parsehtml, printitems, validitems, freeitems, freedocinfo, dimenkind,
dimenspec, targetid, targetname, fromStr, toStr - HTML parser
Item* parsehtml(uchar* data, int datalen, Rune* src, int mtype,
int chset, Docinfo** pdi)
void printitems(Item* items, char* msg)
int validitems(Item* items)
void freeitems(Item* items)
void freedocinfo(Docinfo* d)
int dimenkind(Dimen d)
int dimenspec(Dimen d)
int targetid(Rune* s)
Rune* targetname(int targid)
uchar* fromStr(Rune* buf, int n, int chset)
Rune* toStr(uchar* buf, int n, int chset)
This library implements a parser for HTML 4.0 documents. The parsed
HTML is converted into an intermediate representation that describes
how the formatted HTML should be laid out.
Parsehtml parses an entire HTML document contained in the buffer data
and having length datalen. The URL of the document should be passed in
as src. Mtype is the media type of the document, which should be
either TextHtml or TextPlain. The character set of the document is
described in chset, which can be one of US_Ascii, ISO_8859_1, UTF_8 or
Unicode. The return value is a linked list of Item structures,
described in detail below. As a side effect, *pdi is set to point to a
newly created Docinfo structure, containing information pertaining to
the entire document.
The library expects two allocation routines to be provided by the call‐
er, emalloc and erealloc. These routines are analogous to the standard
malloc and realloc routines, except that they should not return if the
memory allocation fails. In addition, emalloc is required to zero the
For debugging purposes, printitems may be called to display the con‐
tents of an item list; individual items may be printed using the %I
print verb, installed on the first call to parsehtml. validitems tra‐
verses the item list, checking that all of the pointers are valid. It
returns 1 is everything is ok, and 0 if an error was found. Normally,
one would not call these routines directly. Instead, one sets the
global variable dbgbuild and the library calls them automatically. One
can also set warn, to cause the library to print a warning whenever it
finds a problem with the input document, and dbglex, to print debugging
information in the lexer.
When an item list is finished with, it should be freed with freeitems.
Then, freedocinfo should be called on the pointer returned in *pdi.
Dimenkind and dimenspec are provided to interpret the Dimen type, as
described in the section Dimension Specifications.
Frame target names are mapped to integer ids via a global, permanent
mapping. To find the value for a given name, call targetid, which
allocates a new id if the name hasn't been seen before. The name of a
given, known id may be retrieved using targetname. The library prede‐
fines FTtop, FTself, FTparent and FTblank.
The library handles all text as Unicode strings (type Rune*). Charac‐
ter set conversion is provided by fromStr and toStr. FromStr takes n
Unicode characters from buf and converts them to the character set
described by chset. ToStr takes n bytes from buf, interpretted as
belonging to character set chset, and converts them to a Unicode
string. Both routines null-terminate the result, and use emalloc to
allocate space for it.
The return value of parsehtml is a linked list of variant structures,
with the generic portion described by the following definition:
typedef struct Item Item;
The field next points to the successor in the linked list of items,
while width, height, and ascent are intended for use by the caller as
part of the layout process. Anchorid, if non-zero, gives the integer
id assigned by the parser to the anchor that this item is in (see sec‐
tion Anchors). State is a collection of flags and values described as
IFbrk = 0x80000000,
IFbrksp = 0x40000000,
IFnobrk = 0x20000000,
IFcleft = 0x10000000,
IFcright = 0x08000000,
IFwrap = 0x04000000,
IFhang = 0x02000000,
IFrjust = 0x01000000,
IFcjust = 0x00800000,
IFsmap = 0x00400000,
IFindentshift = 8,
IFindentmask = (255<<IFindentshift),
IFhangmask = 255
IFbrk is set if a break is to be forced before placing this item.
