Fix DDMS-JDWP race

DDMS would race against the JDWP-Handshake in some circumstances
causing clients to become confused as DDMS packets were recieved
before the handshake reply.

Test: atest CtsJdwpTunnelHostTestCases
Test: ./tools/dt_fds_forward.py
Bug: 178655046
Change-Id: Iabeb68829455ee4d2682f0a14591c8b7b0f4fc5f

2 files changed, 14 insertions, 0 deletions

diff --git a/dt_fd_forward/dt_fd_forward.cc b/dt_fd_forward/dt_fd_forward.cc
index d5b6de5ead..2a6bfda0ad 100644
--- a/dt_fd_forward/dt_fd_forward.cc
+++ b/dt_fd_forward/dt_fd_forward.cc
@@ -52,6 +52,8 @@
 
 #include <base/strlcpy.h>
 
+#include "fd_transport.h"
+
 namespace dt_fd_forward {
 
 // Helper that puts line-number in error message.
@@ -287,6 +289,11 @@ static void SendAcceptMessage(int fd) {
   TEMP_FAILURE_RETRY(send(fd, kAcceptMessage, sizeof(kAcceptMessage), MSG_EOR));
 }
 
+static void SendHandshakeCompleteMessage(int fd) {
+  TEMP_FAILURE_RETRY(
+      send(fd, kHandshakeCompleteMessage, sizeof(kHandshakeCompleteMessage), MSG_EOR));
+}
+
 IOResult FdForwardTransport::ReceiveFdsFromSocket(bool* do_handshake) {
   union {
     cmsghdr cm;
@@ -402,6 +409,8 @@ jdwpTransportError FdForwardTransport::Accept() {
         continue;
       }
     }
+    // Tell everyone we have finished the handshake.
+    SendHandshakeCompleteMessage(close_notify_fd_);
     break;
   }
   CHECK(ChangeState(TransportState::kOpening, TransportState::kOpen));
diff --git a/dt_fd_forward/export/fd_transport.h b/dt_fd_forward/export/fd_transport.h
index 144ac5c6ec..40dbe42470 100644
--- a/dt_fd_forward/export/fd_transport.h
+++ b/dt_fd_forward/export/fd_transport.h
@@ -65,6 +65,11 @@ static constexpr char kListenEndMessage[] = "dt_fd_forward:END-LISTEN";
 // fds are closed.
 static constexpr char kAcceptMessage[] = "dt_fd_forward:ACCEPTED";
 
+// This message is sent over the fd associated with the transport when we have
+// completed the handshake. If the handshake was already performed this is sent
+// immediately.
+static constexpr char kHandshakeCompleteMessage[] = "dt_fd_forward:HANDSHAKE-COMPLETE";
+
 // This message is sent over the fd associated with the transport when we are closing the fds. This
 // can be used by the proxy to send additional data on a dup'd fd. The write_lock_fd_ will be held
 // until the other two fds are closed and then it will be released and closed.