io.opencensus.trace.propagation

Class TextFormat

java.lang.Object

io.opencensus.trace.propagation.TextFormat

@ExperimentalApi
public abstract class TextFormat
extends Object

Injects and extracts trace identifiers as text into carriers that travel in-band across process boundaries. Identifiers are often encoded as messaging or RPC request headers.

When using http, the carrier of propagated data on both the client (injector) and server (extractor) side is usually an http request. Propagation is usually implemented via library- specific request interceptors, where the client-side injects span identifiers and the server-side extracts them.

Example of usage on the client:

 private static final Tracer tracer = Tracing.getTracer();
 private static final TextFormat textFormat = Tracing.getPropagationComponent().getTextFormat();
 private static final TextFormat.Setter setter = new TextFormat.Setter<HttpURLConnection>() {
   public void put(HttpURLConnection carrier, String key, String value) {
     carrier.setRequestProperty(field, value);
   }
 }

 void makeHttpRequest() {
   Span span = tracer.spanBuilder("Sent.MyRequest").startSpan();
   try (Scope s = tracer.withSpan(span)) {
     HttpURLConnection connection =
         (HttpURLConnection) new URL("http://myserver").openConnection();
     textFormat.inject(span.getContext(), connection, httpURLConnectionSetter);
     // Send the request, wait for response and maybe set the status if not ok.
   }
   span.end();  // Can set a status.
 }
 

Example of usage on the server:

 private static final Tracer tracer = Tracing.getTracer();
 private static final TextFormat textFormat = Tracing.getPropagationComponent().getTextFormat();
 private static final TextFormat.Getter<HttpRequest> getter = ...;

 void onRequestReceived(HttpRequest request) {
   SpanContext spanContext = textFormat.extract(request, getter);
   Span span = tracer.spanBuilderWithRemoteParent("Recv.MyRequest", spanContext).startSpan();
   try (Scope s = tracer.withSpan(span)) {
     // Handle request and send response back.
   }
   span.end()
 }
 

Since:

0.11

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TextFormat.Getter<C> Class that allows a TextFormat to read propagated fields from a carrier.
static class	TextFormat.Setter<C> Class that allows a TextFormat to set propagated fields into a carrier.

Constructor Summary

Constructors

Constructor and Description
TextFormat()

Method Summary

Modifier and Type	Method and Description
abstract <C> SpanContext	extract(C carrier, TextFormat.Getter<C> getter) Extracts the span context from upstream.
abstract List<String>	fields() The propagation fields defined.
abstract <C> void	inject(SpanContext spanContext, C carrier, TextFormat.Setter<C> setter) Injects the span context downstream.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TextFormat

public TextFormat()

Method Detail

fields

public abstract List<String> fields()

The propagation fields defined. If your carrier is reused, you should delete the fields here before calling inject(SpanContext, Object, Setter).

For example, if the carrier is a single-use or immutable request object, you don't need to clear fields as they couldn't have been set before. If it is a mutable, retryable object, successive calls should clear these fields first.

Since:

0.11

inject

public abstract <C> void inject(SpanContext spanContext,
                                C carrier,
                                TextFormat.Setter<C> setter)

Injects the span context downstream. For example, as http headers.

Parameters:

spanContext - possibly not sampled.

carrier - holds propagation fields. For example, an outgoing message or http request.

setter - invoked for each propagation key to add or remove.

Since:

0.11

extract

public abstract <C> SpanContext extract(C carrier,
                                        TextFormat.Getter<C> getter)
                                 throws SpanContextParseException

Extracts the span context from upstream. For example, as http headers.

Parameters:

carrier - holds propagation fields. For example, an outgoing message or http request.

getter - invoked for each propagation key to get.

Throws:

SpanContextParseException - if the input is invalid

Since:

0.11