IFbrksp is set if a 1 line space should be added to the break (in which
case IFbrk is also set). IFnobrk is set if a break is not permitted
before the item. IFcleft is set if left floats should be cleared (that
is, if the list of pending left floats should be placed) before this
item is placed, and IFcright is set for right floats. In both cases,
IFbrk is also set. IFwrap is set if the line containing this item is
allowed to wrap. IFhang is set if this item hangs into the left
indent. IFrjust is set if the line containing this item should be
right justified, and IFcjust is set for center justified lines. IFsmap
is used to indicate that an image is a server-side map. The low 8
bits, represented by IFhangmask, indicate the current hang into left
indent, in tenths of a tabstop. The next 8 bits, represented by IFind‐
entmask and IFindentshift, indicate the current indent in tab stops.
The field genattr is an optional pointer to an auxiliary structure,
described in the section Generic Attributes.
Finally, tag describes which variant type this item has. It can have
one of the values Itexttag, Iruletag, Iimagetag, Iformfieldtag, Itable‐
tag, Ifloattag or Ispacertag. For each of these values, there is an
additional structure defined, which includes Item as an unnamed initial
substructure, and then defines additional fields.
Items of type Itexttag represent a piece of text, using the following
Here s is a null-terminated Unicode string of the actual characters
making up this text item, fnt is the font number (described in the sec‐
tion Font Numbers), and fg is the RGB encoded color for the text. Voff
measures the vertical offset from the baseline; subtract Voffbias to
get the actual value (negative values represent a displacement down the
page). The field ul is the underline style: ULnone if no underline,
ULunder for conventional underline, and ULmid for strike-through.
Items of type Iruletag represent a horizontal rule, as follows:
Here align is the alignment specification (described in the correspond‐
ing section), noshade is set if the rule should not be shaded, size is
the height of the rule (as set by the size attribute), and wspec is the
desired width (see section Dimension Specifications).
Items of type Iimagetag describe embedded images, for which the follow‐
ing structure is defined:
Here imsrc is the URL of the image source, imwidth and imheight, if
non-zero, contain the specified width and height for the image, and
altrep is the text to use as an alternative to the image, if the image
is not displayed. Map, if set, points to a structure describing an
associated client-side image map. Ctlid is reserved for use by the
application, for handling animated images. Align encodes the alignment
specification of the image. Hspace contains the number of pixels to
pad the image with on either side, and Vspace the padding above and
below. Border is the width of the border to draw around the image.
Nextimage points to the next image in the document (the head of this
list is Docinfo.images).
For items of type Iformfieldtag, the following structure is defined:
This adds a single field, formfield, which points to a structure
describing a field in a form, described in section Forms.
For items of type Itabletag, the following structure is defined:
Table points to a structure describing the table, described in the sec‐
For items of type Ifloattag, the following structure is defined:
The item points to a single item (either a table or an image) that
floats (the text of the document flows around it), and side indicates
the margin that this float sticks to; it is either ALleft or ALright.
X and y are reserved for use by the caller; these are typically used
for the coordinates of the top of the float. Infloats is used by the
caller to keep track of whether it has placed the float. Nextfloat is
used by the caller to link together all of the floats that it has
For items of type Ispacertag, the following structure is defined:
Spkind encodes the kind of spacer, and may be one of ISPnull (zero
height and width), ISPvline (takes on height and ascent of the current
font), ISPhspace (has the width of a space in the current font) and
ISPgeneral (for all other purposes, such as between markers and lists).
The genattr field of an item, if non-nil, points to a structure that
holds the values of attributes not specific to any particular item
type, as they occur on a wide variety of underlying HTML tags. The
structure is as follows:
typedef struct Genattr Genattr;
Fields id, class, style and title, when non-nil, contain values of cor‐
respondingly named attributes of the HTML tag associated with this
item. Events is a linked list of events (with corresponding scripted
actions) associated with the item:
typedef struct SEvent SEvent;
Here, next points to the next event in the list, type is one of SEon‐
blur, SEonchange, SEonclick, SEondblclick, SEonfocus, SEonkeypress,
SEonkeyup, SEonload, SEonmousedown, SEonmousemove, SEonmouseout, SEon‐
mouseover, SEonmouseup, SEonreset, SEonselect, SEonsubmit or SEonun‐
load, and script is the text of the associated script.
