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Jaeger Java bindings for OpenTracing API
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/*
 * Copyright (c) 2016, Uber Technologies, Inc
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package com.uber.jaeger.propagation;

import com.uber.jaeger.Constants;
import com.uber.jaeger.SpanContext;
import io.opentracing.propagation.TextMap;

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.util.HashMap;
import java.util.Map;

public class TextMapCodec implements Injector, Extractor {
  /** Key used to store serialized span context representation */
  private static final String SPAN_CONTEXT_KEY = "uber-trace-id";

  /** Key prefix used for baggage items */
  private static final String BAGGAGE_KEY_PREFIX = "uberctx-";

  private static final PrefixedKeys keys = new PrefixedKeys();

  private final String contextKey;

  private final String baggagePrefix;

  private final boolean urlEncoding;

  public TextMapCodec(boolean urlEncoding) {
    this(builder().withURLEncoding(urlEncoding));
  }

  private TextMapCodec(Builder builder) {
    this.urlEncoding = builder.urlEncoding;
    this.contextKey = builder.spanContextKey;
    this.baggagePrefix = builder.baggagePrefix;
  }

  @Override
  public void inject(SpanContext spanContext, TextMap carrier) {
    carrier.put(contextKey, encodedValue(spanContext.contextAsString()));
    for (Map.Entry entry : spanContext.baggageItems()) {
      carrier.put(keys.prefixedKey(entry.getKey(), baggagePrefix), encodedValue(entry.getValue()));
    }
  }

  @Override
  public SpanContext extract(TextMap carrier) {
    SpanContext context = null;
    Map baggage = null;
    String debugID = null;
    for (Map.Entry entry : carrier) {
      // TODO there should be no lower-case here
      String key = entry.getKey().toLowerCase();
      if (key.equals(contextKey)) {
        context = SpanContext.contextFromString(decodedValue(entry.getValue()));
      } else if (key.equals(Constants.DEBUG_ID_HEADER_KEY)) {
        debugID = decodedValue(entry.getValue());
      } else if (key.startsWith(baggagePrefix)) {
        if (baggage == null) {
          baggage = new HashMap<>();
        }
        baggage.put(keys.unprefixedKey(key, baggagePrefix), decodedValue(entry.getValue()));
      }
    }
    if (context == null) {
      if (debugID != null) {
        return SpanContext.withDebugID(debugID);
      }
      return null;
    }
    if (baggage == null) {
      return context;
    }
    return context.withBaggage(baggage);
  }

  @Override
  public String toString() {
    StringBuilder buffer = new StringBuilder();
    buffer.append("TextMapCodec{").append("contextKey=").append(contextKey).append(',')
            .append("baggagePrefix=").append(baggagePrefix).append(',')
            .append("urlEncoding=").append(urlEncoding).append('}');
    return buffer.toString();
  }

  private String encodedValue(String value) {
    if (!urlEncoding) {
      return value;
    }
    try {
      return URLEncoder.encode(value, "UTF-8");
    } catch (UnsupportedEncodingException e) {
      // not much we can do, try raw value
      return value;
    }
  }

  private String decodedValue(String value) {
    if (!urlEncoding) {
      return value;
    }
    try {
      return URLDecoder.decode(value, "UTF-8");
    } catch (UnsupportedEncodingException e) {
      // not much we can do, try raw value
      return value;
    }
  }

  /**
   * Returns a builder for TextMapCodec
   * @return Builder
   */
  public static Builder builder() {
    return new Builder();
  }

  public static class Builder {

    private boolean urlEncoding;
    private String spanContextKey = SPAN_CONTEXT_KEY;
    private String baggagePrefix = BAGGAGE_KEY_PREFIX;

    public Builder withURLEncoding(boolean urlEncoding) {
      this.urlEncoding = urlEncoding;
      return this;
    }

    public Builder withSpanContextKey(String spanContextKey) {
      this.spanContextKey = spanContextKey;
      return this;
    }

    public Builder withBaggagePrefix(String baggagePrefix) {
      this.baggagePrefix = baggagePrefix;
      return this;
    }

    public TextMapCodec build() {
      return new TextMapCodec(this);
    }

  }
}