Merge pull request #8 from slashmo/feature/regenerate-parent-id

Add methods for regenerating the parent id

Author: slashmo

Sources/W3CTraceContext/TraceContext.swift

@@ -15,7 +15,7 @@
 /// combining `TraceParent` and `TraceState`.
 public struct TraceContext: Equatable {
     /// The `TraceParent` identifying this trace context.
-    public let parent: TraceParent
+    public private(set) var parent: TraceParent
 
     /// The `TraceState` containing potentially vendor-specific trace information.
     public let state: TraceState
@@ -44,3 +44,37 @@ public struct TraceContext: Equatable {
         self.state = TraceState(rawValue: stateRawValue) ?? TraceState([])
     }
 }
+
+extension TraceContext {
+    /// Replace the parent-id of the current `traceParent` with a newly generated one, using the system random number generator.
+    public mutating func regenerateParentID() {
+        var generator = SystemRandomNumberGenerator()
+        self.regenerateParentID(using: &generator)
+    }
+
+    /// Replace the parent-id of the current `traceParent` with a newly generated one, using the given generator as a source for
+    /// randomness.
+    ///
+    /// - Parameter generator: The random number generator used as a source for generating the new parent-id.
+    public mutating func regenerateParentID<G: RandomNumberGenerator>(using generator: inout G) {
+        self.parent.parentID = TraceParent.randomParentID(using: &generator)
+    }
+
+    /// Return a copy with its `traceParent.parentID` replaced with a newly generated one, using the system random number generator.
+    ///
+    /// - Returns: A copy of this `TraceContext` with a new trace-parent parent-id.
+    public func regeneratingParentID() -> TraceContext {
+        var generator = SystemRandomNumberGenerator()
+        return self.regeneratingParentID(using: &generator)
+    }
+
+    /// Return a copy with its `traceParent.parentID` replaced with a newly generated one, using the system random number generator.
+    ///
+    /// - Parameter generator: The random number generator used as a source for generating the new parent-id.
+    /// - Returns: A copy of this `TraceContext` with a new trace-parent parent-id.
+    public func regeneratingParentID<G: RandomNumberGenerator>(using generator: inout G) -> TraceContext {
+        var copy = self
+        copy.regenerateParentID(using: &generator)
+        return copy
+    }
+}

Sources/W3CTraceContext/TraceParent.swift

@@ -26,7 +26,7 @@ public struct TraceParent {
     /// a client request).
     ///
     /// - SeeAlso: [W3C TraceContext: parent-id](https://www.w3.org/TR/2020/REC-trace-context-1-20200206/#parent-id)
-    public let parentID: String
+    public internal(set) var parentID: String
 
     /// An 8-bit field that controls tracing flags such as sampling, trace level, etc.
     ///

Tests/W3CTraceContextTests/TraceContextTests.swift

@@ -61,4 +61,20 @@ final class TraceContextTests: XCTestCase {
             )
         )
     }
+
+    func test_regenerate_trace_parent_parent_id_in_place() {
+        var traceContext = TraceContext(parent: .random(), state: .none)
+        let previousTraceParentID = traceContext.parent.parentID
+
+        traceContext.regenerateParentID()
+
+        XCTAssertNotEqual(traceContext.parent.parentID, previousTraceParentID)
+    }
+
+    func test_regenerate_trace_parent_parent_id() {
+        let traceContext = TraceContext(parent: .random(), state: .none)
+        let newTraceContext = traceContext.regeneratingParentID()
+
+        XCTAssertNotEqual(newTraceContext.parent.parentID, traceContext.parent.parentID)
+    }
 }