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AxumRust

Axum Integration

Integrate ImmutableLog into any Axum application with a `from_fn_with_state` middleware that automatically captures all HTTP requests. Sending runs in a fire-and-forget `tokio::spawn` — it never blocks the response.

Dependencies

Add the dependencies below to your `Cargo.toml`. Sending uses `reqwest` with a 5s timeout.

toml
[dependencies]
axum = "0.7"
tokio = { version = "1", features = ["full"] }
reqwest = { version = "0.12", features = ["json"] }
serde_json = "1"
uuid = { version = "1", features = ["v4"] }

Middleware code

Save it in `src/immutablelog.rs`. The middleware reads `request_id` and the trail from headers before `next.run(req)`, captures the status on the response, and sends the event in a separate task.

rust
// src/immutablelog.rs
use std::collections::HashMap;
use std::sync::Arc;
use std::time::{Duration, Instant};

use axum::{extract::{Request, State}, middleware::Next, response::Response};
use serde_json::json;
use uuid::Uuid;

// Margem de seguranca: o limite real do servidor e 16KB (retorna 413 acima disso).
const MAX_PAYLOAD_BYTES: usize = 12_000;

#[derive(Clone)]
pub struct Config {
    pub api_key: String,
    pub api_url: String,
    pub service: String,
    pub env: String,
    pub client_tz: String,
    pub client_offset_minutes: i32,
    pub http: reqwest::Client,
}

impl Config {
    pub fn from_env(service: &str) -> Self {
        Self {
            api_key: std::env::var("IMTBL_API_KEY").unwrap_or_default(),
            api_url: std::env::var("IMTBL_URL").unwrap_or_else(|_| "https://api.immutablelog.com".into()),
            service: service.to_string(),
            env: std::env::var("IMTBL_ENV").unwrap_or_else(|_| "production".into()),
            // Timezone do cliente — usado pelo dashboard para exibir os timestamps.
            client_tz: "America/Sao_Paulo".to_string(),
            client_offset_minutes: -180,
            http: reqwest::Client::builder()
                .timeout(Duration::from_secs(5))
                .build()
                .expect("build http client"),
        }
    }
}

// Marcadores opcionais que um handler anexa na resposta.
#[derive(Clone)]
pub struct EventName(pub String);
#[derive(Clone)]
pub struct Trail(pub String);

// Normaliza o immutable_trail (trim, nao-vazio, max 256, sem ':').
// O servidor responde 400 invalid_immutable_trail se a regra for violada.
fn sanitize_trail(v: &str) -> Option<String> {
    let mut s = v.trim().replace(':', "-");
    if s.is_empty() { return None; }
    if s.chars().count() > 256 { s = s.chars().take(256).collect(); }
    Some(s)
}

fn kind_from(status: u16) -> &'static str {
    if status >= 400 { "error" }
    else if status >= 300 { "info" }
    else if status >= 200 { "success" }
    else { "info" }
}

// Registre com: middleware::from_fn_with_state(cfg.clone(), audit)
pub async fn audit(State(cfg): State<Arc<Config>>, req: Request, next: Next) -> Response {
    let started = Instant::now();
    let method = req.method().to_string();
    let path = req.uri().path().to_string();

    let request_id = req
        .headers()
        .get("x-request-id")
        .and_then(|v| v.to_str().ok())
        .map(str::to_string)
        .unwrap_or_else(|| Uuid::new_v4().to_string());
    let header_trail = req
        .headers()
        .get("x-imtbl-trail")
        .and_then(|v| v.to_str().ok())
        .and_then(sanitize_trail);

    let res = next.run(req).await;
    let status = res.status().as_u16();

