feat: expose md5 function (#43)

Author: kneekey23

Source/AwsCommonRuntimeKit/Utilities.swift

@@ -5,6 +5,7 @@ import struct Foundation.Date
 import struct Foundation.Data
 import class Foundation.FileHandle
 import AwsCCommon
+import AwsCCal
 
 @inlinable
 func zeroStruct<T>(_ ptr: UnsafeMutablePointer<T>) {
@@ -25,6 +26,21 @@ extension String {
     var awsByteCursor: aws_byte_cursor {
         return aws_byte_cursor_from_c_str(self.asCStr())
     }
+
+    public func base64EncodedMD5(allocator: Allocator = defaultAllocator, truncate: Int = 0) -> String? {
+        let input: UnsafePointer<aws_byte_cursor> = fromPointer(ptr: self.awsByteCursor)
+        let emptyBuffer: UInt8 = 0
+        let bufferPtr: UnsafeMutablePointer<UInt8> = fromPointer(ptr: emptyBuffer)
+        let buffer = aws_byte_buf(len: 0, buffer: bufferPtr, capacity: 16, allocator: allocator.rawValue)
+        let output: UnsafeMutablePointer<aws_byte_buf> = fromPointer(ptr: buffer)
+
+        guard AWS_OP_SUCCESS == aws_md5_compute(allocator.rawValue, input, output, truncate) else {
+            return nil
+        }
+
+        let byteCursor = aws_byte_cursor_from_buf(output)
+        return byteCursor.toData().base64EncodedString()
+    }
 }
 
 public extension Int32 {

Test/AwsCommonRuntimeKitTests/crt/UtilityTests.swift

@@ -0,0 +1,26 @@
+//  Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+//  SPDX-License-Identifier: Apache-2.0.
+import XCTest
+#if os(Linux)
+     import Glibc
+ #else
+     import Darwin
+ #endif
+@testable import AwsCommonRuntimeKit
+
+class UtilityTests: XCTestCase {
+    func testMd5() throws {
+        let hello = "Hello"
+        let md5 = hello.base64EncodedMD5()
+        XCTAssertEqual(md5, "ixqZU8RhEpaoJ6v4xHgE1w==")
+    }
+    
+    func testMd5_payload() throws {
+        let payload = "{\"foo\":\"base64 encoded md5 checksum\"}"
+
+        let md5 = payload.base64EncodedMD5()
+        
+        XCTAssertEqual(md5, "iB0/3YSo7maijL0IGOgA9g==")
+    }
+}
+