.\"	$Id: mandoc_html.3,v 1.10 2017/07/15 17:57:51 schwarze Exp $
.\"
.\" Copyright (c) 2014, 2017 Ingo Schwarze <schwarze@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.Dd $Mdocdate: July 15 2017 $
.Dt MANDOC_HTML 3
.Os
.Sh NAME
.Nm mandoc_html
.Nd internals of the mandoc HTML formatter
.Sh SYNOPSIS
.In "html.h"
.Ft void
.Fn print_gen_decls "struct html *h"
.Ft void
.Fn print_gen_head "struct html *h"
.Ft struct tag *
.Fo print_otag
.Fa "struct html *h"
.Fa "enum htmltag tag"
.Fa "const char *fmt"
.Fa ...
.Fc
.Ft void
.Fo print_tagq
.Fa "struct html *h"
.Fa "const struct tag *until"
.Fc
.Ft void
.Fo print_stagq
.Fa "struct html *h"
.Fa "const struct tag *suntil"
.Fc
.Ft void
.Fo print_text
.Fa "struct html *h"
.Fa "const char *word"
.Fc
.Ft char *
.Fo html_make_id
.Fa "const struct roff_node *n"
.Fc
.Ft int
.Fo html_strlen
.Fa "const char *cp"
.Fc
.Sh DESCRIPTION
The mandoc HTML formatter is not a formal library.
However, as it is compiled into more than one program, in particular
.Xr mandoc 1
and
.Xr man.cgi 8 ,
and because it may be security-critical in some contexts,
some documentation is useful to help to use it correctly and
to prevent XSS vulnerabilities.
.Pp
The formatter produces HTML output on the standard output.
Since proper escaping is usually required and best taken care of
at one central place, the language-specific formatters
.Po
.Pa *_html.c ,
see
.Sx FILES
.Pc
are not supposed to print directly to
.Dv stdout
using functions like
.Xr printf 3 ,
.Xr putc 3 ,
.Xr puts 3 ,
or
.Xr write 2 .
Instead, they are expected to use the output functions declared in
.Pa html.h
and implemented as part of the main HTML formatting engine in
.Pa html.c .
.Ss Data structures
These structures are declared in
.Pa html.h .
.Bl -tag -width Ds
.It Vt struct html
Internal state of the HTML formatter.
.It Vt struct tag
One entry for the LIFO stack of HTML elements.
Members are
.Fa "enum htmltag tag"
and
.Fa "struct tag *next" .
.El
.Ss Private interface functions
The function
.Fn print_gen_decls
prints the opening
.Ao Pf \&? Ic xml ? Ac
and
.Aq Pf \&! Ic DOCTYPE
declarations required for the current document type.
.Pp
The function
.Fn print_gen_head
prints the opening
.Aq Ic META
and
.Aq Ic LINK
elements for the document
.Aq Ic HEAD ,
using the
.Fa style
member of
.Fa h
unless that is
.Dv NULL .
It uses
.Fn print_otag
which takes care of properly encoding attributes,
which is relevant for the
.Fa style
link in particular.
.Pp
The function
.Fn print_otag
prints the start tag of an HTML element with the name
.Fa tag ,
optionally including the attributes specified by
.Fa fmt .
If
.Fa fmt
is the empty string, no attributes are written.
Each letter of
.Fa fmt
specifies one attribute to write.
Most attributes require one
.Va char *
argument which becomes the value of the attribute.
The arguments have to be given in the same order as the attribute letters.
If an argument is
.Dv NULL ,
the respective attribute is not written.
.Bl -tag -width 1n -offset indent
.It Cm c
Print a
.Cm class
attribute.
This attribute letter can optionally be followed by the modifier letter
.Cm T .
In that case, a
.Cm title
attribute with the same value is also printed.
.It Cm h
Print a
.Cm href
attribute.
This attribute letter can optionally be followed by a modifier letter.
If followed by
.Cm R ,
it formats the link as a local one by prefixing a
.Sq #
character.
If followed by
.Cm I ,
it interpretes the argument as a header file name
and generates a link using the
.Xr mandoc 1
.Fl O Cm includes
option.
If followed by
.Cm M ,
it takes two arguments instead of one, a manual page name and
section, and formats them as a link to a manual page using the
.Xr mandoc 1
.Fl O Cm man
option.
.It Cm i
Print an
.Cm id
attribute.
.It Cm \&?
Print an arbitrary attribute.
This format letter requires two
.Vt char *
arguments, the attribute name and the value.
