Add guards for Int64 overflow in `Timer` methods (#29)

Motivation:

`Timer.record*` methods are generic to cover all cases of `BinaryInteger` values and converts the passed value into `Int64` before doing time unit conversions and overflow checks.

Modifications:

All methods that accept `BinaryInteger` types and converts to `Int64` now guards against values higher than `Int64.max`

Result:

Users can reliably use the `Timer.record*` APIs with `BinaryInteger` types without concern for unknowing fatal errors.

Sources/CoreMetrics/Metrics.swift

@@ -273,6 +273,8 @@ public class Timer {
     ///     - value: Duration to record.
     @inlinable
     public func recordMicroseconds<DataType: BinaryInteger>(_ duration: DataType) {
+        guard duration <= Int64.max else { return self.recordNanoseconds(Int64.max) }
+
         let result = Int64(duration).multipliedReportingOverflow(by: 1000)
         if result.overflow {
             self.recordNanoseconds(Int64.max)
@@ -296,6 +298,8 @@ public class Timer {
     ///     - value: Duration to record.
     @inlinable
     public func recordMilliseconds<DataType: BinaryInteger>(_ duration: DataType) {
+        guard duration <= Int64.max else { return self.recordNanoseconds(Int64.max) }
+
         let result = Int64(duration).multipliedReportingOverflow(by: 1_000_000)
         if result.overflow {
             self.recordNanoseconds(Int64.max)
@@ -319,6 +323,8 @@ public class Timer {
     ///     - value: Duration to record.
     @inlinable
     public func recordSeconds<DataType: BinaryInteger>(_ duration: DataType) {
+        guard duration <= Int64.max else { return self.recordNanoseconds(Int64.max) }
+
         let result = Int64(duration).multipliedReportingOverflow(by: 1_000_000_000)
         if result.overflow {
             self.recordNanoseconds(Int64.max)

Tests/MetricsTests/CoreMetricsTests+XCTest.swift

@@ -35,6 +35,7 @@ extension MetricsTests {
             ("testTimerBlock", testTimerBlock),
             ("testTimerVariants", testTimerVariants),
             ("testTimerOverflow", testTimerOverflow),
+            ("testTimerHandlesUnsignedOverflow", testTimerHandlesUnsignedOverflow),
             ("testGauge", testGauge),
             ("testGaugeBlock", testGaugeBlock),
             ("testMUX", testMUX),

Tests/MetricsTests/CoreMetricsTests.swift

@@ -217,6 +217,27 @@ class MetricsTests: XCTestCase {
         XCTAssertEqual(testTimer.values[3].1, Int64.max, "expected value to match")
     }
 
+    func testTimerHandlesUnsignedOverflow() throws {
+        // bootstrap with our test metrics
+        let metrics = TestMetrics()
+        MetricsSystem.bootstrapInternal(metrics)
+        // run the test
+        let timer = Timer(label: "test-timer")
+        let testTimer = timer.handler as! TestTimer
+        // micro
+        timer.recordMicroseconds(UInt64.max)
+        XCTAssertEqual(testTimer.values.count, 1, "expected number of entries to match")
+        XCTAssertEqual(testTimer.values[0].1, Int64.max, "expected value to match")
+        // milli
+        timer.recordMilliseconds(UInt64.max)
+        XCTAssertEqual(testTimer.values.count, 2, "expected number of entries to match")
+        XCTAssertEqual(testTimer.values[1].1, Int64.max, "expected value to match")
+        // seconds
+        timer.recordSeconds(UInt64.max)
+        XCTAssertEqual(testTimer.values.count, 3, "expected number of entries to match")
+        XCTAssertEqual(testTimer.values[2].1, Int64.max, "expected value to match")
+    }
+
     func testGauge() throws {
         // bootstrap with our test metrics
         let metrics = TestMetrics()