104 lines
3.0 KiB
Rust
104 lines
3.0 KiB
Rust
//! When calling this dynamic library with outside programs,
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//! outer programs may usually need to fetch string resource produced by Rust code.
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//! However it is impossible pass Rust string directly to outer program.
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//!
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//! This module provide **thread independent** string cache for resolving this issue.
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//! When we need pass string to outer programs, we push that string into this string as C-like format,
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//! then return its pointer to outer program.
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//! So that outside program can utilize it like calling C/C++ library.
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//! The only thing that outer programs should note is that this string is volatile,
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//! once they get it, they must dupliate it immediately before any futher calling to this dynamic library.
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use std::cell::RefCell;
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use std::ffi::{CStr, CString, c_char};
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use thiserror::Error as TeError;
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/// The type representing the raw pointer to immutable C-style NUL-terminated string.
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pub type CStyleString = *const c_char;
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// region: Error
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/// Error occurs in this crate.
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#[derive(Debug, TeError)]
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pub enum Error {
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#[error("unexpected NUL when parsing into C/C++ string")]
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UnexpectedNul(#[from] std::ffi::NulError),
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#[error("given string pointer is nullptr when parsing from C/C++ string")]
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NullPtr,
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#[error("invalid UTF8 sequence when parsing from C/C++ string")]
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InvalidEncoding(#[from] std::str::Utf8Error),
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}
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/// Result type used in this crate.
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type Result<T> = std::result::Result<T, Error>;
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// endregion
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// region: String Cache for Exposing
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struct StringCache {
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msg: CString,
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}
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impl StringCache {
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fn new() -> Self {
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Self {
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msg: CString::new("").expect("empty string must be valid for CString"),
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}
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}
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pub fn set_msg(&mut self, msg: &str) -> Result<()> {
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self.msg = CString::new(msg)?;
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Ok(())
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}
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pub fn get_msg(&self) -> CStyleString {
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self.msg.as_ptr()
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}
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pub fn clear_msg(&mut self) {
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self.msg = CString::new("").expect("empty string must be valid for CString");
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}
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}
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// endregion
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// region: Exposed Functions
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thread_local! {
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static STRING_CACHE: RefCell<StringCache> = RefCell::new(StringCache::new());
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}
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/// Set thread local string exposed for C code.
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pub fn set_ffi_string(msg: &str) -> Result<()> {
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STRING_CACHE.with(|e| {
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e.borrow_mut().set_msg(msg)
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})
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}
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/// Get const pointer to thread local string exposed for C code.
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pub fn get_ffi_string() -> CStyleString {
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STRING_CACHE.with(|e| e.borrow().get_msg())
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}
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/// Clear thread local string exposed for C code.
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///
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/// This function usually should be called at the beginning of every exposed C functions.
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pub fn clear_ffi_string() {
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STRING_CACHE.with(|e| {
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e.borrow_mut().clear_msg();
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});
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}
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/// Parse string given by C code into Rust string.
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pub fn parse_ffi_string<'a>(ptr: CStyleString) -> Result<&'a str> {
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if ptr.is_null() {
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Err(Error::NullPtr)
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} else {
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let c_str = unsafe { CStr::from_ptr(ptr) };
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Ok(c_str.to_str()?)
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}
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}
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// endregion
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