= keyring:  getmsg, sendmsg, senderrmsg: send and receive messages on undelimited streams     include "keyring.m";    keyring := load Keyring Keyring->PATH;     getmsg:  fn(fd: ref Sys->FD): array of byte;    sendmsg: fn(fd: ref Sys->FD, buf: array of byte, n: int): int;    senderrmsg: fn(fd: ref Sys->FD, s: string): int; These functions allow arbitrary data, packed into  arrays  ofbytes,  to  be exchanged on network connections using connec‐tion-oriented transport protocols that do not preserve recordboundaries  (eg,  TCP/IP  without  ssl(3)).  They are used toimplement   various   authentication   protocols,   includingauth(6), as implemented by keyring-auth(2). Each data message is transmitted with a five-byte header con‐taining a four-character zero-padded decimal count  n  termi‐nated  by a newline, followed by n bytes of message data.  Anerror message has a similar structure, except that the  firstcharacter  of  the  count  is replaced by an exclamation mark(!); the  message  data  following  contains  the  diagnosticstring in its UTF-8 encoding (see utf(6)). Getmsg  reads  the  next message from fd and returns its datacontent. Sendmsg sends the first n bytes of buf as a  message  on  fd,and returns n. Senderrmsg sends the error message s. == source/libinterp/keyring.c == diagnosticsSendmsg  and senderrmsg return -1 if there was an error writ‐ing to fd; they set the system error string.  Getmsg  returnsnil if there was an error reading from fd; it sets the systemerror string to reflect the cause.  It also returns nil if anerror  message  was  received  instead of a data message; thesystem error string will contain the error message's diagnos‐tic.