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impl jsstr_to_string and latin1_to_string using &JSContext #718

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b8ac842
impl jsstr_to_string and latin1_to_string using &JSContext
sagudev Mar 15, 2026
db92583
use safe variant in tests
sagudev Mar 15, 2026
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6 changes: 2 additions & 4 deletions mozjs/benches/latin1_string_conversion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ use criterion::{
criterion_group, criterion_main, BenchmarkGroup, BenchmarkId, Criterion, Throughput,
};
use mozjs::context::JSContext;
use mozjs::conversions::jsstr_to_string;
use mozjs::conversions::jsstr_to_string_safe;
use mozjs::glue::{CreateJSExternalStringCallbacks, JSExternalStringCallbacksTraps};
use mozjs::jsapi::OnNewGlobalHookOption;
use mozjs::realm::AutoRealm;
Expand Down Expand Up @@ -52,9 +52,7 @@ fn bench_str_repetition(
&latin1_jsstr,
|b, js_str| {
b.iter(|| {
unsafe {
jsstr_to_string(context.raw_cx(), NonNull::new(js_str.get()).unwrap())
};
jsstr_to_string_safe(context, NonNull::new(js_str.get()).unwrap());
})
},
);
Expand Down
40 changes: 30 additions & 10 deletions mozjs/src/conversions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -30,16 +30,17 @@

use crate::error::throw_type_error;
use crate::jsapi::AssertSameCompartment;
use crate::jsapi::NewArrayObject1;
use crate::jsapi::JS;
use crate::jsapi::{ForOfIterator, ForOfIterator_NonIterableBehavior};
use crate::jsapi::{Heap, JS_DefineElement, JS_GetLatin1StringCharsAndLength};
use crate::jsapi::{Heap, JS_DefineElement};
use crate::jsapi::{JSContext, JSObject, JSString, RootedObject, RootedValue};
use crate::jsapi::{JS_DeprecatedStringHasLatin1Chars, JS_NewStringCopyUTF8N, JSPROP_ENUMERATE};
use crate::jsapi::{JS_GetTwoByteStringCharsAndLength, NewArrayObject1};
use crate::jsval::{BooleanValue, DoubleValue, Int32Value, NullValue, UInt32Value, UndefinedValue};
use crate::jsval::{JSVal, ObjectOrNullValue, ObjectValue, StringValue, SymbolValue};
use crate::rooted;
use crate::rust::maybe_wrap_value;
use crate::rust::wrappers2::{JS_GetLatin1StringCharsAndLength, JS_GetTwoByteStringCharsAndLength};
use crate::rust::{maybe_wrap_object_or_null_value, maybe_wrap_object_value, ToString};
use crate::rust::{HandleValue, MutableHandleValue};
use crate::rust::{ToBoolean, ToInt32, ToInt64, ToNumber, ToUint16, ToUint32, ToUint64};
Expand Down Expand Up @@ -596,12 +597,12 @@ impl FromJSValConvertible for f64 {

/// Converts a `JSString`, encoded in "Latin1" (i.e. U+0000-U+00FF encoded as 0x00-0xFF) into a
/// `String`.
pub unsafe fn latin1_to_string(cx: *mut JSContext, s: NonNull<JSString>) -> String {
assert!(JS_DeprecatedStringHasLatin1Chars(s.as_ptr()));
pub fn latin1_to_string_safe(cx: &crate::context::JSContext, s: NonNull<JSString>) -> String {
assert!(unsafe { JS_DeprecatedStringHasLatin1Chars(s.as_ptr()) });

let mut length = 0;
let chars = unsafe {
let chars = JS_GetLatin1StringCharsAndLength(cx, ptr::null(), s.as_ptr(), &mut length);
let chars = JS_GetLatin1StringCharsAndLength(cx, s.as_ptr(), &mut length);
assert!(!chars.is_null());

slice::from_raw_parts(chars, length as usize)
Expand All @@ -620,18 +621,37 @@ pub unsafe fn latin1_to_string(cx: *mut JSContext, s: NonNull<JSString>) -> Stri
}

/// Converts a `JSString` into a `String`, regardless of used encoding.
pub unsafe fn jsstr_to_string(cx: *mut JSContext, jsstr: NonNull<JSString>) -> String {
if JS_DeprecatedStringHasLatin1Chars(jsstr.as_ptr()) {
return latin1_to_string(cx, jsstr);
pub fn jsstr_to_string_safe(cx: &crate::context::JSContext, jsstr: NonNull<JSString>) -> String {
if unsafe { JS_DeprecatedStringHasLatin1Chars(jsstr.as_ptr()) } {
return latin1_to_string_safe(cx, jsstr);
}

let mut length = 0;
let chars = JS_GetTwoByteStringCharsAndLength(cx, ptr::null(), jsstr.as_ptr(), &mut length);
let chars = unsafe { JS_GetTwoByteStringCharsAndLength(cx, jsstr.as_ptr(), &mut length) };
assert!(!chars.is_null());
let char_vec = slice::from_raw_parts(chars, length as usize);
let char_vec = unsafe { slice::from_raw_parts(chars, length as usize) };
String::from_utf16_lossy(char_vec)
}

/// Converts a `JSString`, encoded in "Latin1" (i.e. U+0000-U+00FF encoded as 0x00-0xFF) into a
/// `String`.
///
/// Use [`latin1_to_string_safe`] if possible as this function will be eventually removed.
pub unsafe fn latin1_to_string(cx: *mut JSContext, s: NonNull<JSString>) -> String {
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@jschwe jschwe Mar 15, 2026

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Should we perhaps add a deprecated annotation on it, or call it _legacy to make the comment about "will eventually be removed" more obvious at the usage sites?

