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use std::slice;
use libc::c_char;
use std::ffi::CStr;
/// 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
pub trait Smartlist<T> {
fn get_list(&self) -> Vec<T>;
}
#[repr(C)]
pub struct Stringlist {
pub list: *const *const c_char,
pub num_used: u8,
pub capacity: u8,
}
impl Smartlist<String> for Stringlist {
fn get_list(&self) -> Vec<String> {
let empty: Vec<String> = Vec::new();
let mut v: Vec<String> = Vec::new();
if self.list.is_null() {
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.
unsafe {
let elems =
slice::from_raw_parts(self.list, self.num_used as usize);
for i in elems.iter() {
let c_str = CStr::from_ptr(*i);
let r_str = match c_str.to_str() {
Ok(n) => n,
Err(_) => return empty,
};
v.push(String::from(r_str));
}
}
v
}
}
#[cfg(test)]
mod test {
#[test]
fn test_get_list_of_strings() {
extern crate libc;
use std::ffi::CString;
use libc::c_char;
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();
// then, collect a pointer for the list itself
let p: *const *const c_char = p_args.as_ptr();
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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