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Return message string from model panic handler to be displayed in UI … #1534

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merged 1 commit into from
Feb 7, 2023
Merged

Return message string from model panic handler to be displayed in UI … #1534

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6 changes: 3 additions & 3 deletions crates/fj-proc/src/expand.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -64,9 +64,9 @@ impl ToTokens for Metadata {
let Self { name, arguments } = self;

tokens.extend(quote! {
fn metadata(&self) -> fj::models::ModelMetadata {
fj::models::ModelMetadata::new(#name)
#( .with_argument(#arguments) )*
fn metadata(&self) -> std::result::Result<fj::models::ModelMetadata, Box<dyn std::error::Error + Send + Sync +'static>> {
Ok(fj::models::ModelMetadata::new(#name)
#( .with_argument(#arguments) )*)
}
});
}
Expand Down
40 changes: 31 additions & 9 deletions crates/fj/src/abi/context.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,8 +5,13 @@ use crate::abi::ffi_safe::StringSlice;
#[repr(C)]
pub struct Context<'a> {
user_data: *const c_void,
get_argument:
unsafe extern "C" fn(*const c_void, StringSlice) -> StringSlice,
get_argument: unsafe extern "C" fn(
*const c_void,
StringSlice,
) -> crate::abi::ffi_safe::Result<
StringSlice,
crate::abi::ffi_safe::String,
>,
_lifetime: PhantomData<&'a ()>,
}

Expand All @@ -15,15 +20,24 @@ impl<'a> From<&'a &dyn crate::models::Context> for Context<'a> {
unsafe extern "C" fn get_argument(
user_data: *const c_void,
name: StringSlice,
) -> StringSlice {
) -> crate::abi::ffi_safe::Result<
StringSlice,
crate::abi::ffi_safe::String,
> {
let ctx = &*(user_data as *const &dyn crate::models::Context);

match std::panic::catch_unwind(AssertUnwindSafe(|| {
ctx.get_argument(&name)
})) {
Ok(Some(arg)) => StringSlice::from_str(arg),
Ok(None) => StringSlice::from_str(""),
Err(payload) => crate::abi::on_panic(payload),
Ok(Some(arg)) => {
crate::abi::ffi_safe::Result::Ok(StringSlice::from_str(arg))
}
Ok(None) => {
crate::abi::ffi_safe::Result::Ok(StringSlice::from_str(""))
}
Err(payload) => crate::abi::ffi_safe::Result::Err(
crate::abi::on_panic(payload),
),
}
}

Expand All @@ -47,9 +61,17 @@ impl crate::models::Context for Context<'_> {

let name = StringSlice::from_str(name);

match get_argument(user_data, name).into_str() {
"" => None,
other => Some(other),
match name.trim().is_empty() {
true => None,
false => match get_argument(user_data, name) {
super::ffi_safe::Result::Ok(other) => {
match other.is_empty() {
true => None,
false => Some(other.into_str()),
}
}
super::ffi_safe::Result::Err(_) => None,
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It's not ideal to swallow the error here, as that could cause bugs to be hidden. Instead of getting an error message, making it clear that a bug has occurred, it could lead to a specified argument just not being recognized, which would be very confusing.

I think Context::get_argument should also return Result instead of an Option.

},
}
}
}
Expand Down
2 changes: 1 addition & 1 deletion crates/fj/src/abi/ffi_safe.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -338,7 +338,7 @@ impl Deref for StringSlice {
#[derive(Debug)]
#[repr(C)]
pub struct BoxedError {
msg: String,
pub(crate) msg: String,
}

impl Display for BoxedError {
Expand Down
10 changes: 5 additions & 5 deletions crates/fj/src/abi/mod.rs
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Expand Up @@ -72,7 +72,7 @@ pub use self::{
/// struct MyModel { }
///
/// impl Model for MyModel {
/// fn metadata(&self) -> ModelMetadata { todo!() }
/// fn metadata(&self) -> std::result::Result<fj::models::ModelMetadata, Box<(dyn std::error::Error + Send + Sync + 'static)>> { todo!() }
///
/// fn shape(&self, ctx: &dyn Context) -> Result<fj::Shape, Error> {
/// todo!()
Expand Down Expand Up @@ -111,12 +111,14 @@ macro_rules! register_model {
pub type InitFunction = unsafe extern "C" fn(*mut Host<'_>) -> InitResult;
pub type InitResult = ffi_safe::Result<Metadata, ffi_safe::BoxedError>;
pub type ShapeResult = ffi_safe::Result<crate::Shape, ffi_safe::BoxedError>;
pub type ModelMetadataResult =
ffi_safe::Result<ModelMetadata, ffi_safe::BoxedError>;

