xref: /freebsd/lib/libbsdconf/bsdconf.3 (revision 3fe5961a0b708da599d42cbb6b5e4f030c28ea45)

.\" Copyright (c) 2013-2026 Devin Teske <dteske@FreeBSD.org>
.\" Copyright (c) 2021-2026 Faraz Vahedi <kfv@FreeBSD.org>
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.Dd August 2, 2026
.Dt BSDCONF 3
.Os
.Sh NAME
.Nm bsdconf ,
.Nm bsdconf_parse ,
.Nm bsdconf_fparse ,
.Nm bsdconf_get_option ,
.Nm bsdconf_spool ,
.Nm bsdconf_unquote
.Nd configuration file reading library
.Sh LIBRARY
.Lb libbsdconf
.Sh SYNOPSIS
.In bsdconf.h
.Ft int
.Fo bsdconf_parse
.Fa "struct bsdconf_option options[]"
.Fa "const char *path"
.Fa "int \*[lp]*unknown\*[rp]\*[lp]struct bsdconf_option *option"
.Fa "uint32_t line"
.Fa "char *directive"
.Fa "char *value\*[rp]"
.Fa "uint16_t processing_options"
.Fc
.Ft int
.Fo bsdconf_fparse
.Fa "struct bsdconf_option options[]"
.Fa "int fd"
.Fa "int \*[lp]*unknown\*[rp]\*[lp]struct bsdconf_option *option"
.Fa "uint32_t line"
.Fa "char *directive"
.Fa "char *value\*[rp]"
.Fa "uint16_t processing_options"
.Fc
.Ft "struct bsdconf_option *"
.Fo bsdconf_get_option
.Fa "struct bsdconf_option options[]"
.Fa "const char *directive"
.Fc
.Ft int
.Fo bsdconf_spool
.Fa "int fd"
.Fc
.Ft "char *"
.Fo bsdconf_unquote
.Fa "char *value"
.Fc
.Sh DESCRIPTION
The
.Nm
library provides a light-weight,
portable framework for reading and writing configuration
files.
It is the successor to the retired
.Nm figpar
library,
extending the original read-only token parser into a unified,
resilient reader/writer engine.
.Pp
Due to the fact that configuration files may have basic syntax differences,
the library does not attempt to impose any structure on the data but instead
provides raw data to a set of callback functions.
These callback functions can in-turn initiate abort through their return
value,
allowing custom syntax validation during parsing.
.Pp
Syntax differences between well-known file formats are described by format
descriptors:
a format descriptor is a small read-only table of properties
.Pq Vt struct bsdconf_format_def ; see Xr bsdconf_format 3
naming a format's target keyword,
backing files,
and tokenizing/quoting rules,
which parameterize a single shared engine.
.Pp
Despite the name, it bears no relation to a file descriptor;
it is closer in spirit to a driver's method table:
static data describing behavior,
consulted rather than executed.
Writing is documented in
.Xr bsdconf_put 3 ;
built-in formats and discovery in
.Xr bsdconf_format 3 .
.Pp
Configuration directives,
types,
and callback functions are provided through data structures defined in
.In bsdconf.h :
.Bd -literal -offset indent
struct bsdconf_option {
    enum bsdconf_type		type;	/* value type */
    const char			*directive; /* keyword */
    union bsdconf_value		value;	/* value */
    enum bsdconf_op		op;	/* assignment operator */
    uint8_t			action;	/* bsdconf_put() action */
    uint16_t			result;	/* set by bsdconf_put() */
    uint32_t			line;	/* set by bsdconf_put() */
    uint32_t			match_line;
					/* put: 0=any, else line */

    /* Pointer to function used when directive is found */
    int (*parse)(struct bsdconf_option *option, uint32_t line,
        char *directive, char *value);
};

enum bsdconf_type {
    BSDCONF_TYPE_NONE      = 0x0000, /* directives with no value */
    BSDCONF_TYPE_BOOL      = 0x0001, /* boolean */
    BSDCONF_TYPE_INT       = 0x0002, /* signed 32-bit integer */
    BSDCONF_TYPE_UINT      = 0x0004, /* unsigned 32-bit integer */
    BSDCONF_TYPE_STR       = 0x0008, /* string pointer */
    BSDCONF_TYPE_STRARRAY  = 0x0010, /* string array pointer */
    BSDCONF_TYPE_DATA1     = 0x0020, /* void data type-1 (open) */
    BSDCONF_TYPE_DATA2     = 0x0040, /* void data type-2 (open) */
    BSDCONF_TYPE_DATA3     = 0x0080, /* void data type-3 (open) */
    BSDCONF_TYPE_INT64     = 0x0100, /* signed 64-bit integer */
    BSDCONF_TYPE_UINT64    = 0x0200, /* unsigned 64-bit integer */
    BSDCONF_TYPE_RESERVED  = 0x0400, /* reserved */
};

