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/* 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 http://mozilla.org/MPL/2.0/. */ //! # Runtime support code for uniffi //! //! This crate provides the small amount of runtime code that is required by the generated uniffi //! component scaffolding in order to transfer data back and forth across the C-style FFI layer, //! as well as some utilities for testing the generated bindings. //! //! The key concept here is the [`FfiConverter`] trait, which is responsible for converting between //! a Rust type and a low-level C-style type that can be passed across the FFI: //! //! * How to [represent](FfiConverter::FfiType) values of the Rust type in the low-level C-style type //! system of the FFI layer. //! * How to ["lower"](FfiConverter::lower) values of the Rust type into an appropriate low-level //! FFI value. //! * How to ["lift"](FfiConverter::try_lift) low-level FFI values back into values of the Rust //! type. //! * How to [write](FfiConverter::write) values of the Rust type into a buffer, for cases //! where they are part of a compound data structure that is serialized for transfer. //! * How to [read](FfiConverter::try_read) values of the Rust type from buffer, for cases //! where they are received as part of a compound data structure that was serialized for transfer. //! //! This logic encapsulates the Rust-side handling of data transfer. Each foreign-language binding //! must also implement a matching set of data-handling rules for each data type. //! //! In addition to the core `FfiConverter` trait, we provide a handful of struct definitions useful //! for passing core rust types over the FFI, such as [`RustBuffer`]. use anyhow::{bail, Result}; use bytes::buf::{Buf, BufMut}; use paste::paste; use std::{ collections::HashMap, convert::TryFrom, time::{Duration, SystemTime}, }; pub mod ffi; pub use ffi::*; // It would be nice if this module was behind a cfg(test) guard, but it // doesn't work between crates so let's hope LLVM tree-shaking works well. pub mod testing; // Re-export the libs that we use in the generated code, // so the consumer doesn't have to depend on them directly. pub mod deps { pub use anyhow; pub use bytes; pub use log; pub use static_assertions; } mod panichook; const PACKAGE_VERSION: &str = env!("CARGO_PKG_VERSION"); // For the significance of this magic number 10 here, and the reason that // it can't be a named constant, see the `check_compatible_version` function. static_assertions::const_assert!(PACKAGE_VERSION.as_bytes().len() < 10); /// Check whether the uniffi runtime version is compatible a given uniffi_bindgen version. /// /// The result of this check may be used to ensure that generated Rust scaffolding is /// using a compatible version of the uniffi runtime crate. It's a `const fn` so that it /// can be used to perform such a check at compile time. #[allow(clippy::len_zero)] pub const fn check_compatible_version(bindgen_version: &'static str) -> bool { // While UniFFI is still under heavy development, we require that // the runtime support crate be precisely the same version as the // build-time bindgen crate. // // What we want to achieve here is checking two strings for equality. // Unfortunately Rust doesn't yet support calling the `&str` equals method // in a const context. We can hack around that by doing a byte-by-byte // comparison of the underlying bytes. let package_version = PACKAGE_VERSION.as_bytes(); let bindgen_version = bindgen_version.as_bytes(); // What we want to achieve here is a loop over the underlying bytes, // something like: // ``` // if package_version.len() != bindgen_version.len() { // return false // } // for i in 0..package_version.len() { // if package_version[i] != bindgen_version[i] { // return false // } // } // return true // ``` // Unfortunately stable Rust doesn't allow `if` or `for` in const contexts, // so code like the above would only work in nightly. We can hack around it by // statically asserting that the string is shorter than a certain length // (currently 10 bytes) and then manually unrolling that many iterations of the