/// The name of the function generated by [`register_model`].
///
pub const INIT_FUNCTION_NAME: &str = "fj_model_init";

fn on_panic(payload: Box<dyn Any + Send>) -> ! {
fn on_panic(payload: Box<dyn Any + Send>) -> crate::abi::ffi_safe::String {
let msg: &str =
if let Some(s) = payload.downcast_ref::<std::string::String>() {
s.as_str()
Expand All @@ -126,7 +128,5 @@ fn on_panic(payload: Box<dyn Any + Send>) -> ! {
"A panic occurred"
};

eprintln!("{msg}");
// It's not ideal, but panicking across the FFI boundary is UB.
std::process::abort();
crate::abi::ffi_safe::String::from(msg.to_string())
}
32 changes: 24 additions & 8 deletions crates/fj/src/abi/model.rs
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Original file line number Diff line number Diff line change
@@ -1,14 +1,14 @@
use std::{os::raw::c_void, panic::AssertUnwindSafe};

use crate::{
abi::{Context, ModelMetadata, ShapeResult},
abi::{Context, ModelMetadataResult, ShapeResult},
models::Error,
};

#[repr(C)]
pub struct Model {
ptr: *mut c_void,
metadata: unsafe extern "C" fn(*mut c_void) -> ModelMetadata,
metadata: unsafe extern "C" fn(*mut c_void) -> ModelMetadataResult,
shape: unsafe extern "C" fn(*mut c_void, Context<'_>) -> ShapeResult,
free: unsafe extern "C" fn(*mut c_void),
}
Expand All @@ -30,23 +30,35 @@ impl crate::models::Model for Model {
}
}

fn metadata(&self) -> crate::models::ModelMetadata {
fn metadata(&self) -> Result<crate::models::ModelMetadata, Error> {
let Self { ptr, metadata, .. } = *self;

unsafe { metadata(ptr).into() }
let result = unsafe { metadata(ptr) };

match result {
super::ffi_safe::Result::Ok(meta) => Ok(meta.into()),
super::ffi_safe::Result::Err(err) => Err(err.into()),
}
}
}

impl From<Box<dyn crate::models::Model>> for Model {
fn from(m: Box<dyn crate::models::Model>) -> Self {
unsafe extern "C" fn metadata(user_data: *mut c_void) -> ModelMetadata {
unsafe extern "C" fn metadata(
user_data: *mut c_void,
) -> ModelMetadataResult {
let model = &*(user_data as *mut Box<dyn crate::models::Model>);

match std::panic::catch_unwind(AssertUnwindSafe(|| {
model.metadata()
})) {
Ok(meta) => meta.into(),
Err(payload) => crate::abi::on_panic(payload),
Ok(Ok(meta)) => ModelMetadataResult::Ok(meta.into()),
Ok(Err(err)) => ModelMetadataResult::Err(err.into()),
Err(payload) => {
ModelMetadataResult::Err(crate::abi::ffi_safe::BoxedError {
msg: crate::abi::on_panic(payload),
})
}
}
}

Expand All @@ -61,7 +73,11 @@ impl From<Box<dyn crate::models::Model>> for Model {
})) {
Ok(Ok(shape)) => ShapeResult::Ok(shape),
Ok(Err(err)) => ShapeResult::Err(err.into()),
Err(payload) => crate::abi::on_panic(payload),
Err(payload) => {
ShapeResult::Err(crate::abi::ffi_safe::BoxedError {
msg: crate::abi::on_panic(payload),
})
}
}
}

Expand Down
2 changes: 1 addition & 1 deletion crates/fj/src/models/model.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@ pub trait Model: Send + Sync {
fn shape(&self, ctx: &dyn Context) -> Result<Shape, Error>;

/// Get metadata for the model.
fn metadata(&self) -> ModelMetadata;
fn metadata(&self) -> Result<ModelMetadata, Error>;
}

#[cfg(test)]
Expand Down