Fix hashing of empty inputs

Author: lauzadis

aws-crt-kotlin/native/src/aws/sdk/kotlin/crt/util/hashing/CrcNative.kt

@@ -28,6 +28,8 @@ internal class Crc(val checksumFn: AwsChecksumsCrcFunction) : HashFunction {
     private var crc = 0U
 
     override fun update(input: ByteArray, offset: Int, length: Int) {
+        if (input.isEmpty() || length == 0) { return }
+
         val offsetInput = input.usePinned {
             it.addressOf(offset)
         }

aws-crt-kotlin/native/src/aws/sdk/kotlin/crt/util/hashing/Md5Native.kt

@@ -31,6 +31,8 @@ public class Md5 : HashFunction {
     private var md5 = checkNotNull(aws_md5_new(Allocator.Default)) { "aws_md5_new" }
 
     override fun update(input: ByteArray, offset: Int, length: Int) {
+        if (input.isEmpty() || length == 0) { return }
+
         val inputCursor = input.usePinned {
             aws_byte_cursor_from_array(it.addressOf(offset), length.convert())
         }

aws-crt-kotlin/native/src/aws/sdk/kotlin/crt/util/hashing/ShaNative.kt

@@ -55,6 +55,8 @@ internal class Sha(val initializeFn: InitializeHashFn) : HashFunction {
 
     // aws_hash_update
     override fun update(input: ByteArray, offset: Int, length: Int) {
+        if (input.isEmpty() || length == 0) { return }
+
         val inputCursor = input.usePinned {
             aws_byte_cursor_from_array(it.addressOf(offset), length.convert())
         }

aws-crt-kotlin/native/test/aws/sdk/kotlin/crt/util/hashing/HashFunctionNativeTest.kt

@@ -50,4 +50,21 @@ class HashFunctionTest {
             assertEquals(expected, hash.digest().encodeToHex())
         }
     }
+
+    @Test
+    fun testEmptyUpdate() {
+        // algorithm -> hash("")
+        val tests = listOf(
+            (Sha1() to "da39a3ee5e6b4b0d3255bfef95601890afd80709"),
+            (Sha256() to "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"),
+            (Crc32() to "00000000"),
+            (Crc32c() to "00000000"),
+        )
+
+        tests.forEach { (hash, expected) ->
+            val data = "".encodeToByteArray()
+            hash.update(data, 0, 0)
+            assertEquals(expected, hash.digest().encodeToHex())
+        }
+    }
 }