Receiving data function stalls when requesting large chunk of data - c

Question

I'm creating a mini web server in C.
The following function is supposed to read in data from the client computer.
The objective is to read the second piece of data after the first space. Each piece of incoming data is space separated.
For example, if the incoming data is:
GET /123/456
then I'd expect /123/456.
If the incoming data is:
GET /123/456 789
then I'd still expect /123/456.
This relevant fragment is from an external function that sets up a 10 KB buffer and calls the problematic function:
//nsock is a valid socket handle from an accept() call.
printf("CLIENT CONNECTION!\n");
char req[10000];long reqsz=10000;
getreq(req,&reqsz,nsock);
printf("Received %d bytes\n",reqsz);
printf("Data: %s\n",req);
"CLIENT CONNECTION!" appears on the screen, but "Received" does not appear if bufsize inside the function is a high value. If I set it to a low value like 16, or 100, then everything is displayed correctly. Why do large numbers like 5000 not work?
This is the problematic function:
//getreq params in: req=external buffer for data
// reqsz=size of external buffer. I set 10000
// nsock=valid socket pointer from accept()
//
//getreq params out: reqsz=actual size of data returned
// req=actual data
//
void getreq(char* req,unsigned long *reqsz,long nsock){
//bufsize=how many bytes to read at once. High values like 5000 cause a stall.
//buffer=buffer of data from recv call
const unsigned long ibs=*reqsz,bufsize=5000;
char buffer[ibs],*rp=req;
//spacect=# of spaces in data read
//szct=iterator variable
//mysz=total length of returned data
//bufct=buffer counter to prevent segfault
//recvsz=data size returned from recv or
// forced -2 if buffer hits capacity
// or 2nd space in returned data is found
unsigned long spacect=0,szct=0,mysz=0,bufct=0;
long recvsz=1;char *p=buffer;
//
//Expected data: GET /whatever HTTP/x.x but we
// want /whatever
//
//loop until 2nd space is found or
//ibs bytes of data have been processed
while (recvsz > 0 && bufct < ibs){
recvsz=recv(nsock, p, bufsize, 0);
if (recvsz < 1){break;}
for (szct=1;szct<=recvsz;szct++){
if (*p==' '){spacect++;if (spacect > 2){spacect=2;recvsz=-2;break;}}
if (spacect==1 && *p != ' '){mysz++;if (mysz <= *reqsz){*rp++=*p;}}
p++;bufct++;if (bufct > ibs){recvsz=-2;break;}
}
}
// Process rest of data to try to avoid client errors
while (recvsz == -2){
recvsz=recv(nsock, buffer, bufsize, 0);
}
*reqsz=mysz;
}