getsockopt: increase the buffer size for getsockopt()

As suggested in the ticket, the buffer size is now 1024 by default, but this can be adjusted at perl build time with: -Accflags=-DPERL_GETSOCKOPT_SIZE=2048 or similarly with hints. I considered making this adjustable with a ${^...} variable, but that seemed excessive. I don't see a practical way to regression test this, TCP_INFO is non-portable. I did examine strace output for a one-liner that calls getsockopt() and the new buffer size was used. Fixes #19758

Author: tonycoz

pp_sys.c

@@ -2685,14 +2685,17 @@ PP(pp_shutdown)
  RETPUSHUNDEF;
 }
 
+#ifndef PERL_GETSOCKOPT_SIZE
+#define PERL_GETSOCKOPT_SIZE 1024
+#endif
 
 /* also used for: pp_gsockopt() */
 
 PP(pp_ssockopt)
 {
  dSP;
  const int optype = PL_op->op_type;
- SV * const sv = (optype == OP_GSOCKOPT) ? sv_2mortal(newSV(257)) : POPs;
+ SV * const sv = (optype == OP_GSOCKOPT) ? sv_2mortal(newSV(PERL_GETSOCKOPT_SIZE+1)) : POPs;
  const unsigned int optname = (unsigned int) POPi;
  const unsigned int lvl = (unsigned int) POPi;
  GV * const gv = MUTABLE_GV(POPs);
@@ -2711,14 +2714,14 @@ PP(pp_ssockopt)
  /* Note: there used to be an explicit SvGROW(sv,257) here, but
  * this is redundant given the sv initialization ternary above */
  (void)SvPOK_only(sv);
- SvCUR_set(sv,256);
+ SvCUR_set(sv, PERL_GETSOCKOPT_SIZE);
  *SvEND(sv) ='\0';
  len = SvCUR(sv);
  if (PerlSock_getsockopt(fd, lvl, optname, SvPVX(sv), &len) < 0)
  goto nuts2;
 #if defined(_AIX)
  /* XXX Configure test: does getsockopt set the length properly? */
- if (len == 256)
+ if (len == PERL_GETSOCKOPT_SIZE)
  len = sizeof(int);
 #endif
  SvCUR_set(sv, len);