[Spice-devel] [PATCH spice-streaming-agent v5 2/2] Implement handling of error messages from the server

[Lukáš Hrázký]

Log error messages from the server to syslog (not aborting the agent).
Limits the messages to 1023 bytes, error messages from the server are
not expected to be longer. In the unlikely case the message is longer,
log the first 1023 bytes and throw an exception (because we don't read
out the rest of the message, causing desynchronization between the
server and the streaming agent).

Signed-off-by: Lukáš Hrázký <lhrazky at redhat.com>
---
 src/spice-streaming-agent.cpp | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/spice-streaming-agent.cpp b/src/spice-streaming-agent.cpp
index ee57920..954d1b3 100644
--- a/src/spice-streaming-agent.cpp
+++ b/src/spice-streaming-agent.cpp
@@ -137,10 +137,30 @@ static void handle_stream_capabilities(uint32_t len)
     }
 }
 
-static void handle_stream_error(uint32_t len)
+static void handle_stream_error(size_t len)
 {
-    // TODO read message and use it
-    throw std::runtime_error("got an error message from server");
+    if (len < sizeof(StreamMsgNotifyError)) {
+        throw std::runtime_error("Received NotifyError message size " + std::to_string(len) +
+                                 " is too small (smaller than " +
+                                 std::to_string(sizeof(StreamMsgNotifyError)) + ")");
+    }
+
+    struct : StreamMsgNotifyError {
+        uint8_t msg[1024];
+    } msg;
+
+    size_t len_to_read = std::min(len, sizeof(msg) - 1);
+
+    read_all(&msg, len_to_read);
+    msg.msg[len_to_read - sizeof(StreamMsgNotifyError)] = '\0';
+
+    syslog(LOG_ERR, "Received NotifyError message from the server: %d - %s\n",
+        msg.error_code, msg.msg);
+
+    if (len_to_read < len) {
+        throw std::runtime_error("Received NotifyError message size " + std::to_string(len) +
+                                 " is too big (bigger than " + std::to_string(sizeof(msg)) + ")");
+    }
 }
 
 static void read_command_from_device(void)
-- 
2.16.1