mbedtls 0.12.2

Idiomatic Rust wrapper for MbedTLS, allowing you to use MbedTLS with only safe code while being able to use such great Rust features like error handling and closures. Building on MbedTLS's focus on embedded use, this crate can be used in a no_std environment.
Documentation 
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/* Copyright (c) Fortanix, Inc.
 *
 * Licensed under the GNU General Public License, version 2 <LICENSE-GPL or
 * https://www.gnu.org/licenses/gpl-2.0.html> or the Apache License, Version
 * 2.0 <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0>, at your
 * option. This file may not be copied, modified, or distributed except
 * according to those terms. */

use std::collections::{HashMap, HashSet};
use std::env;

/// Return the crate hash that Cargo will be passing to `rustc -C metadata=`.
// If there's a panic in this code block, that means Cargo's way of running the
// build script has changed, and this code should be updated to handle the new
// case.
fn get_compilation_metadata_hash() -> String {
    let out_dir: std::path::PathBuf = std::env::var_os("OUT_DIR").unwrap().into();
    let mut out_dir_it = out_dir.iter().rev();
    assert_eq!(out_dir_it.next().unwrap(), "out");
    let crate_ = out_dir_it.next().unwrap().to_string_lossy();
    assert!(crate_.starts_with("mbedtls-"));
    crate_[8..].to_owned()
}

fn main() {
    let metadata_hash = get_compilation_metadata_hash();
    println!("cargo:rustc-env=RUST_MBEDTLS_METADATA_HASH={}", metadata_hash);

    let env_components = env::var("DEP_MBEDTLS_PLATFORM_COMPONENTS").unwrap();
    let mut sys_platform_components = HashMap::<_, HashSet<_>>::new();
    for mut kv in env_components.split(",").map(|component| component.splitn(2, "=")) {
        let k = kv.next().unwrap();
        let v = kv.next().unwrap();
        sys_platform_components.entry(k).or_insert_with(Default::default).insert(v);
        println!(r#"cargo:rustc-cfg=sys_{}="{}""#, k, v);
    }

    let mut b = cc::Build::new();
    b.include(env::var_os("DEP_MBEDTLS_INCLUDE").unwrap());
    let config_file = format!(r#""{}""#, env::var("DEP_MBEDTLS_CONFIG_H").unwrap());
    b.define("MBEDTLS_CONFIG_FILE", Some(config_file.as_str()));
    b.define("RUST_MBEDTLS_METADATA_HASH", Some(metadata_hash.as_str()));

    b.file("src/mbedtls_malloc.c");
    if sys_platform_components
        .get("c_compiler")
        .map_or(false, |comps| comps.contains("freestanding"))
    {
        b.flag("-U_FORTIFY_SOURCE")
            .define("_FORTIFY_SOURCE", Some("0"))
            .flag("-ffreestanding");
    }
    b.compile("librust-mbedtls.a");
}