loop. // // Yes, I am aware that this is horrific, but the externally-visible // behaviour is quite nice for consumers! package_version.len() == bindgen_version.len() && (package_version.len() == 0 || package_version[0] == bindgen_version[0]) && (package_version.len() <= 1 || package_version[1] == bindgen_version[1]) && (package_version.len() <= 2 || package_version[2] == bindgen_version[2]) && (package_version.len() <= 3 || package_version[3] == bindgen_version[3]) && (package_version.len() <= 4 || package_version[4] == bindgen_version[4]) && (package_version.len() <= 5 || package_version[5] == bindgen_version[5]) && (package_version.len() <= 6 || package_version[6] == bindgen_version[6]) && (package_version.len() <= 7 || package_version[7] == bindgen_version[7]) && (package_version.len() <= 8 || package_version[8] == bindgen_version[8]) && (package_version.len() <= 9 || package_version[9] == bindgen_version[9]) && package_version.len() < 10 } /// Assert that the uniffi runtime version matches an expected value. /// /// This is a helper hook for the generated Rust scaffolding, to produce a compile-time /// error if the version of `uniffi_bindgen` used to generate the scaffolding was /// incompatible with the version of `uniffi` being used at runtime. #[macro_export] macro_rules! assert_compatible_version { ($v:expr $(,)?) => { uniffi::deps::static_assertions::const_assert!(uniffi::check_compatible_version($v)); }; } /// Trait defining how to transfer values via the FFI layer. /// /// The `FfiConverter` trait defines how to pass values of a particular type back-and-forth over /// the uniffi generated FFI layer, both as standalone argument or return values, and as /// part of serialized compound data structures. /// /// (This trait is like the `IntoFfi` trait from `ffi_support`, but local to this crate /// so that we can add some alternative implementations for different builtin types, /// and so that we can add support for receiving as well as returning). /// /// ## Safety /// /// This is an unsafe trait (implementing it requires `unsafe impl`) because we can't guarantee /// that it's safe to pass your type out to foreign-language code and back again. Buggy /// implementations of this trait might violate some assumptions made by the generated code, /// or might not match with the corresponding code in the generated foreign-language bindings. /// /// In general, you should not need to implement this trait by hand, and should instead rely on /// implementations generated from your component UDL via the `uniffi-bindgen scaffolding` command. pub unsafe trait FfiConverter: Sized { /// The type used in Rust code. /// /// For primitive / standard types, we implement `FfiConverter` on the type itself with `RustType=Self`. /// For user-defined types we create a unit struct and implement it there. This sidesteps /// Rust's orphan rules (ADR-0006). type RustType; /// The low-level type used for passing values of this type over the FFI. /// /// This must be a C-compatible type (e.g. a numeric primitive, a `#[repr(C)]` struct) into /// which values of the target rust type can be converted. /// /// For complex data types, we currently recommend using `RustBuffer` and serializing /// the data for transfer. In theory it could be possible to build a matching /// `#[repr(C)]` struct for a complex data type and pass that instead, but explicit /// serialization is simpler and safer as a starting point. type FfiType; /// Lower a rust value of the target type, into an FFI value of type Self::FfiType. /// /// This trait method is used for sending data from rust to the foreign language code, /// by (hopefully cheaply!) converting it into someting that can be passed over the FFI /// and reconstructed on the other side. /// /// Note that this method takes an owned `Self::RustType`; this allows it to transfer ownership /// in turn to the foreign language code, e.g. by boxing the value and passing a pointer. fn lower(obj: Self::RustType) -> Self::FfiType; /// Lift a rust value of the target type, from an FFI value of type Self::FfiType. /// /// This trait method is used for receiving data from the