Add sha256Checksum property to ByteString in extension

Author: mattt

Sources/Basics/ByteString+Extensions.swift

@@ -0,0 +1,27 @@
+/*
+ This source file is part of the Swift.org open source project
+ Copyright (c) 2020 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+ See http://swift.org/LICENSE.txt for license information
+ See http://swift.org/CONTRIBUTORS.txt for Swift project authors
+ */
+
+import TSCBasic
+
+extension ByteString {
+    /// A lowercase, hexadecimal representation of the SHA256 hash
+    /// generated for the byte string's contents.
+    ///
+    /// This property uses the CryptoKit implementation of
+    /// Secure Hashing Algorithm 2 (SHA-2) hashing with a 256-bit digest, when available,
+    /// falling back on a native implementation in Swift provided by TSCBasic.
+    public var sha256Checksum: String {
+        #if canImport(CryptoKit)
+        if #available(macOS 10.15, *) {
+            return CryptoKitSHA256().hash(self).hexadecimalRepresentation
+        }
+        #endif
+
+        return SHA256().hash(self).hexadecimalRepresentation
+    }
+}

Sources/Basics/CMakeLists.txt

@@ -7,6 +7,7 @@
 # See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 
 add_library(Basics
+  ByteString+Extensions.swift
   ConcurrencyHelpers.swift
   Dictionary+Extensions.swift
   DispatchTimeInterval+Extensions.swift

Tests/BasicsTests/ByteStringExtensionsTests.swift

@@ -0,0 +1,23 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2020 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See http://swift.org/LICENSE.txt for license information
+ See http://swift.org/CONTRIBUTORS.txt for Swift project authors
+ */
+
+import Basics
+import TSCBasic
+import XCTest
+
+final class ByteStringExtensionsTests: XCTestCase {
+    func testSHA256Checksum() {
+        let byteString = ByteString(encodingAsUTF8: "abc")
+        XCTAssertEqual(byteString.contents, [0x61, 0x62, 0x63])
+
+        // See https://csrc.nist.gov/csrc/media/projects/cryptographic-standards-and-guidelines/documents/examples/sha_all.pdf
+        XCTAssertEqual(byteString.sha256Checksum, "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad")
+    }
+}