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TraceEnrichingChannel.java
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TraceEnrichingChannel.java
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/*
* (c) Copyright 2020 Palantir Technologies Inc. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.palantir.dialogue.core;
import com.google.common.collect.ImmutableMap;
import com.google.common.util.concurrent.FutureCallback;
import com.google.common.util.concurrent.ListenableFuture;
import com.palantir.dialogue.Channel;
import com.palantir.dialogue.Endpoint;
import com.palantir.dialogue.Request;
import com.palantir.dialogue.Response;
import com.palantir.dialogue.futures.DialogueFutures;
import com.palantir.tracing.CloseableSpan;
import com.palantir.tracing.DetachedSpan;
import com.palantir.tracing.TagTranslator;
import com.palantir.tracing.Tracer;
import com.palantir.tracing.Tracers;
import com.palantir.tracing.TracingHeadersEnrichingFunction;
import com.palantir.tracing.api.SpanType;
/** A channel that adds Zipkin compatible tracing headers. */
final class TraceEnrichingChannel implements Channel {
private static final String OPERATION = "Dialogue-http-request";
private final NeverThrowChannel delegate; // important to ensure the span is definitely completed!
private final TagTranslator<Response> responseTranslator;
private final TagTranslator<Throwable> throwableTranslator;
TraceEnrichingChannel(Channel delegate, ImmutableMap<String, String> tags) {
this.delegate = new NeverThrowChannel(delegate);
this.responseTranslator = DialogueTracing.responseTranslator(tags);
this.throwableTranslator = DialogueTracing.failureTranslator(tags);
}
@Override
public ListenableFuture<Response> execute(Endpoint endpoint, Request request) {
if (Tracer.hasUnobservableTrace()) {
// in the vast majority of cases, we're not actually sampling span information at all, so we might as
// well save the CPU cycles of creating a DetachedSpan and just send the headers.
return executeInternal(endpoint, request);
}
return executeSampled(endpoint, request);
}
private ListenableFuture<Response> executeSampled(Endpoint endpoint, Request request) {
DetachedSpan span = DetachedSpan.start(OPERATION, SpanType.CLIENT_OUTGOING);
// n.b. This span is required to apply tracing thread state to an initial request. Otherwise if there is
// no active trace, the detached span would not be associated with work initiated by delegateFactory.
try (CloseableSpan ignored = span.attach()) {
ListenableFuture<Response> future = executeInternal(endpoint, request);
return DialogueFutures.addDirectCallback(future, new FutureCallback<Response>() {
@Override
public void onSuccess(Response response) {
span.complete(responseTranslator, response);
}
@Override
public void onFailure(Throwable throwable) {
span.complete(throwableTranslator, throwable);
}
});
}
}
private ListenableFuture<Response> executeInternal(Endpoint endpoint, Request request) {
Request.Builder requestBuilder = Request.builder().from(request);
Tracers.addTracingHeaders(requestBuilder, RequestTracingHeadersEnrichingFunction.INSTANCE);
return delegate.execute(endpoint, requestBuilder.build());
}
@Override
public String toString() {
return "TracedRequestChannel{" + delegate + '}';
}
private enum RequestTracingHeadersEnrichingFunction implements TracingHeadersEnrichingFunction<Request.Builder> {
INSTANCE;
@Override
public void addHeader(String headerName, String headerValue, Request.Builder state) {
state.putHeaderParams(headerName, headerValue);
}
}
}