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// Copyright (c) 2016-2019, 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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