lowdown - Man Page

simple markdown translator library

Library

library “liblowdown”

Synopsis

#include <sys/queue.h>
#include <stdio.h>
#include <lowdown.h>

struct lowdown_metadata
struct lowdown_node
struct lowdown_opts

Description

This library parses lowdown(5) into various output formats.

The library consists first of a high-level interface consisting of lowdown_buf(3), lowdown_buf_diff(3), lowdown_file(3), and lowdown_file_diff(3).

The high-level functions interface with low-level functions that perform parsing and formatting. These consist of lowdown_doc_new(3), lowdown_doc_parse(3), and lowdown_doc_free(3) for parsing lowdown(5) documents into an abstract syntax tree.

The front-end functions for freeing, allocation, and rendering are as follows.

To compile and link, use pkg-config(1):

% cc `pkg-config --cflags lowdown` -c -o sample.o sample.c
% cc -o sample sample.o `pkg-config --libs lowdown`

Pledge Promises

The lowdown library is built to operate in security-sensitive environments, such as those using pledge(2) on OpenBSD. The only promise required is stdio for lowdown_file_diff(3) and lowdown_file(3): both require access to the stream for reading input.

Types

All lowdown functions use one or more of the following structures.

The struct lowdown_opts structure manage features. It has the following fields:

unsigned int feat

Features used during the parse. This bit-field may have the following bits OR'd:

LOWDOWN_ATTRS

Parse PHP extra link, header, and image attributes.

LOWDOWN_AUTOLINK

Parse http, https, ftp, mailto, and relative links or link fragments.

LOWDOWN_COMMONMARK

Tighten input parsing to the CommonMark specification. This also uses the first ordered list value instead of starting all lists at one. This feature is experimental and incomplete.

LOWDOWN_DEFLIST

Parse PHP extra definition lists. This is currently constrained to single-key lists.

LOWDOWN_FENCED

Parse GFM fenced (language-specific) code blocks.

LOWDOWN_FOOTNOTES

Parse MMD style footnotes. This only supports the referenced footnote style, not the "inline" style.

LOWDOWN_HILITE

Parse highlit sequences. This are disabled by default because it may be erroneously interpreted as section headers.

LOWDOWN_IMG_EXT

Deprecated. Use LOWDOWN_ATTRS instead.

LOWDOWN_MANTITLE

Recognise manpage titles in Pandoc metadata title lines. Only applicable if LOWDOWN_METADATA is also provided. Manpages titles must begin with a non-empty title followed by an open parenthesis, digit or "n", optional letters after, then a closing parenthesis. This may be optionally followed by a source and, if a vertical bar is detected, the content after as the volume. These are passed to the renderers as the title, volume, and optionally source and volume metadata key-value pairs. The original title is not recoverable.

LOWDOWN_MATH

Parse mathematics equations.

LOWDOWN_METADATA

Parse in-document metadata.

LOWDOWN_NOCODEIND

Do not parse indented content as code blocks.

LOWDOWN_NOINTEM

Do not parse emphasis within words.

LOWDOWN_STRIKE

Parse strikethrough sequences.

LOWDOWN_SUPER

Parse super-scripts. This accepts foo^bar, which puts the parts following the caret until whitespace in superscripts; or foo^(bar), which puts only the parts in parenthesis.

LOWDOWN_TABLES

Parse GFM tables.

LOWDOWN_TASKLIST

Parse GFM task list items.

The default value is zero (none).

unsigned int oflags

Features used by the output generators. This bit-field may have the following enabled. Note that bits are by definition specific to an output type.

For LOWDOWN_HTML:

LOWDOWN_HTML_ESCAPE

If LOWDOWN_HTML_SKIP_HTML has not been set, escapes in-document HTML so that it is rendered as opaque text.

LOWDOWN_HTML_HARD_WRAP

Retain line-breaks within paragraphs.

LOWDOWN_HTML_HEAD_IDS

Have an identifier written with each header element consisting of an HTML-escaped version of the header contents.

LOWDOWN_HTML_OWASP

When escaping text, be extra paranoid in following the OWASP suggestions for which characters to escape.

LOWDOWN_HTML_NUM_ENT

Convert, when possible, HTML entities to their numeric form. If not set, the entities are used as given in the input.

LOWDOWN_HTML_SKIP_HTML

Do not render in-document HTML at all.

