From 768fd0514e8291c2d44f07a70684a8e168b1e555 Mon Sep 17 00:00:00 2001
From: Ruben Vargas <ruben.vp8510@gmail.com>
Date: Tue, 3 Mar 2020 15:34:54 -0600
Subject: [PATCH] feat: implement W3C Correlation Context propagator

Signed-off-by: Ruben Vargas <ruben.vp8510@gmail.com>
---
 .../distribute-context/distribute-context.ts  | 37 ++++++++++
 .../propagation/HttpTraceContext.ts           | 74 +++++++++++++++++++
 2 files changed, 111 insertions(+)
 create mode 100644 packages/opentelemetry-core/src/distribute-context/distribute-context.ts
 create mode 100644 packages/opentelemetry-core/src/distribute-context/propagation/HttpTraceContext.ts

diff --git a/packages/opentelemetry-core/src/distribute-context/distribute-context.ts b/packages/opentelemetry-core/src/distribute-context/distribute-context.ts
new file mode 100644
index 00000000000..7078807b77e
--- /dev/null
+++ b/packages/opentelemetry-core/src/distribute-context/distribute-context.ts
@@ -0,0 +1,37 @@
+/*!
+ * Copyright 2020, 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 { DistributedContext } from '@opentelemetry/api';
+import { Context } from '@opentelemetry/scope-base';
+
+const DISTRIBUTE_CONTEXTS = Context.createKey(
+  'OpenTelemetry Distributed Contexts Key'
+);
+
+export function getDistributedContext(
+  context: Context
+): DistributedContext | undefined {
+  return (
+    (context.getValue(DISTRIBUTE_CONTEXTS) as DistributedContext) || undefined
+  );
+}
+
+export function setDistributedContext(
+  context: Context,
+  distributedContext: DistributedContext
+): Context {
+  return context.setValue(DISTRIBUTE_CONTEXTS, distributedContext);
+}
diff --git a/packages/opentelemetry-core/src/distribute-context/propagation/HttpTraceContext.ts b/packages/opentelemetry-core/src/distribute-context/propagation/HttpTraceContext.ts
new file mode 100644
index 00000000000..30a7cf2f6de
--- /dev/null
+++ b/packages/opentelemetry-core/src/distribute-context/propagation/HttpTraceContext.ts
@@ -0,0 +1,74 @@
+/*!
+ * Copyright 2020, 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 {
+  Carrier,
+  Context,
+  HttpTextFormat,
+  DistributedContext,
+} from '@opentelemetry/api';
+
+import {
+  getDistributedContext,
+  setDistributedContext,
+} from '../distribute-context';
+
+export const CORRELATION_CONTEXT_HEADER = 'Correlation-Context';
+
+/**
+ * Propagates {@link DistributedContext} through Context format propagation.
+ *
+ * Based on the Correlation Context specification:
+ * https://w3c.github.io/correlation-context/
+ */
+export class HttpTraceContext implements HttpTextFormat {
+  inject(context: Context, carrier: Carrier) {
+    const distContext = getDistributedContext(context);
+    if (distContext) {
+      const headerValue = Object.keys(distContext)
+        .map(
+          (key: string) =>
+            `${encodeURIComponent(key)}=${encodeURIComponent(
+              distContext[key].value
+            )}`
+        )
+        .join(',');
+      if (headerValue.length > 0) {
+        carrier[CORRELATION_CONTEXT_HEADER] = headerValue;
+      }
+    }
+  }
+
+  extract(context: Context, carrier: Carrier): Context {
+    const headerValue: string = carrier[CORRELATION_CONTEXT_HEADER] as string;
+    const distributedContext: DistributedContext = {};
+    if (headerValue.length > 0) {
+      headerValue.split(',').forEach(entry => {
+        const valueProps = entry.split(';');
+        if (valueProps.length > 0) {
+          const keyPair = valueProps[0].split('=');
+          const key = decodeURIComponent(keyPair[0].trim());
+          let value = decodeURIComponent(keyPair[1].trim());
+          if (valueProps.length > 1) {
+            value = value + ';' + valueProps.join(';');
+          }
+          distributedContext[key] = { value };
+        }
+      });
+    }
+    return setDistributedContext(context, distributedContext);
+  }
+}