Create probabilistic sampler (#9)

Co-authored-by: Konrad `ktoso` Malawski <ktoso@apple.com>

Author: slashmo

Package.resolved

@@ -10,7 +10,7 @@ let package = Package(
     dependencies: [
         .package(name: "swift-context", url: "https://github.com/slashmo/gsoc-swift-baggage-context", from: "0.5.0"),
         .package(url: "https://github.com/slashmo/gsoc-swift-tracing.git", .branch("main")),
-        .package(url: "https://github.com/slashmo/swift-w3c-trace-context.git", from: "0.5.0"),
+        .package(url: "https://github.com/slashmo/swift-w3c-trace-context.git", from: "0.6.0"),
         .package(url: "https://github.com/slashmo/swift-nio.git", .branch("feature/baggage-context")),
     ],
     targets: [

Package.swift

@@ -11,14 +11,16 @@
 //
 //===----------------------------------------------------------------------===//
 
+import W3CTraceContext
+
 public struct ConstantSampler: Sampler {
     private let samples: Bool
 
     public init(samples: Bool) {
         self.samples = samples
     }
 
-    public func sample(operationName: String, traceID: String) -> SamplingStatus {
+    public func sample(operationName: String, traceID: TraceID) -> SamplingStatus {
         SamplingStatus(isSampled: self.samples, attributes: [
             "sampler.type": "const",
             "sampler.param": self.samples ? "true" : "false",

Sources/Jaeger/Sampling/ConstantSampler.swift

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Jaeger Client Swift open source project
+//
+// Copyright (c) 2020 Moritz Lang and the Jaeger Client Swift project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import W3CTraceContext
+
+public struct ProbabilisticSampler: Sampler {
+    private let samplingRate: Double
+    private let lowUpperBound: UInt64
+
+    public init(samplingRate: Double = 0.001) {
+        precondition(
+            samplingRate > 0 && samplingRate < 1,
+            "The sampling rate must be greater than 0.0 and less than 1.0. Please use ConstantSampler instead."
+        )
+        self.samplingRate = samplingRate
+        self.lowUpperBound = UInt64(samplingRate * Double(UInt64.max))
+    }
+
+    public func sample(operationName: String, traceID: TraceID) -> SamplingStatus {
+        SamplingStatus(isSampled: traceID.low < self.lowUpperBound, attributes: [
+            "sampler.type": "probabilistic",
+            "sampler.param": .double(self.samplingRate),
+        ])
+    }
+}

Sources/Jaeger/Sampling/ProbabilisticSampler.swift

@@ -12,12 +12,13 @@
 //===----------------------------------------------------------------------===//
 
 import Tracing
+import W3CTraceContext
 
 public struct SamplingStatus {
-    var isSampled: Bool
-    var attributes: SpanAttributes
+    public let isSampled: Bool
+    public let attributes: SpanAttributes
 }
 
 public protocol Sampler {
-    func sample(operationName: String, traceID: String) -> SamplingStatus
+    func sample(operationName: String, traceID: TraceID) -> SamplingStatus
 }

Sources/Jaeger/Sampling/Sampler.swift

@@ -44,7 +44,7 @@ extension JaegerSpan {
 
         return ZipkinRepresentation(
             id: traceContext.parent.parentID,
-            traceID: traceContext.parent.traceID,
+            traceID: String(describing: traceContext.parent.traceID),
             parentID: self.links.first?.baggage.traceContext?.parent.parentID,
             name: self.operationName,
             timestamp: self.startTimestamp.microsSinceEpoch,

Sources/ZipkinReporting/Span+ZipkinRepresentation.swift

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Jaeger Client Swift open source project
+//
+// Copyright (c) 2020 Moritz Lang and the Jaeger Client Swift project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Jaeger
+import W3CTraceContext
+import XCTest
+
+final class ProbabilisticSamplerTests: XCTestCase {
+    func test_sample_comparesLowIDPartToUpperBound() {
+        let samplingRate = Double.random(in: Double.leastNonzeroMagnitude ..< 1.0)
+        let upperBound = UInt64(samplingRate * Double(UInt64.max))
+        let sampler = ProbabilisticSampler(samplingRate: samplingRate)
+
+        do {
+            let traceID = TraceID(high: 0, low: upperBound)
+            let samplingStatus = sampler.sample(operationName: "test", traceID: traceID)
+            XCTAssertFalse(samplingStatus.isSampled)
+        }
+
+        do {
+            let traceID = TraceID(high: 0, low: upperBound - 1)
+            let samplingStatus = sampler.sample(operationName: "test", traceID: traceID)
+            XCTAssert(samplingStatus.isSampled)
+        }
+    }
+
+    func test_sample_returnsSamplingStatus_withAttributes() {
+        let sampler = ProbabilisticSampler(samplingRate: 0.1)
+
+        let samplingStatus = sampler.sample(operationName: "test", traceID: .random())
+
+        XCTAssertEqual(samplingStatus.attributes["sampler.type"], "probabilistic")
+        XCTAssertEqual(samplingStatus.attributes["sampler.param"], 0.1)
+    }
+}

Tests/JaegerTests/Sampling/ProbabilisticSamplerTests.swift

@@ -44,7 +44,7 @@ final class ZipkinSpanRepresentationTests: XCTestCase {
 
         XCTAssertNotNil(zipkinRepresentation)
         XCTAssertEqual(zipkinRepresentation?.id, child.baggage.traceContext?.parent.parentID)
-        XCTAssertEqual(zipkinRepresentation?.traceID, child.baggage.traceContext?.parent.traceID)
+        XCTAssertEqual(zipkinRepresentation?.traceID, child.baggage.traceContext?.parent.traceID.description)
         XCTAssertNotNil(zipkinRepresentation?.parentID)
         XCTAssertEqual(zipkinRepresentation?.parentID, parent.baggage.traceContext?.parent.parentID)
         XCTAssertEqual(zipkinRepresentation?.name, "child")