[comment {-*- tcl -*- doctools manpage}] [vset VERSION 1.2.2] [manpage_begin htmlparse n [vset VERSION]] [see_also struct::tree] [keywords html] [keywords parsing] [keywords queue] [keywords tree] [moddesc {HTML Parser}] [titledesc {Procedures to parse HTML strings}] [category {Text processing}] [require Tcl 8.2] [require struct::stack 1.3] [require cmdline 1.1] [require htmlparse [opt [vset VERSION]]] [description] [para] The [package htmlparse] package provides commands that allow libraries and applications to parse HTML in a string into a representation of their choice. [para] The following commands are available: [list_begin definitions] [call [cmd ::htmlparse::parse] [opt "-cmd [arg cmd]"] [opt "-vroot [arg tag]"] [opt "-split [arg n]"] [opt "-incvar [arg var]"] [opt "-queue [arg q]"] [arg html]] This command is the basic parser for HTML. It takes an HTML string, parses it and invokes a command prefix for every tag encountered. It is not necessary for the HTML to be valid for this parser to function. It is the responsibility of the command invoked for every tag to check this. Another responsibility of the invoked command is the handling of tag attributes and character entities (escaped characters). The parser provides the un-interpreted tag attributes to the invoked command to aid in the former, and the package at large provides a helper command, [cmd ::htmlparse::mapEscapes], to aid in the handling of the latter. The parser [emph does] ignore leading DOCTYPE declarations and all valid HTML comments it encounters. [para] All information beyond the HTML string itself is specified via options, these are explained below. [para] To help understand the options, some more background information about the parser. [para] It is capable of detecting incomplete tags in the HTML string given to it. Under normal circumstances this will cause the parser to throw an error, but if the option [arg -incvar] is used to specify a global (or namespace) variable, the parser will store the incomplete part of the input into this variable instead. This will aid greatly in the handling of incrementally arriving HTML, as the parser will handle whatever it can and defer the handling of the incomplete part until more data has arrived. [para] Another feature of the parser are its two possible modes of operation. The normal mode is activated if the option [arg -queue] is not present on the command line invoking the parser. If it is present, the parser will go into the incremental mode instead. [para] The main difference is that a parser in normal mode will immediately invoke the command prefix for each tag it encounters. In incremental mode however the parser will generate a number of scripts which invoke the command prefix for groups of tags in the HTML string and then store these scripts in the specified queue. It is then the responsibility of the caller of the parser to ensure the execution of the scripts in the queue. [para] [emph Note]: The queue object given to the parser has to provide the same interface as the queue defined in tcllib -> struct. This means, for example, that all queues created via that tcllib module can be immediately used here. Still, the queue doesn't have to come from tcllib -> struct as long as the same interface is provided. [para] In both modes the parser will return an empty string to the caller. [para] The [arg -split] option may be given to a parser in incremental mode to specify the size of the groups it creates. In other words, -split 5 means that each of the generated scripts will invoke the command prefix for 5 consecutive tags in the HTML string. A parser in normal mode will ignore this option and its value. [para] The option [arg -vroot] specifies a virtual root tag. A parser in normal mode will invoke the command prefix for it immediately before and after it processes the tags in the HTML, thus simulating that the HTML string is enclosed in a combination. In incremental mode however the parser is unable to provide the closing virtual root as it never knows when the input is complete. In this case the first script generated by each invocation of the parser will contain an invocation of the command prefix for the virtual root as its first command. The following options are available: [list_begin definitions] [def "[option -cmd] [arg cmd]"] The command prefix to invoke for every tag in the HTML string. Defaults to [arg ::htmlparse::debugCallback]. [def "[option -vroot] [arg tag]"] The virtual root tag to add around the HTML in normal mode. In incremental mode it is the first tag in each chunk processed by the parser, but there will be no closing tags. Defaults to [arg hmstart]. [def "[option -split] [arg n]"] The size of the groups produced by an incremental mode parser. Ignored when in normal mode. Defaults to 10. Values <= 0 are not allowed. [def "[option -incvar] [arg var]"] The name of the variable where to store any incomplete HTML into. This makes most sense for the incremental mode. The parser will throw an error if it sees incomplete HTML and has