# lib.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/zero-0.1.2/src/lib.rs`.
Keywords: rust, rustlang, rust-lang

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    // Copyright 2016 Nicholas Cameron.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! Functions for reading binary data into Rust data structures. All functions
    //! are zero-allocation.
    //!
    //! There are functions for reading a single value, an array of values, a single
    //! null-terminated utf8 string (which should also work with ascii strings), and
    //! an array of null-terminated strings terminated by another null byte.
    //!
    //! Functions preserve the lifetime of the underlying data. These functions are
    //! memory safe, although this is in part based on the assumption that the
    //! client only implements the unsafe trait `Pod` where safe to do so.
    //!
    //! Functions assert that the provided data is large enough. The string
    //! functions check that strings are valid utf8. There is no checking that the
    //! the privided input will produce a valid object (for example, an enum has a
    //! valid discriminant). The user must assert this by implementing the trait
    //! `Pod`.
    //!
    //! There are also unsafe versions of most functions which do not require the
    //! return type to implement `Pod` and which do no checking.

    #![no_std]

    use core::mem;
    use core::slice::from_raw_parts;
    use core::str::{from_utf8, from_utf8_unchecked};

    /// Reads a single `T` from `input`.
    ///
    /// `input` must be at least as large as `T`.
    pub fn read<'a, T: Pod>(input: &'a [u8]) -> &'a T {
        assert!(mem::size_of::<T>() <= input.len());

        unsafe {
            read_unsafe(input)
        }
    }

    /// Read an array of `T`s from input.
    ///
    /// `input` must contain an exact number of `T`s, there must be no extra bytes
    /// after the last `T`. `T` may not be zero-sized.
    pub fn read_array<'a, T: Pod>(input: &'a [u8]) -> &'a [T] {
        let t_size = mem::size_of::<T>();
        assert!(t_size > 0, "Can't read arrays of zero-sized types");
        assert!(input.len() % t_size == 0);

        unsafe {
            read_array_unsafe(input)
        }
    }

    /// Read a string from `input`. The string must be a null-termianted utf8 string.
    /// Note that an ascii C string fulfils this requirement.
    pub fn read_str<'a>(input: &'a [u8]) -> &'a str {
        from_utf8(read_str_bytes(input)).expect("Non-utf8 string")
    }

    /// Returns an iterator which will return a sequence of strings from `input`.
    /// Each string must be a null-terminated utf8 string. The sequence of strings
    /// is terminated either by a second null byte, or the end of input.
    pub fn read_strs_to_null<'a>(input: &'a [u8]) -> StrReaderIterator<'a> {
        StrReaderIterator {
            data: input,
        }
    }

    /// Implementing this trait means that the concrete type is plain old data (POD).
    /// Precisely, by implementing `Pod` the programmer asserts that it is safe to
    /// read the type from binary slices provided to `read`, etc.
    ///
    /// Some guidelines for when `Pod` may be implemented (note that whether `Pod`
    /// should be implemented or not is a function of both the type and the input
    /// data. I.e., just because a type is `Pod` in one context does not mean it
    /// should be in another):
    /// * primitive numeric types (`u8`, `i64`, `f32`, etc.) are fine,
    /// * bools are fine, if the provided data ensures they may have only the values
    ///   `0` or `1` (note that this is a stricter requirement that C),
    /// * structs containing only `Pod` data are fine,
    /// * structs must be `repr(C)` or `repr(packed)`, if the former, the supplied
    ///   data must have the correct alignment,
    /// * enums must have valid discriminants in the supplied data, this is probably
    ///   only feasible if they have a specified representation,
    /// * there must not be invalid enum variants in the data,
    /// * any kind of pointer is probably a bad idea. Theoretically one could make
    ///   raw pointers work.
    pub unsafe trait Pod: Sized {}

    unsafe impl Pod for u8 {}
    unsafe impl Pod for u16 {}
    unsafe impl Pod for u32 {}
    unsafe impl Pod for u64 {}
    unsafe impl Pod for i8 {}
    unsafe impl Pod for i16 {}
    unsafe impl Pod for i32 {}
    unsafe impl Pod for i64 {}

    /// Reads a `T` from `input` with no checks.
    pub unsafe fn read_unsafe<'a, T: Sized>(input: &'a [u8]) -> &'a T {
        mem::transmute(input as *const [u8] as *const u8 as *const T)
    }

    /// Reads an array of `T`s from `input` with no checks.
    pub unsafe fn read_array_unsafe<'a, T: Sized>(input: &'a [u8]) -> &'a [T] {
        let ptr = input.as_ptr() as *const T;
        from_raw_parts(ptr, input.len() / mem::size_of::<T>())
    }

    /// Reads a null-terminated string from `input` with no checks.
    pub unsafe fn read_str_unsafe<'a>(input: &'a [u8]) -> &'a str {
        from_utf8_unchecked(read_str_bytes(input))
    }

    /// Iterates over `self.data`, yielding strings (null-terminated in `self.data`).
    /// See `read_strs_to_null`.
    #[derive(Clone, Debug)]
    pub struct StrReaderIterator<'a> {
        data: &'a [u8]
    }

    impl<'a> Iterator for StrReaderIterator<'a> {
        type Item = &'a str;

        fn next(&mut self) -> Option<&'a str> {
            if self.data.len() == 0 || self.data[0] == 0 {
                return None;
            }

            let result = read_str(self.data);
            self.data = &self.data[result.len() + 1..];
            Some(result)
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            // Potentially no strings here at all. Maximum number is if the whole
            // data is filled with one char-long strings alternating with null bytes.
            (0, Some(self.data.len() / 2))
        }
    }

