[gnugo-devel] GTP sometimes fails

[Darren Cook]

Hi,
I'm connecting to gnugo 3.6 using GTP: using pipes from C++. When
running my unit tests, they sometimes work fine, but sometimes they
fail. If it fails it seems to be on the first command I send after
successfully connecting.

I was originally using lower-level file descriptors, but after having
lots of problems, I looked at gnugo's oracle.c code and switched to
using two FILE*. So my code is now basically the same as oracle.c
(except I use fwrite instead of fprintf). Does anyone have similar
problems with that code?

My send_command() is shown below.

I'm wondering if when fgets() returns NULL if it means Gnugo is still
processing? Should I just do a continue to have it try again? Perhaps
combined with sleeping for a millisecond or something. Or should fgets()
wait forever until the remote program sends a carriage-return?

Darren


P.S. This is on linux, with gnugo running on the same single-CPU machine.


----------------------------------------
const char *send_command(const char *command)const{
size_t sz=strlen(command);
size_t bytes=fwrite(command,1,sz,fp_out);
if(sz!=bytes){
        std::cerr<<"write to pipe failed: sent "<<sz<<" bytes, but only
"<<bytes<<" bytes written apparently\n"<<std::flush;;
        return NULL;
        }
fflush(fp_out);

const int MAX_BUFFER=2048;

static char readbuf[MAX_BUFFER];

size_t ix=0;    //Where in readbuf we're up to
readbuf[0]=0;
while(ix<(MAX_BUFFER-256)){
    char buf[256];  //Max line length assumed to be 256
    char *p=fgets(buf,255,fp_in);
    if(!p){
        std::cerr<<"Failed to read from gtp stream\n"<<std::flush;;
        return NULL;
        }
    size_t len=strlen(p);
    if(len==1){
        if(ix==0)continue;  //gnugo always returns at least "=", so I think
            //this means it has not replied yet.
        break;  //Blank line indicates end of reply
        }
    strncpy(&readbuf[ix],buf,255);
    ix+=len;
    }

if(readbuf[0]!='='){
        std::cerr<<"Sending "<<command<<" returned this
string:"<<readbuf<<"\n"<<std::flush;
        return NULL;
        }

return readbuf;
}