Hickory

Hickory parses HTML into Clojure data structures, so you can analyze, transform, and output back to HTML. HTML can be parsed into hiccup vectors, or into a map-based DOM-like format very similar to that used by clojure.xml. It can be used from both Clojure and Clojurescript.

There is API documentation available.

Usage

Parsing

To start, you will want to process your HTML into a parsed representation. Once the HTML is in this form, it can be converted to either Hiccup or Hickory format for further processing. There are two parsing functions,

parse

parse-fragment

The first function,

parse

parse-fragment

parse-fragment

These parsed objects can be turned into either Hiccup vector trees or Hickory DOM maps using the functions

as-hiccup

as-hickory

Here's a usage example.

user=> (use 'hickory.core)
nil
user=> (def parsed-doc (parse "foo"))
#'user/parsed-doc
user=> (as-hiccup parsed-doc)
([:html {} [:head {}] [:body {} [:a {:href "foo"} "foo"]]])
user=> (as-hickory parsed-doc)
{:type :document, :content [{:type :element, :attrs nil, :tag :html, :content [{:type :element, :attrs nil, :tag :head, :content nil} {:type :element, :attrs nil, :tag :body, :content [{:type :element, :attrs {:href "foo"}, :tag :a, :content ["foo"]}]}]}]}
user=> (def parsed-frag (parse-fragment "foo bar"))
#'user/parsed-frag
user=> (as-hiccup parsed-frag)
IllegalArgumentException No implementation of method: :as-hiccup of protocol: #'hickory.core/HiccupRepresentable found for class: clojure.lang.PersistentVector  clojure.core/-cache-protocol-fn (core_deftype.clj:495)

user=> (map as-hiccup parsed-frag)
([:a {:href "foo"} "foo"] " " [:a {:href "bar"} "bar"])
user=> (map as-hickory parsed-frag)
({:type :element, :attrs {:href "foo"}, :tag :a, :content ["foo"]} " " {:type :element, :attrs {:href "bar"}, :tag :a, :content ["bar"]})

In the example above, you can see an HTML document that is parsed once and then converted to both Hiccup and Hickory formats. Similarly, a fragment is parsed, but it cannot be directly used with

as-hiccup

as-hickory

The namespace

hickory.zip

hiccup-zip

hickory-zip

user=> (use 'hickory.zip)
nil
user=> (require '[clojure.zip :as zip])
nil
user=> (-> (hiccup-zip (as-hiccup (parse "bar
"))) zip/node)
([:html {} [:head {}] [:body {} [:a {:href "foo"} "bar" [:br {}]]]])
user=> (-> (hiccup-zip (as-hiccup (parse "bar
"))) zip/next zip/node)
[:html {} [:head {}] [:body {} [:a {:href "foo"} "bar" [:br {}]]]]
user=> (-> (hiccup-zip (as-hiccup (parse "bar
"))) zip/next zip/next zip/node)
[:head {}]
user=> (-> (hiccup-zip (as-hiccup (parse "bar
")))
           zip/next zip/next
           (zip/replace [:head {:id "a"}])
           zip/node)
[:head {:id "a"}]
user=> (-> (hiccup-zip (as-hiccup (parse "bar
")))
           zip/next zip/next
           (zip/replace [:head {:id "a"}])
           zip/root)
([:html {} [:head {:id "a"}] [:body {} [:a {:href "foo"} "bar" [:br {}]]]])
user=> (-> (hickory-zip (as-hickory (parse "bar
")))
           zip/next zip/next
           (zip/replace {:type :element :tag :head :attrs {:id "a"} :content nil})
           zip/root)
{:type :document, :content [{:type :element, :attrs nil, :tag :html, :content [{:content nil, :type :element, :attrs {:id "a"}, :tag :head} {:type :element, :attrs nil, :tag :body, :content [{:type :element, :attrs {:href "foo"}, :tag :a, :content ["bar" {:type :element, :attrs nil, :tag :br, :content nil}]}]}]}]}
user=> (hickory-to-html *1)
"bar
"

In this example, we can see a basic document being parsed into Hiccup form. Then, using zippers, the HEAD element is navigated to, and then replaced with one that has an id of "a". The final tree, including the modification, is also shown using

zip/root

hickory-to-html

Selectors

Hickory also comes with a set of CSS-style selectors that operate on hickory-format data in the

hickory.select

A selector is simply a function that takes a zipper loc from a hickory html tree data structure as its only argument. The selector will return its argument if the selector applies to it, and nil otherwise. Writing useful selectors can often be involved, so most of the

hickory.select

user=> (use 'hickory.core)
nil
user=> (require '[hickory.select :as s])
nil
user=> (require '[clj-http.client :as client])
nil
user=> (require '[clojure.string :as string])
nil
user=> (def site-htree (-> (client/get "http://formula1.com/default.html") :body parse as-hickory))
#'user/site-htree
user=> (-> (s/select (s/child (s/class "subCalender") ; sic
                              (s/tag :div)
                              (s/id :raceDates)
                              s/first-child
                              (s/tag :b))
                     site-htree)
           first :content first string/trim)
"10, 11, 12 May 2013"