    // Helper function for read_str and read_str_unsafe.
    // Finds the sub-slice of input which contains a string by searching for a null
    // byte.
    fn read_str_bytes<'a>(input: &'a [u8]) -> &'a [u8] {
        for (i, byte) in input.iter().enumerate() {
            if *byte == 0 {
                return &input[..i];
            }
        }

        panic!("No null byte in input");
    }

    #[cfg(test)]
    mod test {
        use super::*;

        #[derive(Copy, Clone, PartialEq, Eq)]
        struct Zero;

        #[derive(Copy, Clone, PartialEq, Eq)]
        #[repr(packed)]
        struct Foo {
            a: u8,
        }

        #[derive(Copy, Clone, PartialEq, Eq)]
        #[repr(packed)]
        struct Bar {
            a: u32,
            b: u64,
            c: i8,
        }

        unsafe impl Pod for Zero {}
        unsafe impl Pod for Foo {}
        unsafe impl Pod for Bar {}

        // read

        #[test]
        fn test_read() {
            let a = &[];
            assert!(read::<Zero>(a) == &Zero);

            let a = &[42];
            assert!(read::<Foo>(a) == &Foo { a: 42 });

            let a = &[42, 0, 0, 0, 0x03, 0xff, 0x62, 0xa2, 0x5b, 0x42, 0x00, 0xf0, -2i8 as u8];
            assert!(read::<Bar>(a) == &Bar { a: 42, b: 0xf000425b_a262ff03, c: -2 });
        }

        #[test]
        #[should_panic]
        fn test_too_small() {
            let a = &[];
            read::<Foo>(a);
        }

        #[test]
        #[should_panic]
        fn test_too_small2() {
            let a = &[42, 0, 0, 0, 0x03, 0xff, 0x62, 0xa2, 0x5b, 0x42, 0x00, 0xf0];
            read::<Bar>(a);
        }

        // read_array

        #[test]
        fn test_read_array() {
            let a = &[42];
            assert!(read_array::<Foo>(a) == &[Foo { a: 42 }]);
            let a = &[42, 43, 44, 45];
            assert!(read_array::<Foo>(a) == &[Foo { a: 42 }, Foo { a: 43 }, Foo { a: 44 }, Foo { a: 45 }]);

            let a = &[42, 0, 0, 0, 0x03, 0xff, 0x62, 0xa2, 0x5b, 0x42, 0x00, 0xf0, -2i8 as u8];
            assert!(read_array::<Bar>(a) == &[Bar { a: 42, b: 0xf000425b_a262ff03, c: -2 }]);
            let a = &[42, 0, 0, 0, 0x03, 0xff, 0x62, 0xa2, 0x5b, 0x42, 0x00, 0xf0, -2i8 as u8,
                      43, 0, 0, 0, 0x03, 0xff, 0x62, 0xa2, 0x5b, 0x42, 0x00, 0xf0, -2i8 as u8,
                      44, 0, 0, 0, 0x03, 0xff, 0x62, 0xa2, 0x5b, 0x42, 0x00, 0xf0, -2i8 as u8];
            assert!(read_array::<Bar>(a) == &[Bar { a: 42, b: 0xf000425b_a262ff03, c: -2 },
                                              Bar { a: 43, b: 0xf000425b_a262ff03, c: -2 },
                                              Bar { a: 44, b: 0xf000425b_a262ff03, c: -2 }]);
        }

        #[test]
        #[should_panic]
        fn test_array_zero_sized() {
            let a = &[0];
            read_array::<Zero>(a);
        }

        // read_str

        #[test]
        fn test_good_strs() {
            let a = &[0];
            assert_eq!(read_str(a), "");
            let a = &[0x61, 0];
            assert_eq!(read_str(a), "a");
            let a = &[0x61, 0x41, 0x7a, 0, 0x61];
            assert_eq!(read_str(a), "aAz");
        }

        #[test]
        #[should_panic]
        fn test_no_null() {
            let a = &[];
            read_str(a);
        }

        #[test]
        #[should_panic]
        fn test_no_null2() {
            let a = &[0x61, 0x41, 0x7a];
            read_str(a);
        }

        #[test]
        #[should_panic]
        fn test_not_unicode() {
            // TODO
            panic!();
        }

        // read_strs_to_null

        #[test]
        fn test_good_strs_to_null() {
            let a = &[0];
            assert_eq!(read_strs_to_null(a).count(), 0);
            let a = &[0, 0];
            assert_eq!(read_strs_to_null(a).count(), 0);
            let a = &[0, 1];
            assert_eq!(read_strs_to_null(a).count(), 0);

            let a = &[0x61, 0];
            let mut iter = read_strs_to_null(a);
            assert_eq!(iter.next(), Some("a"));
            assert_eq!(iter.next(), None);

            let a = &[0x61, 0, 0x61, 0x41, 0x7a, 0, 0x61, 0];
            let mut iter = read_strs_to_null(a);
            assert_eq!(iter.next(), Some("a"));
            assert_eq!(iter.next(), Some("aAz"));
            assert_eq!(iter.next(), Some("a"));
            assert_eq!(iter.next(), None);

            let a = &[0x61, 0, 0x61, 0x41, 0x7a, 0, 0x61, 0, 0, 0x61];
            let mut iter = read_strs_to_null(a);
            assert_eq!(iter.next(), Some("a"));
            assert_eq!(iter.next(), Some("aAz"));
            assert_eq!(iter.next(), Some("a"));
            assert_eq!(iter.next(), None);
        }

        #[test]
        #[should_panic]
        fn test_no_null_to_null() {
            let a = &[0x61];
            let mut iter = read_strs_to_null(a);
            iter.next();
        }
    }