foreign language code in rust, /// by (hopefully cheaply!) converting it from a low-level FFI value of type Self::FfiType /// into a high-level rust value of the target type. /// /// Since we cannot statically guarantee that the foreign-language code will send valid /// values of type Self::FfiType, this method is fallible. fn try_lift(v: Self::FfiType) -> Result<Self::RustType>; /// Write a rust value into a buffer, to send over the FFI in serialized form. /// /// This trait method can be used for sending data from rust to the foreign language code, /// in cases where we're not able to use a special-purpose FFI type and must fall back to /// sending serialized bytes. /// /// Note that this method takes an owned `Self::RustType` because it's transfering ownership /// to the foreign language code via the RustBuffer. fn write(obj: Self::RustType, buf: &mut Vec<u8>); /// Read a rust value from a buffer, received over the FFI in serialized form. /// /// This trait method can be used for receiving data from the foreign language code in rust, /// in cases where we're not able to use a special-purpose FFI type and must fall back to /// receiving serialized bytes. /// /// Since we cannot statically guarantee that the foreign-language code will send valid /// serialized bytes for the target type, this method is fallible. /// /// Note the slightly unusual type here - we want a mutable reference to a slice of bytes, /// because we want to be able to advance the start of the slice after reading an item /// from it (but will not mutate the actual contents of the slice). fn try_read(buf: &mut &[u8]) -> Result<Self::RustType>; } /// A helper function to ensure we don't read past the end of a buffer. /// /// Rust won't actually let us read past the end of a buffer, but the `Buf` trait does not support /// returning an explicit error in this case, and will instead panic. This is a look-before-you-leap /// helper function to instead return an explicit error, to help with debugging. pub fn check_remaining(buf: &[u8], num_bytes: usize) -> Result<()> { if buf.remaining() < num_bytes { bail!(format!( "not enough bytes remaining in buffer ({} < {})", buf.remaining(), num_bytes )); } Ok(()) } /// Blanket implementation of `FfiConverter` for numeric primitives. /// /// Numeric primitives have a straightforward mapping into C-compatible numeric types, /// sice they are themselves a C-compatible numeric type! macro_rules! impl_via_ffi_for_num_primitive { ($($T:ty,)+) => { impl_via_ffi_for_num_primitive!($($T),+); }; ($($T:ty),*) => { $( paste! { unsafe impl FfiConverter for $T { type RustType = Self; type FfiType = Self; fn lower(obj: Self::RustType) -> Self::FfiType { obj } fn try_lift(v: Self::FfiType) -> Result<Self> { Ok(v) } fn write(obj: Self::RustType, buf: &mut Vec<u8>) { buf.[<put_ $T>](obj); } fn try_read(buf: &mut &[u8]) -> Result<Self> { check_remaining(buf, std::mem::size_of::<$T>())?; Ok(buf.[<get_ $T>]()) } } } )* }; } impl_via_ffi_for_num_primitive! { i8, u8, i16, u16, i32, u32, i64, u64, f32, f64 } /// Support for passing boolean values via the FFI. /// /// Booleans are passed as an `i8` in order to avoid problems with handling /// C-compatible boolean values on JVM-based languages. unsafe impl FfiConverter for bool { type RustType = Self; type FfiType = i8; fn lower(obj: Self::RustType) -> Self::FfiType { if obj { 1 } else { 0 } } fn try_lift(v: Self::FfiType) -> Result<Self::RustType> { Ok(match v { 0 => false, 1 => true, _ => bail!("unexpected byte for Boolean"), }) } fn write(obj: Self::RustType, buf: &mut Vec<u8>) { buf.put_i8(<bool as FfiConverter>::lower(obj)); } fn try_read(buf: &mut &[u8]) -> Result<Self::RustType> { check_remaining(buf, 1)?; <bool as FfiConverter>::try_lift(buf.get_i8()) } } /// Support for passing Strings via the FFI. /// /// Unlike many other implementations of `FfiConverter`, this passes a struct containing /// a raw pointer rather than copying the data from one side to the other. This is a /// safety hazard, but turns out to be pretty nice for useability. This struct /// *must* be a valid `RustBuffer` and it *must* contain valid utf-8 data (in other /// words, it *must* be a `Vec<u8>` suitable for use as an actual rust `String`). /// /// When serialized in a buffer, strings are represented as a i32 byte length /// followed by utf8-encoded bytes. (It's a signed integer because unsigned types are /// currently experimental in Kotlin). unsafe impl FfiConverter for String { type RustType = Self; type FfiType = RustBuffer; // This returns a struct with a raw pointer to the underlying bytes, so it's very // important that it consume ownership of the String, which is relinquished to the // foreign language code (and can be restored by it passing the pointer back). fn lower(obj: Self::RustType) -> Self::FfiType { RustBuffer::from_vec(obj.into_bytes()) } // The argument here *must* be a uniquely-owned `RustBuffer` previously obtained // from `lower` above, and hence must be the bytes of a valid rust string. fn try_lift(v: Self::FfiType) -> Result<Self::RustType> { let v = v.destroy_into_vec(); // This turns the buffer back into a `String` without copying the data // and without re-checking it for validity of the utf8. If the `RustBuffer` // came from a valid String then there's no point in re-checking the utf8, // and if it didn't then bad things are probably going to happen regardless // of whether we check for valid utf8 data or not. Ok(unsafe { String::from_utf8_unchecked(v) }) } fn write(obj: Self::RustType, buf: &mut Vec<u8>) { // N.B. `len()` gives us the length in bytes, not in chars or graphemes. // TODO: it would be nice not to panic here. let len = i32::try_from(obj.len()).unwrap(); buf.put_i32(len); // We limit strings to u32::MAX bytes buf.put(obj.as_bytes()); } fn try_read(buf: &mut &[u8]) -> Result<Self::RustType> { check_remaining(buf, 4)?; let len = usize::try_from(buf.get_i32())?; check_remaining(buf, len)?; // N.B: In the general case `Buf::chunk()` may return partial data. // But in the specific case of `<&[u8] as Buf>` it returns the full slice, // so there is no risk of having less than `len` bytes available here. let bytes = &buf.chunk()[..len]; let res = String::from_utf8(bytes.to_vec())?; buf.advance(len); Ok(res) } } /// A helper trait to implement lowering/lifting using a `RustBuffer` /// /// For complex types where it's too fiddly or too unsafe to convert them into a special-purpose /// C-compatible value, you can use this trait to implement `lower()` in terms of `write()` and /// `lift` in terms of `read()`. pub trait RustBufferFfiConverter: Sized { type RustType; fn write(obj: Self::RustType, buf: &mut Vec<u8>); fn try_read(buf: &mut &[u8]) -> Result<Self::RustType>; } unsafe impl<T: RustBufferFfiConverter> FfiConverter for T { type RustType = T::RustType; type FfiType = RustBuffer; fn lower(obj: Self::RustType) -> RustBuffer { let mut buf = Vec::new(); <T as RustBufferFfiConverter>::write(obj, &mut buf); RustBuffer::from_vec(buf) } fn try_lift(v: RustBuffer) -> Result<Self::RustType> { let vec = v.destroy_into_vec(); let mut buf = vec.as_slice(); let value = T::try_read(&mut buf)?; if buf.remaining() != 0 { bail!("junk data left in buffer after lifting") } Ok(value) } fn write(obj: Self::RustType, buf: &mut Vec<u8>) { T::write(obj, buf) } fn try_read(buf: &mut &[u8]) -> Result<Self::RustType> { T::try_read(buf) } } /// Support for passing timestamp values via the FFI. /// /// Timestamps values are currently always passed by serializing to a buffer. /// /// Timestamps are represented on the buffer by an i64 that indicates the /// direction and the magnitude in seconds of the offset from epoch, and a /// u32 that indicates the nanosecond portion of the offset magnitude. The /// nanosecond portion is expected to be between 0 and 999,999,999. /// /// To build an epoch offset the absolute value of the seconds portion of the /// offset should be combined with the nanosecond portion. This is because /// the sign of the seconds portion represents the direction of the offset /// overall. The sign of the seconds portion can then be used to determine /// if the total offset should be added to or subtracted from the unix epoch. impl RustBufferFfiConverter for SystemTime { type RustType = Self; fn write(obj: Self::RustType, buf: &mut Vec<u8>) { let mut sign = 1; let epoch_offset = obj .duration_since(SystemTime::UNIX_EPOCH) .unwrap_or_else(|error| { sign = -1; error.duration() }); // This panic should never happen as SystemTime typically stores seconds as i64 let seconds = sign * i64::try_from(epoch_offset.as_secs()) .expect("SystemTime overflow, seconds greater than i64::MAX"); buf.put_i64(seconds); buf.put_u32(epoch_offset.subsec_nanos()); } fn try_read(buf: &mut &[u8]) -> Result<Self::RustType> { check_remaining(buf, 12)?; let seconds = buf.get_i64(); let nanos = buf.get_u32(); let epoch_offset = Duration::new(seconds.wrapping_abs() as u64, nanos); if seconds >= 0 { Ok(SystemTime::UNIX_EPOCH + epoch_offset) } else { Ok(SystemTime::UNIX_EPOCH - epoch_offset) } } } /// Support for passing duration values via the FFI. /// /// Duration values are currently always passed by serializing to a buffer. /// /// Durations are represented on the buffer by a u64 that indicates the /// magnitude in seconds, and a u32 that indicates the nanosecond portion /// of the magnitude. The nanosecond portion is expected to be between 0 /// and 999,999,999. impl RustBufferFfiConverter for Duration { type RustType = Self; fn write(obj: Self::RustType, buf: &mut Vec<u8>) { buf.put_u64(obj.as_secs()); buf.put_u32(obj.subsec_nanos()); } fn try_read(buf: &mut &[u8]) -> Result<Self::RustType> { check_remaining(buf, 12)?; Ok(Duration::new(buf.get_u64(), buf.get_u32())) } } /// Support for passing optional values via the FFI. /// /// Optional values are currently always passed by serializing to a buffer. /// We write either a zero byte for `None`, or a one byte followed by the containing /// item for `Some`. /// /// In future we could do the same optimization as rust uses internally, where the /// `None` option is represented as a null pointer and the `Some` as a valid pointer, /// but that seems more fiddly and less safe in the short term, so it can wait. impl<T: FfiConverter> RustBufferFfiConverter for Option<T> { type RustType = Option<T::RustType>; fn write(obj: Self::RustType, buf: &mut Vec<u8>) { match obj { None => buf.put_i8(0), Some(v) => { buf.put_i8(1); <T as FfiConverter>::write(v, buf); } } } fn try_read(buf: &mut &[u8]) -> Result<Self::RustType> { check_remaining(buf, 1)?; Ok(match buf.get_i8() { 0 => None, 1 => Some(<T as FfiConverter>::try_read(buf)?), _ => bail!("unexpected tag byte for Option"), }) } } /// Support for passing vectors of values via the FFI. /// /// Vectors are currently always passed by serializing to a buffer. /// We write a `i32` item count followed by each item in turn. /// (It's a signed type due to limits of the JVM). /// /// Ideally we would pass `Vec<u8>` directly as a `RustBuffer` rather /// than serializing, and perhaps even pass other vector types using a /// similar struct. But that's for future work. impl<T: FfiConverter> RustBufferFfiConverter for Vec<T> { type RustType = Vec<T::RustType>; fn write(obj: Self::RustType, buf: &mut Vec<u8>) { // TODO: would be nice not to panic here :-/ let len = i32::try_from(obj.len()).unwrap(); buf.put_i32(len); // We limit arrays to i32::MAX items for item in obj.into_iter() { <T as FfiConverter>::write(item, buf); } } fn try_read(buf: &mut &[u8]) -> Result<Self::RustType> { check_remaining(buf, 4)?; let len = usize::try_from(buf.get_i32())?; let mut vec = Vec::with_capacity(len); for _ in 0..len { vec.push(<T as FfiConverter>::try_read(buf)?) } Ok(vec) } } /// Support for associative arrays via the FFI. /// Note that because of webidl limitations, /// the key must always be of the String type. /// /// HashMaps are currently always passed by serializing to a buffer. /// We write a `i32` entries count followed by each entry (string /// key followed by the value) in turn. /// (It's a signed type due to limits of the JVM). impl<V: FfiConverter> RustBufferFfiConverter for HashMap<String, V> { type RustType = HashMap<String, V::RustType>; fn write(obj: Self::RustType, buf: &mut Vec<u8>) { // TODO: would be nice not to panic here :-/ let len = i32::try_from(obj.len()).unwrap(); buf.put_i32(len); // We