union bsdconf_value {
    void	*data;      /* Opaque pointer (DATA1..DATA3) */
    char	*str;       /* Pointer to NUL-terminated string */
    char	**strarray; /* Pointer to an array of strings */
    int32_t	num;        /* Signed 32-bit integer value */
    uint32_t	u_num;      /* Unsigned 32-bit integer value */
    int64_t	num64;      /* Signed 64-bit integer value */
    uint64_t	u_num64;    /* Unsigned 64-bit integer value */
    bool	boolean;    /* Boolean value */
};
.Ed
.Pp
The
.Fa processing_options
argument to
.Fn bsdconf_parse ,
.Fn bsdconf_fparse ,
and
.Xr bsdconf_put 3
is a mask of bit fields which indicate various processing options.
The possible flags are:
.Bl -tag -width BSDCONF_BREAK_ON_SEMICOLON
.It Dv BSDCONF_BREAK_ON_EQUALS
An equals sign
.Pq Ql =
is normally considered part of the directive.
This flag enables terminating the directive at the equals sign.
Also makes equals sign optional and transient.
.It Dv BSDCONF_BREAK_ON_SEMICOLON
A semicolon
.Pq Ql \&;
is normally considered part of the value.
This flag enables terminating the value at the semicolon.
Also allows multiple statements on a single line separated by semicolon.
.It Dv BSDCONF_CASE_SENSITIVE
Normally directives are matched case insensitively using
.Xr fnmatch 3 .
This flag enables directive matching to be case sensitive.
.It Dv BSDCONF_REQUIRE_EQUALS
If a directive is not followed by an equals,
processing is aborted.
.It Dv BSDCONF_STRICT_EQUALS
Equals must be part of the directive
.Pq no whitespace before or after
to be considered a delimiter between directive and value.
Required by file formats whose readers reject whitespace around the equals
sign,
such as the
.Fx
boot loader's processing of
.Xr loader.conf 5 .
.It Dv BSDCONF_OPERATOR_EQUALS
Recognize
.Xr make 1
style assignment modifiers
.Po
.Ql += ,
.Ql ?= ,
.Ql := ,
and
.Ql !=
.Pc
and split them off the tail of the directive.
The parsed operator is reported through the
.Va op
member of the matched option
.Pq one of Dv BSDCONF_OP_ASSIGN , BSDCONF_OP_APPEND , BSDCONF_OP_COND , BSDCONF_OP_EXPAND , No or Dv BSDCONF_OP_SHELL .
.El
.Pp
The
.Fa options
struct array pointer can be NULL and every directive will run the
.Fn unknown
function argument.
.Pp
The directive for each bsdconf_option item in the
.Fn bsdconf_parse
options argument is matched against each parsed directive using
.Xr fnmatch 3
until a match is found.
If a match is found,
the
.Fn parse
function for that bsdconf_option directive is run with the line number,
directive,
and value.
Otherwise if no match,
the
.Fn unknown
function is run
.Pq with the same arguments .
When
.Dv BSDCONF_OPERATOR_EQUALS
is set,
.Fn unknown
receives a non-NULL
.Fa option
whose
.Va op
member holds the statement's assignment operator
.Pq there is no matched options-array slot to hang it on ;
otherwise
.Fa option
may be
.Dv NULL .
.Pp
If either
.Fn parse
or
.Fn unknown
return non-zero,
.Fn bsdconf_parse
aborts reading the file and returns the error value to its caller.
.Pp
A value normally ends at the first unescaped newline,
but a statement may span multiple lines:
a backslash immediately preceding the newline continues the value on the
next line,
in the manner of
.Xr make 1
.Pq essential to Pa make.conf and its siblings .
The backslash-newline pairs are removed from the value delivered to the
callbacks
.Pq surrounding whitespace is preserved verbatim ,
and reported line numbers are those of each statement's first line.
.Xr bsdconf_put 3
recognizes the same continuations when locating a value;
rewriting a continued value replaces all of its lines with the single new
value.
.Pp
.Fn bsdconf_fparse
is identical to
.Fn bsdconf_parse
except that it operates on an already-open file descriptor
.Fa fd ,
which remains open on return
.Pq the caller retains ownership .
This allows the caller to constrain the process
.Pq for example with Xr capsicum 4
before parsing begins.
The scanner requires a seekable descriptor;
input that cannot seek
.Pq a pipe or socket, standard input included
is detected up front and transparently spooled through
.Fn bsdconf_spool ,
at the cost of one transient copy of the data.
.Pp
.Fn bsdconf_spool
copies the remaining contents of
.Fa fd
to an unlinked temporary file
.Pq created with Xr tmpfile 3
and returns a seekable descriptor referencing it,
which the caller must
.Xr close 2
.Pq the backing storage is reclaimed then .
It is exported for callers that must adapt non-seekable input themselves
before revoking their own ability to create files,
as
.Xr sysconf 8
does before entering its
.Xr capsicum 4
sandbox.
.Pp
.Fn bsdconf_get_option
traverses the options-array and returns the option that matches via
.Xr strcmp 3 ,
or
.Dv NULL
if none matches.
.Pp
.Fn bsdconf_unquote
strips one layer of surrounding double-quotes from
.Fa value
in place and returns it.
Parsed values retain their quotes so that data round-trips losslessly;
this helper is for display and comparison purposes.
.Sh RETURN VALUES
.Fn bsdconf_parse
and
.Fn bsdconf_fparse
return zero on success;
otherwise -1
.Pq or the non-zero result of a callback
is returned and the global variable
.Va errno
is set to indicate the error.
.Fn bsdconf_spool
returns a new seekable file descriptor on success;
otherwise -1 with
.Va errno
set to indicate the error.
.Fn bsdconf_get_option
returns a pointer to the matching option,
or
.Dv NULL
when none matches.
.Sh EXAMPLES
Read two known directives from a
.Ql name=value
file,
routing every statement through a callback:
.Bd -literal -offset indent
#include <err.h>
#include <stdio.h>
#include <bsdconf.h>

