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
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
// SPDX-License-Identifier: CC0-1.0

//! Helpers for displaying bytes as hex strings.
//!
//! This module provides a trait for displaying things as hex as well as an implementation for
//! `&[u8]`.
//!
//! For arrays and slices we support padding and precision for length < 512 bytes.
//!
//! # Examples
//!
//! ```
//! use hex_conservative::DisplayHex;
//!
//! // Display as hex.
//! let v = vec![0xde, 0xad, 0xbe, 0xef];
//! assert_eq!(format!("{}", v.as_hex()), "deadbeef");
//!
//! // Get the most significant bytes.
//! let v = vec![0x01, 0x23, 0x45, 0x67];
//! assert_eq!(format!("{0:.4}", v.as_hex()), "0123");
//!
//! // Padding with zeros
//! let v = vec![0xab; 2];
//! assert_eq!(format!("{:0>8}", v.as_hex()), "0000abab");
//!```

use core::borrow::Borrow;
use core::fmt;

use super::Case;
use crate::buf_encoder::{BufEncoder, FixedLenBuf, OutBytes};
#[cfg(feature = "alloc")]
use crate::prelude::*;

/// Extension trait for types that can be displayed as hex.
///
/// Types that have a single, obvious text representation being hex should **not** implement this
/// trait and simply implement `Display` instead.
///
/// This trait should be generally implemented for references only. We would prefer to use GAT but
/// that is beyond our MSRV. As a lint we require the `IsRef` trait which is implemented for all
/// references.
pub trait DisplayHex: Copy + sealed::IsRef {
    /// The type providing [`fmt::Display`] implementation.
    ///
    /// This is usually a wrapper type holding a reference to `Self`.
    type Display: fmt::Display + fmt::Debug + fmt::LowerHex + fmt::UpperHex;

    /// Display `Self` as a continuous sequence of ASCII hex chars.
    fn as_hex(self) -> Self::Display;

    /// Create a lower-hex-encoded string.
    ///
    /// A shorthand for `to_hex_string(Case::Lower)`, so that `Case` doesn't need to be imported.
    ///
    /// This may be faster than `.display_hex().to_string()` because it uses `reserve_suggestion`.
    #[cfg(feature = "alloc")]
    fn to_lower_hex_string(self) -> String { self.to_hex_string(Case::Lower) }

    /// Create an upper-hex-encoded string.
    ///
    /// A shorthand for `to_hex_string(Case::Upper)`, so that `Case` doesn't need to be imported.
    ///
    /// This may be faster than `.display_hex().to_string()` because it uses `reserve_suggestion`.
    #[cfg(feature = "alloc")]
    fn to_upper_hex_string(self) -> String { self.to_hex_string(Case::Upper) }

    /// Create a hex-encoded string.
    ///
    /// This may be faster than `.display_hex().to_string()` because it uses `reserve_suggestion`.
    #[cfg(feature = "alloc")]
    fn to_hex_string(self, case: Case) -> String {
        let mut string = String::new();
        self.append_hex_to_string(case, &mut string);
        string
    }

    /// Appends hex-encoded content to an existing `String`.
    ///
    /// This may be faster than `write!(string, "{:x}", self.as_hex())` because it uses
    /// `hex_reserve_sugggestion`.
    #[cfg(feature = "alloc")]
    fn append_hex_to_string(self, case: Case, string: &mut String) {
        use fmt::Write;

        string.reserve(self.hex_reserve_suggestion());
        match case {
            Case::Lower => write!(string, "{:x}", self.as_hex()),
            Case::Upper => write!(string, "{:X}", self.as_hex()),
        }
        .unwrap_or_else(|_| {
            let name = core::any::type_name::<Self::Display>();
            // We don't expect `std` to ever be buggy, so the bug is most likely in the `Display`
            // impl of `Self::Display`.
            panic!("The implementation of Display for {} returned an error when it shouldn't", name)
        })
    }

    /// Hints how much bytes to reserve when creating a `String`.
    ///
    /// Implementors that know the number of produced bytes upfront should override this.
    /// Defaults to 0.
    ///
    // We prefix the name with `hex_` to avoid potential collision with other methods.
    fn hex_reserve_suggestion(self) -> usize { 0 }
}

mod sealed {
    /// Trait marking a shared reference.
    pub trait IsRef: Copy {}

    impl<T: ?Sized> IsRef for &'_ T {}
}

impl<'a> DisplayHex for &'a [u8] {
    type Display = DisplayByteSlice<'a>;

