Make the default encoding when reading commits UTF-8

When reading commits the system default encoding was used if no
encoding was specified in the commit. The patch modifies the test
to add a check that commit message was encoded correctly (the
test fails on old implementation if system encoding is not UTF-8)
and fixes Commit.decode() method to use UTF-8 if encoding is not
specified in the commit object.

Change-Id: I27101da3c2eb6edd0c4a9e4c0523e48b286e3cd5
Signed-off-by: Constantine Plotnikov <constantine.plotnikov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/T0003_Basic.java

@@ -344,6 +344,9 @@ public class T0003_Basic extends RepositoryTestCase {
 		commit.setMessage("\u00dcbergeeks");
 		ObjectId cid = new ObjectWriter(db).writeCommit(commit);
 		assertEquals("4680908112778718f37e686cbebcc912730b3154", cid.name());
+		Commit loadedCommit = db.mapCommit(cid);
+		assertNotSame(loadedCommit, commit);
+		assertEquals(commit.getMessage(), loadedCommit.getMessage());
 	}
 
 	public void test024_createCommitNonAscii() throws IOException {

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

@@ -305,17 +305,13 @@ public class Commit implements Treeish {
 				br.read(readBuf);
 				int msgstart = readBuf.length != 0 ? ( readBuf[0] == '\n' ? 1 : 0 ) : 0;
 
-				if (encoding != null) {
-					// TODO: this isn't reliable so we need to guess the encoding from the actual content
-					author = new PersonIdent(new String(rawAuthor.getBytes(),encoding.name()));
-					committer = new PersonIdent(new String(rawCommitter.getBytes(),encoding.name()));
-					message = new String(readBuf,msgstart, readBuf.length-msgstart, encoding.name());
-				} else {
-					// TODO: use config setting / platform / ascii / iso-latin
-					author = new PersonIdent(new String(rawAuthor.getBytes()));
-					committer = new PersonIdent(new String(rawCommitter.getBytes()));
-					message = new String(readBuf, msgstart, readBuf.length-msgstart);
-				}
+				// If encoding is not specified, the default for commit is UTF-8
+				if (encoding == null) encoding = Constants.CHARSET;
+
+				// TODO: this isn't reliable so we need to guess the encoding from the actual content
+				author = new PersonIdent(new String(rawAuthor.getBytes(),encoding.name()));
+				committer = new PersonIdent(new String(rawCommitter.getBytes(),encoding.name()));
+				message = new String(readBuf,msgstart, readBuf.length-msgstart, encoding.name());
 			} catch (IOException e) {
 				e.printStackTrace();
 			} finally {