Without these changes, RDP-specific resources like the CLIPRDR and RDPEI
channels may remain from past connections if the RDP connection is
dynamically reconnected via the "Reconnect" display resize method,
resulting in assertion failures or memory errors if those stale
resources are reused after reconnect is completed.
The FreeRDP library is intended to be threadsafe, but is not reliably so
with respect to legacy RDP encryption and outbound messages. When
outbound messages are sent by multiple threads, the encryption key used
for legacy RDP encryption may not be updated correctly, resulting in a
fatal connection error like:
"ERRINFO_DECRYPT_FAILED (0x00001192):(a) Decryption using Standard RDP
Security mechanisms (section 5.3.6) failed. (b) Session key creation
using Standard RDP Security mechanisms (section 5.3.5) failed."
Without a typecast, errors like the following are generated by the
compiler:
channels/cliprdr.c: In function 'guac_rdp_cliprdr_channel_connected':
channels/cliprdr.c:477:27: error: assignment from incompatible pointer type [-Werror]
cliprdr->MonitorReady = guac_rdp_cliprdr_monitor_ready;
^
channels/cliprdr.c:478:31: error: assignment from incompatible pointer type [-Werror]
cliprdr->ServerFormatList = guac_rdp_cliprdr_format_list;
^
channels/cliprdr.c:479:38: error: assignment from incompatible pointer type [-Werror]
cliprdr->ServerFormatDataRequest = guac_rdp_cliprdr_format_data_request;
^
channels/cliprdr.c:480:39: error: assignment from incompatible pointer type [-Werror]
cliprdr->ServerFormatDataResponse = guac_rdp_cliprdr_format_data_response;
^
cc1: all warnings being treated as errors
This is because FreeRDP commit 65812bd added const to the pointer
argument of each of these handlers, wheras older versions of FreeRDP
lack const here. Our implementations of these functions declare const
and thus do not match the older prototype, though they are compatible
with it.
