReview, feedback_from_response, submit_product_outcome};

let client = reqwest::Client::new();
let response = client.get("https://api.example.com/search?q=logs").send().await?;
let headers = response.headers().clone();
let body = response.bytes().await?;

if let Some(envelope) = feedback_from_response(&headers, &body) {
    let result = submit_product_outcome(
        &client,
        &envelope,
        OutcomeReview {
            outcome: "success".into(),
            note: "The search returned the log entries needed to resolve the incident.".into(),
        },
        &[],  // empty slice uses the default trusted origin
    )
    .await?;
}

submit_product_outcome returns a SubmitError::UntrustedOrigin error if the submit URL’s origin is not in the allowed list. Pass a non-empty slice only when submitting to a self-hosted endpoint.

AgentFeedbackLayer is Clone, so you can hold one value at the application level for shutdown and pass clones into the Tower layer stack without any additional reference-counting overhead.

Get Started

Core Concepts

SDK Guides

Agent Integration

Configuration & Tools

Rust SDK: Agent Feedback Tower Layer for Axum Apps

Requirements

Installation

Creating the layer

Options builder methods

`FeedbackMode`

Stream detection

Graceful shutdown

Agent helper functions

`feedback_from_response`

`submit_product_outcome`

​Requirements

​Installation

​Creating the layer

​Options builder methods

​FeedbackMode

​Stream detection

​Graceful shutdown

​Agent helper functions

​feedback_from_response

​submit_product_outcome

Requirements

Installation

Creating the layer

Options builder methods

`FeedbackMode`

Stream detection

Graceful shutdown

Agent helper functions

`feedback_from_response`

`submit_product_outcome`