Do not send JDWP data in case of error.

When sending JDWP reply packet with an error, we want to ignore any data in the
buffer. While we reflect that in the packet's length (first 4 bytes), we used
to send all data in the buffer. This causes the receiver to read malformed JDWP
packet.

This CL adds "length" argument to JdwpNetStateBase::WritePacket so we control
the amount of data we send. If the reply has no error, it is set to the length
of the buffer. Otherwise it is the length of JDWP packet header indicating no
data is available.

Bug: 13366758
Change-Id: Ib72c10d5faf065fb44901c34b2732496b6667efa

1 files changed, 5 insertions, 6 deletions

diff --git a/runtime/jdwp/jdwp_handler.cc b/runtime/jdwp/jdwp_handler.cc
index 5f21098a8f..c2a2b5415d 100644
--- a/runtime/jdwp/jdwp_handler.cc
+++ b/runtime/jdwp/jdwp_handler.cc
@@ -1659,7 +1659,7 @@ static std::string DescribeCommand(Request& request) {
  *
  * On entry, the JDWP thread is in VMWAIT.
  */
-void JdwpState::ProcessRequest(Request& request, ExpandBuf* pReply) {
+size_t JdwpState::ProcessRequest(Request& request, ExpandBuf* pReply) {
   JdwpError result = ERR_NONE;
 
   if (request.GetCommandSet() != kJDWPDdmCmdSet) {
@@ -1728,14 +1728,11 @@ void JdwpState::ProcessRequest(Request& request, ExpandBuf* pReply) {
    * If we encountered an error, only send the header back.
    */
   uint8_t* replyBuf = expandBufGetBuffer(pReply);
+  size_t replyLength = (result == ERR_NONE) ? expandBufGetLength(pReply) : kJDWPHeaderLen;
+  Set4BE(replyBuf + 0, replyLength);
   Set4BE(replyBuf + 4, request.GetId());
   Set1(replyBuf + 8, kJDWPFlagReply);
   Set2BE(replyBuf + 9, result);
-  if (result == ERR_NONE) {
-    Set4BE(replyBuf + 0, expandBufGetLength(pReply));
-  } else {
-    Set4BE(replyBuf + 0, kJDWPHeaderLen);
-  }
 
   CHECK_GT(expandBufGetLength(pReply), 0U) << GetCommandName(request) << " " << request.GetId();
 
@@ -1757,6 +1754,8 @@ void JdwpState::ProcessRequest(Request& request, ExpandBuf* pReply) {
 
   /* tell the VM that GC is okay again */
   self->TransitionFromRunnableToSuspended(old_state);
+
+  return replyLength;
 }
 
 /*