GPG user ID matching: use case-insensitive matching

Although not mentioned in the GPG documentation at [1], GPG uses
case-insensitive matching also for the '<' (exact e-mail) and '@'
(partial e-mail) operators. Matching for '=' (full exact match) is
case-sensitive. Compare [2].

[1] https://www.gnupg.org/documentation/manuals/gnupg/Specify-a-User-ID.html
[2] https://dev.gnupg.org/source/gnupg/browse/master/g10/keyring.c;22f7dddc34446a8c3e9eddf6cb281f16802351d7$890

Bug: 547789
Change-Id: I2f5ab65807d5dde3aa00ff032894701bbd8418c9
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

org.eclipse.jgit.gpg.bc.test/tst/org/eclipse/jgit/gpg/bc/internal/BouncyCastleGpgKeyLocatorTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2019, Thomas Wolf <thomas.wolf@paranor.ch> and others
+ * Copyright (C) 2019, 2020 Thomas Wolf <thomas.wolf@paranor.ch> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -53,7 +53,7 @@ public class BouncyCastleGpgKeyLocatorTest {
 		assertFalse(match(USER_ID, "<heinrichh>"));
 		assertFalse(match(USER_ID, "<uni-duesseldorf>"));
 		assertFalse(match(USER_ID, "<h@u>"));
-		assertFalse(match(USER_ID, "<HeinrichH@uni-duesseldorf.de>"));
+		assertTrue(match(USER_ID, "<HeinrichH@uni-duesseldorf.de>"));
 		assertFalse(match(USER_ID.substring(0, USER_ID.length() - 1),
 				"<heinrichh@uni-duesseldorf.de>"));
 		assertFalse(match("", "<>"));
@@ -72,8 +72,8 @@ public class BouncyCastleGpgKeyLocatorTest {
 		assertFalse(match(USER_ID, "@ "));
 		assertFalse(match(USER_ID, "@"));
 		assertFalse(match(USER_ID, "@Heine"));
-		assertFalse(match(USER_ID, "@HeinrichH"));
-		assertFalse(match(USER_ID, "@Heinrich"));
+		assertTrue(match(USER_ID, "@HeinrichH"));
+		assertTrue(match(USER_ID, "@Heinrich"));
 		assertFalse(match("", "@"));
 		assertFalse(match("", "@h"));
 	}
@@ -110,6 +110,7 @@ public class BouncyCastleGpgKeyLocatorTest {
 	public void testExplicitFingerprint() throws Exception {
 		assertFalse(match("John Fade <j.fade@example.com>", "0xfade"));
 		assertFalse(match("John Fade <0xfade@example.com>", "0xfade"));
+		assertFalse(match("John Fade <0xfade@example.com>", "0xFADE"));
 		assertFalse(match("", "0xfade"));
 	}
 
@@ -128,7 +129,7 @@ public class BouncyCastleGpgKeyLocatorTest {
 		assertTrue(match("John Fade <0xfade@example.com>", "*0xfade"));
 		assertTrue(match("John Fade <0xfade@example.com>", "*0xFADE"));
 		assertTrue(match("John Fade <0xfade@example.com>", "@0xfade"));
-		assertFalse(match("John Fade <0xfade@example.com>", "@0xFADE"));
+		assertTrue(match("John Fade <0xfade@example.com>", "@0xFADE"));
 		assertFalse(match("", "0x"));
 	}
 }

org.eclipse.jgit.gpg.bc/src/org/eclipse/jgit/gpg/bc/internal/BouncyCastleGpgKeyLocator.java

@@ -219,23 +219,34 @@ public class BouncyCastleGpgKeyLocator {
 			int stop = toMatch.indexOf('>');
 			return begin >= 0 && end > begin + 1 && stop > 0
 					&& userId.substring(begin + 1, end)
-							.equals(toMatch.substring(0, stop));
+							.equalsIgnoreCase(toMatch.substring(0, stop));
 		}
 		case '@': {
 			int begin = userId.indexOf('<');
 			int end = userId.indexOf('>', begin + 1);
 			return begin >= 0 && end > begin + 1
-					&& userId.substring(begin + 1, end).contains(toMatch);
+					&& containsIgnoreCase(userId.substring(begin + 1, end),
+							toMatch);
 		}
 		default:
 			if (toMatch.trim().isEmpty()) {
 				return false;
 			}
-			return userId.toLowerCase(Locale.ROOT)
-					.contains(toMatch.toLowerCase(Locale.ROOT));
+			return containsIgnoreCase(userId, toMatch);
 		}
 	}
 
+	private static boolean containsIgnoreCase(String a, String b) {
+		int alength = a.length();
+		int blength = b.length();
+		for (int i = 0; i + blength <= alength; i++) {
+			if (a.regionMatches(true, i, b, 0, blength)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	private String toFingerprint(String keyId) {
 		if (keyId.startsWith("0x")) { //$NON-NLS-1$
 			return keyId.substring(2);