Some structures include a dimension specification, used where a number
can be followed by a % or a * to indicate percentage of total or rela‐
tive weight. This is encoded using the following structure:
typedef struct Dimen Dimen;
Separate kind and spec values are extracted using dimenkind and dimen‐
spec. Dimenkind returns one of Dnone, Dpixels, Dpercent or Drelative.
Dnone means that no dimension was specified. In all other cases,
dimenspec should be called to find the absolute number of pixels, the
percentage of total, or the relative weight.
It is possible to set the background of the entire document, and also
for some parts of the document (such as tables). This is encoded as
typedef struct Background Background;
Image, if non-nil, is the URL of an image to use as the background. If
this is nil, color is used instead, as the RGB value for a solid fill
Certain items have alignment specifiers taken from the following enu‐
ALnone = 0, ALleft, ALcenter, ALright, ALjustify,
ALchar, ALtop, ALmiddle, ALbottom, ALbaseline
These values correspond to the various alignment types named in the
HTML 4.0 standard. If an item has an alignment of ALleft or ALright,
the library automatically encapsulates it inside a float item.
Tables, and the various rows, columns and cells within them, have a
more complex alignment specification, composed of separate vertical and
typedef struct Align Align;
Halign can be one of ALnone, ALleft, ALcenter, ALright, ALjustify or
ALchar. Valign can be one of ALnone, ALmiddle, ALbottom, ALtop or
Text items have an associated font number (the fnt field), which is
encoded as style*NumSize+size. Here, style is one of FntR, FntI, FntB
or FntT, for roman, italic, bold and typewriter font styles, respec‐
tively, and size is Tiny, Small, Normal, Large or Verylarge. The total
number of possible font numbers is NumFnt, and the default font number
is DefFnt (which is roman style, normal size).
Global information about an HTML page is stored in the following struc‐
typedef struct Docinfo Docinfo;
// stuff from HTTP headers, doc head, and body tag
// info needed to respond to user actions
Src gives the URL of the original source of the document, and base is
the base URL. Doctitle is the document's title, as set by a <title>
element. Background is as described in the section Background Specifi‐
cations, and backgrounditem is set to be an image item for the docu‐
ment's background image (if given as a URL), or else nil. Text gives
the default foregound text color of the document, link the unvisited
hyperlink color, vlink the visited hyperlink color, and alink the color
for highlighting hyperlinks (all in 24-bit RGB format). Target is the
default target frame id. Chset and mediatype are as for the chset and
mtype parameters to parsehtml. Scripttype is the type of any scripts
set if the document contains any scripts. Scripting is currently
unsupported. Refresh is the contents of a <meta http-equiv=Refresh
...> tag, if any. Kidinfo is set if this document is a frameset (see
section Frames). Frameid is this document's frame id.
Anchors is a list of hyperlinks contained in the document, and dests is
a list of hyperlink destinations within the page (see the following
section for details). Forms, tables and maps are lists of the various
forms, tables and client-side maps contained in the document, as
described in subsequent sections. Images is a list of all the image
items in the document.
The library builds two lists for all of the <a> elements (anchors) in a
document. Each anchor is assigned a unique anchor id within the docu‐
ment. For anchors which are hyperlinks (the href attribute was sup‐
plied), the following structure is defined:
typedef struct Anchor Anchor;
Next points to the next anchor in the list (the head of this list is
Docinfo.anchors). Index is the anchor id; each item within this hyper‐
link is tagged with this value in its anchorid field. Name and href
are the values of the correspondingly named attributes of the anchor
(in particular, href is the URL to go to). Target is the value of the
target attribute (if provided) converted to a frame id.
