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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 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()
/// );
/// assert_eq!(format_bytes!(b"{}", std::borrow::Cow::Borrowed("cow".as_bytes())), b"cow");
/// ```
#[macro_export]
macro_rules! format_bytes {
($($args: tt)*) => {{
let mut vec = Vec::<u8>::new();
$crate::write_bytes!(&mut vec, $($args)*)
// Never panics since `impl std::fmt::Write for Vec<u8>` never errors:
.unwrap();
vec
}}
}
#[doc(hidden)]
pub use format_bytes_macros::_write_bytes;
/// 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 [`DisplayBytes`] trait.
/// The macro returns [`std::io::Result<()>`](std::io::Result).
///
/// # 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!(&mut slice, b"{}", 3.14).unwrap();
///
/// // `impl std::io::Write for &mut [u8]` reassigns the slice to the unwritten remainder:
/// let written = BUFFER_LEN - slice.len();
/// assert_eq!(&buffer[..written], b"3.14");
/// ```
#[macro_export]
macro_rules! write_bytes {
($($args: tt)*) => {
$crate::_write_bytes!($($args)*)
};
}
/// Let types decide how to format themselves for presentation to users in a byte-stream output.
///
/// Similar to `std::fmt::Display`, but the output stream is bytes instead of Unicode.
///
/// When output is presented to users, it is decoded with an unspecified character encoding
/// that is presumed to be ASCII-compatible.
///
/// Implementers should return any error from `output` (e.g. with the `?` operator),
/// and not emit other errors.
///
/// # Example
///
/// A typical `impl` for a struct with multiple fields might use the `write_bytes` macro:
///
/// ```
/// use format_bytes::{DisplayBytes, write_bytes};
///
/// struct Point2D { x: f32, y: f32 }
///
/// impl DisplayBytes for Point2D {
/// fn display_bytes(
/// &self,
/// out: &mut dyn std::io::Write,
/// ) -> std::io::Result<()> {
/// write_bytes!(out, b"x = {}, y = {}", self.x, self.y)
/// }
/// }
/// ```
pub trait DisplayBytes {
fn display_bytes(&self, output: &mut dyn io::Write) -> io::Result<()>;
}
macro_rules! impl_through_deref {
// Macro hygiene requires the `$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 $Wrapper {
#[inline]
fn display_bytes(&self, output: &mut dyn io::Write) -> io::Result<()> {
(**self).display_bytes(output)
}
}
)*
};
}
impl_through_deref! {
Inner =>
&'_ Inner,
&'_ mut Inner,
Box<Inner>,
std::rc::Rc<Inner>,
std::sync::Arc<Inner>,
}
/// Forward to the inner type.
impl<Inner> DisplayBytes for std::borrow::Cow<'_, Inner>
where
Inner: ?Sized + ToOwned + DisplayBytes,
{
#[inline]
fn display_bytes(&self, output: &mut dyn io::Write) -> io::Result<()> {
(**self).display_bytes(output)
}
}
macro_rules! impl_for_byte_string {
($($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
}
/// Format a sequence of values with the given separator repeated
/// between any two consecutive values, but not at the start or end of the sequence.
///
/// The return value can be formatted with `DisplayBytes` *once*.
/// Formatting consumes the input iterator. Formatting again will produce an empty output.
///
/// # Example
///
/// ```
/// use format_bytes::{format_bytes, join};
///
/// let formatted = format_bytes!(b"Got {}.", join(&[4, 3, 2], b" and "));
/// assert_eq!(formatted, b"Got 4 and 3 and 2.");
/// ```
pub fn join(
iterable: impl IntoIterator<Item = impl DisplayBytes>,
separator: impl DisplayBytes,
) -> impl DisplayBytes {
Join {
iter: std::cell::Cell::new(Some(iterable.into_iter())),
separator,
}
}
struct Join<I, S> {
iter: std::cell::Cell<Option<I>>,
separator: S,
}
impl<I, T, S> DisplayBytes for Join<I, S>
where
I: Iterator<Item = T>,
T: DisplayBytes,
S: DisplayBytes,
{
fn display_bytes(&self, output: &mut dyn io::Write) -> io::Result<()> {
if let Some(mut iter) = self.iter.take() {
if let Some(first) = iter.next() {
first.display_bytes(output)?;
for item in iter {
self.separator.display_bytes(output)?;
item.display_bytes(output)?;
}
}
}
Ok(())
}
}