    // Handler pode anexar EventName/Trail nas extensions da resposta.
    let event_name = res.extensions().get::<EventName>().map(|e| e.0.clone());
    let route_trail = res.extensions().get::<Trail>().map(|tr| tr.0.clone());

    tokio::spawn(emit(
        cfg, method, path, status, started.elapsed(),
        request_id, event_name, route_trail.or(header_trail),
    ));

    res
}

async fn emit(
    cfg: Arc<Config>, method: String, path: String, status: u16, elapsed: Duration,
    request_id: String, event_name: Option<String>, trail: Option<String>,
) {
    if cfg.api_key.is_empty() { return; }

    let kind = kind_from(status);
    let event_name = event_name.unwrap_or_else(|| format!("http.{}.{}", method, path));
    let trail = trail.and_then(|t| sanitize_trail(&t));

    let mut payload = json!({
        "id": Uuid::new_v4().to_string(),
        "kind": kind,
        "message": format!("{} {} -> {}", method, path, status),
        "request": { "request_id": request_id, "method": method, "path": path },
        "metrics": { "latency_ms": elapsed.as_millis() as u64, "status_code": status },
        "severity": if kind == "error" { "high" } else { "low" },
    });
    if kind == "error" {
        payload["error"] = json!({
            "status_code": status,
            "retryable": [408, 429, 500, 502, 503, 504].contains(&status),
        });
    }

    // clamp: remove o campo grande se passar do limite.
    let mut payload_str = payload.to_string();
    if payload_str.len() > MAX_PAYLOAD_BYTES {
        if let Some(obj) = payload.as_object_mut() { obj.remove("error"); }
        payload_str = payload.to_string();
    }

    // Todos os valores de meta precisam ser strings.
    let mut meta: HashMap<&str, String> = HashMap::new();
    meta.insert("type", kind.to_string());
    meta.insert("event_name", event_name.clone());
    meta.insert("service", cfg.service.clone());
    meta.insert("request_id", request_id.clone());
    meta.insert("env", cfg.env.clone());
    if let Some(t) = &trail { meta.insert("immutable_trail", t.clone()); }

    let event = json!({ "payload": payload_str, "meta": meta });

    let mut builder = cfg.http
        .post(format!("{}/v1/events", cfg.api_url))
        .bearer_auth(&cfg.api_key)
        .header("Content-Type", "application/json")
        // Idempotency-Key e OBRIGATORIO (sem ele a API responde 400).
        .header("Idempotency-Key", format!("{}-{}", event_name, request_id))
        .header("Request-Id", &request_id)
        .header("X-Client-TZ", &cfg.client_tz)
        .header("X-Client-Offset-Minutes", cfg.client_offset_minutes.to_string());
    if let Some(t) = &trail { builder = builder.header("X-Imtbl-Trail", t); }

    let _ = builder.json(&event).send().await; // fire-and-forget
}

Registration and Configuration

Register the middleware with `from_fn_with_state`, passing the shared `Config` via `Arc`. Use environment variables for credentials.

rust
// src/main.rs
use std::sync::Arc;
use axum::{middleware, routing::{get, post}, Router};

mod immutablelog;
use immutablelog::{audit, Config};

#[tokio::main]
async fn main() {
    let cfg = Arc::new(Config::from_env("my-axum-service"));

    let app = Router::new()
        .route("/users", get(|| async { "ok" }))
        .route("/payments", post(payments_handler))
        // Registre o middleware com o Config compartilhado via Arc.
        .layer(middleware::from_fn_with_state(cfg.clone(), audit));

    let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
    axum::serve(listener, app).await.unwrap();
}

Never hardcode the token. Load IMTBL_API_KEY from environment variables (e.g. via dotenvy).

How it works

from_fn_with_state

Reads request_id and trail from headers before next.run

next.run(req).await

Runs the chain; the status comes out on the Response

tokio::spawn(emit)

Event sent in a separate task — never blocks the response

Custom event and trail

Since the middleware reads the response after `next.run`, a handler can attach `EventName` and `Trail` to the response extensions. The middleware reads these markers when emitting the event.

rust
use axum::{response::{IntoResponse, Response}, Json};
use serde_json::json;
use immutablelog::{EventName, Trail};

async fn payments_handler() -> Response {
    let mut res = Json(json!({ "ok": true, "payment_id": "pay_123" })).into_response();

    // Sobrescreve o nome do evento e agrupa numa trilha auditavel.
    res.extensions_mut().insert(EventName("payment.created".into()));
    res.extensions_mut().insert(Trail("order-7782".into()));

    res
}

Auto default: http.METHOD.path.

