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/*! This crate exposes a procedural macro that allows you to format bytestrings. For more background on why you would want to do that, [read this article](https://octobus.net/blog/2020-06-05-not-everything-is-utf8.html). ## Usage Add this to your `Cargo.toml`: ```toml [dependencies] format-bytes = "0.1" ``` then use the macro like so: ```rust use format_bytes::format_bytes; fn main() { assert_eq!( format_bytes!(b"look at those {} bytes", &[0u8, 1, 2]), b"look at those \x00\x01\x02 bytes" ); } ``` See more examples of how it works on the documentation of [`format_bytes!` itself](https://docs.rs/format-bytes/\*\/format_bytes/macro.format_bytes.html). ## Missing features * Named arguments, but they should be added in a future version * Python-like "f-string" functionality is not planned because of its more complex implementation and limited actual benefit * ``format!``-like padding helpers: if the need manifests itself, they might appear ## Why not 1.0? Not until named arguments have landed and the macro gets a bit of mileage (it will be used in [Mercurial](https://www.mercurial-scm.org)). */ use proc_macro_hack::proc_macro_hack; use std::fmt; use std::io; /// Creates a `Vec<u8>` using interpolation of runtime expressions. /// /// The first argument `format_bytes!` receives is a format bytestring. /// This must be a bytestring literal. The power of the formatting string /// is in the `{}`s contained. /// /// Additional arguments passed to `format_bytes!` replace the `{}`s /// within the formatting bytestring in the order given. It only supports /// positional arguments for now, but a future version should add support /// for named arguments. /// /// These additional arguments may have any type that implements /// the [`DisplayBytes`] trait. /// /// # Examples /// /// ``` /// use format_bytes::format_bytes; /// /// assert_eq!(format_bytes!(b""), b""); /// assert_eq!(format_bytes!(b"here"), b"here"); /// assert_eq!(format_bytes!(b"this {{ escapes {{"), b"this {{ escapes {{"); /// assert_eq!(format_bytes!(b"also this {{}}"), b"also this {{}}"); /// assert_eq!(format_bytes!(b"this works {{{}}}", b"a"), b"this works {{a}}"); /// assert_eq!( /// format_bytes!(b"look at those {} bytes", &[0u8, 1, 2]), /// b"look at those \x00\x01\x02 bytes" /// ); /// /// let bytes = vec![0u8, 1, 2]; /// /// assert_eq!( /// format_bytes!(b"look at those {} bytes", bytes), /// b"look at those \x00\x01\x02 bytes" /// ); /// assert_eq!( /// format_bytes!(b"{}.{}.{}.{}", 1_i32, 2_u8, 3_f32, &4), /// b"1.2.3.4" /// ); /// assert_eq!( /// format_bytes!(b"what about this very very long message {}?", "here".as_bytes()), /// b"what about this very very long message here?".to_vec() /// ) /// ``` #[macro_export] macro_rules! format_bytes { ($($args: tt)*) => {{ let mut vec = Vec::<u8>::new(); $crate::write_bytes!(vec, $($args)*) // Never panics since `impl std::fmt::Write for Vec<u8>` never errors: .unwrap(); vec }} } /// Like [`format_bytes!`], but writes to a stream given as an additional first argument. /// /// The stream is an expression of any type that implements the [`WriteBytes`] trait. /// The macro returns `Result<(), WriteBytes::Error>`. /// /// # Examples /// /// ``` /// use format_bytes::write_bytes; /// /// const BUFFER_LEN: usize = 20; /// let mut buffer = [0_u8; BUFFER_LEN]; /// let mut slice = &mut buffer[..]; /// /// write_bytes!(slice, b"{}", 3.14).unwrap(); /// /// let written = BUFFER_LEN - slice.len(); /// assert_eq!(&buffer[..written], b"3.14"); /// ``` #[proc_macro_hack] pub use format_bytes_macros::write_bytes; /// Let types decide how to format themselves for presentation to users in a byte-stream output. /// /// Similar to `std::fmt::Display`, but the output stream is bytes instead of Unicode. /// /// When output is presented to users, it is decoded with an unspecified character encoding /// that is presumed to be ASCII-compatible. /// /// Implementers should return any error from `output` (e.g. with the `?` operator), /// and not emit other errors. pub trait DisplayBytes { fn display_bytes(&self, output: &mut dyn io::Write) -> io::Result<()>; } macro_rules! impl_through_deref { // Macro hygiene requires the `$Inner` ident to be an input // so it matches corresponding idents in `$Wrapper` types: ($Inner: ident => $( $Wrapper: ty, )*) => { $( /// Forward to the inner type. impl<$Inner: ?Sized + DisplayBytes> DisplayBytes for $Wrapper { #[inline] fn display_bytes(&self, output: &mut dyn io::Write) -> io::Result<()> { (**self).display_bytes(output) } } )* }; } impl_through_deref! { Inner => &'_ Inner, &'_ mut Inner, Box<Inner>, std::rc::Rc<Inner>, std::sync::Arc<Inner>, } macro_rules! impl_for_byte_string { ($($Ty: ty),+) => { $( /// Byte strings are "formatted" as-is. impl DisplayBytes for $Ty { #[inline] fn display_bytes(&self, output: &mut dyn io::Write) -> io::Result<()> { output.write_all(self) } } )+ }; } impl_for_byte_string!([u8], Vec<u8>); macro_rules! impl_for_arrays { ($( $LEN: expr )+) => { impl_for_byte_string! { $( [u8; $LEN] ),+ } }; } impl_for_arrays! { 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 } /// Adaptor for types that implement `std::fmt::Display`. The Unicode output is encoded as UTF-8. /// /// # Example /// /// ```rust /// use format_bytes::{format_bytes, Utf8}; /// /// assert_eq!(format_bytes!(b"{}", Utf8("è_é")), b"\xc3\xa8_\xc3\xa9"); /// ``` pub struct Utf8<Inner>(pub Inner); impl<Inner: fmt::Display> DisplayBytes for Utf8<Inner> { fn display_bytes(&self, output: &mut dyn io::Write) -> io::Result<()> { // Calling `Display::fmt` requires a `Formatter` which we can’t create directly, // so let’s go through `write!` with an adaptor type. struct Adapter<'a> { output: &'a mut dyn io::Write, result: io::Result<()>, } impl fmt::Write for Adapter<'_> { fn write_str(&mut self, s: &str) -> fmt::Result { if self.result.is_err() { return Err(fmt::Error); } let utf8 = s.as_bytes(); match self.output.write_all(utf8) { Ok(()) => Ok(()), Err(error) => { // `fmt::Error` cannot carry any data so stash the error self.result = Err(error); Err(fmt::Error) } } } } let mut adapter = Adapter { output, result: Ok(()), }; { // `write!` requires this import: https://github.com/rust-lang/rust/issues/21826 use fmt::Write; write!(adapter, "{}", self.0) // Recover stashed error .map_err(|fmt::Error| adapter.result.unwrap_err()) } } } macro_rules! impl_ascii_only { ($( $Ty: ident )*) => { $( /// Format to ASCII bytes with `std::fmt::Display`. /// /// The `Display` impl for this type only emits ASCII characters, /// so it’s less useful than in the general case /// to make users explicitly opt-in to UTF-8 encoding. impl DisplayBytes for $Ty { #[inline] fn display_bytes(&self, output: &mut dyn io::Write) -> io::Result<()> { Utf8(self).display_bytes(output) } } )* }; } impl_ascii_only! { u8 u16 u32 u64 u128 usize i8 i16 i32 i64 i128 isize f32 f64 }