Fix UnionInputStream.read to be more Java-like

Relax the read() method to not block until exactly "len" bytes have
been read. Instead, return when one or more bytes have been read, up
to "len", so UnionInputStream more closely resembles InputStream's
read() method.

Change-Id: I3f632be8eb85a4a0baf27c9f067c8d817162de2b

2 files changed, 31 insertions, 13 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/io/UnionInputStreamTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/io/UnionInputStreamTest.java
index 9fb323c4db..daebffbc1b 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/io/UnionInputStreamTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/io/UnionInputStreamTest.java
@@ -50,6 +50,7 @@ import static org.junit.Assert.fail;
 
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.Arrays;
 
 import org.junit.Test;
@@ -238,4 +239,26 @@ public class UnionInputStreamTest {
 			assertEquals("I AM A TEST", e.getMessage());
 		}
 	}
+
+	@Test
+	public void testNonBlockingPartialRead() throws Exception {
+		InputStream errorReadStream = new InputStream() {
+			@Override
+			public int read() throws IOException {
+				throw new IOException("Expected");
+			}
+		};
+		final UnionInputStream u = new UnionInputStream(
+				new ByteArrayInputStream(new byte[]{1,2,3}),
+				errorReadStream);
+		byte buf[] = new byte[10];
+		assertEquals(3, u.read(buf, 0, 10));
+		assertTrue(Arrays.equals(new byte[] {1,2,3}, slice(buf, 3)));
+		try {
+			u.read(buf, 0, 1);
+			fail("Expected exception from errorReadStream");
+		} catch (IOException e) {
+			assertEquals("Expected", e.getMessage());
+		}
+	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/io/UnionInputStream.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/io/UnionInputStream.java
index 0df3775f11..20dcd4659e 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/io/UnionInputStream.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/io/UnionInputStream.java
@@ -138,23 +138,18 @@ public class UnionInputStream extends InputStream {
 
 	@Override
 	public int read(byte[] b, int off, int len) throws IOException {
-		int cnt = 0;
-		while (0 < len) {
+		if (len == 0)
+			return 0;
+		for (;;) {
 			final InputStream in = head();
 			final int n = in.read(b, off, len);
-			if (0 < n) {
-				cnt += n;
-				off += n;
-				len -= n;
-			} else if (in == EOF)
-				return 0 < cnt ? cnt : -1;
-			else {
+			if (0 < n)
+				return n;
+			else if (in == EOF)
+				return -1;
+			else
 				pop();
-				if (0 < cnt)
-					break;
-			}
 		}
-		return cnt;
 	}
 
 	@Override