Allow to check for signing key

The new API is intended for UIs to check if signing will be possible or
would fail

Bug: 543579
Change-Id: I6ce1fd4210e46d49dcdf420c99d08c93e022136c
Signed-off-by: Gunnar Wagenknecht <gunnar@wagenknecht.org>

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/CommitCommandTest.java

@@ -56,6 +56,7 @@ import java.util.List;
 import java.util.TimeZone;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import org.eclipse.jgit.api.errors.CanceledException;
 import org.eclipse.jgit.api.errors.EmptyCommitException;
 import org.eclipse.jgit.api.errors.WrongRepositoryStateException;
 import org.eclipse.jgit.diff.DiffEntry;
@@ -651,6 +652,14 @@ public class CommitCommandTest extends RepositoryTestCase {
 					signingCommitters[0] = signingCommitter;
 					callCount.incrementAndGet();
 				}
+
+				@Override
+				public boolean canLocateSigningKey(String gpgSigningKey,
+						PersonIdent signingCommitter,
+						CredentialsProvider credentialsProvider)
+						throws CanceledException {
+					return false;
+				}
 			});
 
 			// first call should use config, which is expected to be null at
@@ -706,6 +715,14 @@ public class CommitCommandTest extends RepositoryTestCase {
 						PersonIdent signingCommitter, CredentialsProvider credentialsProvider) {
 					callCount.incrementAndGet();
 				}
+
+				@Override
+				public boolean canLocateSigningKey(String gpgSigningKey,
+						PersonIdent signingCommitter,
+						CredentialsProvider credentialsProvider)
+						throws CanceledException {
+					return false;
+				}
 			});
 
 			// first call should use config, which is expected to be null at

org.eclipse.jgit/src/org/eclipse/jgit/lib/GpgSigner.java

@@ -43,6 +43,7 @@
 package org.eclipse.jgit.lib;
 
 import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.api.errors.CanceledException;
 import org.eclipse.jgit.lib.internal.BouncyCastleGpgSigner;
 import org.eclipse.jgit.transport.CredentialsProvider;
@@ -95,9 +96,11 @@ public abstract class GpgSigner {
 	 *            the commit to sign (must not be <code>null</code> and must be
 	 *            complete to allow proper calculation of payload)
 	 * @param gpgSigningKey
-	 *            the signing key (passed as is to the GPG signing tool)
+	 *            the signing key to locate (passed as is to the GPG signing
+	 *            tool as is; eg., value of <code>user.signingkey</code>)
 	 * @param committer
-	 *            the signing identity (to help with key lookup)
+	 *            the signing identity (to help with key lookup in case signing
+	 *            key is not specified)
 	 * @param credentialsProvider
 	 *            provider to use when querying for signing key credentials (eg.
 	 *            passphrase)
@@ -106,7 +109,30 @@ public abstract class GpgSigner {
 	 *             passphrase)
 	 */
 	public abstract void sign(@NonNull CommitBuilder commit,
-			String gpgSigningKey, @NonNull PersonIdent committer,
+			@Nullable String gpgSigningKey, @NonNull PersonIdent committer,
+			CredentialsProvider credentialsProvider) throws CanceledException;
+
+	/**
+	 * Indicates if a signing key is available for the specified committer
+	 * and/or signing key.
+	 *
+	 * @param gpgSigningKey
+	 *            the signing key to locate (passed as is to the GPG signing
+	 *            tool as is; eg., value of <code>user.signingkey</code>)
+	 * @param committer
+	 *            the signing identity (to help with key lookup in case signing
+	 *            key is not specified)
+	 * @param credentialsProvider
+	 *            provider to use when querying for signing key credentials (eg.
+	 *            passphrase)
+	 * @return <code>true</code> if a signing key is available,
+	 *         <code>false</code> otherwise
+	 * @throws CanceledException
+	 *             when signing was canceled (eg., user aborted when entering
+	 *             passphrase)
+	 */
+	public abstract boolean canLocateSigningKey(@Nullable String gpgSigningKey,
+			@NonNull PersonIdent committer,
 			CredentialsProvider credentialsProvider) throws CanceledException;
 
