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Support propagating OTel API created baggage via outgoing W3C headers #9987

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Merged
merged 3 commits into from
Nov 18, 2025
+68 −15
Merged

Support propagating OTel API created baggage via outgoing W3C headers #9987

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27e32a4
Support propagating OTel API created baggage via outgoing W3C headers
mcculls Nov 17, 2025
934f018
Merge branch 'master' into mcculls/w3c-otel-baggage-interop-pt2
mcculls Nov 18, 2025
9fa02e6
Decouple OTel baggage built from the same builder
mcculls Nov 18, 2025
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2 changes: 1 addition & 1 deletion ...t-otel/otel-shim/src/main/java/datadog/opentelemetry/shim/baggage/OtelBaggageBuilder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,6 @@ public BaggageBuilder remove(@Nullable String key) {

@Override
public Baggage build() {
return new OtelBaggage(items);
return new OtelBaggage(new HashMap<>(items));
}
}
6 changes: 6 additions & 0 deletions ...nt/agent-otel/otel-shim/src/main/java/datadog/opentelemetry/shim/context/OtelContext.java
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Expand Up @@ -80,6 +80,12 @@ public <V> Context with(ContextKey<V> key, V value) {
if (value instanceof OtelBaggage) {
Baggage baggage = ((OtelBaggage) value).asAgentBaggage();
return new OtelContext(delegate.with(baggage));
} else if (value instanceof io.opentelemetry.api.baggage.Baggage) {
Baggage baggage = Baggage.empty();
// transfer baggage to our internal container for propagation purposes
((io.opentelemetry.api.baggage.Baggage) value)
.forEach((k, b) -> baggage.addItem(k, b.getValue()));
Comment on lines +84 to +87
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@PerfectSlayer PerfectSlayer Nov 18, 2025 •
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🎯 suggestion: ‏That might be an over optimization but (follow me here), what about implementing a custom Map implementation that projects the Map<String, BaggageEntry> returned by (OTel) Baggage.asMap() into a Map<String, String>?

We can then use (DD) Baggage.create(Map) from it, meaning having zero collection allocation as OTel uses the ReadOnlyArrayMap projection and we can have ours to translate value to their string counter parts.

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@mcculls mcculls Nov 18, 2025

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One hiccup is that projection would be read-only - and our internal Baggage container has mutable operations (addItem / removeItem) that assume a mutable map.

So I'd prefer to do that as part of a refactoring to optimize the internal Baggage API, ideally making it inherently immutable once created/built.

return new OtelContext(delegate.with(baggage));
}
// fall-through and store as non-datadog baggage
}
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75 changes: 61 additions & 14 deletions ...pentelemetry/opentelemetry-1.4/src/test/groovy/opentelemetry14/context/ContextTest.groovy
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Expand Up @@ -338,43 +338,90 @@ class ContextTest extends InstrumentationSpecification {
otelBaggageFromContext.isEmpty()
otelBaggageFromContextOrNull == null

when:
def otelScope = Baggage.builder()
.put("foo", "otel_value_to_be_replaced")
.put("FOO","OTEL_UNTOUCHED")
.put("remove_me_key", "otel_remove_me_value")
.build()
.makeCurrent()
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@mhlidd mhlidd Nov 17, 2025

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❓ (For my own understanding). I assume that this makeCurrent() invokes our OTelContext instead of the OpenTelemetry Context implementation. How does the makeCurrent() know to use our implementation? 🤔

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@mcculls mcculls Nov 17, 2025

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Note this is Baggage.makeCurrent() :)

Baggage inherits this default method from ImplicitContextKeyed: https://github.com/open-telemetry/opentelemetry-java/blob/main/context/src/main/java/io/opentelemetry/context/ImplicitContextKeyed.java#L33

  default Scope makeCurrent() {
    return Context.current().with(this).makeCurrent();
  }

Notice how it's implemented by getting the current Context (which will be our OtelContext wrapper) to which it adds the new baggage via with (which we'll intercept via our OtelContext wrapper) before activating the resulting context.

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@mhlidd mhlidd Nov 17, 2025

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Most of this makes sense. The part that I'm confused about is how our OtelContext wrapper gets magically used here instead of the OTel implementation of Context, since I don't see anywhere where we explicitly "set" OtelContext as the global implementation for io.opentelemetry.context.Context.

Hope the question makes sense!