no place to store it to. This makes sense for the normal mode. Only incomplete tags are detected, not missing tags. Optional, defaults to 'no variable'. [list_end] [list_begin definitions] [def [emph "Interface to the command prefix"]] In normal mode the parser will invoke the command prefix with four arguments appended. See [cmd ::htmlparse::debugCallback] for a description. [para] In incremental mode, however, the generated scripts will invoke the command prefix with five arguments appended. The last four of these are the same which were mentioned above. The first is a placeholder string ([const "@win@"]) for a clientdata value to be supplied later during the actual execution of the generated scripts. This could be a tk window path, for example. This allows the user of this package to preprocess HTML strings without committing them to a specific window, object, whatever during parsing. This connection can be made later. This also means that it is possible to cache preprocessed HTML. Of course, nothing prevents the user of the parser from replacing the placeholder with an empty string. [list_end] [call [cmd ::htmlparse::debugCallback] [opt [arg clientdata]] [arg "tag slash param textBehindTheTag"]] This command is the standard callback used by the parser in [cmd ::htmlparse::parse] if none was specified by the user. It simply dumps its arguments to stdout. This callback can be used for both normal and incremental mode of the calling parser. In other words, it accepts four or five arguments. The last four arguments are described below. The optional fifth argument contains the clientdata value passed to the callback by a parser in incremental mode. All callbacks have to follow the signature of this command in the last four arguments, and callbacks used in incremental parsing have to follow this signature in the last five arguments. [para] The first argument, [arg clientdata], is optional and present only if this command is invoked by a parser in incremental mode. It contains whatever the user of this package wishes. [para] The second argument, [arg tag], contains the name of the tag which is currently processed by the parser. [para] The third argument, [arg slash], is either empty or contains a slash character. It allows the callback to distinguish between opening (slash is empty) and closing tags (slash contains a slash character). [para] The fourth argument, [arg param], contains the un-interpreted list of parameters to the tag. [para] The fifth and last argument, [arg textBehindTheTag], contains the text found by the parser behind the tag named in [arg tag]. [call [cmd ::htmlparse::mapEscapes] [arg html]] This command takes a HTML string, substitutes all escape sequences with their actual characters and then returns the resulting string. HTML strings which do not contain escape sequences are returned unchanged. [call [cmd ::htmlparse::2tree] [arg {html tree}]] This command is a wrapper around [cmd ::htmlparse::parse] which takes an HTML string (in [arg html]) and converts it into a tree containing the logical structure of the parsed document. The name of the tree is given to the command as its second argument ([arg tree]). The command does [cmd not] generate the tree by itself but expects that the caller provided it with an existing and empty tree. It also expects that the specified tree object follows the same interface as the tree object in tcllib -> struct. It doesn't have to be from tcllib -> struct, but it must provide the same interface. [para] The internal callback does some basic checking of HTML validity and tries to recover from the most basic errors. The command returns the contents of its second argument. Side effects are the creation and manipulation of a tree object. [para] Each node in the generated tree represent one tag in the input. The name of the tag is stored in the attribute [emph type] of the node. Any html attributes coming with the tag are stored unmodified in the attribute [emph data] of the tag. In other words, the command does [emph not] parse html attributes into their names and values. [para] If a tag contains text its node will have children of type [emph PCDATA] containing this text. The text will be stored in the attribute [emph data] of these children. [call [cmd ::htmlparse::removeVisualFluff] [arg tree]] This command walks a tree as generated by [cmd ::htmlparse::2tree] and removes all the nodes which represent visual tags and not structural ones. The purpose of the command is to make the tree easier to navigate without getting bogged down in visual information not relevant to the search. Its only argument is the name of the tree to cut down. [call [cmd ::htmlparse::removeFormDefs] [arg tree]] Like [cmd ::htmlparse::removeVisualFluff] this command is here to cut down on the size of the tree as generated by [cmd ::htmlparse::2tree]. It removes all nodes representing forms and form elements. Its only argument is the name of the tree to cut down. [list_end] [vset CATEGORY htmlparse] [include ../common-text/feedback.inc] [manpage_end]