The name must not be
.Dv NULL .
.It Cm s
Print a
.Cm style
attribute.
If present, it must be the last format letter.
In contrast to the other format letters, this one does not yet
print the value and does not take an argument.
Instead, the rest of the format string consists of pairs of
argument type letters and style name letters.
.El
.Pp
Argument type letters each require one argument as follows:
.Bl -tag -width 1n -offset indent
.It Cm h
Requires one
.Vt int
argument, interpreted as a horizontal length in units of
.Dv SCALE_EN .
.It Cm s
Requires one
.Vt char *
argument, used as a style value.
.It Cm u
Requires one
.Vt struct roffsu *
argument, used as a length.
.It Cm w
Requires one
.Vt char *
argument, interpreted as an
.Xr mdoc 7 Ns -style
width specifier.
If the argument is
.Dv NULL ,
nothing is printed for this pair.
.Pp
The
.Cm w
argument type letter can optionally be followed by one, two, or three
modifier letters.
The modifier
.Cm *
suppresses printing of the pair if the argument matches 6n.
The modifier
.Cm +
increases the width by 20% to make even bold text fit
and adds three units for padding between columns.
The modifier
.Cm \-
makes the width negative by multiplying it with \-1.
.El
.Pp
Style name letters decide what to do with the preceding argument:
.Bl -tag -width 1n -offset indent
.It Cm h
Set
.Cm height
to the given length.
.It Cm i
Set
.Cm text-indent
to the given length.
.It Cm l
Set
.Cm margin-left
to the given length.
.It Cm w
Set
.Cm width
to the given length.
.It Cm W
Set
.Cm min-width
to the given length.
.It Cm \&?
The special pair
.Cm s?
requires two
.Vt char *
arguments.
The first is the style name, the second its value.
The style name must not be
.Dv NULL .
.El
.Pp
.Fn print_otag
uses the private function
.Fn print_encode
to take care of HTML encoding.
If required by the element type, it remembers in
.Fa h
that the element is open.
The function
.Fn print_tagq
is used to close out all open elements up to and including
.Fa until ;
.Fn print_stagq
is a variant to close out all open elements up to but excluding
.Fa suntil .
.Pp
The function
.Fn print_text
prints HTML element content.
It uses the private function
.Fn print_encode
to take care of HTML encoding.
If the document has requested a non-standard font, for example using a
.Xr roff 7
.Ic \ef
font escape sequence,
.Fn print_text
wraps
.Fa word
in an HTML font selection element using the
.Fn print_otag
and
.Fn print_tagq
functions.
.Pp
The function
.Fn html_make_id
takes a node containing one or more text children
and returns a newly allocated string containing the concatenation
of the child strings, with blanks replaced by underscores.
If the node
.Fa n
contains any non-text child node,
.Fn html_make_id
returns
.Dv NULL
instead.
The caller is responsible for freeing the returned string.
.Pp
The function
.Fn html_strlen
counts the number of characters in
.Fa cp .
It is used as a crude estimate of the width needed to display a string.
.Pp
The functions
.Fn print_eqn ,
.Fn print_tbl ,
and
.Fn print_tblclose
are not yet documented.
.Sh FILES
.Bl -tag -width mandoc_aux.c -compact
.It Pa main.h
declarations of public functions for use by the main program,
not yet documented
.It Pa html.h
declarations of data types and private functions
for use by language-specific HTML formatters
.It Pa html.c
main HTML formatting engine and utility functions
.It Pa mdoc_html.c
.Xr mdoc 7
HTML formatter
.It Pa man_html.c
.Xr man 7
HTML formatter
.It Pa tbl_html.c
.Xr tbl 7
HTML formatter
.It Pa eqn_html.c
.Xr eqn 7
HTML formatter
.It Pa out.h
declarations of data types and private functions
for shared use by all mandoc formatters,
not yet documented
.It Pa out.c
private functions for shared use by all mandoc formatters
.It Pa mandoc_aux.h
declarations of common mandoc utility functions, see
.Xr mandoc 3
.It Pa mandoc_aux.c
implementation of common mandoc utility functions
.El
.Sh SEE ALSO
.Xr mandoc 1 ,
.Xr mandoc 3 ,
.Xr man.cgi 8
.Sh AUTHORS
.An -nosplit
The mandoc HTML formatter was written by
.An Kristaps Dzonsons Aq Mt kristaps@bsd.lv .
It is maintained by
.An Ingo Schwarze Aq Mt schwarze@openbsd.org ,
who also wrote this manual.