Destinations within the document (anchors with the name attribute set)
are held in the Docinfo.dests list, using the following structure:
typedef struct DestAnchor DestAnchor;
Next is the next element of the list, index is the anchor id, name is
the value of the name attribute, and item is points to the item within
the parsed document that should be considered to be the destination.
Any forms within a document are kept in a list, headed by
Docinfo.forms. The elements of this list are as follows:
typedef struct Form Form;
Next points to the next form in the list. Formid is a serial number
for the form within the document. Name is the value of the form's name
or id attribute. Action is the value of any action attribute. Target
is the value of the target attribute (if any) converted to a frame tar‐
get id. Method is one of HGet or HPost. Nfields is the number of
fields in the form, and fields is a linked list of the actual fields.
The individual fields in a form are described by the following struc‐
typedef struct Formfield Formfield;
Here, next points to the next field in the list. Ftype is the type of
the field, which can be one of Ftext, Fpassword, Fcheckbox, Fradio,
Fsubmit, Fhidden, Fimage, Freset, Ffile, Fbutton, Fselect or Ftextarea.
Fieldid is a serial number for the field within the form. Form points
back to the form containing this field. Name, value, size, maxlength,
rows and cols each contain the values of corresponding attributes of
the field, if present. Flags contains per-field flags, of which
FFchecked and FFmultiple are defined. Image is only used for fields of
type Fimage; it points to an image item containing the image to be dis‐
played. Ctlid is reserved for use by the caller, typically to store a
unique id of an associated control used to implement the field. Events
is the same as the corresponding field of the generic attributes asso‐
ciated with the item containing this field. Options is only used by
fields of type Fselect; it consists of a list of possible options that
may be selected for that field, using the following structure:
typedef struct Option Option;
Next points to the next element of the list. Selected is set if this
option is to be displayed initially. Value is the value to send when
the form is submitted if this option is selected. Display is the
string to display on the screen for this option.
The library builds a list of all the tables in the document, headed by
Docinfo.tables. Each element of this list has the following format:
typedef struct Table Table;
Next points to the next element in the list of tables. Tableid is a
serial number for the table within the document. Rows is an array of
row specifications (described below) and nrow is the number of elements
in this array. Similarly, cols is an array of column specifications,
and ncol the size of this array. Cells is a list of all cells within
the table (structure described below) and ncell is the number of ele‐
ments in this list. Note that a cell may span multiple rows and/or
columns, thus ncell may be smaller than nrow*ncol. Grid is a two-
dimensional array of cells within the table; the cell at row i and col‐
umn j is Table.grid[i][j]. A cell that spans multiple rows and/or col‐
umns will be referenced by grid multiple times, however it will only
occur once in cells. Align gives the alignment specification for the
entire table, and width gives the requested width as a dimension speci‐
fication. Border, cellspacing and cellpadding give the values of the
corresponding attributes for the table, and background gives the
requested background for the table. Caption is a linked list of items
to be displayed as the caption of the table, either above or below
depending on whether caption_place is ALtop or ALbottom. Most of the
remaining fields are reserved for use by the caller, except tabletok,
which is reserved for internal use. The type Lay is not defined by the
library; the caller can provide its own definition.
The Tablecol structure is defined for use by the caller. The library
ensures that the correct number of these is allocated, but leaves them
blank. The fields are as follows:
typedef struct Tablecol Tablecol;
The rows in the table are specified as follows:
typedef struct Tablerow Tablerow;
Next is only used during parsing; it should be ignored by the caller.
Cells provides a list of all the cells in a row, linked through their
nextinrow fields (see below). Height, ascent and pos are reserved for
use by the caller. Align is the alignment specification for the row,
and background is the background to use, if specified. Flags is used
by the parser; ignore this field.
