[Spice-devel] [RFC PATCH spice-streaming-agent 1/2] Move reading stream messages into a function

[Lukáš Hrázký]

On Thu, 2018-02-22 at 09:34 -0500, Frediano Ziglio wrote:
> > 
> > Signed-off-by: Lukáš Hrázký <lhrazky at redhat.com>
> > ---
> >  src/spice-streaming-agent.cpp | 22 ++++++++++++----------
> >  1 file changed, 12 insertions(+), 10 deletions(-)
> > 
> > diff --git a/src/spice-streaming-agent.cpp b/src/spice-streaming-agent.cpp
> > index aeee5d3..b88225f 100644
> > --- a/src/spice-streaming-agent.cpp
> > +++ b/src/spice-streaming-agent.cpp
> > @@ -79,6 +79,15 @@ static int have_something_to_read(int timeout)
> >      return 0;
> >  }
> >  
> > +static void read_message(void *msg, size_t len)
> > +{
> > +    size_t n = read(streamfd, msg, len);
> > +    if (n != len) {
> > +        throw std::runtime_error("Reading message from device failed: read "
> > + std::to_string(n) +
> > +                                 ", expected " + std::to_string(len));
> > +    }
> > +}
> > +
> 
> Why not for symmetry a read_all handling EINTR and partial reads?
> I think is also a more or less straight forward copy of the write_all.
> I would pass the "int fd" for reuse as a low level routine.

I'm not that well versed in low-level stuff, so I didn't think of it. I
will surely try and resend the patch.

I am still wondering about the _all in the name, though I think I'm
starting to understand it's supposed to mean those are not partial
reads/writes? I'm not sure why someone would want to do that... :) So
the name still seems weird to me, but if you think it's good...

In both mine and Christophe's ideas of how to move the code to a C++
style, this as well as write_all would become methods of the Stream
class, so not standalone low-level routines. I mean, they could still
be, just that there is no reason for now as they are not needed
elsewhere. I'm not insisting on this though.

> >  static void handle_stream_start_stop(uint32_t len)
> >  {
> >      uint8_t msg[256];
> > @@ -87,11 +96,8 @@ static void handle_stream_start_stop(uint32_t len)
> >          throw std::runtime_error("msg size (" + std::to_string(len) + ") is
> >          too long "
> >                                   "(longer than " +
> >                                   std::to_string(sizeof(msg)) + ")");
> >      }
> > -    int n = read(streamfd, &msg, len);
> > -    if (n != len) {
> > -        throw std::runtime_error("read command from device FAILED -- read "
> > + std::to_string(n) +
> > -                                 " expected " + std::to_string(len));
> > -    }
> > +
> > +    read_message(msg, len);
> >      streaming_requested = (msg[0] != 0); /* num_codecs */
> >      syslog(LOG_INFO, "GOT START_STOP message -- request to %s streaming\n",
> >             streaming_requested ? "START" : "STOP");
> > @@ -108,12 +114,8 @@ static void handle_stream_capabilities(uint32_t len)
> >      if (len > sizeof(caps)) {
> >          throw std::runtime_error("capability message too long");
> >      }
> > -    int n = read(streamfd, caps, len);
> > -    if (n != len) {
> > -        throw std::runtime_error("read command from device FAILED -- read "
> > + std::to_string(n) +
> > -                                 " expected " + std::to_string(len));
> > -    }
> >  
> > +    read_message(caps, len);
> >      // we currently do not support extensions so just reply so
> >      StreamDevHeader hdr = {
> >          STREAM_DEVICE_PROTOCOL,
> 
> Frediano