Auto merge of #20431 - talklittle:issues-13234-5600-squashed, r=jdm

TextDecoder: streaming decode, ignoreBOM

<!-- Please describe your changes on the following line: -->
Implement streaming decode and ignoreBOM flag for TextDecoder.

https://encoding.spec.whatwg.org/#dom-textdecoder-decode

https://encoding.spec.whatwg.org/#dom-textdecoder-ignorebom

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #13234 (github issue number if applicable).
- [x] These changes fix #5600 (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because the wpt tests are used for testing:

* /encoding/textdecoder-fatal-streaming.html
* /encoding/textdecoder-streaming.html
* /encoding/textdecoder-ignorebom.html

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3 files changed, 81 insertions, 27 deletions

diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index be38b14a540..0fd94953e3b 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -47,7 +47,7 @@ use dom::bindings::root::{Dom, DomRoot};
 use dom::bindings::str::{DOMString, USVString};
 use dom::bindings::utils::WindowProxyHandler;
 use dom::document::PendingRestyle;
-use encoding_rs::Encoding;
+use encoding_rs::{Decoder, Encoding};
 use euclid::{Transform2D, Transform3D, Point2D, Vector2D, Rect, TypedSize2D, TypedScale};
 use euclid::Length as EuclidLength;
 use html5ever::{Prefix, LocalName, Namespace, QualName};
@@ -127,6 +127,9 @@ unsafe_no_jsmanaged_fields!(CSSError);
 
 unsafe_no_jsmanaged_fields!(&'static Encoding);
 
+unsafe_no_jsmanaged_fields!(RefCell<Decoder>);
+unsafe_no_jsmanaged_fields!(RefCell<Vec<u8>>);
+
 unsafe_no_jsmanaged_fields!(Reflector);
 
 unsafe_no_jsmanaged_fields!(Duration);
diff --git a/components/script/dom/textdecoder.rs b/components/script/dom/textdecoder.rs
index 3c061322f07..b9e0bdd9d55 100644
--- a/components/script/dom/textdecoder.rs
+++ b/components/script/dom/textdecoder.rs
@@ -11,22 +11,34 @@ use dom::bindings::root::DomRoot;
 use dom::bindings::str::{DOMString, USVString};
 use dom::globalscope::GlobalScope;
 use dom_struct::dom_struct;
-use encoding_rs::Encoding;
+use encoding_rs::{Decoder, DecoderResult, Encoding};
 use std::borrow::ToOwned;
+use std::cell::{Cell, RefCell};
 
 #[dom_struct]
 pub struct TextDecoder {
     reflector_: Reflector,
     encoding: &'static Encoding,
     fatal: bool,
+    ignoreBOM: bool,
+    #[ignore_malloc_size_of = "defined in encoding_rs"]
+    decoder: RefCell<Decoder>,
+    in_stream: RefCell<Vec<u8>>,
+    do_not_flush: Cell<bool>,
 }
 
 impl TextDecoder {
-    fn new_inherited(encoding: &'static Encoding, fatal: bool) -> TextDecoder {
+    fn new_inherited(encoding: &'static Encoding, fatal: bool, ignoreBOM: bool) -> TextDecoder {
         TextDecoder {
             reflector_: Reflector::new(),
             encoding: encoding,
             fatal: fatal,
+            ignoreBOM: ignoreBOM,
+            decoder: RefCell::new(
+                if ignoreBOM { encoding.new_decoder() } else { encoding.new_decoder_without_bom_handling() }
+            ),
+            in_stream: RefCell::new(Vec::new()),
+            do_not_flush: Cell::new(false),
         }
     }
 
@@ -34,8 +46,9 @@ impl TextDecoder {
         Err(Error::Range("The given encoding is not supported.".to_owned()))
     }
 
-    pub fn new(global: &GlobalScope, encoding: &'static Encoding, fatal: bool) -> DomRoot<TextDecoder> {
-        reflect_dom_object(Box::new(TextDecoder::new_inherited(encoding, fatal)),
+    pub fn new(global: &GlobalScope, encoding: &'static Encoding, fatal: bool, ignoreBOM: bool)
+            -> DomRoot<TextDecoder> {
+        reflect_dom_object(Box::new(TextDecoder::new_inherited(encoding, fatal, ignoreBOM)),
                            global,
                            TextDecoderBinding::Wrap)
     }
@@ -49,7 +62,7 @@ impl TextDecoder {
             None => return TextDecoder::make_range_error(),
             Some(enc) => enc
         };
-        Ok(TextDecoder::new(global, encoding, options.fatal))
+        Ok(TextDecoder::new(global, encoding, options.fatal, options.ignoreBOM))
     }
 }
 
