BUFIO(2) BUFIO(2)
NAME
bufio, bufiofill - buffered input/output module
SYNOPSIS
include "bufio.m";
bufio := load Bufio Bufio->PATH;
Iobuf: import bufio;
SEEKSTART: con Sys->SEEKSTART;
SEEKRELA: con Sys->SEEKRELA;
SEEKEND: con Sys->SEEKEND;
OREAD: con Sys->OREAD;
OWRITE: con Sys->OWRITE;
ORDWR: con Sys->ORDWR;
EOF: con -1;
ERROR: con -2;
Iobuf: adt {
seek: fn(b: self ref Iobuf, n: big, where: int): big;
offset: fn(b: self ref Iobuf): big;
read: fn(b: self ref Iobuf, a: array of byte, n: int): int;
write: fn(b: self ref Iobuf, a: array of byte, n: int): int;
getb: fn(b: self ref Iobuf): int;
getc: fn(b: self ref Iobuf): int;
gets: fn(b: self ref Iobuf, sepchar: int): string;
gett: fn(b: self ref Iobuf, sepstring: string): string;
ungetb: fn(b: self ref Iobuf): int;
ungetc: fn(b: self ref Iobuf): int;
putb: fn(b: self ref Iobuf, b: byte): int;
putc: fn(b: self ref Iobuf, c: int): int;
puts: fn(b: self ref Iobuf, s: string): int;
flush: fn(b: self ref Iobuf): int;
close: fn(b: self ref Iobuf);
setfill: fn(b: self ref Iobuf, f: BufioFill);
};
open: fn(name: string, mode: int): ref Iobuf;
create: fn(name: string, mode, perm: int): ref Iobuf;
fopen: fn(fd: ref Sys->FD, mode: int): ref Iobuf;
aopen: fn(a: array of byte): ref Iobuf;
sopen: fn(s: string): ref Iobuf;
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BUFIO(2) BUFIO(2)
BufioFill: module
{
fill: fn(b: ref Bufio->Iobuf): int;
};
DESCRIPTION
Bufio provides an interface for buffered I/O. A buffer is
an adt which is created with open, fopen, create, aopen and
sopen.
Open takes two parameters, a filename and a mode. The mode
must be one of OREAD, OWRITE, or ORDWR (also defined in the
Sys module).
Create is similar, but creates a new file if necessary, with
file permissions specified by perm (see create in sys-
open(2)), or truncates an existing file (without changing
its permissions), before opening it in the given mode, and
returning a reference to an Iobuf instance.
Buffered I/O on an already open file is made possible using
fopen, which takes a file descriptor fd and an open mode,
which must be compatible with the mode of the file descrip-
tor.
The file open functions return a ref Iobuf to be used in
subsequent calls. Thus:
lc := bufio->open("/net/tcp/0/local", bufio->OREAD);
addr := lc.gets('\n');
lc = nil;
will open the file /net/tcp/0/local and read a line (includ-
ing the terminating newline character) from this file to
initialize the string variable addr. The file is closed
implicitly by discarding (assigning nil to) the only refer-
ence to its Iobuf.
The function aopen makes the contents of an array of byte a
readable through an Iobuf (it may not be written). The
function sopen similarly makes the contents of a string s
readable.
Processes can share the same instance of Bufio and safely
open and close different files concurrently, but two pro-
cesses must not access the same Iobuf concurrently; they
must coordinate their access using some external mechanism
(eg, lock(2)).
Each output file must be flushed or closed individually (see
flush and close operations below).
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BUFIO(2) BUFIO(2)
The calls implemented by Iobuf are:
seek, read, and write
Each has the same parameters as its complement in
Sys (see sys-seek(2), sys-read(2)). Note that
SEEKSTART etc. are defined by Bufio as well as by
Sys, for use by seek.
offset Return the current file offset in bytes, taking
account of buffered data.
getb Read a single byte from the buffered stream and
return its value as an int.
getc Read a single Unicode character, encoded in UTF
(see utf(6)), and return its value as an int.
gets Read a line, up to and including a character speci-
fied by sepchar, typically a newline. If none is
found, read to the end of the file. The returned
string includes the terminating character.
gett Read characters until one of the characters in
sepstring. The returned string includes the separa-
tor. If none of the separator characters is found,
read to the end of the file.
ungetb, ungetc
Undoes the effect of the last getb or getc, so that
a subsequent read will reread the byte (ungetb), or
reread the byte(s) of a UTF-encoded character
(ungetc)
putb, putc, and puts
Each writes its argument, a byte, a character, or a
string, respectively. Text is encoded in UTF.
setfill Associates a BufioFill module instance f with Iobuf
b; discussed below.
flush Flush remaining data in the buffer, if necessary.
For files opened for writing, data is flushed to
the file. For files opened for reading, any inter-
nally buffered data is discarded, and the next read
will read from the file.
close Flush remaining data in the buffer, if necessary,
close the associated file, and discard buffers
associated with the file. After close, no further
method calls are allowed on the iobuf adt.
The BufioFill module interface can be ignored by most
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BUFIO(2) BUFIO(2)
applications. It allows an Iobuf to be used to read data
from an arbitrary source. There is no `standard' implemen-
tation to load. Instead, an application using this inter-
face uses a separate BufioFill module instance such as
bufio-chanfill(2), or provides one itself using sys-self(2).
The resulting module reference is associated, using setfill,
with an Iobuf previously obtained by sopen (the string
parameter limits the buffer space allocated). It is up to
the BufioFill module's implementation how its fill function
replenishes the buffer; it should return the number of bytes
now in the buffer, or Bufio->EOF.
SOURCE
/appl/lib/bufio.b
SEE ALSO
bufio-chanfill(2), intro(2), sys-open(2), sys-read(2), sys-
seek(2)
DIAGNOSTICS
Calls that return a ref type (eg. open, fopen, gets, and
gett) return nil when encountering end of file or errors.
When an error occurs, the error string, printable with the
%r format, will usually be set as a consequence of an error
in the underlying Sys module. The other calls return EOF
upon encountering end of file, and ERROR when encountering
other errors.
BUGS
A given Iobuf instance may not be accessed concurrently.
An Iobuf instance must be manipulated by the same module
instance that created it.
The BufioFill interface is subject to change.
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