JaegerHttpTracePropagator.ts

/*
 * Copyright The OpenTelemetry 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
 *
 *      https://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.
 */

import {
  Context,
  TextMapPropagator,
  SpanContext,
  TraceFlags,
  SetterFunction,
  GetterFunction,
} from '@opentelemetry/api';
import {
  getParentSpanContext,
  setExtractedSpanContext,
} from '@opentelemetry/core';

export const UBER_TRACE_ID_HEADER = 'uber-trace-id';

/**
 * Propagates {@link SpanContext} through Trace Context format propagation.
 * {trace-id}:{span-id}:{parent-span-id}:{flags}
 * {trace-id}
 * 64-bit or 128-bit random number in base16 format.
 * Can be variable length, shorter values are 0-padded on the left.
 * Value of 0 is invalid.
 * {span-id}
 * 64-bit random number in base16 format.
 * {parent-span-id}
 * Set to 0 because this field is deprecated.
 * {flags}
 * One byte bitmap, as two hex digits.
 * Inspired by jaeger-client-node project.
 */
export class JaegerHttpTracePropagator implements TextMapPropagator {
  private readonly _jaegerTraceHeader: string;

  /**
   * @param {string} [customTraceHeader="uber-trace-id"] - HTTP header to inject\extract trace from.
   **/
  constructor(customTraceHeader?: string) {
    this._jaegerTraceHeader = customTraceHeader || UBER_TRACE_ID_HEADER;
  }

  inject(context: Context, carrier: unknown, setter: SetterFunction) {
    const spanContext = getParentSpanContext(context);
    if (!spanContext) return;

    const traceFlags = `0${(spanContext.traceFlags || TraceFlags.NONE).toString(
      16
    )}`;

    setter(
      carrier,
      this._jaegerTraceHeader,
      `${spanContext.traceId}:${spanContext.spanId}:0:${traceFlags}`
    );
  }

  extract(context: Context, carrier: unknown, getter: GetterFunction): Context {
    const uberTraceIdHeader = getter(carrier, this._jaegerTraceHeader);
    const uberTraceId = Array.isArray(uberTraceIdHeader)
      ? uberTraceIdHeader[0]
      : uberTraceIdHeader;

    if (typeof uberTraceId !== 'string') return context;

    const spanContext = deserializeSpanContext(uberTraceId);
    if (!spanContext) return context;

    return setExtractedSpanContext(context, spanContext);
  }
}

/**
 * @param {string} serializedString - a serialized span context.
 * @return {SpanContext} - returns a span context represented by the serializedString.
 **/
function deserializeSpanContext(serializedString: string): SpanContext | null {
  const headers = decodeURIComponent(serializedString).split(':');
  if (headers.length !== 4) {
    return null;
  }
  const [traceId, spanId, , flags] = headers;

  const traceFlags = flags.match(/^[0-9a-f]{2}$/i) ? parseInt(flags) & 1 : 1;

  return { traceId, spanId, isRemote: true, traceFlags };
}