otel_http

OpenTelemetry client instrumentation for package:http, Dart's official cross-platform HTTP client. Built on the Dartastic OpenTelemetry SDK.

Wrap any http.Client and every request gets:

• A CLIENT-kind span around the call.
• The full HTTP semantic-convention attribute set (http.request.method, url.full, server.address, http.response.status_code, …).
• W3C traceparent / tracestate / baggage headers injected so any downstream service that also speaks OTel joins the same trace.
• Exception recording (recordException + error.type + Error status) on transport failures and 4xx / 5xx responses.

Why

package:http is the foundation HTTP client for the Dart and Flutter ecosystems. A missing client span here is a blind spot in every higher-level integration that talks to a backend — auth, analytics relays, GraphQL, Firebase callable functions, you name it. This package is the one place you wire OTel into HTTP so the entire stack above it inherits trace context for free.

The bridge is opt-in: the OTel SDK does not depend on package:http. Add this package only when you want the integration.

⚠️ Self-recursion: don't instrument your OTLP/HTTP export client

OTLP/HTTP export is itself HTTP. The dartastic SDK's built-in OTLP/HTTP exporter sends via package:http. If you somehow wire OTLP export through an OTelHttpClient-wrapped client, every span you export creates an HTTP call that the wrapper turns into a new span, which gets exported, which makes another call — classic instrumentation recursion.

You're safe by default — the SDK's exporter creates its own private http.Client that your OTelHttpClient isn't attached to. The risk only appears if you manually wire OTLP/HTTP export through a Client you also wrapped. If that's your setup, do one of:

1. Don't wrap that client. Use a separate, plain http.Client for OTLP traffic.
2. Wrap export calls in the suppression helper:

   import 'package:otel_http/otel_http.dart';
   
   await runWithoutHttpInstrumentationAsync(() async {
     await myOtlpClient.post(...);
   });
   

   The wrapper checks a zone-scoped flag and skips span creation AND header injection. Sync variant: runWithoutHttpInstrumentation.

Usage

import 'package:otel_http/otel_http.dart';
import 'package:dartastic_opentelemetry/dartastic_opentelemetry.dart';
import 'package:http/http.dart' as http;

Future<void> main() async {
  await OTel.initialize(serviceName: 'my-app');

  // Wrap any http.Client. The OTel client is itself a `BaseClient`,
  // so it slots in anywhere a `Client` is expected.
  final client = OTelHttpClient(http.Client());

  // Inside a server-side / handler span so the client span has a parent.
  await OTel.tracer().startActiveSpanAsync<void>(
    name: 'serve-request',
    fn: (_) async {
      final r = await client.get(
        Uri.parse('https://api.example.com/users/42'),
      );
      print(r.statusCode);
    },
  );

  client.close();
  await OTel.shutdown();
}

Outbound requests carry trace context automatically:

GET /users/42 HTTP/1.1
Host: api.example.com
traceparent: 00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01
tracestate: ...

Span shape

Follows the OTel HTTP client semantic conventions.

Attribute	Source	When set
http.request.method	uppercased request.method	always
url.full	request.url (userinfo redacted)	always
url.scheme	request.url.scheme	always
url.path	request.url.path	when present
url.query	request.url.query	when present
server.address	request.url.host	when present
server.port	request.url.port	when explicit
http.request.body.size	request.contentLength	when set
user_agent.original	User-Agent request header	when present
http.response.status_code	response.statusCode	on response
http.response.body.size	response.contentLength	when set
error.type	runtimeType of underlying error	on exception

• Span name defaults to {HTTP_METHOD} (e.g. GET). Per the OTel spec the recommended name is {METHOD} {url-template} when the template is known; pass spanNameBuilder if you have one.
• Span kind is CLIENT.
• Span status is set to Error for 4xx / 5xx responses and any thrown exception; otherwise it follows the SDK default.

Userinfo in the URL (https://alice:secret@host/...) is redacted to https://REDACTED:REDACTED@host/... per the spec's "URL.full SHOULD NOT contain credentials" requirement.

Configuration

Constructor arg	Default	Effect
tracer	OTel.tracerProvider().getTracer('otel_http')	The tracer that emits the spans.
spanNameBuilder	(req) => req.method.toUpperCase()	Override the span name (e.g. inject a URL template).
recordRequestBodySize	true	Set http.request.body.size from contentLength.
recordResponseBodySize	true	Set http.response.body.size from contentLength.
ignoreUrlPatterns	const []	Requests whose full URL matches any pattern (String substring or RegExp) are not instrumented at all — no span, no header injection.

OTelHttpClient(
  http.Client(),
  ignoreUrlPatterns: [
    RegExp(r'/v1/(traces|metrics|logs)$'), // OTLP upload endpoints
    'analytics.example.com',
  ],
)

If your telemetry exporter shares this client, ignore its endpoints — otherwise every export becomes a span, which is itself exported (the double-count trap). ignoreUrlPatterns is configuration for known URLs; the zone-scoped suppression below stays the right tool for call-site scoping.

Body sizes

http.{request,response}.body.size come from BaseRequest.contentLength and StreamedResponse.contentLength, not by reading the body, so there's no performance hit and no PII risk. Pass recordRequestBodySize: false / recordResponseBodySize: false if your app sets contentLength to something synthetic.

Composing with other clients

Because OTelHttpClient is a http.BaseClient that wraps another http.Client, it composes naturally with other client decorators (retry, auth, caching). Put OTelHttpClient outermost so its span encloses everything the inner clients do:

final client = OTelHttpClient(
  RetryClient(
    AuthClient(http.Client()),
  ),
);

That way retries appear as repeated outbound requests inside one span (or use per-attempt span events if you wire your retry client to emit them).

Caveats

• The client calls OTel.tracerProvider().getTracer(...) in its constructor — OTel.initialize() must have run first.
• OTelHttpClient.close() closes the wrapped inner client. If you share an inner client across multiple wrappers, manage its lifecycle yourself.

License

Apache 2.0 — see LICENSE.