Limit receive commands

Place a configurable upper bound on the amount of command data
received from clients during `git push`.  The limit is applied to the
encoded wire protocol format, not the JGit in-memory representation.
This allows clients to flexibly use the limit; shorter reference names
allow for more commands, longer reference names permit fewer commands
per batch.

Based on data gathered from many repositories at $DAY_JOB, the average
reference name is well under 200 bytes when encoded in UTF-8 (the wire
encoding).  The new 3 MiB default receive.maxCommandBytes allows about
11,155 references in a single `git push` invocation.  A Gerrit Code
Review system with six-digit change numbers could still encode 29,399
references in the 3 MiB maxCommandBytes limit.

Change-Id: I84317d396d25ab1b46820e43ae2b73943646032c
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/PushConnectionTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/PushConnectionTest.java
index 33a910505f..4aebc1d32c 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/PushConnectionTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/PushConnectionTest.java
@@ -173,4 +173,27 @@ public class PushConnectionTest {
 			}
 		}
 	}
+
+	@Test
+	public void limitCommandBytes() throws IOException {
+		Map<String, RemoteRefUpdate> updates = new HashMap<>();
+		for (int i = 0; i < 4; i++) {
+			RemoteRefUpdate rru = new RemoteRefUpdate(
+					null, null, obj2, "refs/test/T" + i,
+					false, null, ObjectId.zeroId());
+			updates.put(rru.getRemoteName(), rru);
+		}
+
+		server.getConfig().setInt("receive", null, "maxCommandBytes", 170);
+		try (Transport tn = testProtocol.open(uri, client, "server");
+				PushConnection connection = tn.openPush()) {
+			try {
+				connection.push(NullProgressMonitor.INSTANCE, updates);
+				fail("server did not abort");
+			} catch (TransportException e) {
+				String msg = e.getMessage();
+				assertEquals("remote: Too many commands", msg);
+			}
+		}
+	}
 }