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.\" Author: Archie Cobbs <archie@freebsd.org>
.\"
.\" $Id: string_fp.3,v 1.1 2012/02/21 23:25:53 misho Exp $
.\"
.Dd April 22, 2002
.Dt STRING_FP 3
.Os
.Sh NAME
.Nm string_buf_input ,
.Nm string_buf_output ,
.Nm string_buf_content ,
.Nm string_buf_length
.Nd string buffer streams
.Sh LIBRARY
PDEL Library (libpdel, \-lpdel)
.Sh SYNOPSIS
.In sys/types.h
.In stdio.h
.In pdel/io/string_fp.h
.Ft "FILE *"
.Fn string_buf_input "const void *buf" " size_t len" "int copy"
.Ft "FILE *"
.Fn string_buf_output "const void *mtype"
.Ft "char *"
.Fn string_buf_content "FILE *fp" "int reset"
.Ft "int"
.Fn string_buf_length "FILE *fp"
.Sh DESCRIPTION
These functions allow string buffers to be read and written as streams.
.Pp
.Fn string_buf_input
creates a read-only stream that reads from the buffer pointed to by
.Fa buf
having length
.Fa len .
If
.Fa copy
is non-zero, the contents of the buffer are copied and therefore
.Fa buf
doesn't need to remain valid while the stream is open.
Otherwise, the data pointed to by
.Fa buf
is not copied and must remain valid while the stream is open.
.Xr fclose 3
should be used to close the stream.
.Pp
.Fn string_buf_output
creates a write-only stream that writes into an internal buffer that
grows dynamically.
.Xr fclose 3
should be used to close the stream; this also frees the internal buffer.
The current buffer length is returned by
.Fn string_buf_length .
.Pp
.Fn string_buf_content
returns the contents of the internal buffer.
As with
.Fn string_buf_length ,
the
.Fa fp
argument must be a stream created by
.Fn string_buf_output .
If
.Fa reset
is zero, then the internal buffer remains valid and the returned pointer
should be treated as read-only and not be freed; it also becomes invalid
with the next operation on the stream.
If
.Fa reset
is non-zero, the current buffer contents are "detached" and returned by
.Fn string_buf_content ,
and a new, empty internal buffer is created; in this case, the caller is
responsible for eventually freeing the returned buffer,
which is allocated with
.Xr typed_mem 3
type
.Fa mtype ,
and its contents remain valid until then.
.Pp
In either case, the data returned by
.Fn string_buf_content
is guaranteed to have one additional '\\0' byte appended.
Therefore, it is always safe to treat this pointer as a normal C string.
However, any '\\0' bytes previously written to the stream will cause
this string to appear truncated.
.Sh RETURN VALUES
.Fn string_buf_input ,
.Fn string_buf_output ,
and
.Fn string_buf_content
return
.Dv NULL
to indicate an error, with
.Va errno
set appropriately.
.Pp
Even if 
.Fn string_buf_content
returns
.Dv NULL ,
the stream will still need to be closed.
.Sh IMPLEMENTATION NOTES
.Fn string_buf_content
and
.Fn string_buf_length
attempt to verify that the supplied stream was indeed created by
.Fn string_buf_output .
If they detect otherwise, an immediate assertion failure is generated.
.Sh SEE ALSO
.Xr base64 3 ,
.Xr filter 3 ,
.Xr fopen 3 ,
.Xr libpdel 3 ,
.Xr typed_mem 3
.Sh HISTORY
The PDEL library was developed at Packet Design, LLC.
.Dv "http://www.packetdesign.com/"
.Sh AUTHORS
.An Archie Cobbs Aq archie@freebsd.org