forked from BigfootDev/flatbuffers
3c54fd964b
This is a port of FlatBuffers to Rust. It provides code generation and a runtime library derived from the C++ implementation. It utilizes the Rust type system to provide safe and fast traversal of FlatBuffers data. There are 188 tests, including many fuzz tests of roundtrips for various serialization scenarios. Initial benchmarks indicate that the canonical example payload can be written in ~700ns, and traversed in ~100ns. Rustaceans may be interested in the Follow, Push, and SafeSliceAccess traits. These traits lift traversals, reads, writes, and slice accesses into the type system, providing abstraction with no runtime penalty.
86 lines
2.9 KiB
Rust
86 lines
2.9 KiB
Rust
/*
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* Copyright 2018 Google Inc. All rights reserved.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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use std::ptr::write_bytes;
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use endian_scalar::{emplace_scalar, read_scalar};
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use primitives::*;
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/// VTableWriter compartmentalizes actions needed to create a vtable.
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#[derive(Debug)]
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pub struct VTableWriter<'a> {
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buf: &'a mut [u8],
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}
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impl<'a> VTableWriter<'a> {
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#[inline(always)]
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pub fn init(buf: &'a mut [u8]) -> Self {
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VTableWriter { buf: buf }
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}
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/// Writes the vtable length (in bytes) into the vtable.
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///
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/// Note that callers already need to have computed this to initialize
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/// a VTableWriter.
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///
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/// In debug mode, asserts that the length of the underlying data is equal
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/// to the provided value.
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#[inline(always)]
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pub fn write_vtable_byte_length(&mut self, n: VOffsetT) {
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emplace_scalar::<VOffsetT>(&mut self.buf[..SIZE_VOFFSET], n);
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debug_assert_eq!(n as usize, self.buf.len());
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}
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/// Writes an object length (in bytes) into the vtable.
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#[inline(always)]
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pub fn write_object_inline_size(&mut self, n: VOffsetT) {
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emplace_scalar::<VOffsetT>(&mut self.buf[SIZE_VOFFSET..2 * SIZE_VOFFSET], n);
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}
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/// Gets an object field offset from the vtable. Only used for debugging.
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///
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/// Note that this expects field offsets (which are like pointers), not
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/// field ids (which are like array indices).
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#[inline(always)]
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pub fn get_field_offset(&self, vtable_offset: VOffsetT) -> VOffsetT {
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let idx = vtable_offset as usize;
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read_scalar::<VOffsetT>(&self.buf[idx..idx + SIZE_VOFFSET])
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}
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/// Writes an object field offset into the vtable.
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///
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/// Note that this expects field offsets (which are like pointers), not
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/// field ids (which are like array indices).
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#[inline(always)]
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pub fn write_field_offset(&mut self, vtable_offset: VOffsetT, object_data_offset: VOffsetT) {
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let idx = vtable_offset as usize;
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emplace_scalar::<VOffsetT>(&mut self.buf[idx..idx + SIZE_VOFFSET], object_data_offset);
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}
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/// Clears all data in this VTableWriter. Used to cleanly undo a
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/// vtable write.
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#[inline(always)]
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pub fn clear(&mut self) {
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// This is the closest thing to memset in Rust right now.
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let len = self.buf.len();
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let p = self.buf.as_mut_ptr() as *mut u8;
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unsafe {
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write_bytes(p, 0, len);
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}
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}
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}
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