88 lines
2.8 KiB
Rust
88 lines
2.8 KiB
Rust
use anyhow::Result;
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/// Callback for nix_store_get_uri and other functions that return a string.
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///
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/// This function is used by the other nix_* crates, and you should never need to call it yourself.
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///
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/// Some functions in the nix library "return" strings without giving you ownership over them, by letting you pass a callback function that gets to look at that string. This callback simply turns that string pointer into an owned rust String.
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///
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/// # Safety
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///
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/// _Manual memory management_
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///
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/// Only for passing to the nix C API. Do not call this function directly.
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pub unsafe extern "C" fn callback_get_result_string(
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start: *const ::std::os::raw::c_char,
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n: std::os::raw::c_uint,
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user_data: *mut std::os::raw::c_void,
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) {
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let ret = user_data as *mut Result<String>;
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if start.is_null() {
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if n != 0 {
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panic!("callback_get_result_string: start is null but n is not zero");
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}
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*ret = Ok(String::new());
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return;
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}
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let slice = std::slice::from_raw_parts(start as *const u8, n as usize);
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if (*ret).is_ok() {
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panic!(
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"callback_get_result_string: Result must be initialized to Err. Did Nix call us twice?"
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);
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}
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*ret = String::from_utf8(slice.to_vec())
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.map_err(|e| anyhow::format_err!("Nix string is not valid UTF-8: {}", e));
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}
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pub fn callback_get_result_string_data(vec: &mut Result<String>) -> *mut std::os::raw::c_void {
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vec as *mut Result<String> as *mut std::os::raw::c_void
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}
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#[macro_export]
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macro_rules! result_string_init {
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() => {
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Err(anyhow::anyhow!("String was not set by Nix C API"))
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};
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use nix_bindings_bindgen_raw as raw;
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/// Typecheck the function signature against the generated bindings in nix_bindings_bindgen_raw.
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static _CALLBACK_GET_RESULT_STRING: raw::get_string_callback = Some(callback_get_result_string);
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#[test]
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fn test_callback_get_result_string_empty() {
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let mut ret: Result<String> = result_string_init!();
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let start: *const std::os::raw::c_char = std::ptr::null();
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let n: std::os::raw::c_uint = 0;
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let user_data: *mut std::os::raw::c_void = callback_get_result_string_data(&mut ret);
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unsafe {
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callback_get_result_string(start, n, user_data);
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}
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let s = ret.unwrap();
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assert_eq!(s, "");
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}
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#[test]
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fn test_callback_result_string() {
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let mut ret: Result<String> = result_string_init!();
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let start = b"helloGARBAGE".as_ptr() as *const std::os::raw::c_char;
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let n: std::os::raw::c_uint = 5;
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let user_data: *mut std::os::raw::c_void = callback_get_result_string_data(&mut ret);
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unsafe {
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callback_get_result_string(start, n, user_data);
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}
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let s = ret.unwrap();
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assert_eq!(s, "hello");
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}
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}
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