.\"	Id: mansearch.3,v 1.4 2015/03/27 17:37:25 schwarze Exp 
.\"
.\" Copyright (c) 2014 Ingo Schwarze <schwarze@openbsd.org>
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.Dd March 27, 2015
.Dt MANSEARCH 3
.Os
.Sh NAME
.Nm mansearch ,
.Nm mansearch_setup
.Nd search manual page databases
.Sh SYNOPSIS
.In stdint.h
.In manconf.h
.In mansearch.h
.Ft int
.Fo mansearch_setup
.Fa "int start"
.Fc
.Ft int
.Fo mansearch
.Fa "const struct mansearch *search"
.Fa "const struct manpaths *paths"
.Fa "int argc"
.Fa "char *argv[]"
.Fa "const char *outkey"
.Fa "struct manpage **res"
.Fa "size_t *sz"
.Fc
.Sh DESCRIPTION
The
.Fn mansearch
function returns information about manuals matching a search query from a
.Xr mandoc.db 5
SQLite3 database.
.Pp
The query arguments are as follows:
.Bl -tag -width Ds
.It Fa "const struct mansearch *search"
Search options, defined in
.In mansearch.h .
.It Fa "const struct manpaths *paths"
Directories to be searched, defined in
.In manconf.h .
.It Fa "int argc" , "char *argv[]"
Search criteria, usually taken from the command line.
.El
.Pp
The
.Fa "const char *outkey"
selects which data to return in the
.Va output
field of the
.Fa res
structures.
It takes any of the macro keys defined in
.Pa mansearch_const.c
and described in
.Xr apropos 1 .
.Pp
The output arguments are as follows:
.Bl -tag -width Ds
.It Fa "struct manpage **res"
Returns a pointer to an array of result structures defined in
.In mansearch.h .
The user is expected to call
.Xr free 3
on the
.Va file ,
.Va names ,
and
.Va output
fields of all structures, as well as the
.Fa res
array itself.
.It Fa "size_t *sz"
Returns the number of result structures contained in
.Fa res .
.El
.Pp
To speed up searches, the
.Fn mansearch_setup
function can optionally be called with a
.Fa start
argument of 1 before
.Fn mansearch
to set up an SQLite3 pagecache.
If it was called, it has to be called again with a
.Fa start
argument of 0 after the last call to
.Fn mansearch
to release the memory used for the pagecache.
.Sh IMPLEMENTATION NOTES
For each manual page tree, the search is done in two steps.
In the first step, a list of pages matching the search criteria is built.
In the second step, the requested information about these pages is
retrieved from the database and assembled into the
.Fa res
array.
.Pp
All function mentioned here are defined in the file
.Pa mansearch.c .
No functions except
.Fn mansearch
and
.Fn sql_statement
build any SQL code, and no functions except
.Fn mansearch ,
.Fn buildnames ,
and
.Fn buildoutput
execute it.
.Ss Finding matches
The query is built using the following grammar:
.Bd -literal -offset indent
<query>     ::=	"SELECT * FROM mpages WHERE" <condition>
<condition> ::=	"(" <condition> ")" |
		<condition> "OR" <condition> |
		<condition> "AND" <condition> |
		"desc" <operator> "?" |
		"id IN (SELECT pageid FROM" <subquery> ")"
<subquery>  ::=	"names WHERE name" <operator> "?" |
		"keys WHERE key" <operator> "? AND bits & ?"
<operator>  ::=	"MATCH" | "REGEXP"
.Ed
.Pp
The MATCH and REGEXP operators are implemented by the functions
.Fn sql_match
and
.Fn sql_regexp ,
respectively.
This is required because SQLite3 natively neither supports
case-insensitive substring matching nor regular expression matching,
but only string identity, shell globbing, and the weird home-brewed
LIKE operator.
.Pp
Command line parsing is done by the function
.Fn exprcomp
building a singly linked list of
.Vt expr
structures, using the helper functions
.Fn exprterm
and
.Fn exprspec .
The resulting SQL statement is assembled by the function
.Fn sql_statement
and evaluated in the main loop of the
.Fn mansearch
function.
.Ss Assembling the results
The names, sections, and architectures of the manuals found
are assembled into the
.Va names
field of the result structure by the function
.Fn buildnames ,
using the following query:
.Pp
.Dl "SELECT * FROM mlinks WHERE pageid=? ORDER BY sec, arch, name"
.Pp
If the
.Fa outkey
differs from
.Qq Ic \&Nd ,
the requested output data is assembled into the
.Va output
field of the result structure by the function
.Fn buildoutput ,
using the following query:
.Pp
.Dl "SELECT * FROM keys WHERE pageid=? AND bits & ?"
.Sh FILES
.Bl -tag -width mandoc.db -compact
.It Pa mandoc.db
The manual page database.
.El
.Sh EXAMPLES
The simplest invocation
.Pp
.Dl apropos keyword
.Pp
results in the following SQL query:
.Bd -literal
SELECT * FROM mpages WHERE (
  id IN (SELECT pageid FROM names WHERE name MATCH 'keyword') OR
  desc MATCH 'keyword'
);
.Ed
.Pp
A more complicated request like
.Pp
.Dl apropos -s 2 Nm,Xr=getuid
.Pp
results in:
.Bd -literal
SELECT * FROM mpages WHERE (
  id IN (SELECT pageid FROM names WHERE name MATCH 'getuid') OR
  id IN (SELECT pageid FROM keys WHERE key MATCH 'getuid' AND bits & 4)
) AND id IN (SELECT pageid FROM keys WHERE key REGEXP '^2$' AND bits & 2);
.Ed
.Sh SEE ALSO
.Xr apropos 1 ,
.Xr mandoc.db 5 ,
.Xr makewhatis 8
.Sh HISTORY
The
.Fn mansearch
subsystem first appeared in
.Ox 5.6 .
.Sh AUTHORS
.An -nosplit
A module to search manual page databases was first written by
.An Kristaps Dzonsons Aq Mt kristaps@bsd.lv
in 2011, at first using the Berkeley DB;
he rewrote it for SQLite3 in 2012.
The current version received major changes from
.An Ingo Schwarze Aq Mt schwarze@openbsd.org .