= keyring: getstring, putstring, getbytearray, putbytearray, puterror: exchange data on delimited streams     include "keyring.m"    keyring:= load Keyring Keyring->PATH;     getstring:    fn(fd: ref Sys->FD): (string, string);    putstring:    fn(fd: ref Sys->FD, s: string): int;    getbytearray: fn(fd: ref Sys->FD): (array of byte, string);    putbytearray: fn(fd: ref Sys->FD, a: array of byte, n: int): int;    puterror:     fn(fd: ref Sys->FD, s: string): int; These functions provide I/O  for  strings,  byte  arrays  anderror  strings over network connections that provide a recordstructure for communication (as provided for  arbitrary  net‐works by ssl(3)). Putstring  writes  string  s to fd.  It returns the number ofbytes written, or -1 if an error occurred.  Messages  writtenby putstring are truncated to 4096 bytes. Getstring  reads a string as written by putstring from fd andreturns a tuple (result,error).   If  successful,  the  errorstring is nil. Putbytearray  writes  the array of bytes a to fd.  It returnsthe number of bytes written, or  -1  if  an  error  occurred.Messages written by putbytearray are truncated to 4096 bytes. Getbytearray reads an array of bytes as written by putbytear‐ray from fd and returns a tuple of the  form  (result,error).If successful, the error string is nil. Puterror  writes  an error string s to fd.  It can be used inplace of putstring or putbytearray to cause  a  correspondinggetstring or getbytearray to fail (in the receiving process),forcing them to return the error string s.   It  may  not  belonger than Sys->ERRMAX bytes. == source/libinterp/keyring.c == diagnosticsThe  output  functions return an int which is -1 if there wasan I/O error, and a non-negative value otherwise.  The  inputfunctions  return  a  tuple that includes a string indicatingthe cause of the error, as the second element of the tuple.