LOWDOWN_HTML_TITLEBLOCK

If used with LOWDOWN_STANDALONE, output a Pandoc-style title block. This is a <header id="title-block-header"> element right after the opening <body> containing elements for specified title, author(s), and date. These are <h1> and <p> elements, respectively, with classes set to what's being output (title, etc.). At least one of these must be specified for the title block to be output.

For LOWDOWN_GEMINI, there are several flags for controlling link placement. By default, links (images, autolinks, and links) are queued when specified in-line then emitted in a block sequence after the nearest block element.

LOWDOWN_GEMINI_LINK_END

Emit the queue of links at the end of the document instead of after the nearest block element.

LOWDOWN_GEMINI_LINK_IN

Render all links within the flow of text. This will cause breakage when nested links, such as images within links, links in blockquotes, etc. It should not be used unless in carefully crafted documents.

LOWDOWN_GEMINI_LINK_NOREF

Do not format link labels. Takes precedence over LOWDOWN_GEMINI_LINK_ROMAN.

LOWDOWN_GEMINI_LINK_ROMAN

When formatting link labels, use lower-case Roman numerals instead of the default lowercase hexavigesimal (i.e., “a”, “b”, ..., “aa”, “ab”, ...).

LOWDOWN_GEMINI_METADATA

Print metadata as the canonicalised key followed by a colon then the value, each on one line (newlines replaced by spaces). The metadata block is terminated by a double newline. If there is no metadata, this does nothing.

There may only be one of LOWDOWN_GEMINI_LINK_END or LOWDOWN_GEMINI_LINK_IN. If both are specified, the latter is unset.

For LOWDOWN_FODT:

LOWDOWN_ODT_SKIP_HTML

Do not render in-document HTML at all. Text within HTML elements remains.

For LOWDOWN_LATEX:

LOWDOWN_LATEX_NUMBERED

Use the default numbering scheme for sections, subsections, etc. If not specified, these are inhibited.

LOWDOWN_LATEX_SKIP_HTML

Do not render in-document HTML at all. Text within HTML elements remains.

And for LOWDOWN_MAN and LOWDOWN_NROFF:

LOWDOWN_NROFF_GROFF

Use GNU extensions (i.e., for groff(1)) when rendering output. The groff arguments must include -mpdfmark for formatting links with LOWDOWN_MAN or -mspdf instead of -ms for LOWDOWN_NROFF. Applies to the LOWDOWN_MAN and LOWDOWN_NROFF output types.

LOWDOWN_NROFF_NUMBERED

Use numbered sections if LOWDOWON_NROFF_GROFF is not specified. Only applies to the LOWDOWN_NROFF output type.

LOWDOWN_NROFF_SKIP_HTML

Do not render in-document HTML at all. Text within HTML elements remains.

LOWDOWN_NROFF_SHORTLINK

Render link URLs in short form. Applies to images, autolinks, and regular links. Only in LOWDOWN_MAN or when LOWDOWN_NROFF_GROFF is not specified.

LOWDOWN_NROFF_NOLINK

Don't show links at all if they have embedded text. Applies to images and regular links. Only in LOWDOWN_MAN or when LOWDOWN_NROFF_GROFF is not specified.

For LOWDOWN_TERM:

LOWDOWN_TERM_NOANSI

Don't apply ANSI style codes at all. This implies LOWDOWN_TERM_NOCOLOUR.

LOWDOWN_TERM_NOCOLOUR

Don't apply ANSI colour codes. This will still show underline, bold, etc. This should not be used in difference mode, as the output will make no sense.

LOWDOWN_TERM_NOLINK

Don't show links at all. Applies to images and regular links: autolinks are still shown. This may be combined with LOWDOWN_TERM_SHORTLINK to also shorten autolinks.

LOWDOWN_TERM_SHORTLINK

Render link URLs in short form. Applies to images, autolinks, and regular links. This may be combined with LOWDOWN_TERM_NOLINK to only show shortened autolinks.

For any mode, you may specify:

LOWDOWN_SMARTY

Don't use smart typography formatting.