    #[inline]
    fn as_hex(self) -> Self::Display { DisplayByteSlice { bytes: self } }

    #[inline]
    fn hex_reserve_suggestion(self) -> usize {
        // Since the string wouldn't fit into address space if this overflows (actually even for
        // smaller amounts) it's better to panic right away. It should also give the optimizer
        // better opportunities.
        self.len().checked_mul(2).expect("the string wouldn't fit into address space")
    }
}

#[cfg(feature = "alloc")]
impl<'a> DisplayHex for &'a alloc::vec::Vec<u8> {
    type Display = DisplayByteSlice<'a>;

    #[inline]
    fn as_hex(self) -> Self::Display { DisplayByteSlice { bytes: self } }

    #[inline]
    fn hex_reserve_suggestion(self) -> usize {
        // Since the string wouldn't fit into address space if this overflows (actually even for
        // smaller amounts) it's better to panic right away. It should also give the optimizer
        // better opportunities.
        self.len().checked_mul(2).expect("the string wouldn't fit into address space")
    }
}

/// Displays byte slice as hex.
///
/// Created by [`<&[u8] as DisplayHex>::as_hex`](DisplayHex::as_hex).
pub struct DisplayByteSlice<'a> {
    // pub because we want to keep lengths in sync
    pub(crate) bytes: &'a [u8],
}

impl<'a> DisplayByteSlice<'a> {
    fn display(&self, f: &mut fmt::Formatter, case: Case) -> fmt::Result {
        let mut buf = [0u8; 1024];
        let mut encoder = BufEncoder::new(&mut buf);

        // Its unlikely that someone will want special formatting for a hex string that
        // is over 1024 characters so just handle padding for short slices.
        if self.bytes.len() < 512 {
            encoder.put_bytes(self.bytes, case);
            return f.pad(encoder.as_str());
        }

        let mut chunks = self.bytes.chunks_exact(512);
        for chunk in &mut chunks {
            encoder.put_bytes(chunk, case);
            f.write_str(encoder.as_str())?;
            encoder.clear();
        }
        encoder.put_bytes(chunks.remainder(), case);
        f.write_str(encoder.as_str())
    }
}

impl<'a> fmt::Display for DisplayByteSlice<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(self, f) }
}

impl<'a> fmt::Debug for DisplayByteSlice<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(self, f) }
}

impl<'a> fmt::LowerHex for DisplayByteSlice<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { self.display(f, Case::Lower) }
}

impl<'a> fmt::UpperHex for DisplayByteSlice<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { self.display(f, Case::Upper) }
}

/// Displays byte array as hex.
///
/// Created by [`<&[u8; LEN] as DisplayHex>::as_hex`](DisplayHex::as_hex).
// See `buf_encoder::impl_encode!` for `DisplayHex` implementation.
pub struct DisplayArray<A: Clone + IntoIterator, B: FixedLenBuf>
where
    A::Item: Borrow<u8>,
{
    array: A,
    _buffer_marker: core::marker::PhantomData<B>,
}

impl<A: Clone + IntoIterator, B: FixedLenBuf> DisplayArray<A, B>
where
    A::Item: Borrow<u8>,
{
    /// Creates the wrapper.
    pub fn new(array: A) -> Self { DisplayArray { array, _buffer_marker: Default::default() } }

    fn display(&self, f: &mut fmt::Formatter, case: Case) -> fmt::Result {
        let mut buf = B::uninit();
        let mut encoder = BufEncoder::new(&mut buf);
        encoder.put_bytes(self.array.clone(), case);
        f.pad_integral(true, "0x", encoder.as_str())
    }
}

impl<A: Clone + IntoIterator, B: FixedLenBuf> fmt::Display for DisplayArray<A, B>
where
    A::Item: Borrow<u8>,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(self, f) }
}

impl<A: Clone + IntoIterator, B: FixedLenBuf> fmt::Debug for DisplayArray<A, B>
where
    A::Item: Borrow<u8>,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(self, f) }
}

impl<A: Clone + IntoIterator, B: FixedLenBuf> fmt::LowerHex for DisplayArray<A, B>
where
    A::Item: Borrow<u8>,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { self.display(f, Case::Lower) }
}

impl<A: Clone + IntoIterator, B: FixedLenBuf> fmt::UpperHex for DisplayArray<A, B>
where
    A::Item: Borrow<u8>,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { self.display(f, Case::Upper) }
}