In this example, we get the contents of the homepage and use

select

Using the selectors allows you to search large HTML documents for nodes of interest with a relatively small amount of code. There are many selectors available in the

hickory.select

• node-type

  : Give this function a keyword or string that names the contents of the

  :type

  field in a hickory node, and it gives you a selector that will select nodes of that type. Example:

  (node-type :comment)

• tag

  : Give this function a keyword or string that names the contents of the

  :tag

  field in a hickory node, and it gives you a selector that will select nodes with that tag. Example:

  (tag :div)

• attr

  : Give this function a keyword or string that names an attribute in the

  :attrs

  map of a hickory node, and it gives you a selector that will select nodes whose

  :attrs

  map contains that key. Give a single-argument function as an additional argument, and the resulting selector function will additionally require the value of that key to be such that the function given as the last argument returns true. Example:

  (attr :id #(.startsWith % "foo"))

• id

  : Give this function a keyword or string that names the

  :id

  attribute in the

  :attrs

  map and it will return a selector function that selects nodes that have that id (this comparison is case-insensitive). Example:

  (id :raceDates)

• class

  : Give this function a keyword or string that names a class that the node should have in the

  :class

  attribute in the

  :attrs

  map, and it will return a function that selects nodes that have the given class somewhere in their class string. Example:

  (class :foo)

• any

  : This selector takes no arguments, do not invoke it; returns any node that is an element, similarly to CSS's '*' selector.

• element

  : This selector is equivalent to the

  any

  selector; this alternate name can make it clearer when the intention is to exclude non-element nodes from consideration.

• root

  : This selector takes no arguments and should not be invoked; simply returns the root node (the HTML element).

• n-moves-until

  : This selector returns a selector function that selects its argument if that argument is some distance from a boundary. The first two arguments,

  n

  and

  c

  define the counting: it only selects nodes whose distance can be written in the form

  nk+c

  for some natural number

  k

  . The distance and boundary are defined by the number of times the zipper-movement function in the third argument is applied before the boundary function in the last argument is true. See doc string for details.

• nth-of-type

  : This selector returns a selector function that selects its argument if that argument is the

  (nk+c)

  'th child of the given tag type of some parent node for some natural

  k

  . Optionally, instead of the

  n

  and

  c

  arguments, the keywords

  :odd

  and

  :even

  can be given.

• nth-last-of-type

  : Just like

  nth-of-type

  but counts backwards from the last sibling.

• nth-child

  : This selector returns a selector function that selects its argument if that argument is the

  (nk+c)

  'th child of its parent node for some natural

  k

  . Instead of the

  n

  and

  c

  arguments, the keywords

  :odd

  and

  :even

  can be given.

• nth-last-child

  : Just like

  nth-last-child

  but counts backwards from the last sibling.

• first-child

  : Takes no arguments, do not invoke it; equivalent to

  (nth-child 1)

  .

• last-child

  : Takes no arguments, do not invoke it; equivalent to

  (nth-last-child 1)

  .

There are also selector combinators, which take as argument some number of other selectors, and return a new selector that combines them into one larger selector. An example of this is the

child

• and

  : Takes any number of selectors, and returns a selector that only selects nodes for which all of the argument selectors are true.

• or

  : Takes any number of selectors, and retrurns a selector that only selects nodes for which at least one of the argument selectors are true.

• not

  : Takes a single selector as argument and returns a selector that only selects nodes that its argument selector does not.

• el-not

  : Takes a single selector as argument and returns a selector that only selects element nodes that its argument selector does not.

• child

  : Takes any number of selectors as arguments and returns a selector that returns true when the zipper location given as the argument is at the end of a chain of direct child relationships specified by the selectors given as arguments.

• descendant

  : Takes any number of selectors as arguments and returns a selector that returns true when the zipper location given as the argument is at the end of a chain of descendant relationships specified by the selectors given as arguments.

We can illustrate the selector combinators by continuing the Formula 1 example above. We suspect, to our dismay, that Sebastian Vettel is leading the championship for the fourth year in a row.

user=> (-> (s/select (s/descendant (s/class "subModule")
                                   (s/class "standings")
                                   (s/and (s/tag :tr)
                                          s/first-child)
                                   (s/and (s/tag :td)
                                          (s/nth-child 2))
                                   (s/tag :a))
                     site-htree)
           first :content first string/trim)
"Sebastian Vettel"           

Our fears are confirmed, Sebastian Vettel is well on his way to a fourth consecutive championship. If you were to inspect the page by hand (as of around May 2013, at least), you would see that unlike the

child

descendant

and

tag

first-child

td

A

Finally, it's worth noting that the

select

select-locs

clojure.zip

select-locs

select-next-loc

The doc strings for the functions in the

hickory.select

For more details, see the API Documentation.