Immutable trail (immutable_trail)

A trail groups related events into a single auditable timeline. Attach `Trail(...)` to a handler's response, or propagate it across services with the `X-Imtbl-Trail` header. The value goes through `sanitize_trail` before sending.

rust
async fn run_flow(/* ... */) -> Response {
    let mut res = Json(json!({ "status": "ok" })).into_response();
    res.extensions_mut().insert(Trail("flow-123".into()));
    res
}

The trail cannot be empty, exceed 256 characters, or contain `:` — violations return `400 invalid_immutable_trail`. `sanitize_trail` fixes the value before sending.

Response and status codes

The ingestion API is asynchronous. Success returns 202 (new) or 200 (idempotent duplicate). Since the middleware is fire-and-forget, these codes matter mostly if you send events manually.

StatusMeaning
202Event accepted and queued (new)
200Idempotency-Key already exists — duplicate: true
400Missing/empty Idempotency-Key or invalid_immutable_trail
403Inactive/expired subscription, scope or retention
413payload_too_large (server limit: 16KB)
429monthly_limit_exceeded — do not retry
503mempool_full — transient, retryable

meta fields

Beyond the payload, the meta object carries the fields the SIEM uses to normalize (ECS) and enrich the event. All meta values are strings.

Field in metaWhat it does in the SIEM
event_nameThe event label (e.g. http.GET.auth-me-user, Payment error) — the identifier shown in the listing. Becomes event.action and derives event.category (e.g. a name with login → authentication).
client_ipBecomes source.ip with maximum precedence and provenance client_asserted. See the section below.
immutable_trailBecomes imtbl.immutable_trail — groups related events for investigation (e.g. one order, one user).
typeEvent severity: error / warning / info / success. Colors the badge in the listing. (event_type is accepted as a synonym.)
service, env, request_idMetadata: indexed and queryable in the dashboard (search/filters).

client_ip — end-user IP

The problem it solves

Between the browser and the core there are proxies/ALB. The IP the core sees on the connection is the previous hop (the client's backend or an AWS proxy), not the user's. Without action, source.ip would be the proxy IP — useless for geo, threat and IP-based detection. (Real example: XFF arrived as 44.192.13.3 (AWS) while the user was 179.110.4.205.)

The solution

The client's backend is the only one that sees the browser's real IP — so it forwards that IP in meta.client_ip when calling POST /v1/events.

How the SIEM handles it

  • Validates it is an IP (v4/v6). A non-IP value is ignored — it does not drop the event.
  • Writes to source.ip with maximum precedence (see order below).
  • Stamps imtbl.source_ip_origin = "client_asserted" — the UI shows the “User IP” badge.
  • Feeds GeoIP, threat intel and IP-based detection rules.
source.ip precedence:client_ipX-Forwarded-For (1º hop)X-Real-IPconnection IP

Provenance and trust

client_ip is asserted by the tenant — the client's backend claims the IP, and it is spoofable by whoever controls that backend. However it is self-contained to the tenant (it never crosses another tenant's boundary). A threat/geo hit on a client_asserted value is a claim, not an edge observation.

How to obtain the IP in your backend

Take the first IP from X-Forwarded-For (closest to the user); as a fallback, use the connection IP.

rust
fn client_ip(req: &HttpRequest) -> Option<String> {
    if let Some(xff) = req.headers().get("x-forwarded-for") {
        if let Ok(s) = xff.to_str() {
            if let Some(first) = s.split(',').next() {
                return Some(first.trim().to_string()); // primeiro hop
            }
        }
    }
    req.peer_addr().map(|a| a.ip().to_string())
}

let meta = json!({ "event_name": "user.login", "client_ip": client_ip(&req) });

Payload example

json
{
  "payload": "{\"user\":\"bob\",\"action\":\"login\"}",
  "meta": {
    "event_name": "user.login",
    "client_ip": "179.110.4.205",
    "immutable_trail": "user-bob"
  }
}

PII note: client_ip is PII and gets sealed into the immutable block (permanent). Decide consciously between forensic evidence and “right to be forgotten” before sending it.

This documentation reflects the current integration behavior. For questions or advanced integrations, contact the support team.