/// Format known-length array as hex.
///
/// This supports all formatting options of formatter and may be faster than calling `as_hex()` on
/// an arbitrary `&[u8]`. Note that the implementation intentionally keeps leading zeros even when
/// not requested. This is designed to display values such as hashes and keys and removing leading
/// zeros would be confusing.
///
/// Note that the bytes parameter is `IntoIterator` this means that if you would like to do some
/// manipulation to the byte array before formatting then you can. For example `bytes.iter().rev()`
/// to print the array backwards.
///
/// ## Parameters
///
/// * `$formatter` - a [`fmt::Formatter`].
/// * `$len` known length of `$bytes`, must be a const expression.
/// * `$bytes` - bytes to be encoded, most likely a reference to an array.
/// * `$case` - value of type [`Case`] determining whether to format as lower or upper case.
///
/// ## Panics
///
/// This macro panics if `$len` is not equal to `$bytes.len()`. It also fails to compile if `$len`
/// is more than half of `usize::MAX`.
#[macro_export]
macro_rules! fmt_hex_exact {
    ($formatter:expr, $len:expr, $bytes:expr, $case:expr) => {{
        // statically check $len
        #[allow(deprecated)]
        const _: () = [()][($len > usize::MAX / 2) as usize];
        assert_eq!($bytes.len(), $len);
        let mut buf = [0u8; $len * 2];
        let buf = $crate::buf_encoder::AsOutBytes::as_mut_out_bytes(&mut buf);
        $crate::display::fmt_hex_exact_fn($formatter, buf, $bytes, $case)
    }};
}
pub use fmt_hex_exact;

// Implementation detail of `write_hex_exact` macro to de-duplicate the code
#[doc(hidden)]
#[inline]
pub fn fmt_hex_exact_fn<I>(
    f: &mut fmt::Formatter,
    buf: &mut OutBytes,
    bytes: I,
    case: Case,
) -> fmt::Result
where
    I: IntoIterator,
    I::Item: Borrow<u8>,
{
    let mut encoder = BufEncoder::new(buf);
    encoder.put_bytes(bytes, case);
    f.pad_integral(true, "0x", encoder.as_str())
}

#[cfg(test)]
mod tests {
    #[cfg(feature = "alloc")]
    use super::*;

    #[cfg(feature = "alloc")]
    mod alloc {
        use super::*;

        fn check_encoding(bytes: &[u8]) {
            use core::fmt::Write;

            let s1 = bytes.to_lower_hex_string();
            let mut s2 = String::with_capacity(bytes.len() * 2);
            for b in bytes {
                write!(s2, "{:02x}", b).unwrap();
            }
            assert_eq!(s1, s2);
        }

        #[test]
        fn empty() { check_encoding(b""); }

        #[test]
        fn single() { check_encoding(b"*"); }

        #[test]
        fn two() { check_encoding(b"*x"); }

        #[test]
        fn just_below_boundary() { check_encoding(&[42; 512]); }

        #[test]
        fn just_above_boundary() { check_encoding(&[42; 513]); }

        #[test]
        fn just_above_double_boundary() { check_encoding(&[42; 1025]); }

        #[test]
        fn fmt_exact_macro() {
            use crate::alloc::string::ToString;

            struct Dummy([u8; 32]);

            impl fmt::Display for Dummy {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    fmt_hex_exact!(f, 32, &self.0, Case::Lower)
                }
            }

            assert_eq!(Dummy([42; 32]).to_string(), "2a".repeat(32));
        }

        #[test]
        fn display_short_with_padding() {
            let v = vec![0xbe, 0xef];
            assert_eq!(format!("Hello {:<8}!", v.as_hex()), "Hello beef    !");
            assert_eq!(format!("Hello {:-<8}!", v.as_hex()), "Hello beef----!");
            assert_eq!(format!("Hello {:^8}!", v.as_hex()), "Hello   beef  !");
            assert_eq!(format!("Hello {:>8}!", v.as_hex()), "Hello     beef!");
        }

        // We only pad arrays 512 bytes and shorter.
        #[test]
        fn display_long_no_padding() {
            // Sanity.
            let x = 1;
            // This is here to show how long 2000 is so one can visually see the test below does not pad.
            let want = "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001";
            let got = format!("{:0>2000}", x);
            assert_eq!(got, want);

            // Note this string is shorter than the one above.
            let v = vec![0xab; 512];
            let want = "abababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababababab";
            let got = format!("{:0>2000}", v.as_hex());
            assert_eq!(got, want)
        }
    }
}