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Avoid duplicate headers when injecting on java.net http client #10315

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Merged
amarziali merged 2 commits into from
Jan 8, 2026
Merged

Avoid duplicate headers when injecting on java.net http client #10315

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e56b785
Avoid duplicate headers when injecting on java.net http client
amarziali Jan 8, 2026
ea116a8
Use TreeMap
amarziali Jan 8, 2026
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8 changes: 6 additions & 2 deletions ...java-net-11.0/src/main/java11/datadog/trace/instrumentation/httpclient/HeadersAdvice.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,17 +4,21 @@
import static datadog.trace.instrumentation.httpclient.HttpHeadersInjectAdapter.KEEP;
import static datadog.trace.instrumentation.httpclient.HttpHeadersInjectAdapter.SETTER;
import static datadog.trace.instrumentation.httpclient.JavaNetClientDecorator.DECORATE;
import static java.lang.String.CASE_INSENSITIVE_ORDER;

import java.net.http.HttpHeaders;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import net.bytebuddy.asm.Advice;

public class HeadersAdvice {
@Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class)
public static void methodExit(@Advice.Return(readOnly = false) HttpHeaders headers) {
final Map<String, List<String>> headerMap = new HashMap<>(headers.map());
// Note: adding duplicate keys will throw an IllegalArgumentException so we need to dedupe
// case insensitively
final Map<String, List<String>> headerMap = new TreeMap<>(CASE_INSENSITIVE_ORDER);
headerMap.putAll(headers.map());
DECORATE.injectContext(getCurrentContext(), headerMap, SETTER);
headers = HttpHeaders.of(headerMap, KEEP);
}
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19 changes: 18 additions & 1 deletion ...t-11.0/src/test/groovy/datadog/trace/instrumentation/httpclient/JavaHttpClientTest.groovy
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Original file line number Diff line number Diff line change
@@ -1,8 +1,9 @@
package datadog.trace.instrumentation.httpclient

import datadog.trace.agent.test.base.HttpClientTest

import static datadog.trace.instrumentation.httpclient.JavaNetClientDecorator.DECORATE

import datadog.trace.agent.test.base.HttpClientTest
import java.net.http.HttpClient
import java.net.http.HttpRequest
import java.net.http.HttpResponse
Expand Down Expand Up @@ -42,6 +43,22 @@ abstract class JavaHttpClientTest extends HttpClientTest {
boolean testRedirects() {
false
}

def 'should not inject duplicate headers'() {
when:
def status = doRequest("GET", server.address.resolve("/success"),
// our codec inject names all lowercase
["X-Datadog-Trace-ID": "0"])

then:
status == 200
assertTraces(2) {
trace(size(1)) {
clientSpan(it, null)
}
server.distributedRequestTrace(it, trace(0).last())
}
}
}

class JavaHttpClientV0Test extends JavaHttpClientTest {
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