Communications server (TCPIP) on z/OS provides some samples. I had problems getting these to compile, because the JCL in the documentation was a) wrong and b) about 20 years behind times.

Samples

There are some samples in TCPIP.SEZAINST

• TCPS: a server which listens on a port
• TCPC: a client which connects to a server using IP address and port
• UDPC: C socket UDP client
• UDPS: C socket UDP server
• MTCCLNT: C socket Multitasking client
• MTCSRVR: C socket Multitasking server
• MTCCSUB: C socket subtask MTCCSUB

The JCL I used is

//COLCOMPI   JOB 1,MSGCLASS=H,COND=(4,LE) 
//S1          JCLLIB ORDER=CBC.SCCNPRC 
// SET LOADLIB=COLIN.LOAD 
// SET LIBPRFX=CEE 
// SET SOURCE=COLIN.C.SOURCE(TCPSORIG) 
//COMPILE  EXEC PROC=EDCCB, 
//       LIBPRFX=&LIBPRFX, 
//       CPARM='OPTFILE(DD:SYSOPTF),LSEARCH(/usr/include/)', 
// BPARM='SIZE=(900K,124K),RENT,LIST,RMODE=ANY,AMODE=31' 
//COMPILE.SYSLIB DD 
//               DD 
//               DD DISP=SHR,DSN=TCPIP.SEZACMAC 
//*              DD DISP=SHR,DSN=TCPIP.SEZANMAC  for IOCTL 
//COMPILE.SYSOPTF DD * 
DEF(_OE_SOCKETS) 
DEF(MVS) 
LIST,SOURCE 
TEST 
RENT ILP32        LO 
INFO(PAR,USE) 
NOMARGINS EXPMAC   SHOWINC XREF 
LANGLVL(EXTENDED) sscom dll 
DEBUG 
/* 
//COMPILE.SYSIN    DD  DISP=SHR,DSN=&SOURCE 
//BIND.SYSLMOD DD DISP=SHR,DSN=&LOADLIB. 
//BIND.SYSLIB  DD DISP=SHR,DSN=TCPIP.SEZARNT1 
//             DD DISP=SHR,DSN=&LIBPRFX..SCEELKED 
//* BIND.GSK     DD DISP=SHR,DSN=SYS1.SIEALNKE 
//* BIND.CSS    DD DISP=SHR,DSN=SYS1.CSSLIB 
//BIND.SYSIN DD * 
  NAME  TCPS(R) 
//START1   EXEC PGM=TCPS,REGION=0M, 
// PARM='4000          ' 
//STEPLIB  DD DISP=SHR,DSN=&LOADLIB 
//SYSERR   DD SYSOUT=*,DCB=(LRECL=200) 
//SYSOUT   DD SYSOUT=*,DCB=(LRECL=200) 
//SYSPRINT DD SYSOUT=*,DCB=(LRECL=200) 

Change the source

The samples do not compile with the above JCL. I needed to remove some includes

#include <manifest.h> 
// #include <bsdtypes.h> 
#include <socket.h> 
#include <in.h> 
// #include <netdb.h> 
#include <stdio.h> 

With the original sample I got compiler messages

ERROR CCN3334 CEE.SCEEH.SYS.H(TYPES):66 Identifier dev_t has already been defined on line 98 of “TCPIP.SEZACMAC(BSDTYPES)”.
ERROR CCN3334 CEE.SCEEH.SYS.H(TYPES):77 Identifier gid_t has already been defined on line 101 of “TCPIP.SEZACMAC(BSDTYPES)”.
ERROR CCN3334 CEE.SCEEH.SYS.H(TYPES):162 Identifier uid_t has already been defined on line 100 of “TCPIP.SEZACMAC(BSDTYPES)”.
ERROR CCN3334 CEE.SCEEH.H(NETDB):87 Identifier in_addr has already been defined on line 158 of “TCPIP.SEZACMAC(IN)”.

INFORMATIONAL CCN3409 TCPIP.SEZAINST(TCPS):133 The static variable “ibmcopyr” is defined but never referenced.

I tried many combinations of #define but could not get it to compile, unless I removed the #includes.

Compile problems I stumbled upon

Identifier dev_t has already been defined on line ...                                                     
Identifier gid_t has already been defined on line ...                                                     
Identifier uid_t has already been defined on line ....

This was caused by the wrong libraries in SYSLIB. I needed

• CEE.SCEEH.H
• CEE.SCEEH.SYS.H
• TCPIP.SEZACMAC
• TCPIP.SEZANMAC

The compile problems were caused by CEE.SCEEH.SYS.H being missing.

Execution problems

I had some strange execution problem when I tried to use AT-TLS within the program.

EDC5000I No error occurred. (errno2=0x05620062)

The errno2 reason from TSO BPXMTEXT 05620062 was

BPXFSOPN 04/27/18
JRNoFileNoCreatFlag: A service tried to open a nonexistent file without O_CREAT

Action: The open service request cannot be processed. Correct the name or the open flags and retry the operation.

Which seems very strange. I have a feeling that this field is not properly initialised and that this value can be ignored.