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

[Uri Lublin]

On 02/28/2018 02:53 PM, Lukáš Hrázký wrote:
> 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';

That looks wrong. It should be:
        msg.msg[len_to_read] = '\0';
Otherwise, the end of the message (last 4 bytes) is cut out.


After re-reading it, I realize there are two meanings to msg.msg:
one from the definition above and one inherited.

Uri.