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- // Copyright (c) 2016-2018, The Tor Project, Inc. */
- // See LICENSE for licensing information */
- use libc::{c_char, c_int};
- use std::ffi::CStr;
- use std::slice;
- /// Smartlists are a type used in C code in tor to define a collection of a
- /// generic type, which has a capacity and a number used. Each Smartlist
- /// defines how to extract the list of values from the underlying C structure
- ///
- /// Implementations are required to have a C representation, as this module
- /// serves purely to translate smartlists as defined in tor to vectors in Rust.
- pub trait Smartlist<T> {
- fn get_list(&self) -> Vec<T>;
- }
- #[repr(C)]
- pub struct Stringlist {
- pub list: *const *const c_char,
- pub num_used: c_int,
- pub capacity: c_int,
- }
- impl Smartlist<String> for Stringlist {
- fn get_list(&self) -> Vec<String> {
- let empty: Vec<String> = Vec::new();
- let mut rust_list: Vec<String> = Vec::new();
- if self.list.is_null() || self.num_used == 0 {
- return empty;
- }
- // unsafe, as we need to extract the smartlist list into a vector of
- // pointers, and then transform each element into a Rust string.
- let elems: &[*const c_char] =
- unsafe { slice::from_raw_parts(self.list, self.num_used as usize) };
- for elem in elems.iter() {
- if elem.is_null() {
- continue;
- }
- // unsafe, as we need to create a cstring from the referenced
- // element
- let c_string = unsafe { CStr::from_ptr(*elem) };
- let r_string = match c_string.to_str() {
- Ok(n) => n,
- Err(_) => return empty,
- };
- rust_list.push(String::from(r_string));
- }
- rust_list
- }
- }
- // TODO: CHK: this module maybe should be tested from a test in C with a
- // smartlist as defined in tor.
- #[cfg(test)]
- mod test {
- #[test]
- fn test_get_list_of_strings() {
- extern crate libc;
- use libc::c_char;
- use std::ffi::CString;
- use super::Smartlist;
- use super::Stringlist;
- {
- // test to verify that null pointers are gracefully handled
- use std::ptr;
- let sl = Stringlist {
- list: ptr::null(),
- num_used: 0,
- capacity: 0,
- };
- let data = sl.get_list();
- assert_eq!(0, data.len());
- }
- {
- let args = vec![String::from("a"), String::from("b")];
- // for each string, transform it into a CString
- let c_strings: Vec<_> = args
- .iter()
- .map(|arg| CString::new(arg.as_str()).unwrap())
- .collect();
- // then, collect a pointer for each CString
- let p_args: Vec<_> = c_strings.iter().map(|arg| arg.as_ptr()).collect();
- let p: *const *const c_char = p_args.as_ptr();
- // This is the representation that we expect when receiving a
- // smartlist at the Rust/C FFI layer.
- let sl = Stringlist {
- list: p,
- num_used: 2,
- capacity: 2,
- };
- let data = sl.get_list();
- assert_eq!("a", &data[0]);
- assert_eq!("b", &data[1]);
- }
- }
- }
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