plan9fox/sys/man/2/bio

.TH BIO 2
.SH NAME
Bopen, Bfdopen, Binit, Binits, Brdline, Brdstr, Bgetc, Bgetrune, Bgetd, Bungetc, Bungetrune, Bread, Bseek, Boffset, Bfildes, Blinelen, Bputc, Bputrune, Bprint, Bvprint, Bwrite, Bflush, Bterm, Bbuffered, Blethal, Biofn \- buffered input/output
.SH SYNOPSIS
.ta \w'Biobuf* 'u
.B #include <u.h>
.br
.B #include <libc.h>
.br
.B #include <bio.h>
.PP
.ft L
.nf
.ta \w'    'u +\w'    'u +\w'    'u +\w'    'u +\w'    'u
typedef struct Biobufhdr	Biobufhdr;
struct Biobufhdr {
	void	*aux;		/* user data */
	...			/* internals */
};
.fi
.PP
.B
Biobuf* Bopen(char *file, int mode)
.PP
.B
Biobuf* Bfdopen(int fd, int mode)
.PP
.B
int	Binit(Biobuf *bp, int fd, int mode)
.PP
.B
int	Binits(Biobufhdr *bp, int fd, int mode, uchar *buf, int size)
.PP
.B
int	Bterm(Biobufhdr *bp)
.PP
.B
int	Bprint(Biobufhdr *bp, char *format, ...)
.PP
.B
int	Bvprint(Biobufhdr *bp, char *format, va_list arglist);
.PP
.B
void*	Brdline(Biobufhdr *bp, int delim)
.PP
.B
char*	Brdstr(Biobufhdr *bp, int delim, int nulldelim)
.PP
.B
int	Blinelen(Biobufhdr *bp)
.PP
.B
vlong	Boffset(Biobufhdr *bp)
.PP
.B
int	Bfildes(Biobufhdr *bp)
.PP
.B
int	Bgetc(Biobufhdr *bp)
.PP
.B
long	Bgetrune(Biobufhdr *bp)
.PP
.B
int	Bgetd(Biobufhdr *bp, double *d)
.PP
.B
int	Bungetc(Biobufhdr *bp)
.PP
.B
int	Bungetrune(Biobufhdr *bp)
.PP
.B
vlong	Bseek(Biobufhdr *bp, vlong n, int type)
.PP
.B
int	Bputc(Biobufhdr *bp, int c)
.PP
.B
int	Bputrune(Biobufhdr *bp, long c)
.PP
.B
long	Bread(Biobufhdr *bp, void *addr, long nbytes)
.PP
.B
long	Bwrite(Biobufhdr *bp, void *addr, long nbytes)
.PP
.B
int	Bflush(Biobufhdr *bp)
.PP
.B
int	Bbuffered(Biobufhdr *bp)
.PP
.B
void	Blethal(Biobufhdr *bp, void (*errorf)(char *))
.PP
.B
void	Biofn(Biobufhdr *bp, int (*iof)(Biobufhdr *, void *, long))
.PP
.SH DESCRIPTION
These routines implement fast buffered I/O.
I/O on different file descriptors is independent.
.PP
.I Bopen
opens
.I file
for mode
.B OREAD
or creates for mode
.BR OWRITE .
It calls
.IR malloc (2)
to allocate a buffer.
.PP
.I Bfdopen
allocates a buffer for the already-open file descriptor
.I fd
for mode
.B OREAD
or
.BR OWRITE .
It calls
.IR malloc (2)
to allocate a buffer.
.PP
.I Binit
initializes a standard size buffer, type
.IR Biobuf ,
with the open file descriptor passed in
by the user.
.I Binits
initializes a non-standard size buffer, type
.IR Biobufhdr ,
with the open file descriptor,
buffer area, and buffer size passed in
by the user.
.I Biobuf
and
.I Biobufhdr
are related by the declaration:
.IP
.EX
typedef struct Biobuf Biobuf;
struct Biobuf
{
	Biobufhdr;
	uchar b[Bungetsize+Bsize];
};
.EE
.PP
Arguments
of types pointer to Biobuf and pointer to Biobufhdr
can be used interchangeably in the following routines.
.PP
.IR Bopen ,
.IR Binit ,
or
.I Binits
should be called before any of the
other routines on that buffer.
.I Bfildes
returns the integer file descriptor of the associated open file.
.PP
.I Bterm
flushes the buffer for
.I bp
and returns
.IR Bflush 's
return value.
If the buffer was allocated by
.I Bopen
or
.IR Bfdopen ,
the buffer is
.I freed
and the file is closed.
.PP
.I Brdline
reads a string from the file associated with
.I bp
up to and including the first
.I delim
character.
The delimiter character at the end of the line is
not altered, thus the returned string probably won't be NUL-terminated.