static int
show(struct bsdconf_option *option, uint32_t line,
    char *directive, char *value)
{
	printf("%u: %s is %s\en", line, directive,
	    bsdconf_unquote(value));
	return (0);
}

static struct bsdconf_option options[] = {
	{ .directive = "hostname", .parse = show },
	{ .directive = "timeout",  .parse = show },
	{ .directive = NULL }
};

int
main(void)
{
	if (bsdconf_parse(options, "/usr/local/etc/myapp.conf",
	    NULL, BSDCONF_BREAK_ON_EQUALS) != 0)
		err(1, "myapp.conf");
	return (0);
}
.Ed
.Pp
Callbacks own the semantics,
so a directive that legitimately repeats is accumulated rather than
overwritten;
no format descriptor is involved.
The file here is Apache-style
.Pq space-separated, no equals sign ,
so
.Dv BSDCONF_BREAK_ON_EQUALS
is simply omitted:
.Bd -literal -offset indent
static char *servers[16];
static size_t nservers;

static int
addserver(struct bsdconf_option *option, uint32_t line,
    char *directive, char *value)
{
	if (nservers >= 16 ||
	    (servers[nservers] = strdup(value)) == NULL)
		return (-1); /* abort the parse */
	nservers++;
	return (0);
}

static struct bsdconf_option cumulative[] = {
	{ .directive = "server", .parse = addserver },
	{ .directive = NULL }
};

	...
	if (bsdconf_parse(cumulative, path, NULL, 0) != 0)
		err(1, "%s", path);
.Ed
.Sh SEE ALSO
.Xr bsdconf_format 3 ,
.Xr bsdconf_put 3 ,
.Xr loader.conf 5 ,
.Xr sysctl.conf 5 ,
.Xr sysconf 8
.Sh HISTORY
The
.Nm
library first appeared in
.Fx 16.0 .
It supersedes the
.Nm figpar
library which first appeared in
.Fx 10.2
and was retired to the ports tree.
.Sh AUTHORS
.An Devin Teske Aq Mt dteske@FreeBSD.org
.An Faraz Vahedi Aq Mt kfv@FreeBSD.org
.Sh BUGS
This is the first implementation of the library,
and the interface may be subject to refinement.
.Pp
Write-path limitations for cumulative directives are discussed in the
.Sx LIMITATIONS
section of
.Xr bsdconf_put 3 .
.Sh SECURITY CONSIDERATIONS
Parsing allocates buffers sized by the longest directive and value
encountered rather than by untrusted length fields,
and
.Fn bsdconf_fparse
accepts an already-open descriptor precisely so that a caller may
sandbox itself
.Pq for example with Xr capsicum 4
before touching untrusted input,
as
.Xr sysconf 8
does for its read-only operations.
Write-path hardening is documented in
.Xr bsdconf_put 3 .