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// Copyright (c) 2016-2017, The Tor Project, Inc. */
// See LICENSE for licensing information */
//! Utilities for working with static strings.
/// A byte-array containing a single NUL byte (`b"\0"`).
pub const NUL_BYTE: &'static [u8] = b"\0";
/// Determine if a byte slice is a C-like string.
///
/// These checks guarantee that:
///
/// 1. there are no intermediate NUL bytes
/// 2. the last byte *is* a NUL byte
///
/// # Warning
///
/// This function does _not_ guarantee that the bytes represent any valid
/// encoding such as ASCII or UTF-8.
///
/// # Examples
///
/// ```
/// # use tor_util::strings::byte_slice_is_c_like;
/// #
/// let bytes: &[u8] = b"foo bar baz";
///
/// assert!(byte_slice_is_c_like(&bytes) == false);
///
/// let bytes: &[u8] = b"foo\0bar baz";
///
/// assert!(byte_slice_is_c_like(&bytes) == false);
///
/// let bytes: &[u8] = b"foo bar baz\0";
///
/// assert!(byte_slice_is_c_like(&bytes) == true);
/// ```
pub fn byte_slice_is_c_like(bytes: &[u8]) -> bool {
if !bytes[..bytes.len() - 1].contains(&0x00) && bytes[bytes.len() - 1] == 0x00 {
return true;
}
false
}
/// Create a `CStr` from a literal byte slice, appending a NUL byte to it first.
///
/// # Warning
///
/// The literal byte slice which is taken as an argument *MUST NOT* have any NUL
/// bytes (`b"\0"`) in it, anywhere, or else an empty string will be returned
/// (`CStr::from_bytes_with_nul_unchecked(b"\0")`) so as to avoid `panic!()`ing.
///
/// # Examples
///
/// ```
/// #[macro_use]
/// extern crate tor_util;
///
/// use std::ffi::CStr;
///
/// # fn do_test() -> Result<&'static CStr, &'static str> {
/// let message: &'static str = "This is a test of the tsunami warning system.";
/// let tuesday: &'static CStr;
/// let original: &str;
///
/// tuesday = cstr!("This is a test of the tsunami warning system.");
/// original = tuesday.to_str().or(Err("Couldn't unwrap CStr!"))?;
///
/// assert!(original == message);
/// #
/// # Ok(tuesday)
/// # }
/// # fn main() {
/// # do_test(); // so that we can use the ? operator in the test
/// # }
/// ```
/// It is also possible to pass several string literals to this macro. They
/// will be concatenated together in the order of the arguments, unmodified,
/// before finally being suffixed with a NUL byte:
///
/// ```
/// #[macro_use]
/// extern crate tor_util;
/// #
/// # use std::ffi::CStr;
/// #
/// # fn do_test() -> Result<&'static CStr, &'static str> {
///
/// let quux: &'static CStr = cstr!("foo", "bar", "baz");
/// let orig: &'static str = quux.to_str().or(Err("Couldn't unwrap CStr!"))?;
///
/// assert!(orig == "foobarbaz");
/// # Ok(quux)
/// # }
/// # fn main() {
/// # do_test(); // so that we can use the ? operator in the test
/// # }
/// ```
/// This is useful for passing static strings to C from Rust FFI code. To do so
/// so, use the `.as_ptr()` method on the resulting `&'static CStr` to convert
/// it to the Rust equivalent of a C `const char*`:
///
/// ```
/// #[macro_use]
/// extern crate tor_util;
///
/// use std::ffi::CStr;
/// use std::os::raw::c_char;
///
/// pub extern "C" fn give_static_borrowed_string_to_c() -> *const c_char {
/// let hello: &'static CStr = cstr!("Hello, language my parents wrote.");
///
/// hello.as_ptr()
/// }
/// # fn main() {
/// # let greetings = give_static_borrowed_string_to_c();
/// # }
/// ```
/// Note that the C code this static borrowed string is passed to *MUST NOT*
/// attempt to free the memory for the string.
///
/// # Note
///
/// An unfortunate limitation of the rustc compiler (as of 1.25.0-nightly), is
/// that the above code compiles, however if we were to change the assignment of
/// `tuesday` as follows, it will fail to compile, because Rust macros are
/// expanded at parse time, and at parse time there is no symbols table
/// available.
///
/// ```ignore
/// tuesday = cstr!(message);
/// ```
/// with the error message `error: expected a literal`.
///
/// # Returns
///
/// If the string literals passed as arguments contain no NUL bytes anywhere,
/// then an `&'static CStr` containing the (concatenated) bytes of the string
/// literal(s) passed as arguments, with a NUL byte appended, is returned.
/// Otherwise, an `&'static CStr` containing a single NUL byte is returned (an
/// "empty" string in C).
#[macro_export]
macro_rules! cstr {
($($bytes:expr),*) => (
::std::ffi::CStr::from_bytes_with_nul(
concat!($($bytes),*, "\0").as_bytes()
).unwrap_or(
unsafe{
::std::ffi::CStr::from_bytes_with_nul_unchecked(b"\0")
}
)
)
}
#[cfg(test)]
mod test {
use std::ffi::CStr;
#[test]
fn cstr_macro() {
let _: &'static CStr = cstr!("boo");
}
#[test]
fn cstr_macro_multi_input() {
let quux: &'static CStr = cstr!("foo", "bar", "baz");
assert!(quux.to_str().unwrap() == "foobarbaz");
}
#[test]
fn cstr_macro_bad_input() {
let waving: &'static CStr = cstr!("waving not drowning o/");
let drowning: &'static CStr = cstr!("\0 drowning not waving");
assert!(waving.to_str().unwrap() == "waving not drowning o/");
assert!(drowning.to_str().unwrap() == "")
}
}
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