io.opencensus.tags.propagation

Class TagContextTextFormat

java.lang.Object

io.opencensus.tags.propagation.TagContextTextFormat

public abstract class TagContextTextFormat
extends Object

Object for injecting and extracting TagContext as text into carriers that travel in-band across process boundaries. Tags 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 tags and the server-side extracts them.

Example of usage on the client:

 private static final Tagger tagger = Tags.getTagger();
 private static final TagContextTextFormat textFormat =
     Tags.getPropagationComponent().getCorrelationContextFormat();
 private static final TagContextTextFormat.Setter setter =
     new TagContextTextFormat.Setter<HttpURLConnection>() {
       public void put(HttpURLConnection carrier, String key, String value) {
         carrier.setRequestProperty(field, value);
       }
     };

 void makeHttpRequest() {
   TagContext tagContext = tagger.emptyBuilder().put(K, V).build();
   try (Scope s = tagger.withTagContext(tagContext)) {
     HttpURLConnection connection =
         (HttpURLConnection) new URL("http://myserver").openConnection();
     textFormat.inject(tagContext, connection, httpURLConnectionSetter);
     // Send the request, wait for response and maybe set the status if not ok.
   }
 }
 

Example of usage on the server:

 private static final Tagger tagger = Tags.getTagger();
 private static final TagContextTextFormat textFormat =
     Tags.getPropagationComponent().getCorrelationContextFormat();
 private static final TagContextTextFormat.Getter<HttpRequest> getter = ...;

 void onRequestReceived(HttpRequest request) {
   TagContext tagContext = textFormat.extract(request, getter);
   try (Scope s = tagger.withTagContext(tagContext)) {
     // Handle request and send response back.
   }
 }
 

Since:

0.21

Nested Class Summary

Nested Classes

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

Constructor Summary

Constructors

Constructor and Description
TagContextTextFormat()

Method Summary

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

Methods inherited from class java.lang.Object

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

Constructor Detail

TagContextTextFormat

public TagContextTextFormat()

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(TagContext, 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:

0.21

inject

public abstract <C> void inject(TagContext tagContext,
                                C carrier,
                                TagContextTextFormat.Setter<C> setter)
                         throws TagContextSerializationException

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

Parameters:

tagContext - the tag context.

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

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

Throws:

TagContextSerializationException - if the given tag context cannot be serialized.

Since:

0.21

extract

public abstract <C> TagContext extract(C carrier,
                                       TagContextTextFormat.Getter<C> getter)
                                throws TagContextDeserializationException

Extracts the tag 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:

TagContextDeserializationException - if the input is invalid

Since:

0.21