Add comments for html5ever/examples (#506)

* Adding comments for arena

* Adding comments for noop-tokenize

* Adding comments for noop-tree-builder

* Adding comments for print-tree-actions

* Add comments for tokenize

* Removing redundant comments

---------

Co-authored-by: Or Gany <gangana3@gmail.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

html5ever/examples/arena.rs

@@ -19,36 +19,32 @@ use std::collections::HashSet;
 use std::io::{self, Read};
 use std::ptr;
 
-fn main() {
-    let mut bytes = Vec::new();
-    io::stdin().read_to_end(&mut bytes).unwrap();
-    let arena = typed_arena::Arena::new();
-    html5ever_parse_slice_into_arena(&bytes, &arena);
-}
-
+/// By using our Sink type, the arena is filled with parsed HTML.
 fn html5ever_parse_slice_into_arena<'a>(bytes: &[u8], arena: Arena<'a>) -> Ref<'a> {
     let sink = Sink {
         arena,
         document: arena.alloc(Node::new(NodeData::Document)),
         quirks_mode: QuirksMode::NoQuirks,
     };
+
     parse_document(sink, Default::default())
         .from_utf8()
         .one(bytes)
 }
 
 type Arena<'arena> = &'arena typed_arena::Arena<Node<'arena>>;
-
 type Ref<'arena> = &'arena Node<'arena>;
-
 type Link<'arena> = Cell<Option<Ref<'arena>>>;
 
+/// Sink struct is responsible for handling how the data that comes out of the HTML parsing
+/// unit (TreeBuilder in our case) is handled.
 struct Sink<'arena> {
     arena: Arena<'arena>,
     document: Ref<'arena>,
     quirks_mode: QuirksMode,
 }
 
+/// DOM node which contains links to other nodes in the tree.
 pub struct Node<'arena> {
     parent: Link<'arena>,
     next_sibling: Link<'arena>,
@@ -58,6 +54,7 @@ pub struct Node<'arena> {
     data: NodeData<'arena>,
 }
 
+/// HTML node data which can be an element, a comment, a string, a DOCTYPE, etc...
 pub enum NodeData<'arena> {
     Document,
     Doctype {
@@ -178,6 +175,11 @@ impl<'arena> Sink<'arena> {
     }
 }
 
+/// By implementing the TreeSink trait we determine how the data from the tree building step
+/// is processed. In our case, our data is allocated in the arena and added to the Node data
+/// structure.
+///
+/// For deeper understating of each function go to the TreeSink declaration.
 impl<'arena> TreeSink for Sink<'arena> {
     type Handle = Ref<'arena>;
     type Output = Ref<'arena>;
@@ -333,3 +335,18 @@ impl<'arena> TreeSink for Sink<'arena> {
         }
     }
 }
+
+/// In this example an "arena" is created and filled with the DOM nodes.
+/// "Arena" is a type of allocation in which a block of memory is allocated
+/// and later filled with data, DOM nodes in this case. When the arena is deallocated
+/// it is destroyed with all of its items.
+///
+/// Further info about arena: https://docs.rs/typed-arena/latest/typed_arena/
+fn main() {
+    // Read HTML from the standard input
+    let mut bytes = Vec::new();
+    io::stdin().read_to_end(&mut bytes).unwrap();
+
+    let arena = typed_arena::Arena::new();
+    html5ever_parse_slice_into_arena(&bytes, &arena);
+}

html5ever/examples/noop-tokenize.rs

@@ -16,22 +16,27 @@ use std::io;
 use html5ever::tendril::*;
 use html5ever::tokenizer::{BufferQueue, Token, TokenSink, TokenSinkResult, Tokenizer};
 
+
+/// In our case, our sink only contains a tokens vector
 struct Sink(Vec<Token>);
 
 impl TokenSink for Sink {
     type Handle = ();
 
+    /// Each processed token will be handled by this method
     fn process_token(&mut self, token: Token, _line_number: u64) -> TokenSinkResult<()> {
-        // Don't use the token, but make sure we don't get
-        // optimized out entirely.
         self.0.push(token);
         TokenSinkResult::Continue
     }
 }
 
+/// In this example we implement the TokenSink trait which lets us implement how each
+/// parsed token is treated. In our example we take each token and insert it into a vector.
 fn main() {
+    // Read HTML from standard input
     let mut chunk = ByteTendril::new();
     io::stdin().read_to_tendril(&mut chunk).unwrap();
+
     let mut input = BufferQueue::default();
     input.push_back(chunk.try_reinterpret().unwrap());
 

html5ever/examples/noop-tree-builder.rs

@@ -32,6 +32,10 @@ impl Sink {
     }
 }
 
+/// By implementing the TreeSink trait we determine how the data from the tree building step
+/// is processed. In this case the DOM elements are written into the "names" hashmap.
+///
+/// For deeper understating of each function go to the TreeSink declaration.
 impl TreeSink for Sink {
     type Handle = usize;
     type Output = Self;
@@ -98,11 +102,15 @@ impl TreeSink for Sink {
     fn mark_script_already_started(&mut self, _node: &usize) {}
 }
 
+/// In this example we implement the TreeSink trait which takes each parsed elements and insert
+/// it to a hashmap, while each element is given a numeric id.
 fn main() {
     let sink = Sink {
         next_id: 1,
         names: HashMap::new(),
     };
+
+    // Read HTML from the standard input and parse it
     let stdin = io::stdin();
     parse_document(sink, Default::default())
         .from_utf8()

html5ever/examples/print-tree-actions.rs

@@ -158,6 +158,9 @@ impl TreeSink for Sink {
     }
 }
 
+/// Same example as the "noop-tree-builder", but this time every function implemented in our
+/// Sink object prints a log, so it's easier to get an understating of when each function is
+/// called.
 fn main() {
     let sink = Sink {
         next_id: 1,

html5ever/examples/tokenize.rs

@@ -81,10 +81,15 @@ impl TokenSink for TokenPrinter {
     }
 }
 
+/// In this example we implement the TokenSink trait in such a way that each token is printed.
+/// If a there's an error while processing a token it is printed as well.
 fn main() {
     let mut sink = TokenPrinter { in_char_run: false };
+
+    // Read HTML from standard input
     let mut chunk = ByteTendril::new();
     io::stdin().read_to_tendril(&mut chunk).unwrap();
+
     let mut input = BufferQueue::default();
     input.push_back(chunk.try_reinterpret().unwrap());
 
@@ -96,6 +101,7 @@ fn main() {
         },
     );
     let _ = tok.feed(&mut input);
+
     assert!(input.is_empty());
     tok.end();
     sink.is_char(false);