Add Strideable conformance to HTTP2StreamID (#133)

Motivation:

While working on other tests I realised that HTTP2StreamID is a type
that can meaningfully be strided, but it does not conform to Strideable.
We may as well add that conformance.

Modifications:

- Added Strideable conformance to HTTP2StreamID.

Result:

Users can stride over HTTP2StreamIDs.

Sources/NIOHTTP2/HTTP2StreamID.swift

@@ -104,6 +104,20 @@ extension HTTP2StreamID: ExpressibleByIntegerLiteral {
 }
 
 
+// MARK:- Strideable conformance for HTTP2StreamID
+extension HTTP2StreamID: Strideable {
+    public typealias Stride = Int
+
+    public func advanced(by n: Stride) -> HTTP2StreamID {
+        return HTTP2StreamID(self.networkStreamID + Int32(n))
+    }
+
+    public func distance(to other: HTTP2StreamID) -> Stride {
+        return Int(other.networkStreamID - self.networkStreamID)
+    }
+}
+
+
 // MARK:- Helper initializers for integer conversion.
 public extension Int {
     /// Create an Int holding the integer value of this streamID.

Tests/LinuxMain.swift

@@ -43,5 +43,6 @@ import XCTest
          testCase(OutboundFlowControlBufferTests.allTests),
          testCase(ReentrancyTests.allTests),
          testCase(SimpleClientServerTests.allTests),
+         testCase(StreamIDTests.allTests),
     ])
 #endif

Tests/NIOHTTP2Tests/StreamIDTests+XCTest.swift

@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftNIO open source project
+//
+// Copyright (c) 2017-2018 Apple Inc. and the SwiftNIO project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+//
+// StreamIDTests+XCTest.swift
+//
+import XCTest
+
+///
+/// NOTE: This file was generated by generate_linux_tests.rb
+///
+/// Do NOT edit this file directly as it will be regenerated automatically when needed.
+///
+
+extension StreamIDTests {
+
+   static var allTests : [(String, (StreamIDTests) -> () throws -> Void)] {
+      return [
+                ("testStreamIDsAreStrideable", testStreamIDsAreStrideable),
+           ]
+   }
+}
+

Tests/NIOHTTP2Tests/StreamIDTests.swift

@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftNIO open source project
+//
+// Copyright (c) 2019 Apple Inc. and the SwiftNIO project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import XCTest
+import NIOHTTP2
+
+
+final class StreamIDTests: XCTestCase {
+    func testStreamIDsAreStrideable() {
+        XCTAssertEqual(Array(HTTP2StreamID(1)..<HTTP2StreamID(30)), Array(stride(from: HTTP2StreamID(1), to: HTTP2StreamID(30), by: 1)))
+        XCTAssertEqual([10, 9, 8, 7, 6, 5, 4, 3, 2, 1], Array(stride(from: HTTP2StreamID(10), through: HTTP2StreamID(1), by: -1)))
+        XCTAssertEqual([1, 3, 5, 7, 9], Array(stride(from: HTTP2StreamID(1), to: HTTP2StreamID(10), by: 2)))
+    }
+}