script: Implement TextEncoder::encodeInto() (#33360)

* Implement TextEncoder::encodeInto()

Signed-off-by: webbeef <me@webbeef.org>

* Update components/script/dom/textencoder.rs

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

* Update components/script/dom/textencoder.rs

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

---------

Signed-off-by: webbeef <me@webbeef.org>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/textencoder.rs

@@ -5,12 +5,16 @@
 use std::ptr;
 
 use dom_struct::dom_struct;
+use js::gc::CustomAutoRooterGuard;
 use js::jsapi::JSObject;
 use js::rust::HandleObject;
+use js::typedarray;
 use js::typedarray::Uint8Array;
 
 use crate::dom::bindings::buffer_source::create_buffer_source;
-use crate::dom::bindings::codegen::Bindings::TextEncoderBinding::TextEncoderMethods;
+use crate::dom::bindings::codegen::Bindings::TextEncoderBinding::{
+    TextEncoderEncodeIntoResult, TextEncoderMethods,
+};
 use crate::dom::bindings::error::Fallible;
 use crate::dom::bindings::reflector::{reflect_dom_object_with_proto, Reflector};
 use crate::dom::bindings::root::DomRoot;
@@ -43,7 +47,7 @@ impl TextEncoder {
         )
     }
 
-    // https://encoding.spec.whatwg.org/#dom-textencoder
+    /// <https://encoding.spec.whatwg.org/#dom-textencoder>
     #[allow(non_snake_case)]
     pub fn Constructor(
         global: &GlobalScope,
@@ -55,12 +59,12 @@ impl TextEncoder {
 }
 
 impl TextEncoderMethods for TextEncoder {
-    // https://encoding.spec.whatwg.org/#dom-textencoder-encoding
+    /// <https://encoding.spec.whatwg.org/#dom-textencoder-encoding>
     fn Encoding(&self) -> DOMString {
         DOMString::from("utf-8")
     }
 
-    // https://encoding.spec.whatwg.org/#dom-textencoder-encode
+    /// <https://encoding.spec.whatwg.org/#dom-textencoder-encode>
     fn Encode(&self, cx: JSContext, input: USVString) -> Uint8Array {
         let encoded = input.0.as_bytes();
 
@@ -68,4 +72,55 @@ impl TextEncoderMethods for TextEncoder {
         create_buffer_source(cx, encoded, js_object.handle_mut())
             .expect("Converting input to uint8 array should never fail")
     }
+
+    /// <https://encoding.spec.whatwg.org/#dom-textencoder-encodeinto>
+    #[allow(unsafe_code)]
+    fn EncodeInto(
+        &self,
+        source: USVString,
+        mut destination: CustomAutoRooterGuard<typedarray::Uint8Array>,
+    ) -> TextEncoderEncodeIntoResult {
+        let available = destination.len();
+
+        // Bail out if the destination has no space available.
+        if available == 0 {
+            return TextEncoderEncodeIntoResult {
+                read: Some(0),
+                written: Some(0),
+            };
+        }
+
+        let mut read = 0;
+        let mut written = 0;
+
+        let dest = unsafe { destination.as_mut_slice() };
+
+        // Step 3, 4, 5, 6
+        // Turn the source into a queue of scalar values.
+        // Iterate over the source values.
+        for result in source.0.chars() {
+            let utf8_len = result.len_utf8();
+            if available - written >= utf8_len {
+                // Step 6.4.1
+                // If destination’s byte length − written is greater than or equal to the number of bytes in result
+                read += if result > '\u{FFFF}' { 2 } else { 1 };
+
+                // Write the bytes in result into destination, with startingOffset set to written.
+                let target = &mut dest[written..written + utf8_len];
+                result.encode_utf8(target);
+
+                // Increment written by the number of bytes in result.
+                written += utf8_len;
+            } else {
+                // Step 6.4.2
+                // Bail out when destination buffer is full.
+                break;
+            }
+        }
+
+        TextEncoderEncodeIntoResult {
+            read: Some(read),
+            written: Some(written as _),
+        }
+    }
 }

components/script/dom/webidls/TextEncoder.webidl

@@ -3,10 +3,17 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 /* https://encoding.spec.whatwg.org/#interface-textencoder */
+
+dictionary TextEncoderEncodeIntoResult {
+  unsigned long long read;
+  unsigned long long written;
+};
+
 [Exposed=(Window,Worker)]
 interface TextEncoder {
    [Throws] constructor();
    readonly attribute DOMString encoding;
    [NewObject]
    Uint8Array encode(optional USVString input = "");
+   TextEncoderEncodeIntoResult encodeInto(USVString source, [AllowShared] Uint8Array destination);
 };