@@ -65,30 +78,68 @@ impl TextDecoderMethods for TextDecoder {
         self.fatal
     }
 
+    // https://encoding.spec.whatwg.org/#dom-textdecoder-ignorebom
+    fn IgnoreBOM(&self) -> bool {
+        self.ignoreBOM
+    }
+
     // https://encoding.spec.whatwg.org/#dom-textdecoder-decode
     fn Decode(
         &self,
         input: Option<ArrayBufferViewOrArrayBuffer>,
-        _options: &TextDecodeOptions
+        options: &TextDecodeOptions
     ) -> Fallible<USVString> {
-        match input {
-            Some(arr) => {
-                let vec: Vec<u8> = match arr {
-                    ArrayBufferViewOrArrayBuffer::ArrayBufferView(ref a) => a.to_vec(),
-                    ArrayBufferViewOrArrayBuffer::ArrayBuffer(ref a) => a.to_vec()
-                };
-                let s = if self.fatal {
-                    match self.encoding.decode_without_bom_handling_and_without_replacement(&vec) {
-                        Some(s) => s,
-                        None => return Err(Error::Type("Decoding failed".to_owned())),
-                    }
-                } else {
-                    let (s, _has_errors) = self.encoding.decode_without_bom_handling(&vec);
-                    s
-                };
-                Ok(USVString(s.into_owned()))
+        // Step 1.
+        if !self.do_not_flush.get() {
+            if self.ignoreBOM {
+                self.decoder.replace(self.encoding.new_decoder_without_bom_handling());
+            } else {
+                self.decoder.replace(self.encoding.new_decoder());
             }
-            None => Ok(USVString("".to_owned()))
+            self.in_stream.replace(Vec::new());
         }
+
+        // Step 2.
+        self.do_not_flush.set(options.stream);
+
+        // Step 3.
+        match input {
+            Some(ArrayBufferViewOrArrayBuffer::ArrayBufferView(ref a)) => {
+                self.in_stream.borrow_mut().extend_from_slice(&a.to_vec());
+            },
+            Some(ArrayBufferViewOrArrayBuffer::ArrayBuffer(ref a)) => {
+                self.in_stream.borrow_mut().extend_from_slice(&a.to_vec());
+            },
+            None => {},
+        };
+
+        let mut decoder = self.decoder.borrow_mut();
+        let (remaining, s) = {
+            let mut in_stream = self.in_stream.borrow_mut();
+
+            let (remaining, s) = if self.fatal {
+                // Step 4.
+                let mut out_stream = String::with_capacity(
+                    decoder.max_utf8_buffer_length_without_replacement(in_stream.len()).unwrap()
+                );
+                // Step 5: Implemented by encoding_rs::Decoder.
+                match decoder.decode_to_string_without_replacement(&in_stream, &mut out_stream, !options.stream) {
+                    (DecoderResult::InputEmpty, read) => {
+                        (in_stream.split_off(read), out_stream)
+                    },
+                    // Step 5.3.3.
+                    _ => return Err(Error::Type("Decoding failed".to_owned())),
+                }
+            } else {
+                // Step 4.
+                let mut out_stream = String::with_capacity(decoder.max_utf8_buffer_length(in_stream.len()).unwrap());
+                // Step 5: Implemented by encoding_rs::Decoder.
+                let (_result, read, _replaced) = decoder.decode_to_string(&in_stream, &mut out_stream, !options.stream);
+                (in_stream.split_off(read), out_stream)
+            };
+            (remaining, s)
+        };
+        self.in_stream.replace(remaining);
+        Ok(USVString(s))
     }
 }
diff --git a/components/script/dom/webidls/TextDecoder.webidl b/components/script/dom/webidls/TextDecoder.webidl
index b511fec3d79..4e9c3683dd7 100644
--- a/components/script/dom/webidls/TextDecoder.webidl
+++ b/components/script/dom/webidls/TextDecoder.webidl
@@ -5,18 +5,18 @@
 // https://encoding.spec.whatwg.org/#interface-textdecoder
 dictionary TextDecoderOptions {
   boolean fatal = false;
-  // boolean ignoreBOM = false;
+  boolean ignoreBOM = false;
 };
 
 dictionary TextDecodeOptions {
-  // boolean stream = false;
+  boolean stream = false;
 };
 
 [Constructor(optional DOMString label = "utf-8", optional TextDecoderOptions options), Exposed=(Window,Worker)]
 interface TextDecoder {
   readonly attribute DOMString encoding;
   readonly attribute boolean fatal;
-  // readonly attribute boolean ignoreBOM;
+  readonly attribute boolean ignoreBOM;
   [Throws]
   USVString decode(optional BufferSource input, optional TextDecodeOptions options);
 };