 }

org.eclipse.jgit/src/org/eclipse/jgit/lib/internal/BouncyCastleGpgSigner.java

@@ -59,8 +59,10 @@ import org.bouncycastle.openpgp.PGPSignatureGenerator;
 import org.bouncycastle.openpgp.operator.jcajce.JcaPGPContentSignerBuilder;
 import org.bouncycastle.openpgp.operator.jcajce.JcePBESecretKeyDecryptorBuilder;
 import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.api.errors.CanceledException;
 import org.eclipse.jgit.api.errors.JGitInternalException;
+import org.eclipse.jgit.errors.UnsupportedCredentialItem;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.CommitBuilder;
 import org.eclipse.jgit.lib.GpgSignature;
@@ -90,26 +92,49 @@ public class BouncyCastleGpgSigner extends GpgSigner {
 	}
 
 	@Override
-	public void sign(@NonNull CommitBuilder commit, String gpgSigningKey,
-			@NonNull PersonIdent committer,
-			CredentialsProvider credentialsProvider) throws CanceledException {
+	public boolean canLocateSigningKey(@Nullable String gpgSigningKey,
+			PersonIdent committer, CredentialsProvider credentialsProvider)
+			throws CanceledException {
+		try (BouncyCastleGpgKeyPassphrasePrompt passphrasePrompt = new BouncyCastleGpgKeyPassphrasePrompt(
+				credentialsProvider)) {
+			BouncyCastleGpgKey gpgKey = locateSigningKey(gpgSigningKey,
+					committer, passphrasePrompt);
+			return gpgKey != null;
+		} catch (PGPException | IOException | URISyntaxException e) {
+			return false;
+		}
+	}
+
+	private BouncyCastleGpgKey locateSigningKey(@Nullable String gpgSigningKey,
+			PersonIdent committer,
+			BouncyCastleGpgKeyPassphrasePrompt passphrasePrompt)
+			throws CanceledException, UnsupportedCredentialItem, IOException,
+			PGPException, URISyntaxException {
 		if (gpgSigningKey == null || gpgSigningKey.isEmpty()) {
 			gpgSigningKey = committer.getEmailAddress();
 		}
 
-		try (BouncyCastleGpgKeyPassphrasePrompt passphrasePrompt = new BouncyCastleGpgKeyPassphrasePrompt(
-				credentialsProvider)) {
 		BouncyCastleGpgKeyLocator keyHelper = new BouncyCastleGpgKeyLocator(
 				gpgSigningKey, passphrasePrompt);
 
-			BouncyCastleGpgKey gpgKey = keyHelper.findSecretKey();
+		return keyHelper.findSecretKey();
+	}
+
+	@Override
+	public void sign(@NonNull CommitBuilder commit,
+			@Nullable String gpgSigningKey, @NonNull PersonIdent committer,
+			CredentialsProvider credentialsProvider) throws CanceledException {
+		try (BouncyCastleGpgKeyPassphrasePrompt passphrasePrompt = new BouncyCastleGpgKeyPassphrasePrompt(
+				credentialsProvider)) {
+			BouncyCastleGpgKey gpgKey = locateSigningKey(gpgSigningKey,
+					committer, passphrasePrompt);
 			PGPSecretKey secretKey = gpgKey.getSecretKey();
 			if (secretKey == null) {
 				throw new JGitInternalException(
 						JGitText.get().unableToSignCommitNoSecretKey);
 			}
-			char[] passphrase = passphrasePrompt
-					.getPassphrase(secretKey.getPublicKey().getFingerprint(),
+			char[] passphrase = passphrasePrompt.getPassphrase(
+					secretKey.getPublicKey().getFingerprint(),
 					gpgKey.getOrigin());
 			PGPPrivateKey privateKey = secretKey
 					.extractPrivateKey(new JcePBESecretKeyDecryptorBuilder()