LOWDOWN_STANDALONE

Emit a full document instead of a document fragment. This envelope is largely populated from metadata if LOWDOWN_METADATA was provided as an option or as given in meta or metaovr.

size_t maxdepth

The maximum parse depth before the parser exits. Most documents will have a parse depth in the single digits.

size_t cols

For LOWDOWN_TERM, the "soft limit" for width of terminal output not including margins. If zero, 80 shall be used.

size_t hmargin

For LOWDOWN_TERM, the left margin (space characters).

size_t vmargin

For LOWDOWN_TERM, the top/bottom margin (newlines).

enum lowdown_type type

May be set to LOWDOWN_HTML for HTML5 output, LOWDOWN_LATEX for LaTeX, LOWDOWN_MAN for -man macros, LOWDOWN_FODT for “flat” OpenDocument, LOWDOWN_TERM for ANSI-compatible UTF-8 terminal output, LOWDOWN_GEMINI for the Gemini format, or LOWDOWN_NROFF for -ms macros. The LOWDOWN_TREE type causes a debug tree to be written.

struct lowdown_opts_odt odt

If type is LOWDOWN_FODT, this contains const char *sty, which is either NULL or the OpenDocument styles used when creating standalone documents. If NULL, the default styles are used.

char **meta

An array of metadata key-value pairs or NULL. Each pair must appear as if provided on one line (or multiple lines) of the input, including the terminating newline character. If not consisting of a valid pair (e.g., no newline, no colon), then it is ignored. When processed, these values are overridden by those in the document (if LOWDOWN_METADATA is specified) or by those in metaovr.

size_t metasz

Number of pairs in metaovr.

char **metaovr

See meta. The difference is that metaovr is applied after meta and in-document metadata, so it overrides prior values.

size_t metaovrsz

Number of pairs in metaovr.

Another common structure is struct lowdown_metadata, which is used to hold parsed (and output-formatted) metadata keys and values if LOWDOWN_METADATA was provided as an input bit. This structure consists of the following fields:

char *key

The metadata key in its lowercase, canonical form.

char *value

The metadata value as rendered in the current output format. This may be an empty string.

The abstract syntax tree is encoded in struct lowdown_node, which consists of the following.

enum lowdown_rndrt type

The node type. (Described below.)

size_t id

An identifier unique within the document. This can be used as a table index since the number is assigned from a monotonically increasing point during the parse.

struct lowdown_node *parent

The parent of the node, or NULL at the root.

enum lowdown_chng chng

Change tracking: whether this node was inserted (LOWDOWN_CHNG_INSERT), deleted (LOWDOWN_CHNG_DELETE), or neither (LOWDOWN_CHNG_NONE).

struct lowdown_nodeq children

A possibly-empty list of child nodes.

<anon union>

An anonymous union of type-specific structures. See below for a description of each one.

The nodes may be one of the following types, with default rendering in HTML5 to illustrate functionality.

LOWDOWN_BLOCKCODE

A block-level (and possibly language-specific) snippet of code. Described by the <pre><code> elements.

LOWDOWN_BLOCKHTML

A block-level snippet of HTML. This is simply opaque HTML content. (Only if configured during parse.)

LOWDOWN_BLOCKQUOTE

A block-level quotation. Described by the <blockquote> element.

LOWDOWN_CODESPAN

A snippet of code. Described by the <code> element.

LOWDOWN_DOC_HEADER

A header with data gathered from document metadata (if configured). Described by the <head> element. (Only if configured during parse.)

LOWDOWN_DOUBLE_EMPHASIS

Bold (or otherwise notable) content. Described by the <strong> element.

LOWDOWN_EMPHASIS

Italic (or otherwise notable) content. Described by the <em> element.

LOWDOWN_ENTITY

An HTML entity, which may either be named or numeric.

LOWDOWN_FOOTNOTE

A footnote. (Only if configured during parse.)

LOWDOWN_HEADER

A block-level header. Described (in the HTML case) by one of <h1> through <h6>.

LOWDOWN_HIGHLIGHT

Marked test. Described by the <mark> element. (Only if configured during parse.)

LOWDOWN_HRULE

A horizontal line. Described by <hr>.

LOWDOWN_IMAGE

An image. Described by the <img> element.

LOWDOWN_LINEBREAK

A hard line-break within a block context. Described by the <br> element.

LOWDOWN_LINK

A link to external media. Described by the <a> element.

LOWDOWN_LINK_AUTO

Like LOWDOWN_LINK, except inferred from text content. Described by the <a> element. (Only if configured during parse.)