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@sagudev sagudev Apr 26, 2026

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The way we are currently doing is just adding comments without renames/deprecation notice for less friction in servo. But eventually we should start doing this.

// while this can break direct invariants of JSContext
// it is ok in the current usage of this function and it avoids duplicating the code
let cx = crate::context::JSContext::from_ptr(NonNull::new(cx).unwrap());
latin1_to_string_safe(&cx, s)
}

/// Converts a `JSString` into a `String`, regardless of used encoding.
///
/// Use [`jsstr_to_string_safe`] if possible as this function will be eventually removed.
pub unsafe fn jsstr_to_string(cx: *mut JSContext, jsstr: NonNull<JSString>) -> String {
let cx = crate::context::JSContext::from_ptr(NonNull::new(cx).unwrap());
jsstr_to_string_safe(&cx, jsstr)
}

// https://heycam.github.io/webidl/#es-USVString
impl ToJSValConvertible for str {
#[inline]
Expand Down
8 changes: 4 additions & 4 deletions mozjs/tests/external_string.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ use std::ptr::NonNull;

#[cfg(test)]
use mozjs::context::JSContext;
use mozjs::conversions::jsstr_to_string;
use mozjs::conversions::jsstr_to_string_safe;
use mozjs::glue::{CreateJSExternalStringCallbacks, JSExternalStringCallbacksTraps};
use mozjs::jsapi::OnNewGlobalHookOption;
use mozjs::realm::AutoRealm;
Expand Down Expand Up @@ -100,7 +100,7 @@ fn external_string() {
callbacks
));
assert_eq!(
jsstr_to_string(context.raw_cx(), NonNull::new(utf16_jsstr.get()).unwrap()),
jsstr_to_string_safe(context, NonNull::new(utf16_jsstr.get()).unwrap()),
utf16_base
);
}
Expand All @@ -122,7 +122,7 @@ unsafe fn test_latin1_string(context: &mut JSContext, latin1_base: &str) {
callbacks
));
assert_eq!(
jsstr_to_string(context.raw_cx(), NonNull::new(latin1_jsstr.get()).unwrap()),
jsstr_to_string_safe(context, NonNull::new(latin1_jsstr.get()).unwrap()),
latin1_base
);
}
Expand All @@ -143,7 +143,7 @@ unsafe fn test_latin1_string_bytes(context: &mut JSContext, latin1_base: &[u8])
callbacks
));
assert_eq!(
jsstr_to_string(context.raw_cx(), NonNull::new(latin1_jsstr.get()).unwrap()),
jsstr_to_string_safe(context, NonNull::new(latin1_jsstr.get()).unwrap()),
encoding_rs::mem::decode_latin1(latin1_base)
);
}
Expand Down
13 changes: 8 additions & 5 deletions mozjs/tests/stack_gc_vector.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@
use std::ptr::{self, NonNull};
use std::sync::{LazyLock, Mutex};

use mozjs::conversions::jsstr_to_string;
use mozjs::conversions::jsstr_to_string_safe;
use mozjs::gc::StackGCVector;
use mozjs::jsapi::{
CompilationType, Handle, HandleString, HandleValue, JSContext, JSSecurityCallbacks, JSString,
Expand Down Expand Up @@ -34,29 +34,32 @@ unsafe extern "C" fn content_security_policy_allows(
_body_arg: HandleValue,
can_compile_strings: *mut bool,
) -> bool {
// SAFETY: We are in SM hook
let mut cx = unsafe { mozjs::context::JSContext::from_ptr(NonNull::new(cx).unwrap()) };
let cx = &mut cx;
let parameter_strings = SafeHandle::from_raw(parameter_strings);
assert_eq!(parameter_strings.len(), 2);

let string0 = parameter_strings.at(0).expect("should have a value");
let string0 = NonNull::new(*string0).expect("should be non-null");
assert_eq!(jsstr_to_string(cx, string0), "a".to_string());
assert_eq!(jsstr_to_string_safe(cx, string0), "a".to_string());

let string1 = parameter_strings.at(1).expect("should have a value");
let string1 = NonNull::new(*string1).expect("should be non-null");
assert_eq!(jsstr_to_string(cx, string1), "b".to_string());
assert_eq!(jsstr_to_string_safe(cx, string1), "b".to_string());

let parameter_args = SafeHandle::from_raw(parameter_args);
assert_eq!(parameter_args.len(), 2);

let arg0 = parameter_args.at(0).expect("should have a value");
let string0 = arg0.to_string();
let string0 = NonNull::new(string0).expect("should be non-null");
assert_eq!(jsstr_to_string(cx, string0), "a".to_string());
assert_eq!(jsstr_to_string_safe(cx, string0), "a".to_string());

let arg1 = parameter_args.at(1).expect("should have a value");
let string1 = arg1.to_string();
let string1 = NonNull::new(string1).expect("should be non-null");
assert_eq!(jsstr_to_string(cx, string1), "b".to_string());
assert_eq!(jsstr_to_string_safe(cx, string1), "b".to_string());

*RAN_CSP_CALLBACK.lock().unwrap() = true;
*can_compile_strings = true;
Expand Down
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