1htmlparse(n) HTML Parser htmlparse(n)
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6
8 htmlparse - Procedures to parse HTML strings
9
11 package require Tcl 8.2
12 package require struct::stack 1.3
14 package require cmdline 1.1
16 package require htmlparse ?1.1.3?
18 ::htmlparse::parse ?-cmd cmd? ?-vroot tag? ?-split n? ?-incvar var?
20 ?-queue q? html
21 ::htmlparse::debugCallback ?clientdata? tag slash param textBehind‐
23 TheTag
24 ::htmlparse::mapEscapes html
26 ::htmlparse::2tree html tree
28 ::htmlparse::removeVisualFluff tree
30 ::htmlparse::removeFormDefs tree
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34
36 The htmlparse package provides commands that allow libraries and appli‐
37 cations to parse HTML in a string into a representation of their
38 choice.
39 The following commands are available:
41 ::htmlparse::parse ?-cmd cmd? ?-vroot tag? ?-split n? ?-incvar var?
43 ?-queue q? html
44 This command is the basic parser for HTML. It takes an HTML
45 string, parses it and invokes a command prefix for every tag
46 encountered. It is not necessary for the HTML to be valid for
47 this parser to function. It is the responsibility of the command
48 invoked for every tag to check this. Another responsibility of
49 the invoked command is the handling of tag attributes and char‐
50 acter entities (escaped characters). The parser provides the un-
51 interpreted tag attributes to the invoked command to aid in the
52 former, and the package at large provides a helper command,
53 ::htmlparse::mapEscapes, to aid in the handling of the latter.
54 The parser does ignore leading DOCTYPE declarations and all
55 valid HTML comments it encounters.
56 All information beyond the HTML string itself is specified via
58 options, these are explained below.
59 To help understand the options, some more background information
61 about the parser.
62 It is capable of detecting incomplete tags in the HTML string
64 given to it. Under normal circumstances this will cause the
65 parser to throw an error, but if the option -incvar is used to
66 specify a global (or namespace) variable, the parser will store
67 the incomplete part of the input into this variable instead.
68 This will aid greatly in the handling of incrementally arriving
69 HTML, as the parser will handle whatever it can and defer the
70 handling of the incomplete part until more data has arrived.
71 Another feature of the parser are its two possible modes of
73 operation. The normal mode is activated if the option -queue is
74 not present on the command line invoking the parser. If it is
75 present, the parser will go into the incremental mode instead.
76 The main difference is that a parser in normal mode will immedi‐
78 ately invoke the command prefix for each tag it encounters. In
79 incremental mode however the parser will generate a number of
80 scripts which invoke the command prefix for groups of tags in
81 the HTML string and then store these scripts in the specified
82 queue. It is then the responsibility of the caller of the parser
83 to ensure the execution of the scripts in the queue.
84 Note: The queue object given to the parser has to provide the
86 same interface as the queue defined in tcllib -> struct. This
87 means, for example, that all queues created via that tcllib mod‐
88 ule can be immediately used here. Still, the queue doesn't have
89 to come from tcllib -> struct as long as the same interface is
90 provided.
91 In both modes the parser will return an empty string to the
93 caller.
94 The -split option may be given to a parser in incremental mode
96 to specify the size of the groups it creates. In other words,
97 -split 5 means that each of the generated scripts will invoke
98 the command prefix for 5 consecutive tags in the HTML string. A
99 parser in normal mode will ignore this option and its value.
100 The option -vroot specifies a virtual root tag. A parser in nor‐
102 mal mode will invoke the command prefix for it immediately
103 before and after it processes the tags in the HTML, thus simu‐
104 lating that the HTML string is enclosed in a <vroot> </vroot>
105 combination. In incremental mode however the parser is unable to
106 provide the closing virtual root as it never knows when the
107 input is complete. In this case the first script generated by
108 each invocation of the parser will contain an invocation of the
109 command prefix for the virtual root as its first command. The
110 following options are available:
111 -cmd cmd
113 The command prefix to invoke for every tag in the HTML
114 string. Defaults to ::htmlparse::debugCallback.
115 -vroot tag
117 The virtual root tag to add around the HTML in normal
118 mode. In incremental mode it is the first tag in each
119 chunk processed by the parser, but there will be no clos‐
120 ing tags. Defaults to hmstart.
121 -split n
123 The size of the groups produced by an incremental mode
124 parser. Ignored when in normal mode. Defaults to 10. Val‐
125 ues <= 0 are not allowed.