LOWDOWN_LIST

A block-level list enclosure. Described by <ul> or <ol>.

LOWDOWN_LISTITEM

A block-level list item, always appearing within a LOWDOWN_LIST. Described by <li>.

LOWDOWN_MATH_BLOCK

A block (or inline) of mathematical text in LaTeX format. Described within \[xx\] or \(xx\). This is usually (in HTML) externally handled by a JavaScript renderer. (Only if configured during parse.)

LOWDOWN_META

Meta-data keys and values. (Only if configured during parse.) These are described by elements in the <head> element.

LOWDOWN_NORMAL_TEXT

Normal text content.

LOWDOWN_PARAGRAPH

A block-level paragraph. Described by the <p> element.

LOWDOWN_RAW_HTML

An inline of raw HTML. (Only if configured during parse.)

LOWDOWN_ROOT

The root of the document. This is always the topmost node, and the only node where the parent field is NULL.

LOWDOWN_STRIKETHROUGH

Content struck through. Described by the <del> element. (Only if configured during parse.)

LOWDOWN_SUPERSCRIPT

A superscript. Described by the <sup> element. (Only if configured during parse.)

LOWDOWN_TABLE_BLOCK

A table block. Described by <table>. (Only if configured during parse.)

LOWDOWN_TABLE_BODY

A table body section. Described by <tbody>. Parent is always LOWDOWN_TABLE_BLOCK. (Only if configured during parse.)

LOWDOWN_TABLE_CELL

A table cell. Described by <td> or <th> if in the header. Parent is always LOWDOWN_TABLE_ROW. (Only if configured during parse.)

LOWDOWN_TABLE_HEADER

A table header section. Described by <thead>. Parent is always LOWDOWN_TABLE_BLOCK. (Only if configured during parse.)

LOWDOWN_TABLE_ROW

A table row. Described by <tr>. Parent is always LOWDOWN_TABLE_HEADER or LOWDOWN_TABLE_BODY. (Only if configured during parse.)

LOWDOWN_TRIPLE_EMPHASIS

Combination of LOWDOWN_EMPHASIS and LOWDOWN_DOUBLE_EMPHASIS.

The following anonymous union structures correspond to certain nodes. Note that all buffers may be zero-length.

rndr_autolink

For LOWDOWN_LINK_AUTO, the link address as link and the link type type, which may be one of HALINK_EMAIL for e-mail links and HALINK_NORMAL otherwise. Any buffer may be empty-sized.

rndr_blockcode

For LOWDOWN_BLOCKCODE, the opaque text of the block and the optional lang of the code language.

rndr_blockhtml

For LOWDOWN_BLOCKHTML, the opaque HTML text.

rndr_codespan

The opaque text of the contents.

rndr_definition

For LOWDOWN_DEFINITION, containing flags that may be HLIST_FL_BLOCK if the definition list should be interpreted as containing block elements.

rndr_entity

For LOWDOWN_ENTITY, the entity text.

rndr_header

For LOWDOWN_HEADER, the level of the header starting at zero (this value is relative to the metadata base header level, defaulting to one), optional space-separated class list attr_cls, and optional single identifier attr_id.

rndr_image

For LOWDOWN_IMAGE, the image address link, the image title title, dimensions NxN (width by height) in dims, and alternate text alt. CSS in-line style for width and height may be given in attr_width and/or attr_height, and a space-separated list of classes may be in attr_cls and a single identifier may be in attr_id.

rndr_link

Like rndr_autolink, but without a type and further defining an optional link title title, optional space-separated class list attr_cls, and optional single identifier attr_id.

rndr_list

For LOWDOWN_LIST, consists of a bitfield flags that may be set to HLIST_FL_ORDERED for an ordered list and HLIST_FL_UNORDERED for an unordered one. If HLIST_FL_BLOCK is set, the list should be output as if items were separate blocks. The start value for HLIST_FL_ORDERED is the starting list item position, which is one by default and never zero. The items is the number of list items.