Hickory format

Why two formats? It's very easy to see in the example above, Hiccup is very convenient to use for writing HTML. It has a compact syntax, with CSS-like shortcuts for specifying classes and ids. It also allows parts of the vector to be skipped if they are not important.

It's a little bit harder to process data in Hiccup format. First of all, each form has to be checked for the presence of the attribute map, and the traversal adjusted accordingly. Raw Hiccup vectors might also have information about class and id in one of two different places. Finally, not every piece of an HTML document can be expressed in Hiccup without resorting to writing HTML in strings. For example, if you want to put a doctype or comment on your document, it has to be done as a string in your Hiccup form containing "

" or
"
".

The Hickory format is another data format intended to allow a
roundtrip from HTML as text, into a data structure that is easy to
process and modify, and back into equivalent (but not identical, in
general) HTML. Because it can express all parts of an HTML document in
a parsed form, it is easier to search and modify the structure of the
document.

A Hickory node is either a map or a string. If it is a map, it will
have some subset of the following four keys, depending on the 
:type
:

• :type

  - This will be one of

  :comment

  ,

  :document

  ,

  :document-type

  ,

  :element

• :tag

  - A node's tag (for example,

  :img

  ). This will only be present for nodes of type

  :element

  .

• :attrs

  - A node's attributes, as a map of keywords to values (for example, {:href "/a"}). This will only be present for nodes of type

  :element

  .

• :content

  - A node's child nodes, in a vector. Only

  :comment

  ,

  :document

  , and

  :element

  nodes have children.

Text and CDATA nodes are represented as strings.

This is almost the exact same structure used by clojure.xml, the only difference being the addition of the

:type

Obtaining

To get hickory, add

[hickory "0.7.1"]

to your project.clj, or an equivalent entry for your Maven-compatible build tool.

ClojureScript support

Hickory expects a DOM implementation and thus won't work out of the box on node. On browsers it works for IE9+ (you can find a workaround for IE9 here).

Changes

• Version 0.7.1. Thanks to Matt Grimm for adding the up-pred zipper function.

• Version 0.7.0. Thanks to Ricardo J. Méndez for the following updates.

  • Removed dependency on cljx, since it was deprecated in June 2015.
  • Converted all files and conditionals to cljc.
  • Moved tests to cljs.test with doo, since cemerick.test was deprecated over a year ago.
  • Updated Clojure and ClojureScript dependencies to avoid conflicts.
  • Updated JSoup to 1.9.2, which should bring improved parsing performance.

• Released version 0.6.0.

  • Updated JSoup to version 1.8.3. This version of JSoup contains bug fixes, but slightly changes the way it handles HTML: some parses and output might have different case than before. HTML is still case-insensitive, of course, but Hickory minor version has been increased just in case. API and semantics are otherwise unchanged.

• Released version 0.5.4.

  • Fixed project dependencies so ClojureScript is moved to a dev-dependency.

• Released version 0.5.3.

  • Minor bug fix to accommodate ClojureScript's new type hinting support.

• Released version 0.5.2.

  • Updates the Clojurescript version to use the latest version of Clojurescript (0.0-1934).

• Released version 0.5.1.

  • Added

    has-child

    and

    has-descendant

    selectors. Be careful with

    has-descendant

    , as it must do a full subtree search on each node, which is not fast.

• Released version 0.5.0.

  • Now works in Clojurescript as well, huge thanks to Julien Eluard for doing the heavy lifting on this.
  • Reorganized parts of the API into more granular namespaces for better organization.
  • Added functions to convert between Hiccup and Hickory format; note that this conversion is not always exact or roundtripable, and can cause a full HTML reparse.
  • Added new selector,

    element-child

    , which selects element nodes that are the child of another element node.
  • Numerous bug fixes and improvements.

• Released version 0.4.1, which adds a number of new selectors and selector combinators, including

  find-in-text

  ,

  precede-adjacent

  ,

  follow-adjacent

  ,

  precede

  and

  follow

  .

• Released version 0.4.0. Adds the

  hickory.select

  namespace with many helpful functions for searching through hickory-format HTML documents for specific nodes.

• Released version 0.3.0. Provides a more helpful error message when hickory-to-html has an error. Now requires Clojure 1.4.

• Released version 0.2.3. Fixes a bug where hickory-to-html was not html-escaping the values of tag attributes.

• Released version 0.2.2. Fixes a bug where hickory-to-html was improperly html-escaping the contents of script/style tags.

• Released version 0.2.1. This version fixes bugs:

  • hickory-to-html now properly escapes text nodes
  • text nodes will now preserve whitespace correctly

• Released version 0.2.0. This version adds a second parsed data format, explained above. To support this, the API for

  parse

  and

  parse-fragment

  has been changed to allow their return values to be passed to functions

  as-hiccup

  or

  as-hickory

  to determine the final format. Also added are zippers for both Hiccup and Hickory formats.

License

Copyright © 2012 David Santiago

Distributed under the Eclipse Public License, the same as Clojure.