tor/src/rust/protover/ffi.rs

// Copyright (c) 2016-2017, The Tor Project, Inc. */
// See LICENSE for licensing information */

//! FFI functions, only to be called from C.
//!
//! Equivalent C versions of this api are in `src/or/protover.c`

use libc::{c_char, c_int, uint32_t};
use std::ffi::CStr;
use std::ffi::CString;

use protover::*;
use smartlist::*;
use tor_allocate::allocate_and_copy_string;

/// Translate C enums to Rust Proto enums, using the integer value of the C
/// enum to map to its associated Rust enum
///
/// C_RUST_COUPLED: src/or/protover.h `protocol_type_t`
fn translate_to_rust(c_proto: uint32_t) -> Result<Proto, &'static str> {
    match c_proto {
        0 => Ok(Proto::Link),
        1 => Ok(Proto::LinkAuth),
        2 => Ok(Proto::Relay),
        3 => Ok(Proto::DirCache),
        4 => Ok(Proto::HSDir),
        5 => Ok(Proto::HSIntro),
        6 => Ok(Proto::HSRend),
        7 => Ok(Proto::Desc),
        8 => Ok(Proto::Microdesc),
        9 => Ok(Proto::Cons),
        _ => Err("Invalid protocol type"),
    }
}

/// Provide an interface for C to translate arguments and return types for
/// protover::all_supported
#[no_mangle]
pub extern "C" fn protover_all_supported(
    c_relay_version: *const c_char,
    missing_out: *mut *mut c_char,
) -> c_int {

    if c_relay_version.is_null() {
        return 1;
    }

    // Require an unsafe block to read the version from a C string. The pointer
    // is checked above to ensure it is not null.
    let c_str: &CStr = unsafe { CStr::from_ptr(c_relay_version) };

    let relay_version = match c_str.to_str() {
        Ok(n) => n,
        Err(_) => return 1,
    };

    let (is_supported, unsupported) = all_supported(relay_version);

    if unsupported.len() > 0 {
        let c_unsupported = match CString::new(unsupported) {
            Ok(n) => n,
            Err(_) => return 1,
        };

        let ptr = c_unsupported.into_raw();
        unsafe { *missing_out = ptr };
    }

    return if is_supported { 1 } else { 0 };
}

/// Provide an interface for C to translate arguments and return types for
/// protover::list_supports_protocol
#[no_mangle]
pub extern "C" fn protocol_list_supports_protocol(
    c_protocol_list: *const c_char,
    c_protocol: uint32_t,
    version: uint32_t,
) -> c_int {
    if c_protocol_list.is_null() {
        return 1;
    }

    // Require an unsafe block to read the version from a C string. The pointer
    // is checked above to ensure it is not null.
    let c_str: &CStr = unsafe { CStr::from_ptr(c_protocol_list) };

    let protocol_list = match c_str.to_str() {
        Ok(n) => n,
        Err(_) => return 1,
    };

    let protocol = match translate_to_rust(c_protocol) {
        Ok(n) => n,
        Err(_) => return 0,
    };

    let is_supported =
        protover_string_supports_protocol(protocol_list, protocol, version);

    return if is_supported { 1 } else { 0 };
}

/// Provide an interface for C to translate arguments and return types for
/// protover::list_supports_protocol_or_later
#[no_mangle]
pub extern "C" fn protocol_list_supports_protocol_or_later(
    c_protocol_list: *const c_char,
    c_protocol: uint32_t,
    version: uint32_t,
) -> c_int {
    if c_protocol_list.is_null() {
        return 1;
    }

    // Require an unsafe block to read the version from a C string. The pointer
    // is checked above to ensure it is not null.
    let c_str: &CStr = unsafe { CStr::from_ptr(c_protocol_list) };

    let protocol_list = match c_str.to_str() {
        Ok(n) => n,
        Err(_) => return 1,
    };

    let protocol = match translate_to_rust(c_protocol) {
        Ok(n) => n,
        Err(_) => return 0,
    };

    let is_supported =
        protover_string_supports_protocol_or_later(
            protocol_list, protocol, version);

    return if is_supported { 1 } else { 0 };
}

/// Provide an interface for C to translate arguments and return types for
/// protover::get_supported_protocols
#[no_mangle]
pub extern "C" fn protover_get_supported_protocols() -> *const c_char {
    let supported: &'static CStr;

    // If we're going to pass it to C, there cannot be any intermediate NUL
    // bytes.  An assert is okay here, since changing the const byte slice
    // in protover.rs to contain a NUL byte somewhere in the middle would be a
    // programming error.
    assert!(!SUPPORTED_PROTOCOLS[..SUPPORTED_PROTOCOLS.len() - 1].contains(&0x00));
    assert!(SUPPORTED_PROTOCOLS[SUPPORTED_PROTOCOLS.len() - 1] == 0x00);

    // It's okay to call the "unchecked" version of the function because
    // we can see that the bytes we're passing into it 1) are valid UTF-8,
    // 2) have no intermediate NUL bytes, and 3) are terminated with a NUL
    // byte.
    unsafe {
        supported = CStr::from_bytes_with_nul_unchecked(SUPPORTED_PROTOCOLS);
    }

    supported.as_ptr()
}

/// Provide an interface for C to translate arguments and return types for
/// protover::compute_vote
#[no_mangle]
pub extern "C" fn protover_compute_vote(
    list: *const Stringlist,
    threshold: c_int,
) -> *mut c_char {

    if list.is_null() {
        let empty = String::new();
        return allocate_and_copy_string(&empty);
    }

    // Dereference of raw pointer requires an unsafe block. The pointer is
    // checked above to ensure it is not null.
    let data: Vec<String> = unsafe { (*list).get_list() };

    let vote = compute_vote(data, threshold);

    allocate_and_copy_string(&vote)
}

/// Provide an interface for C to translate arguments and return types for
/// protover::is_supported_here
#[no_mangle]
pub extern "C" fn protover_is_supported_here(
    c_protocol: uint32_t,
    version: uint32_t,
) -> c_int {
    let protocol = match translate_to_rust(c_protocol) {
        Ok(n) => n,
        Err(_) => return 0,
    };

    let is_supported = is_supported_here(protocol, version);

    return if is_supported { 1 } else { 0 };
}

/// Provide an interface for C to translate arguments and return types for
/// protover::compute_for_old_tor
#[no_mangle]
pub extern "C" fn protover_compute_for_old_tor(
    version: *const c_char,
) -> *mut c_char {
    // Not handling errors when unwrapping as the content is controlled
    // and is an empty string
    let empty = String::new();

    if version.is_null() {
        return allocate_and_copy_string(&empty);
    }

    // Require an unsafe block to read the version from a C string. The pointer
    // is checked above to ensure it is not null.
    let c_str: &CStr = unsafe { CStr::from_ptr(version) };

    let version = match c_str.to_str() {
        Ok(n) => n,
        Err(_) => return allocate_and_copy_string(&empty),
    };

    let supported = compute_for_old_tor(&version);

    allocate_and_copy_string(&supported)
}