.I Brdline
returns a pointer to the start of the line or
.L 0
on end-of-file or read error.
.I Blinelen
returns the length (including the delimiter)
of the most recent string returned by
.IR Brdline .
.PP
.I Brdstr
returns a
.IR malloc (2)-allocated
buffer containing the next line of input delimited by
.IR delim ,
terminated by a NUL (0) byte.
Unlike
.IR Brdline ,
which returns when its buffer is full even if no delimiter has been found,
.I Brdstr
will return an arbitrarily long line in a single call.
If
.I nulldelim
is set, the terminal delimiter will be overwritten with a NUL.
After a successful call to
.IR Brdstr ,
the return value of
.I Blinelen
will be the length of the returned buffer, excluding the NUL.
.PP
.I Bgetc
returns the next character from
.IR bp ,
or a negative value
at end of file.
.I Bungetc
may be called immediately after
.I Bgetc
to allow the same character to be reread.
.PP
.I Bgetrune
calls
.I Bgetc
to read the bytes of the next
.SM UTF
sequence in the input stream and returns the value of the rune
represented by the sequence.
It returns a negative value
at end of file.
.I Bungetrune
may be called immediately after
.I Bgetrune
to allow the same
.SM UTF
sequence to be reread as either bytes or a rune.
.I Bungetc
and
.I Bungetrune
may back up a maximum of five bytes.
.PP
.I Bgetd
uses
.I charstod
(see
.IR atof (2))
and
.I Bgetc
to read the formatted
floating-point number in the input stream,
skipping initial blanks and tabs.
The value is stored in
.BR *d.
.PP
.I Bread
reads
.I nbytes
of data from
.I bp
into memory starting at
.IR addr .
The number of bytes read is returned on success
and a negative value is returned if a read error occurred.
.PP
.I Bseek
applies
.IR seek (2)
to
.IR bp .
It returns the new file offset.
.I Boffset
returns the file offset of the next character to be processed.
.PP
.I Bputc
outputs the low order 8 bits of
.I c
on
.IR bp .
If this causes a
.I write
to occur and there is an error,
a negative value is returned.
Otherwise, a zero is returned.
.PP
.I Bputrune
calls
.I Bputc
to output the low order
16 bits of
.I c
as a rune
in
.SM UTF
format
on the output stream.
.PP
.I Bprint
is a buffered interface to
.IR print (2).
If this causes a
.I write
to occur and there is an error,
a negative value
.RB ( Beof )
is returned.
Otherwise, 
.I Bprint
returns the number of bytes written.
.I Bvprint
does the same except it takes as argument a
.B va_list
parameter, so it can be called within a variadic function.
.PP
.I Bwrite
outputs
.I nbytes
of data starting at
.I addr
to
.IR bp .
If this causes a
.I write
to occur and there is an error,
a negative value is returned.
Otherwise, the number of bytes written is returned.
.PP
.I Bflush
causes any buffered output associated with
.I bp
to be written.
The return is as for
.IR Bputc .
.I Bflush
is called on
exit for every buffer still open
for writing.
.PP
.I Bbuffered
returns the number of bytes in the buffer.
When reading, this is the number of bytes still available from the last
read on the file; when writing, it is the number of bytes ready to be
written.
.PP
.I Blethal
arranges
.I errorf
to be called in case of an error happening on read/write.
An argument of
.B nil
will have the program terminated in case of error.
.PP
If
.I Biofn
is called with a non-nil
.I iof
function, then that function is called for I/O in lieu of
.IR read (2)
and
.IR write .
A nil argument for
.I iof
restores normal behaviour.
.SH SOURCE
.B /sys/src/libbio
.SH SEE ALSO
.IR open (2),
.IR read (2),
.IR print (2),
.IR exits (2),
.IR utf (6),
.SH DIAGNOSTICS
.I Bio
routines that return integers yield
.B Beof
if 
.I bp
is not the descriptor of an open file.
.I Bopen
returns zero if the file cannot be opened in the given mode.
All routines set
.I errstr
on error.
.PP
An error during read or write will call an error handler specified by
.IR Blethal ,
if any.
.SH BUGS
.I Brdline
returns an error on strings longer than the buffer associated
with the file
and also if the end-of-file is encountered
before a delimiter.
.I Blinelen
will tell how many characters are available
in these cases.
In the case of a true end-of-file,
.I Blinelen
will return zero.
At the cost of allocating a buffer,
.I Brdstr
sidesteps these issues.
.PP
Only the low byte of
.IR Brdstr 's
.I delim
is examined, so
.I delim
cannot be an arbitrary rune.
.PP
The data returned by
.I Brdline
may be overwritten by calls to any other
.I bio
routine on the same
.IR bp.