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.\"
.\" SPDX-Copyright-Identifier: BSD-2-Clause
.\"
.\" Copyright (C) 2024 Kyle Evans <kevans@FreeBSD.org>
.\"
.Dd March 2, 2024
.Dt LIBDER_READ 3
.Os
.Sh NAME
.Nm libder_read ,
.Nm libder_read_fd ,
.Nm libder_read_file
.Nd reading DER encoded streams
.Sh LIBRARY
.Lb libder
.Sh SYNOPSIS
.In libder.h
.Ft struct libder_object *
.Fn libder_read "struct libder_ctx *ctx" "const uint8_t *buf" "size_t *bufsz"
.Ft struct libder_object *
.Fn libder_read_fd "struct libder_ctx *ctx" "int fd" "size_t *readsz"
.Ft struct libder_object *
.Fn libder_read_file "struct libder_ctx *ctx" "FILE *fp" "size_t *readsz"
.Sh DESCRIPTION
The
.Nm
family of functions are used to parse BER/DER encoded data into an object tree
that
.Xr libder 3
can work with.
All of these functions will return an object on success and update
.Fa *readsz
with the number of bytes consumed, or
.Dv NULL
on failure.
.Pp
The
.Fn libder_read
function will read from a buffer
.Fa buf
of known size
.Fa bufsz .
It is not considered an error for
.Fa buf
to have contents past the first valid object encountered.
The application is
expected to check
.Fa *bufsz
upon success and determine if any residual buffer exists, and if that residual
is OK.
.Pp
.Xr libder 3
can also stream a BER encoded object with either of the
.Fn libder_read_fd
or
.Fn libder_read_file
functions from a file descriptor or
.Xr stdio 3
stream respectively.
Both functions will try very hard not to over-read from the stream to avoid
putting it in a precarious state, but bogus looking data may still cause them
to consume more of the stream than intended.
.Pp
Note that
.Fn libder_read_fd
will ignore an
.Ev EINTR
return value from
.Xr read 2
by default and continue reading from the
.Fa fd .
If the application is signalled, it can abort the
.Xr read 2
operation instead with
.Xr libder_abort 3 .
Note that
.Nm libder
does not currently have other points that an abort can be signalled from, so if
.Fn libder_read_fd
is not specifically waiting for data from the
.Va fd
when a signal hits, then the operation will continue until successful with
one exception.
If
.Xr libder_abort 3
is called at any other point in the middle of
.Fn libder_read_fd ,
then the abort flag will not be cleared until it does receive an interrupted
.Xr read 2
call, or until the next call to one of the
.Nm
family of functions.
In the future,
.Nm
may support resuming an aborted operation and allow cancellation at other
specific points within the operation.
.Sh SEE ALSO
.Xr libder 3 ,
.Xr libder_obj 3 ,
.Xr libder_type 3 ,
.Xr libder_write 3
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