Jaeger Bindings for Javascript OpenTracing API
JavaScript Other
Latest commit 20b4f1a Jan 21, 2017 @oibe oibe committed on GitHub Merge pull request #87 from uber/release_v3.0.0


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Jaeger Bindings for Javascript OpenTracing API

This is a client side library that implements Javascript OpenTracing API, with Zipkin-compatible data model.

This project is currently WIP and not ready for use. Do not use it until this notice goes away.


Please see CONTRIBUTING.md.

TChannel Span Bridging

Because tchannel-node does not have instrumentation for OpenTracing, Jaeger-Client exposes methods wrapping tchannel handlers, and encoded channels. An encoded channel is a channel wrapped in either a thrift encoder TChannelAsThrift, or json encoder TChannelAsJson. To wrap a server handler for thrift one can initialize a tchannel bridge, and wrap the encoded handler function with a tracedHandler decorator. The tchannel bridge takes an OpenTracing tracer, and a context factory. The context factory must be a function that returns a context with the methods 'getSpan', and 'setSpan' which retrieve and assign the span to the context respectively.

    import { TChannelBridge } from 'jaeger-client';
    import Context from 'some-conformant-context';

    function contextFactory() {
        return new Context();

    let bridge = new TChannelBridge(tracer, {contextFactory: contextFactory});
    let server = new TChannel({ serviceName: 'server' });
    server.listen(4040, '');
    let serverThriftChannel = TChannelAsThrift({
        channel: server,
        entryPoint: path.join(__dirname, 'thrift', 'echo.thrift') // file path to a thrift file

    let perProcessOptions = {};
    serverThriftChannel.register(server, 'Echo::echo', perProcessOptions, bridge.tracedHandler(
        (perProcessOptions, req, head, body, callback) => {
            /* Your handler code goes here. */

Outbound calls can be made in two ways, shown below.

Using encoded channel to create a request and calling request.send()

    import { TChannelBridge } from 'jaeger-client';

    let bridge = new TChannelBridge(tracer);
    // Create the toplevel client channel.
    let client = new TChannel();

    // Create the client subchannel that makes requests.
    let clientSubChannel = client.makeSubChannel({
        serviceName: 'server',
        peers: ['']

    let encodedThriftChannel = TChannelAsThrift({
        channel: clientSubChannel,
        entryPoint: path.join(__dirname, 'thrift', 'echo.thrift') // file path to a thrift file

    // wrap encodedThriftChannel in a tracing decorator
    let tracedChannel = bridge.tracedChannel(encodedThriftChannel);

    // The encodedThriftChannel's (also true for json encoded channels) request object can call 'send' directly.
    let req = tracedChannel.request({
        serviceName: 'server',
        context: context, // must be passed through from the service handler shown above
        headers: { cn: 'echo' }

    // headers should contain your outgoing tchannel headers if any.
    // In this instance 'send' is being called on the request object, and not the channel.
    req.send('Echo::echo', headers, { value: 'some-string' });

Using top level channel to create a request and calling encodedChannel.send(request)

    let tracedChannel = bridge.tracedChannel(encodedThriftChannel);

    // tracedChannel.channel refers to encodedThriftChannel's inner channel which
    // is clientSubChannel in this instance.
    let req = tracedChannel.channel.request({
        serviceName: 'server',
        headers: { cn: 'echo' },
        context: context, // must be passed through from the service handler shown above
        timeout: someTimeout,
    // send() can be called directly on the tracing decorator
    tracedChannel.send(req, 'Echo::echo', o.headers, { value: 'some-string' }, clientCallback);

Debug Traces (Forced Sampling)


The OpenTracing API defines a sampling.priority standard tag that can be used to affect the sampling of a span and its children:

span.setTag(opentracing_tags.SAMPLING_PRIORITY, 1);

Via HTTP Headers

Jaeger Tracer also understands a special HTTP Header jaeger-debug-id, which can be set in the incoming request, e.g.

curl -H "jaeger-debug-id: some-correlation-id" http://myhost.com

When Jaeger sees this header in the request that otherwise has no tracing context, it ensures that the new trace started for this request will be sampled in the "debug" mode (meaning it should survive all downsampling that might happen in the collection pipeline), and the root span will have a tag as if this statement was executed:

span.setTag("jaeger-debug-id", "some-correlation-id");

This allows using Jaeger UI to find the trace by this tag.