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Refactors ExtraFieldPlugin into a top-level type
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Adrian Cole
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Aug 28, 2019
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141 changes: 141 additions & 0 deletions
141
brave/src/main/java/brave/propagation/ExtraFieldPlugin.java
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| @@ -0,0 +1,141 @@ | ||
| /* | ||
| * Copyright 2013-2019 The OpenZipkin Authors | ||
| * | ||
| * 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 brave.propagation; | ||
|
|
||
| import brave.Tracing; | ||
| import brave.handler.FinishedSpanHandler; | ||
| import brave.propagation.ExtraFieldPropagation.FieldUpdater; | ||
| import java.util.ArrayList; | ||
| import java.util.Arrays; | ||
| import java.util.Collections; | ||
| import java.util.LinkedHashSet; | ||
| import java.util.List; | ||
| import java.util.Set; | ||
|
|
||
| /** | ||
| * Propagation plugins are self-contained and support advanced integration patterns such as metrics | ||
| * aggregation or sampling overlays. | ||
| */ | ||
| public abstract class ExtraFieldPlugin { | ||
| /** | ||
| * Returns a list of unique lower-case field names used by this plugin. | ||
| * | ||
| * <p>The value of this is only read when building {@link ExtraFieldPropagation} and during | ||
| * {@link #toString()}. | ||
| */ | ||
| protected abstract List<String> fieldNames(); | ||
|
|
||
| /** | ||
| * This is called once during {@link TraceContext.Extractor#extract(Object)}, allowing you to | ||
| * decorate the primary trace state with secondary data from extra fields. | ||
| * | ||
| * <p>One use case is to override the sampling decision based on an alternate header. If the | ||
| * decision is intended to be permanent for the rest of the trace, use {@link | ||
| * TraceContextOrSamplingFlags.Builder#sampled(boolean)}, which affects the primary (usually B3) | ||
| * headers. Otherwise, you can set {@link TraceContextOrSamplingFlags.Builder#sampledLocal()} to | ||
| * make an overlaid decision. | ||
| * | ||
| * <p>If you are making an overlaid decision, you should either implement {@link | ||
| * #finishedSpanHandler()} here, or set {@link Tracing.Builder#alwaysReportSpans()} if your | ||
| * backend can tolerate inconsistent data. | ||
| * | ||
| * <p>The resulting field updater will called for each {@link #fieldNames() field name} in the | ||
| * order they were configured, not in the order headers were received. | ||
| */ | ||
| protected FieldUpdater extractFieldUpdater(TraceContextOrSamplingFlags.Builder builder) { | ||
| return FieldUpdater.NOOP; | ||
| } | ||
|
|
||
| /** | ||
| * This allows you to customize or prevent extra fields from going to the next host. | ||
| * | ||
| * <p>The resulting field updater will be called for each {@link #fieldNames() field name} in | ||
| * the order they were configured. | ||
| */ | ||
| protected FieldUpdater injectFieldUpdater(TraceContext context) { | ||
| return FieldUpdater.NOOP; | ||
| } | ||
|
|
||
| /** This allows you to set tags based on extra fields, most commonly for log correlation. */ | ||
| // Intentionally protected to prevent accidental registration with Tracing.Builder | ||
| protected FinishedSpanHandler finishedSpanHandler() { | ||
| return FinishedSpanHandler.NOOP; | ||
| } | ||
|
|
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| @Override public String toString() { | ||
| return getClass().getSimpleName() + "{" + fieldNames() + "}"; | ||
| } | ||
|
|
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| static final class Multiple extends ExtraFieldPlugin { | ||
| final ExtraFieldPlugin[] plugins; // Array ensures no iterators are created at runtime | ||
| final List<String> fieldNames; | ||
|
|
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| Multiple(ExtraFieldPlugin[] plugins) { | ||
| this.plugins = plugins; | ||
| Set<String> fieldNames = new LinkedHashSet<>(); | ||
| for (ExtraFieldPlugin plugin : plugins) fieldNames.addAll(plugin.fieldNames()); | ||
| this.fieldNames = Collections.unmodifiableList(new ArrayList<>(fieldNames)); | ||
| } | ||
|
|
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| @Override protected List<String> fieldNames() { | ||
| return fieldNames; | ||
| } | ||
|
|
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| @Override | ||
| protected FieldUpdater extractFieldUpdater(TraceContextOrSamplingFlags.Builder builder) { | ||
| FieldUpdater[] fieldUpdaters = fieldUpdatersArray(); | ||
| for (int i = 0, length = plugins.length; i < length; i++) { | ||
| fieldUpdaters[i] = plugins[i].extractFieldUpdater(builder); | ||
| } | ||
| return compositeFieldUpdater(fieldUpdaters); | ||
| } | ||
|
|
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| @Override protected FieldUpdater injectFieldUpdater(TraceContext context) { | ||
| FieldUpdater[] fieldUpdaters = fieldUpdatersArray(); | ||
| for (int i = 0, length = plugins.length; i < length; i++) { | ||
| fieldUpdaters[i] = plugins[i].injectFieldUpdater(context); | ||
| } | ||
| return compositeFieldUpdater(fieldUpdaters); | ||
| } | ||
|
|
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| @Override protected FinishedSpanHandler finishedSpanHandler() { | ||
| throw new AssertionError(); // expect special-casing as this is an internal class | ||
| } | ||
|
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| @Override public String toString() { | ||
| return Arrays.toString(plugins); | ||
| } | ||
|
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| static FieldUpdater compositeFieldUpdater(ExtraFieldPropagation.FieldUpdater[] fieldUpdaters) { | ||
| return (name, value) -> { | ||
| for (FieldUpdater fieldUpdater : fieldUpdaters) { | ||
| value = fieldUpdater.update(name, value); | ||
| } | ||
| return value; | ||
| }; | ||
| } | ||
|
|
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| @SuppressWarnings("ThreadLocalUsage") // intentional: instances may have different plugin counts | ||
| final ThreadLocal<Object[]> FIELD_UPDATERS = new ThreadLocal<>(); | ||
|
|
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| FieldUpdater[] fieldUpdatersArray() { | ||
| Object[] fieldUpdatersArray = FIELD_UPDATERS.get(); | ||
| if (fieldUpdatersArray == null) { | ||
| fieldUpdatersArray = new FieldUpdater[plugins.length]; | ||
| FIELD_UPDATERS.set(fieldUpdatersArray); | ||
| } | ||
| return (FieldUpdater[]) fieldUpdatersArray; | ||
| } | ||
| } | ||
| } |
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