ref: a411870ee4640241e3c494367d922847da84f972
dir: /man/2/msgio/
.TH MSGIO 2 .SH NAME msgio: getmsg, sendmsg, senderrmsg, getstring, putstring, getbytearray, putbytearray, puterror \- exchange data on delimited and undelimited streams .SH SYNOPSIS .EX include "msgio.m"; msgio := load Msgio Msgio->PATH; init: fn(); 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; 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; .EE .SH DESCRIPTION .B Msgio provides two complementary sets of functions for the exchange of data over a network connection that uses a connection-oriented transport protocols. The connection is represented by a file descriptor .IR fd . .PP .B Init must be called before any other operation of the module. .PP The first set allows arbitrary data, packed into arrays of bytes, to be exchanged on network connections using protocols such as TCP/IP that do not preserve record boundaries. They are used to implement various authentication protocols, including .IR auth (6). .PP Each data message is transmitted with a five-byte header containing a four-character zero-padded decimal count .I n terminated by a newline, followed by .I n bytes of message data. An error message has a similar structure, except that the first character of the count is replaced by an exclamation mark .RB ( ! ); the message data following contains the diagnostic string in its UTF-8 encoding (see .IR utf (6)). .PP .B Getmsg reads the next message from .I fd and returns its data content. .PP .B Sendmsg sends the first .I n bytes of .I buf as a message on .IR fd , and returns .IR n . .PP .B Senderrmsg sends the error message .IR s . .PP The second set of functions provide I/O for strings, byte arrays and error strings over network connections that provide a record structure for communication (as provided for arbitrary networks by .IR ssl (3)). .PP .B Putstring writes string .I s to .IR fd. It returns the number of bytes written, or -1 if an error occurred. Messages written by .B putstring are truncated to 4096 bytes. .PP .B Getstring reads a string as written by .B putstring from .IR fd and returns a tuple .RI ( result , error ). If successful, the error string is nil. .PP .B Putbytearray writes the array of bytes .I a to .IR fd . It returns the number of bytes written, or -1 if an error occurred. Messages written by .B putbytearray are truncated to 4096 bytes. .PP .B Getbytearray reads an array of bytes as written by .B putbytearray from .IR fd and returns a tuple of the form .RI ( result , error ). If successful, the error string is nil. .PP .B Puterror writes an error string .I s to .IR fd . It can be used in place of .B putstring or .B putbytearray to cause a corresponding .B getstring or .B getbytearray to fail (in the receiving process), forcing them to return the error string .IR s . It may not be longer than .BR Sys->ERRMAX bytes. .SH SOURCE .B /appl/lib/msgio.b .SH DIAGNOSTICS The output functions return an .B int which is -1 if there was an I/O error, and a non-negative value otherwise; they also set the system error string. .B Getmsg returns nil if there was an error reading from .IR fd ; it sets the system error string to reflect the cause. It also returns nil if an error message was received instead of a data message; the system error string will contain the error message's diagnostic. The other input functions (for streams with delimiters) return a tuple that includes a string indicating the cause of the error, as the second element of the tuple. .SH BUGS The module is really intended to retrofit the original Inferno authentication protocols into a new regime, and is not yet intended for general-purpose use, hence the irregular naming and calling conventions, inherited from the original implementation in .BR Keyring .