The individual cells of the table are described as follows:
typedef struct Tablecell Tablecell;
Next is used to link together the list of all cells within a table (Ta‐
ble.cells), whereas nextinrow is used to link together all the cells
within a single row (Tablerow.cells). Cellid provides a serial number
for the cell within the table. Content is a linked list of the items
to be laid out within the cell. Lay is reserved for the user to
describe how these items have been laid out. Rowspan and colspan are
the number of rows and columns spanned by this cell, respectively.
Align is the alignment specification for the cell. Flags is some com‐
bination of TFparsing, TFnowrap and TFisth or'd together. Here TFpars‐
ing is used internally by the parser, and should be ignored. TFnowrap
means that the contents of the cell should not be wrapped if they don't
fit the available width, rather, the table should be expanded if need
be (this is set when the nowrap attribute is supplied). TFisth means
that the cell was created by the <th> element (rather than the <td>
element), indicating that it is a header cell rather than a data cell.
Wspec provides a suggested width as a dimension specification, and
hspec provides a suggested height in pixels. Background gives a back‐
ground specification for the individual cell. Minw, maxw, ascent and
pos are reserved for use by the caller during layout. Row and col give
the indices of the row and column of the top left-hand corner of the
cell within the table grid.
The library builds a list of client-side maps, headed by Docinfo.maps,
and having the following structure:
typedef struct Map Map;
Next points to the next element in the list, name is the name of the
map (use to bind it to an image), and areas is a list of the areas
within the image that comprise the map, using the following structure:
typedef struct Area Area;
Next points to the next element in the map's list of areas. Shape
describes the shape of the area, and is one of SHrect, SHcircle or
SHpoly. Href is the URL associated with this area in its role as a
hypertext link, and target is the target frame it should be loaded in.
Coords is an array of coordinates for the shape, and ncoords is the
size of this array (number of elements).
If the Docinfo.kidinfo field is set, the document is a frameset. In
this case, it is typical for parsehtml to return nil, as a document
which is a frameset should have no actual items that need to be laid
out (such will appear only in subsidiary documents). It is possible
that items will be returned by a malformed document; the caller should
check for this and free any such items.
The Kidinfo structure itself reflects the fact that framesets can be
nested within a document. If is defined as follows:
typedef struct Kidinfo Kidinfo;
// fields for "frame"
// fields for "frameset"
Next is only used if this structure is part of a containing frameset;
it points to the next element in the list of children of that frameset.
Isframeset is set when this structure represents a frameset; if clear,
it is an individual frame.
Some fields are used only for framesets. Rows is an array of dimension
specifications for rows in the frameset, and nrows is the length of
this array. Cols is the corresponding array for columns, of length
ncols. Kidinfos points to a list of components contained within this
frameset, each of which may be a frameset or a frame. Nextframeset is
only used during parsing, and should be ignored.
The remaining fields are used if the structure describes a frame, not a
frameset. Src provides the URL for the document that should be ini‐
tially loaded into this frame. Note that this may be a relative URL,
in which case it should be interpretted using the containing document's
URL as the base. Name gives the name of the frame, typically supplied
via a name attribute in the HTML. If no name was given, the library
allocates one. Marginw, marginh and framebd are the values of the
marginwidth, marginheight and frameborder attributes, respectively.
Flags can contain some combination of the following: FRnoresize (the
frame had the noresize attribute set, and the user should not be
allowed to resize it), FRnoscroll (the frame should not have any scroll
bars), FRhscroll (the frame should have a horizontal scroll bar),
FRvscroll (the frame should have a vertical scroll bar), FRhscrollauto
(the frame should be automatically given a horizontal scroll bar if its
contents would not otherwise fit), and FRvscrollauto (the frame gets a
vertical scrollbar only if required).
W3C World Wide Web Consortium, ``HTML 4.01 Specification''.
The entire HTML document must be loaded into memory before any of it
can be parsed.