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@mcculls mcculls Nov 17, 2025

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sure, that's done by instrumenting the underlying storage: https://github.com/DataDog/dd-trace-java/blob/master/dd-java-agent/instrumentation/opentelemetry/opentelemetry-1.4/src/main/java/datadog/trace/instrumentation/opentelemetry14/context/OpenTelemetryContextStorageInstrumentation.java#L97

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@mhlidd mhlidd Nov 17, 2025

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Ahh that makes sense. We instrument the calls made to OTel Context and specify to use our OtelContext instead. Thanks for the explanation! :)

otelBaggage = Baggage.current()
otelBaggageFromContext = Baggage.fromContext(Context.current())
otelBaggageFromContextOrNull = Baggage.fromContextOrNull(Context.current())

then: "OTel baggage must be current"
otelBaggage != null
otelBaggage.size() == 3
otelBaggage.getEntryValue("foo") == "otel_value_to_be_replaced"
otelBaggage.getEntryValue("FOO") == "OTEL_UNTOUCHED"
otelBaggage.getEntryValue("remove_me_key") == "otel_remove_me_value"
otelBaggage.asMap() == otelBaggageFromContext.asMap()
otelBaggage.asMap() == otelBaggageFromContextOrNull.asMap()

when:
def ddContext = datadog.context.Context.current()
def ddBaggage = datadog.trace.bootstrap.instrumentation.api.Baggage.create([
"foo" : "value_to_be_replaced",
"FOO" : "UNTOUCHED",
"remove_me_key" : "remove_me_value"
])
def ddBaggage = datadog.trace.bootstrap.instrumentation.api.Baggage.fromContext(ddContext)
ddBaggage.addItem("new_foo", "dd_new_value")
ddBaggage.addItem("foo", "dd_overwrite_value")
ddBaggage.removeItem("remove_me_key")
def ddScope = ddContext.with(ddBaggage).attach()
otelBaggage = Baggage.current()
otelBaggageFromContext = Baggage.fromContext(Context.current())
otelBaggageFromContextOrNull = Baggage.fromContextOrNull(Context.current())

then: "baggage must contain Datadog changes"
otelBaggage != null
otelBaggage.size() == 3
otelBaggage.getEntryValue("foo") == "dd_overwrite_value"
otelBaggage.getEntryValue("FOO") == "OTEL_UNTOUCHED"
otelBaggage.getEntryValue("new_foo") == "dd_new_value"
otelBaggage.asMap() == otelBaggageFromContext.asMap()
otelBaggage.asMap() == otelBaggageFromContextOrNull.asMap()

when:
ddScope.close()
otelScope.close()

then: "current baggage must be empty or null"
Baggage.current().isEmpty()

when:
ddContext = datadog.context.Context.current()
ddBaggage = datadog.trace.bootstrap.instrumentation.api.Baggage.create([
"foo" : "dd_value_to_be_replaced",
"FOO" : "DD_UNTOUCHED",
"remove_me_key" : "dd_remove_me_value"
])
ddScope = ddContext.with(ddBaggage).attach()
otelBaggage = Baggage.current()
otelBaggageFromContext = Baggage.fromContext(Context.current())
otelBaggageFromContextOrNull = Baggage.fromContextOrNull(Context.current())

then: "Datadog baggage must be current"
otelBaggage != null
otelBaggage.size() == 3
otelBaggage.getEntryValue("foo") == "value_to_be_replaced"
otelBaggage.getEntryValue("FOO") == "UNTOUCHED"
otelBaggage.getEntryValue("remove_me_key") == "remove_me_value"
otelBaggage.getEntryValue("foo") == "dd_value_to_be_replaced"
otelBaggage.getEntryValue("FOO") == "DD_UNTOUCHED"
otelBaggage.getEntryValue("remove_me_key") == "dd_remove_me_value"
otelBaggage.asMap() == otelBaggageFromContext.asMap()
otelBaggage.asMap() == otelBaggageFromContextOrNull.asMap()

when:
def builder = otelBaggage.toBuilder()
builder.put("new_foo", "new_value")
builder.put("foo", "overwrite_value")
builder.put("new_foo", "otel_new_value")
builder.put("foo", "otel_overwrite_value")
builder.remove("remove_me_key")
def otelScope = builder.build().makeCurrent()
otelScope = builder.build().makeCurrent()
otelBaggage = Baggage.current()
otelBaggageFromContext = Baggage.fromContext(Context.current())
otelBaggageFromContextOrNull = Baggage.fromContextOrNull(Context.current())

then: "baggage must contain OTel changes"
otelBaggage != null
otelBaggage.size() == 3
otelBaggage.getEntryValue("foo") == "overwrite_value"
otelBaggage.getEntryValue("FOO") == "UNTOUCHED"
otelBaggage.getEntryValue("new_foo") == "new_value"
otelBaggage.getEntryValue("foo") == "otel_overwrite_value"
otelBaggage.getEntryValue("FOO") == "DD_UNTOUCHED"
otelBaggage.getEntryValue("new_foo") == "otel_new_value"
otelBaggage.asMap() == otelBaggageFromContext.asMap()
otelBaggage.asMap() == otelBaggageFromContextOrNull.asMap()

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