From deb8c0c2bd6fa7a16c7e2480a554c044bba3371c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A5kon=20Hallingstad?= <hakon@vespa.ai>
Date: Tue, 21 Jan 2025 10:45:54 +0100
Subject: [PATCH] Add hex formatting of MD5 hash

---
 vespajlib/abi-spec.json                                |  1 +
 vespajlib/src/main/java/com/yahoo/collections/MD5.java |  6 ++++++
 .../src/main/java/com/yahoo/text/StringUtilities.java  | 10 ++++++++++
 .../test/java/com/yahoo/collections/MD5TestCase.java   |  7 +++++++
 4 files changed, 24 insertions(+)

diff --git a/vespajlib/abi-spec.json b/vespajlib/abi-spec.json
index de020bf85471..28e9a2199b6c 100644
--- a/vespajlib/abi-spec.json
+++ b/vespajlib/abi-spec.json
@@ -3343,6 +3343,7 @@
     ],
     "methods" : [
       "public void <init>()",
+      "public static java.lang.String toHex(byte[])",
       "public static java.lang.String escape(java.lang.String)",
       "public static java.lang.String escape(java.lang.String, char)",
       "public static java.lang.String unescape(java.lang.String)",
diff --git a/vespajlib/src/main/java/com/yahoo/collections/MD5.java b/vespajlib/src/main/java/com/yahoo/collections/MD5.java
index 6bd32b62b745..52cb3b91e2e7 100644
--- a/vespajlib/src/main/java/com/yahoo/collections/MD5.java
+++ b/vespajlib/src/main/java/com/yahoo/collections/MD5.java
@@ -1,6 +1,7 @@
 // Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.collections;
 
+import com.yahoo.text.StringUtilities;
 import com.yahoo.text.Utf8;
 
 import java.security.MessageDigest;
@@ -69,4 +70,9 @@ public byte[] hashFull(String s) {
         return digester.digest(Utf8.toBytes(s));
     }
 
+    /** Returns the 32 byte representation of the MD5 hash of the given string. Compatible with md5sum(1). */
+    public String hashToHex(String s) {
+        return StringUtilities.toHex(hashFull(s));
+    }
+
 }
diff --git a/vespajlib/src/main/java/com/yahoo/text/StringUtilities.java b/vespajlib/src/main/java/com/yahoo/text/StringUtilities.java
index 025eeba3998f..9760ea27e3fd 100644
--- a/vespajlib/src/main/java/com/yahoo/text/StringUtilities.java
+++ b/vespajlib/src/main/java/com/yahoo/text/StringUtilities.java
@@ -22,6 +22,16 @@ public class StringUtilities {
 
     private static byte toHex(int val) { return (byte) (val < 10 ? '0' + val : 'a' + (val - 10)); }
 
+    /** Returns a String where each byte b in `bytes` is replaced by "%02x".formatted(b). */
+    public static String toHex(byte[] bytes) {
+        byte[] encoded = new byte[bytes.length * 2];
+        for (int i = 0; i < bytes.length; i++) {
+            encoded[i * 2] = toHex((bytes[i] >> 4) & 0xF);
+            encoded[i * 2 + 1] = toHex(bytes[i] & 0xF);
+        }
+        return new String(encoded, StandardCharsets.US_ASCII);
+    }
+
     private static class ReplacementCharacters {
 
         public byte[] needEscape = new byte[256];
diff --git a/vespajlib/src/test/java/com/yahoo/collections/MD5TestCase.java b/vespajlib/src/test/java/com/yahoo/collections/MD5TestCase.java
index 28cd3c90b905..3d44c9ef9d41 100644
--- a/vespajlib/src/test/java/com/yahoo/collections/MD5TestCase.java
+++ b/vespajlib/src/test/java/com/yahoo/collections/MD5TestCase.java
@@ -11,6 +11,13 @@
  */
 public class MD5TestCase {
 
+    @Test
+    public void testHashToHex() {
+        MD5 md5 = new MD5();
+        // Matches output from `md5sum <<< hello`
+        assertEquals("b1946ac92492d2347c6235b4d2611184", md5.hashToHex("hello\n"));
+    }
+
     @Test
     public void testMD5() {
         MD5 md5 = new MD5();