servo/components/script/dom/bindings/error.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

//! Utilities to throw exceptions from Rust bindings.

use std::slice::from_raw_parts;

#[cfg(feature = "js_backtrace")]
use backtrace::Backtrace;
use js::error::{throw_range_error, throw_type_error};
#[cfg(feature = "js_backtrace")]
use js::jsapi::StackFormat as JSStackFormat;
use js::jsapi::{ExceptionStackBehavior, JS_ClearPendingException, JS_IsExceptionPending};
use js::jsval::UndefinedValue;
use js::rust::wrappers::{JS_ErrorFromException, JS_GetPendingException, JS_SetPendingException};
use js::rust::{HandleObject, HandleValue, MutableHandleValue};
use libc::c_uint;
use script_bindings::conversions::SafeToJSValConvertible;
pub(crate) use script_bindings::error::*;
use script_bindings::root::DomRoot;
use script_bindings::str::DOMString;

#[cfg(feature = "js_backtrace")]
use crate::dom::bindings::cell::DomRefCell;
use crate::dom::bindings::conversions::{
    ConversionResult, SafeFromJSValConvertible, root_from_object,
};
use crate::dom::bindings::str::USVString;
use crate::dom::domexception::{DOMErrorName, DOMException};
use crate::dom::globalscope::GlobalScope;
use crate::dom::types::QuotaExceededError;
use crate::realms::InRealm;
use crate::script_runtime::{CanGc, JSContext as SafeJSContext};

#[cfg(feature = "js_backtrace")]
thread_local! {
    /// An optional stringified JS backtrace and stringified native backtrace from the
    /// the last DOM exception that was reported.
    static LAST_EXCEPTION_BACKTRACE: DomRefCell<Option<(Option<String>, String)>> = DomRefCell::new(None);
}

/// Error values that have no equivalent DOMException representation.
pub(crate) enum JsEngineError {
    /// An EMCAScript TypeError.
    Type(String),
    /// An ECMAScript RangeError.
    Range(String),
    /// The JS engine reported a thrown exception.
    JSFailed,
}

/// Set a pending exception for the given `result` on `cx`.
pub(crate) fn throw_dom_exception(
    cx: SafeJSContext,
    global: &GlobalScope,
    result: Error,
    can_gc: CanGc,
) {
    #[cfg(feature = "js_backtrace")]
    unsafe {
        capture_stack!(in(*cx) let stack);
        let js_stack = stack.and_then(|s| s.as_string(None, JSStackFormat::Default));
        let rust_stack = Backtrace::new();
        LAST_EXCEPTION_BACKTRACE.with(|backtrace| {
            *backtrace.borrow_mut() = Some((js_stack, format!("{:?}", rust_stack)));
        });
    }

    match create_dom_exception(global, result, can_gc) {
        Ok(exception) => unsafe {
            assert!(!JS_IsExceptionPending(*cx));
            rooted!(in(*cx) let mut thrown = UndefinedValue());
            exception.safe_to_jsval(cx, thrown.handle_mut());
            JS_SetPendingException(*cx, thrown.handle(), ExceptionStackBehavior::Capture);
        },

        Err(JsEngineError::Type(message)) => unsafe {
            assert!(!JS_IsExceptionPending(*cx));
            throw_type_error(*cx, &message);
        },

        Err(JsEngineError::Range(message)) => unsafe {
            assert!(!JS_IsExceptionPending(*cx));
            throw_range_error(*cx, &message);
        },

        Err(JsEngineError::JSFailed) => unsafe {
            assert!(JS_IsExceptionPending(*cx));
        },
    }
}