126 -incvar var
128 The name of the variable where to store any incomplete
129 HTML into. This makes most sense for the incremental
130 mode. The parser will throw an error if it sees incom‐
131 plete HTML and has no place to store it to. This makes
132 sense for the normal mode. Only incomplete tags are
133 detected, not missing tags. Optional, defaults to 'no
134 variable'.
135 Interface to the command prefix
138 In normal mode the parser will invoke the command prefix
139 with four arguments appended. See ::htmlparse::debugCall‐
140 back for a description.
141 In incremental mode, however, the generated scripts will
143 invoke the command prefix with five arguments appended.
144 The last four of these are the same which were mentioned
145 above. The first is a placeholder string (\\win\\) for a
146 clientdata value to be supplied later during the actual
147 execution of the generated scripts. This could be a tk
148 window path, for example. This allows the user of this
149 package to preprocess HTML strings without committing
150 them to a specific window, object, whatever during pars‐
151 ing. This connection can be made later. This also means
152 that it is possible to cache preprocessed HTML. Of
153 course, nothing prevents the user of the parser from
154 replacing the placeholder with an empty string.
155 ::htmlparse::debugCallback ?clientdata? tag slash param textBehind‐
157 TheTag
158 This command is the standard callback used by the parser in
159 ::htmlparse::parse if none was specified by the user. It simply
160 dumps its arguments to stdout. This callback can be used for
161 both normal and incremental mode of the calling parser. In other
162 words, it accepts four or five arguments. The last four argu‐
163 ments are described below. The optional fifth argument contains
164 the clientdata value passed to the callback by a parser in
165 incremental mode. All callbacks have to follow the signature of
166 this command in the last four arguments, and callbacks used in
167 incremental parsing have to follow this signature in the last
168 five arguments.
169 The first argument, clientdata, is optional and present only if
171 this command is invoked by a parser in incremental mode. It con‐
172 tains whatever the user of this package wishes.
173 The second argument, tag, contains the name of the tag which is
175 currently processed by the parser.
176 The third argument, slash, is either empty or contains a slash
178 character. It allows the callback to distinguish between opening
179 (slash is empty) and closing tags (slash contains a slash char‐
180 acter).
181 The fourth argument, param, contains the un-interpreted list of
183 parameters to the tag.
184 The fifth and last argument, textBehindTheTag, contains the text
186 found by the parser behind the tag named in tag.
187 ::htmlparse::mapEscapes html
189 This command takes a HTML string, substitutes all escape
190 sequences with their actual characters and then returns the
191 resulting string. HTML strings which do not contain escape
192 sequences are returned unchanged.
193 ::htmlparse::2tree html tree
195 This command is a wrapper around ::htmlparse::parse which takes
196 an HTML string (in html) and converts it into a tree containing
197 the logical structure of the parsed document. The name of the
198 tree is given to the command as its second argument (tree). The
199 command does not generate the tree by itself but expects that
200 the caller provided it with an existing and empty tree. It also
201 expects that the specified tree object follows the same inter‐
202 face as the tree object in tcllib -> struct. It doesn't have to
203 be from tcllib -> struct, but it must provide the same inter‐
204 face.
205 The internal callback does some basic checking of HTML validity
207 and tries to recover from the most basic errors. The command
208 returns the contents of its second argument. Side effects are
209 the creation and manipulation of a tree object.
210 Each node in the generated tree represent one tag in the input.
212 The name of the tag is stored in the attribute type of the node.
213 Any html attributes coming with the tag are stored unmodified in
214 the attribute data of the tag. In other words, the command does
215 not parse html attributes into their names and values.
216 If a tag contains text its node will have children of type
218 PCDATA containing this text. The text will be stored in the
219 attribute data of these children.
220 ::htmlparse::removeVisualFluff tree
222 This command walks a tree as generated by ::htmlparse::2tree and
223 removes all the nodes which represent visual tags and not struc‐
224 tural ones. The purpose of the command is to make the tree eas‐
225 ier to navigate without getting bogged down in visual informa‐
226 tion not relevant to the search. Its only argument is the name
227 of the tree to cut down.
228 ::htmlparse::removeFormDefs tree
230 Like ::htmlparse::removeVisualFluff this command is here to cut
231 down on the size of the tree as generated by ::htmlparse::2tree.
232 It removes all nodes representing forms and form elements. Its
233 only argument is the name of the tree to cut down.
234
236 This document, and the package it describes, will undoubtedly contain
237 bugs and other problems. Please report such in the category htmlparse
238 of the Tcllib SF Trackers [http://source‐
239 forge.net/tracker/?group_id=12883]. Please also report any ideas for
240 enhancements you may have for either package and/or documentation.
241
243 struct::tree
244
246 html, parsing, queue, tree
247htmlparse 1.1.3 htmlparse(n)