refactor(propagation): Parse OpenTelemetry tracestate member

dd-trace-core/src/main/java/datadog/trace/core/propagation/HttpCodec.java

@@ -286,8 +286,7 @@ private <C> void applyTraceContextToFirstContext(
         ExtractedContext traceContext,
         ExtractionCache<C> extractionCache) {
       // Propagate newly extracted W3C tracestate to first valid context
-      String extractedTracestate = traceContext.getPropagationTags().getW3CTracestate();
-      firstContext.getPropagationTags().updateW3CTracestate(extractedTracestate);
+      firstContext.getPropagationTags().updateW3CTracestateFrom(traceContext.getPropagationTags());
       // Check if parent spans differ to reconcile them
       if (firstContext.getSpanId() != traceContext.getSpanId()) {
         // Override parent span id with W3C one

dd-trace-core/src/main/java/datadog/trace/core/propagation/PropagationTags.java

@@ -95,6 +95,11 @@ public interface Factory {
    */
   public abstract void updateW3CTracestate(String tracestate);
 
+  /** Updates the original W3C tracestate header from {@code source}. */
+  public void updateW3CTracestateFrom(PropagationTags source) {
+    updateW3CTracestate(source.getW3CTracestate());
+  }
+
   /**
    * Constructs a header value that includes valid propagated _dd.p.* tags and possibly a new
    * sampling decision tag _dd.p.dm based on the current state. Returns null if the value length

dd-trace-core/src/main/java/datadog/trace/core/propagation/ptags/OtelTraceState.java

@@ -0,0 +1,36 @@
+package datadog.trace.core.propagation.ptags;
+
+final class OtelTraceState {
+  private final CharSequence value;
+  private final int originalPosition;
+  private final int originalSize;
+
+  private OtelTraceState(CharSequence value, int originalPosition, int originalSize) {
+    this.value = value;
+    this.originalPosition = originalPosition;
+    this.originalSize = originalSize;
+  }
+
+  static OtelTraceState parse(CharSequence raw, int originalPosition, int originalSize) {
+    if (raw == null || raw.length() == 0) {
+      return null;
+    }
+    return new OtelTraceState(raw, originalPosition, originalSize);
+  }
+
+  CharSequence getValue() {
+    return value;
+  }
+
+  int length() {
+    return value.length();
+  }
+
+  int getOriginalPosition() {
+    return originalPosition;
+  }
+
+  int getOriginalSize() {
+    return originalSize;
+  }
+}

dd-trace-core/src/main/java/datadog/trace/core/propagation/ptags/PTagsFactory.java

@@ -112,6 +112,8 @@ static class PTags extends PropagationTags {
 
     private volatile TagValue orgPropagationMarkerTagValue;
 
+    private volatile OtelTraceState otelTraceState;
+
     // Static cache for the most-recently-seen rate → TagValue. In steady state a service uses one
     // rate, so this eliminates the char[] + String allocation on every new PTags instance.
     // Writes are benign-racy: two threads computing the same rate produce equal TagValues.
@@ -540,7 +542,34 @@ public String getW3CTracestate() {
 
     @Override
     public void updateW3CTracestate(String tracestate) {
+      setW3CTracestate(tracestate, W3CPTagsCodec.extractOtelTraceState(tracestate));
+    }
+
+    @Override
+    public void updateW3CTracestateFrom(PropagationTags source) {
+      if (!(source instanceof PTags)) {
+        super.updateW3CTracestateFrom(source);
+        return;
+      }
+      PTags sourcePTags = (PTags) source;
+      setW3CTracestate(sourcePTags.tracestate, sourcePTags.getOtelTraceState());
+    }
+
+    private void setW3CTracestate(String tracestate, OtelTraceState otelTraceState) {
+      clearCachedHeader(W3C);
       this.tracestate = tracestate;
+      this.otelTraceState = otelTraceState;
+    }
+
+    OtelTraceState getOtelTraceState() {
+      return otelTraceState;
+    }
+
+    void setOtelTraceState(OtelTraceState otelTraceState) {
+      if (this.otelTraceState != otelTraceState) {
+        this.otelTraceState = otelTraceState;
+        clearCachedHeader(W3C);
+      }
     }
 
     String getError() {