/// If possible, create a new DOMException representing the provided error.
/// If no such DOMException exists, return a subset of the original error values
/// that may need additional handling.
pub(crate) fn create_dom_exception(
    global: &GlobalScope,
    result: Error,
    can_gc: CanGc,
) -> Result<DomRoot<DOMException>, JsEngineError> {
    let new_custom_exception = |error_name, message| {
        Ok(DOMException::new_with_custom_message(
            global, error_name, message, can_gc,
        ))
    };

    let code = match result {
        Error::IndexSize => DOMErrorName::IndexSizeError,
        Error::NotFound(Some(custom_message)) => {
            return new_custom_exception(DOMErrorName::NotFoundError, custom_message);
        },
        Error::NotFound(None) => DOMErrorName::NotFoundError,
        Error::HierarchyRequest => DOMErrorName::HierarchyRequestError,
        Error::WrongDocument => DOMErrorName::WrongDocumentError,
        Error::InvalidCharacter => DOMErrorName::InvalidCharacterError,
        Error::NotSupported => DOMErrorName::NotSupportedError,
        Error::InUseAttribute => DOMErrorName::InUseAttributeError,
        Error::InvalidState => DOMErrorName::InvalidStateError,
        Error::Syntax(Some(custom_message)) => {
            return new_custom_exception(DOMErrorName::SyntaxError, custom_message);
        },
        Error::Syntax(None) => DOMErrorName::SyntaxError,
        Error::Namespace => DOMErrorName::NamespaceError,
        Error::InvalidAccess => DOMErrorName::InvalidAccessError,
        Error::Security => DOMErrorName::SecurityError,
        Error::Network => DOMErrorName::NetworkError,
        Error::Abort => DOMErrorName::AbortError,
        Error::Timeout => DOMErrorName::TimeoutError,
        Error::InvalidNodeType => DOMErrorName::InvalidNodeTypeError,
        Error::DataClone(Some(custom_message)) => {
            return new_custom_exception(DOMErrorName::DataCloneError, custom_message);
        },
        Error::DataClone(None) => DOMErrorName::DataCloneError,
        Error::Data => DOMErrorName::DataError,
        Error::TransactionInactive => DOMErrorName::TransactionInactiveError,
        Error::ReadOnly => DOMErrorName::ReadOnlyError,
        Error::Version => DOMErrorName::VersionError,
        Error::NoModificationAllowed => DOMErrorName::NoModificationAllowedError,
        Error::QuotaExceeded { quota, requested } => {
            return Ok(DomRoot::upcast(QuotaExceededError::new(
                global,
                DOMString::new(),
                quota,
                requested,
                can_gc,
            )));
        },
        Error::TypeMismatch => DOMErrorName::TypeMismatchError,
        Error::InvalidModification => DOMErrorName::InvalidModificationError,
        Error::NotReadable => DOMErrorName::NotReadableError,
        Error::Operation => DOMErrorName::OperationError,
        Error::NotAllowed => DOMErrorName::NotAllowedError,
        Error::Encoding => DOMErrorName::EncodingError,
        Error::Constraint => DOMErrorName::ConstraintError,
        Error::Type(message) => return Err(JsEngineError::Type(message)),
        Error::Range(message) => return Err(JsEngineError::Range(message)),
        Error::JSFailed => return Err(JsEngineError::JSFailed),
    };
    Ok(DOMException::new(global, code, can_gc))
}

/// A struct encapsulating information about a runtime script error.
#[derive(Default)]
pub(crate) struct ErrorInfo {
    /// The error message.
    pub(crate) message: String,
    /// The file name.
    pub(crate) filename: String,
    /// The line number.
    pub(crate) lineno: c_uint,
    /// The column number.
    pub(crate) column: c_uint,
}

impl ErrorInfo {
    fn from_native_error(object: HandleObject, cx: SafeJSContext) -> Option<ErrorInfo> {
        let report = unsafe { JS_ErrorFromException(*cx, object) };
        if report.is_null() {
            return None;
        }

        let filename = {
            let filename = unsafe { (*report)._base.filename.data_ as *const u8 };
            if !filename.is_null() {
                let filename = unsafe {
                    let length = (0..).find(|idx| *filename.offset(*idx) == 0).unwrap();
                    from_raw_parts(filename, length as usize)
                };
                String::from_utf8_lossy(filename).into_owned()
            } else {
                "none".to_string()
            }
        };

        let lineno = unsafe { (*report)._base.lineno };
        let column = unsafe { (*report)._base.column._base };

        let message = {
            let message = unsafe { (*report)._base.message_.data_ as *const u8 };
            let message = unsafe {
                let length = (0..).find(|idx| *message.offset(*idx) == 0).unwrap();
                from_raw_parts(message, length as usize)
            };
            String::from_utf8_lossy(message).into_owned()
        };

