[lldb/gdb-remote] drop all junk bytes in incoming packet

[borneoa]

Summary

The loop that detects the junk bytes exits:
a) when it reaches the last byte in m_bytes, or
b) when it finds a valid 'first byte'.
The current code drops the first 'idx-1' bytes. This is consistent
with case b), but it left one junk byte in case a).

Let the code dropping all the junk bytes in both the cases above.

[clayborg]

It would be nice to add a test case for this if possible. The solution looks good.

[clayborg]

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp

689–706

This might be more easily and cleanly done with:

const idx = m_bytes.find_first_of("+-\x03%$");
if (idx != 0) {
      LLDB_LOGF(log, "GDBRemoteCommunication::%s tossing %u junk bytes: '%.*s'",
                __FUNCTION__, idx, idx, m_bytes.c_str());
      m_bytes.erase(0, idx);
}

[labath]

The find_first_of solution does look better. For the test, I /think/ it would be sufficient to add a new case to the test in unittests/Process/gdb-remote/GDBRemoteCommunicationTest.cpp.

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp

case '$':
       }
       break;
 
     default: {
       // We have an unexpected byte and we need to flush all bad data that is
       // in m_bytes, so we need to find the first byte that is a '+' (ACK), '-'
       // (NACK), \x03 (CTRL+C interrupt), or '$' character (start of packet
       // header) or of course, the end of the data in m_bytes...
       const size_t bytes_len = m_bytes.size();
       bool done = false;
       uint32_t idx;
-      for (idx = 1; !done && idx < bytes_len; ++idx) {
+      for (idx = 1; !done && idx < bytes_len;) {
         switch (m_bytes[idx]) {
         case '+':
         case '-':
         case '\x03':
         case '%':
         case '$':
           done = true;
           break;
 
         default:
+           ++idx;
           break;
         }
       }
       LLDB_LOGF(log, "GDBRemoteCommunication::%s tossing %u junk bytes: '%.*s'",
-                __FUNCTION__, idx - 1, idx - 1, m_bytes.c_str());
-      m_bytes.erase(0, idx - 1);
+                __FUNCTION__, idx, idx, m_bytes.c_str());
+      m_bytes.erase(0, idx);
     } break;
     }
 
     if (content_length == std::string::npos) {
       packet.Clear();
       return GDBRemoteCommunication::PacketType::Invalid;
     } else if (total_length > 0) {