limit HashMaps to i32::MAX entries for (key, value) in obj.into_iter() { <String as FfiConverter>::write(key, buf); <V as FfiConverter>::write(value, buf); } } fn try_read(buf: &mut &[u8]) -> Result<Self::RustType> { check_remaining(buf, 4)?; let len = usize::try_from(buf.get_i32())?; let mut map = HashMap::with_capacity(len); for _ in 0..len { let key = String::try_read(buf)?; let value = <V as FfiConverter>::try_read(buf)?; map.insert(key, value); } Ok(map) } } /// Support for passing reference-counted shared objects via the FFI. /// /// To avoid dealing with complex lifetime semantics over the FFI, any data passed /// by reference must be encapsulated in an `Arc`, and must be safe to share /// across threads. unsafe impl<T: Sync + Send> FfiConverter for std::sync::Arc<T> { type RustType = Self; // Don't use a pointer to <T> as that requires a `pub <T>` type FfiType = *const std::os::raw::c_void; /// When lowering, we have an owned `Arc<T>` and we transfer that ownership /// to the foreign-language code, "leaking" it out of Rust's ownership system /// as a raw pointer. This works safely because we have unique ownership of `self`. /// The foreign-language code is responsible for freeing this by calling the /// `ffi_object_free` FFI function provided by the corresponding UniFFI type. /// /// Safety: when freeing the resulting pointer, the foreign-language code must /// call the destructor function specific to the type `T`. Calling the destructor /// function for other types may lead to undefined behaviour. fn lower(obj: Self::RustType) -> Self::FfiType { std::sync::Arc::into_raw(obj) as Self::FfiType } /// When lifting, we receive a "borrow" of the `Arc<T>` that is owned by /// the foreign-language code, and make a clone of it for our own use. /// /// Safety: the provided value must be a pointer previously obtained by calling /// the `lower()` or `write()` method of this impl. fn try_lift(v: Self::FfiType) -> Result<Self::RustType> { let v = v as *const T; // We musn't drop the `Arc<T>` that is owned by the foreign-language code. let foreign_arc = std::mem::ManuallyDrop::new(unsafe { Self::from_raw(v) }); // Take a clone for our own use. Ok(std::sync::Arc::clone(&*foreign_arc)) } /// When writing as a field of a complex structure, make a clone and transfer ownership /// of it to the foreign-language code by writing its pointer into the buffer. /// The foreign-language code is responsible for freeing this by calling the /// `ffi_object_free` FFI function provided by the corresponding UniFFI type. /// /// Safety: when freeing the resulting pointer, the foreign-language code must /// call the destructor function specific to the type `T`. Calling the destructor /// function for other types may lead to undefined behaviour. fn write(obj: Self::RustType, buf: &mut Vec<u8>) { static_assertions::const_assert!(std::mem::size_of::<*const std::ffi::c_void>() <= 8); buf.put_u64(Self::lower(obj) as u64); } /// When reading as a field of a complex structure, we receive a "borrow" of the `Arc<T>` /// that is owned by the foreign-language code, and make a clone for our own use. /// /// Safety: the buffer must contain a pointer previously obtained by calling /// the `lower()` or `write()` method of this impl. fn try_read(buf: &mut &[u8]) -> Result<Self::RustType> { static_assertions::const_assert!(std::mem::size_of::<*const std::ffi::c_void>() <= 8); check_remaining(buf, 8)?; Self::try_lift(buf.get_u64() as Self::FfiType) } } #[cfg(test)] mod test { use super::*; #[test] fn trybuild_ui_tests() { let t = trybuild::TestCases::new(); t.compile_fail("tests/ui/*.rs"); } #[test] fn timestamp_roundtrip_post_epoch() { let expected = SystemTime::UNIX_EPOCH + Duration::new(100, 100); let result = SystemTime::try_lift(SystemTime::lower(expected)).expect("Failed to lift!"); assert_eq!(expected, result) } #[test] fn timestamp_roundtrip_pre_epoch() { let expected = SystemTime::UNIX_EPOCH - Duration::new(100, 100); let result = SystemTime::try_lift(SystemTime::lower(expected)).expect("Failed to lift!"); assert_eq!( expected, result, "Expected results after lowering and lifting to be equal" ) } }