        Some(ErrorInfo {
            filename,
            message,
            lineno,
            column,
        })
    }

    fn from_dom_exception(object: HandleObject, cx: SafeJSContext) -> Option<ErrorInfo> {
        let exception = unsafe { root_from_object::<DOMException>(object.get(), *cx).ok()? };
        Some(ErrorInfo {
            filename: "".to_string(),
            message: exception.stringifier().into(),
            lineno: 0,
            column: 0,
        })
    }

    fn from_object(object: HandleObject, cx: SafeJSContext) -> Option<ErrorInfo> {
        if let Some(info) = ErrorInfo::from_native_error(object, cx) {
            return Some(info);
        }
        if let Some(info) = ErrorInfo::from_dom_exception(object, cx) {
            return Some(info);
        }
        None
    }

    fn from_value(value: HandleValue, cx: SafeJSContext) -> ErrorInfo {
        if value.is_object() {
            rooted!(in(*cx) let object = value.to_object());
            if let Some(info) = ErrorInfo::from_object(object.handle(), cx) {
                return info;
            }
        }

        match USVString::safe_from_jsval(cx, value, ()) {
            Ok(ConversionResult::Success(USVString(string))) => ErrorInfo {
                message: format!("uncaught exception: {}", string),
                filename: String::new(),
                lineno: 0,
                column: 0,
            },
            _ => {
                panic!("uncaught exception: failed to stringify primitive");
            },
        }
    }
}

/// Report a pending exception, thereby clearing it.
///
/// The `dispatch_event` argument is temporary and non-standard; passing false
/// prevents dispatching the `error` event.
pub(crate) fn report_pending_exception(
    cx: SafeJSContext,
    dispatch_event: bool,
    realm: InRealm,
    can_gc: CanGc,
) {
    unsafe {
        if !JS_IsExceptionPending(*cx) {
            return;
        }
    }
    rooted!(in(*cx) let mut value = UndefinedValue());

    unsafe {
        if !JS_GetPendingException(*cx, value.handle_mut()) {
            JS_ClearPendingException(*cx);
            error!("Uncaught exception: JS_GetPendingException failed");
            return;
        }

        JS_ClearPendingException(*cx);
    }
    let error_info = ErrorInfo::from_value(value.handle(), cx);

    error!(
        "Error at {}:{}:{} {}",
        error_info.filename, error_info.lineno, error_info.column, error_info.message
    );

    #[cfg(feature = "js_backtrace")]
    {
        LAST_EXCEPTION_BACKTRACE.with(|backtrace| {
            if let Some((js_backtrace, rust_backtrace)) = backtrace.borrow_mut().take() {
                if let Some(stack) = js_backtrace {
                    eprintln!("JS backtrace:\n{}", stack);
                }
                eprintln!("Rust backtrace:\n{}", rust_backtrace);
            }
        });
    }

    if dispatch_event {
        GlobalScope::from_safe_context(cx, realm).report_an_error(
            error_info,
            value.handle(),
            can_gc,
        );
    }
}

pub(crate) trait ErrorToJsval {
    fn to_jsval(
        self,
        cx: SafeJSContext,
        global: &GlobalScope,
        rval: MutableHandleValue,
        can_gc: CanGc,
    );
}

impl ErrorToJsval for Error {
    /// Convert this error value to a JS value, consuming it in the process.
    #[allow(clippy::wrong_self_convention)]
    fn to_jsval(
        self,
        cx: SafeJSContext,
        global: &GlobalScope,
        rval: MutableHandleValue,
        can_gc: CanGc,
    ) {
        match self {
            Error::JSFailed => (),
            _ => unsafe { assert!(!JS_IsExceptionPending(*cx)) },
        }
        throw_dom_exception(cx, global, self, can_gc);
        unsafe {
            assert!(JS_IsExceptionPending(*cx));
            assert!(JS_GetPendingException(*cx, rval));
            JS_ClearPendingException(*cx);
        }
    }
}