add zipkin baggage propagator

Author: danielqsj

Sources/OpenTelemetryApi/Baggage/Propagation/ZipkinBaggagePropagator.swift

@@ -0,0 +1,45 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import Foundation
+
+/**
+ * Implementation of the Zipkin propagation protocol and by default it uses `baggage-` prefix. See
+ * https://github.com/openzipkin/brave/blob/master/brave/README.md#remote-baggage
+ */
+
+public class ZipkinBaggagePropagator: TextMapBaggagePropagator {
+    public static let baggagePrefix = "baggage-"
+
+    public let fields: Set<String> = []
+
+    public init() {}
+
+    public func inject<S>(baggage: Baggage, carrier: inout [String: String], setter: S) where S: Setter {
+        baggage.getEntries().forEach {
+            setter.set(carrier: &carrier, key: ZipkinBaggagePropagator.baggagePrefix + $0.key.name, value: $0.value.string)
+        }
+    }
+
+    public func extract<G>(carrier: [String: String], getter: G) -> Baggage? where G: Getter {
+        let builder = OpenTelemetry.instance.baggageManager.baggageBuilder()
+
+        carrier.forEach {
+            if $0.key.hasPrefix(ZipkinBaggagePropagator.baggagePrefix) {
+                if $0.key.count == ZipkinBaggagePropagator.baggagePrefix.count {
+                    return
+                }
+
+                if let key = EntryKey(name: String($0.key.dropFirst(ZipkinBaggagePropagator.baggagePrefix.count))),
+                   let value = EntryValue(string: $0.value)
+                {
+                    builder.put(key: key, value: value, metadata: nil)
+                }
+            }
+        }
+
+        return builder.build()
+    }
+}

Tests/OpenTelemetryApiTests/Baggage/Propagation/ZipkinBaggagePropagatorTests.swift

@@ -0,0 +1,53 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+@testable import OpenTelemetryApi
+import XCTest
+
+class ZipkinBaggagePropagatorTests: XCTestCase {
+    let builder = DefaultBaggageBuilder()
+    let zipkinPropagator = ZipkinBaggagePropagator()
+    let setter = TestSetter()
+    let getter = TestGetter()
+
+    func testInjectBaggage() {
+        // Metadata won't be propagated, but it MUST NOT cause ay problem.
+        let baggage = builder.put(key: "nometa", value: "nometa-value")
+            .put(key: "nometa", value: "nometa-value")
+            .put(key: "meta", value: "meta-value", metadata: "somemetadata; someother=foo")
+            .build()
+
+        var carrier = [String: String]()
+        zipkinPropagator.inject(baggage: baggage, carrier: &carrier, setter: setter)
+
+        let expected1 = [ZipkinBaggagePropagator.baggagePrefix + "nometa": "nometa-value",
+                         ZipkinBaggagePropagator.baggagePrefix + "meta": "meta-value"]
+        let expected2 = [ZipkinBaggagePropagator.baggagePrefix + "meta": "meta-value",
+                         ZipkinBaggagePropagator.baggagePrefix + "nometa": "nometa-value"]
+        XCTAssert(carrier == expected1 || carrier == expected2)
+    }
+
+    func testExtractBaggageWithPrefix() {
+        var carrier = [String: String]()
+        carrier[ZipkinBaggagePropagator.baggagePrefix + "nometa"] = "nometa-value"
+        carrier[ZipkinBaggagePropagator.baggagePrefix + "meta"] = "meta-value"
+        carrier["another"] = "value"
+
+        let expectedBaggage = builder.put(key: "nometa", value: "nometa-value")
+            .put(key: "meta", value: "meta-value")
+            .build()
+
+        let result = zipkinPropagator.extract(carrier: carrier, getter: getter)
+        XCTAssertEqual(result?.getEntries().sorted(), expectedBaggage.getEntries().sorted())
+    }
+
+    func testExtractBaggageWithPrefixEmptyKey() {
+        var carrier = [String: String]()
+        carrier[ZipkinBaggagePropagator.baggagePrefix] = "value"
+
+        let result = zipkinPropagator.extract(carrier: carrier, getter: getter)!
+        XCTAssertTrue(result.getEntries().isEmpty)
+    }
+}