rndr_listitem

For LOWDOWN_LISTITEM, consists of a bitfield flags that may be set to HLIST_FL_ORDERED for an ordered list, HLIST_FL_UNORDERED for an unordered list, HLIST_FL_DEF for definition list data, HLIST_FL_CHECKED or HLIST_FL_UNCHECKED for an unordered “task” list element, and/or HLIST_FL_BLOCK for list item output as if containing block elements. The HLIST_FL_BLOCK should not be used: use the parent list (or definition list) flags for this. The num is the index in a HLIST_FL_ORDERED list. It is monotonically increasing with each item in the list, starting at the start variable given in struct rndr_list.

rndr_math

For LOWDOWN_MATH, the mode of display in blockmode: if 1, in-line math; if 2, multi-line. The opaque equation, which is assumed to be in LaTeX format, is in the opaque text.

rndr_meta

Each LOWDOWN_META key-value pair is represented. The keys are lower-case without spaces or non-ASCII characters. If provided, enclosed nodes may consist only of LOWDOWN_NORMAL_TEXT and LOWDOWN_ENTITY.

rndr_normal_text

The basic text content for LOWDOWN_NORMAL_TEXT. If flags is set to HTEXT_ESCAPED, the text may be escaped for output, but may not be altered by any smart typography or similar (it should be passed as-is).

rndr_paragraph

For LOWDOWN_PARAGRAPH, species how many lines the paragraph has in the input file and beoln, set to non-zero if the paragraph ends with an empty line instead of a breaking block element.

rndr_raw_html

For LOWDOWN_RAW_HTML, the opaque HTML text.

rndr_table

For LOWDOWN_TABLE_BLOCK, the number of columns in each row or header row. The number of columns in rndr_table, rndr_table_header, and rndr_table_cell are the same.

rndr_table_cell

For LOWDOWN_TABLE_CELL, the current col column number out of columns. See rndr_table_header for a description of the bits in flags. The number of columns in rndr_table, rndr_table_header, and rndr_table_cell are the same.

rndr_table_header

For LOWDOWN_TABLE_HEADER, the number of columns in each row and the per-column flags, which may tested for equality against HTBL_FL_ALIGN_LEFT, HTBL_FL_ALIGN_RIGHT, or HTBL_FL_ALIGN_CENTER after being masked with HTBL_FL_ALIGNMASK; or HTBL_FL_HEADER. If no alignment is specified after the mask, the default should be left-aligned. The number of columns in rndr_table, rndr_table_header, and rndr_table_cell are the same.

See Also

lowdown(1), lowdown_buf(3), lowdown_buf_diff(3), lowdown_diff(3), lowdown_doc_free(3), lowdown_doc_new(3), lowdown_doc_parse(3), lowdown_file(3), lowdown_file_diff(3), lowdown_gemini_free(3), lowdown_gemini_new(3), lowdown_gemini_rndr(3), lowdown_html_free(3), lowdown_html_new(3), lowdown_html_rndr(3), lowdown_latex_free(3), lowdown_latex_new(3), lowdown_latex_rndr(3), lowdown_metaq_free(3), lowdown_nroff_free(3), lowdown_nroff_new(3), lowdown_nroff_rndr(3), lowdown_odt_free(3), lowdown_odt_new(3), lowdown_odt_rndr(3), lowdown_term_free(3), lowdown_term_new(3), lowdown_term_rndr(3), lowdown_tree_rndr(3), lowdown(5)

Authors

lowdown was forked from hoedown by Kristaps Dzonsons, kristaps@bsd.lv. It has been considerably modified since.

Referenced By

lowdown(1), lowdown_buf(3), lowdown_buf_diff(3), lowdown_buf_free(3), lowdown_buf_new(3), lowdown-diff(1), lowdown_diff(3), lowdown_doc_free(3), lowdown_doc_new(3), lowdown_doc_parse(3), lowdown_file(3), lowdown_file_diff(3), lowdown_gemini_free(3), lowdown_gemini_new(3), lowdown_gemini_rndr(3), lowdown_html_free(3), lowdown_html_new(3), lowdown_html_rndr(3), lowdown_latex_free(3), lowdown_latex_new(3), lowdown_latex_rndr(3), lowdown_metaq_free(3), lowdown_node_free(3), lowdown_nroff_free(3), lowdown_nroff_new(3), lowdown_nroff_rndr(3), lowdown_odt_free(3), lowdown_odt_new(3), lowdown_odt_rndr(3), lowdown_term_free(3), lowdown_term_new(3), lowdown_term_rndr(3), lowdown_tree_rndr(3).

February 3, 2024