parsehtml, printitems, validitems, freeitems, freedocinfo, dimenkind, dimenspec, targetid, targetname, fromStr, toStr – HTML parser


#include <u.h>
#include <libc.h>
#include <html.h>

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 caller, 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 memory.

For debugging purposes, printitems may be called to display the contents of an item list; individual items may be printed using the %I print verb, installed on the first call to parsehtml. validitems traverses 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 predefines FTtop, FTself, FTparent and FTblank.

The library handles all text as Unicode strings (type Rune*). Character 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;
struct Item
Item*      next;
int        width;
int        height;
int        ascent;
int        anchorid;
int        state;
Genattr* genattr;
int        tag;

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 section Anchors). State is a collection of flags and values described as follows:

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 IFindentmask 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, Itabletag, 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 structure:

struct Itext
Rune* s;
int     fnt;
int     fg;
uchar voff;
uchar ul;

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 section 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:

struct Irule
uchar align;
uchar noshade;
int     size;
Dimen wspec;

Here align is the alignment specification (described in the corresponding 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 following structure is defined:

struct Iimage
Rune*     imsrc;
int       imwidth;
int       imheight;
Rune*     altrep;
Map*      map;
int       ctlid;
uchar     align;
uchar     hspace;
uchar     vspace;
uchar     border;
Iimage* nextimage;

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:

struct Iformfield
Formfield* formfield;

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:

struct Itable
Table* table;

Table points to a structure describing the table, described in the section Tables.

For items of type Ifloattag, the following structure is defined:

struct Ifloat
Item*     item;
int       x;
int       y;
uchar     side;
uchar     infloats;
Ifloat* nextfloat;

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 placed.

For items of type Ispacertag, the following structure is defined:

struct Ispacer
int     spkind;

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).

Generic Attributes

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;
struct Genattr
Rune*     id;
Rune*     class;
Rune*     style;
Rune*     title;
SEvent* events;

Fields id, class, style and title, when non–nil, contain values of correspondingly 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;
struct SEvent
SEvent* next;
int       type;
Rune*     script;

Here, next points to the next event in the list, type is one of SEonblur, SEonchange, SEonclick, SEondblclick, SEonfocus, SEonkeypress, SEonkeyup, SEonload, SEonmousedown, SEonmousemove, SEonmouseout, SEonmouseover, SEonmouseup, SEonreset, SEonselect, SEonsubmit or SEonunload, and script is the text of the associated script.

Dimension Specifications

Some structures include a dimension specification, used where a number can be followed by a % or a * to indicate percentage of total or relative weight. This is encoded using the following structure:

typedef struct Dimen Dimen;
struct Dimen
int kindspec;

Separate kind and spec values are extracted using dimenkind and dimenspec. 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.

Background Specifications

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 follows:

typedef struct Background Background;
struct Background
Rune* image;
int     color;

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 color.

Alignment Specifications

Certain items have alignment specifiers taken from the following enumerated type:

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 horizontal alignments:

typedef struct Align Align;
struct Align
uchar halign;
uchar valign;

Halign can be one of ALnone, ALleft, ALcenter, ALright, ALjustify or ALchar. Valign can be one of ALnone, ALmiddle, ALbottom, ALtop or ALbaseline.

Font Numbers

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, respectively, 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).

Document Info

Global information about an HTML page is stored in the following structure:

typedef struct Docinfo Docinfo;
struct Docinfo
// stuff from HTTP headers, doc head, and body tag
Rune*         src;
Rune*         base;
Rune*         doctitle;
Background    background;
Iimage*       backgrounditem;
int           text;
int           link;
int           vlink;
int           alink;
int           target;
int           chset;
int           mediatype;
int           scripttype;
int           hasscripts;
Rune*         refresh;
Kidinfo*      kidinfo;
int           frameid;
// info needed to respond to user actions
Anchor*       anchors;
DestAnchor* dests;
Form*         forms;
Table*        tables;
Map*          maps;
Iimage*       images;

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 Specifications, and backgrounditem is set to be an image item for the document'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 contained in the document, and is always TextJavascript. Hasscripts is 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 document. For anchors which are hyperlinks (the href attribute was supplied), the following structure is defined:

typedef struct Anchor Anchor;
struct Anchor
Anchor* next;
int       index;
Rune*     name;
Rune*     href;
int       target;

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 hyperlink 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;
struct DestAnchor
DestAnchor* next;
int           index;
Rune*         name;
Item*         item;

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;
struct Form
Form*        next;
int          formid;
Rune*        name;
Rune*        action;
int          target;
int          method;
int          nfields;
Formfield* fields;

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 target 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 structure:

typedef struct Formfield Formfield;
struct Formfield
Formfield* next;
int          ftype;
int          fieldid;
Form*        form;
Rune*        name;
Rune*        value;
int          size;
int          maxlength;
int          rows;
int          cols;
uchar        flags;
Option*      options;
Item*        image;
int          ctlid;
SEvent*      events;

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 displayed. 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 associated 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;
struct Option
Option* next;
int       selected;
Rune*     value;
Rune*     display;

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;
struct Table
Table*         next;
int           tableid;
Tablerow*      rows;
int           nrow;
Tablecol*      cols;
int           ncol;
Tablecell*     cells;
int           ncell;
Tablecell*** grid;
Align          align;
Dimen          width;
int           border;
int           cellspacing;
int           cellpadding;
Background     background;
Item*          caption;
uchar          caption_place;
Lay*           caption_lay;
int           totw;
int           toth;
int           caph;
int           availw;
Token*         tabletok;
uchar          flags;

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 elements 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 column j is Table.grid[i][j]. A cell that spans multiple rows and/or columns 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 specification. 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;
struct Tablecol
int     width;
Align align;
Point pos;

The rows in the table are specified as follows:

typedef struct Tablerow Tablerow;
struct Tablerow
Tablerow*    next;
Tablecell* cells;
int          height;
int          ascent;
Align        align;
Background background;
Point        pos;
uchar        flags;

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;
struct Tablecell
Tablecell* next;
Tablecell* nextinrow;
int          cellid;
Item*        content;
Lay*         lay;
int          rowspan;
int          colspan;
Align        align;
uchar        flags;
Dimen        wspec;
int          hspec;
Background background;
int          minw;
int          maxw;
int          ascent;
int          row;
int          col;
Point        pos;

Next is used to link together the list of all cells within a table (Table.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 combination of TFparsing, TFnowrap and TFisth or'd together. Here TFparsing 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 background 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.

Client–side Maps

The library builds a list of client–side maps, headed by Docinfo.maps, and having the following structure:

typedef struct Map Map;
struct Map
Map*    next;
Rune* name;
Area* areas;

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;
struct Area
Area*    next;
int      shape;
Rune*    href;
int      target;
Dimen* coords;
int      ncoords;

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;
struct Kidinfo
Kidinfo* next;
int        isframeset;
// fields for "frame"
Rune*      src;
Rune*      name;
int        marginw;
int        marginh;
int        framebd;
int        flags;
// fields for "frameset"
Dimen*     rows;
int        nrows;
Dimen*     cols;
int        ncols;
Kidinfo* kidinfos;
Kidinfo* nextframeset;

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 initially 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.
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