1 use std::fmt;
2 
3 /// Alternative implementation of `fmt::Debug` for byte slice.
4 ///
5 /// Standard `Debug` implementation for `[u8]` is comma separated
6 /// list of numbers. Since large amount of byte strings are in fact
7 /// ASCII strings or contain a lot of ASCII strings (e. g. HTTP),
8 /// it is convenient to print strings as ASCII when possible.
9 ///
10 /// This struct wraps `&[u8]` just to override `fmt::Debug`.
11 ///
12 /// `BsDebug` is not a part of public API of bytes crate.
13 pub struct BsDebug<'a>(pub &'a [u8]);
14 
15 impl<'a> fmt::Debug for BsDebug<'a> {
fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error>16     fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
17         write!(fmt, "b\"")?;
18         for &c in self.0 {
19             // https://doc.rust-lang.org/reference.html#byte-escapes
20             if c == b'\n' {
21                 write!(fmt, "\\n")?;
22             } else if c == b'\r' {
23                 write!(fmt, "\\r")?;
24             } else if c == b'\t' {
25                 write!(fmt, "\\t")?;
26             } else if c == b'\\' || c == b'"' {
27                 write!(fmt, "\\{}", c as char)?;
28             } else if c == b'\0' {
29                 write!(fmt, "\\0")?;
30                 // ASCII printable
31             } else if c >= 0x20 && c < 0x7f {
32                 write!(fmt, "{}", c as char)?;
33             } else {
34                 write!(fmt, "\\x{:02x}", c)?;
35             }
36         }
37         write!(fmt, "\"")?;
38         Ok(())
39     }
40 }
41 
42 #[cfg(test)]
43 mod test {
44     use super::BsDebug;
45 
46     #[test]
debug()47     fn debug() {
48         let vec: Vec<_> = (0..0x100).map(|b| b as u8).collect();
49 
50         let expected = "b\"\
51             \\0\\x01\\x02\\x03\\x04\\x05\\x06\\x07\
52             \\x08\\t\\n\\x0b\\x0c\\r\\x0e\\x0f\
53             \\x10\\x11\\x12\\x13\\x14\\x15\\x16\\x17\
54             \\x18\\x19\\x1a\\x1b\\x1c\\x1d\\x1e\\x1f\
55             \x20!\\\"#$%&'()*+,-./0123456789:;<=>?\
56             @ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\\\]^_\
57             `abcdefghijklmnopqrstuvwxyz{|}~\\x7f\
58             \\x80\\x81\\x82\\x83\\x84\\x85\\x86\\x87\
59             \\x88\\x89\\x8a\\x8b\\x8c\\x8d\\x8e\\x8f\
60             \\x90\\x91\\x92\\x93\\x94\\x95\\x96\\x97\
61             \\x98\\x99\\x9a\\x9b\\x9c\\x9d\\x9e\\x9f\
62             \\xa0\\xa1\\xa2\\xa3\\xa4\\xa5\\xa6\\xa7\
63             \\xa8\\xa9\\xaa\\xab\\xac\\xad\\xae\\xaf\
64             \\xb0\\xb1\\xb2\\xb3\\xb4\\xb5\\xb6\\xb7\
65             \\xb8\\xb9\\xba\\xbb\\xbc\\xbd\\xbe\\xbf\
66             \\xc0\\xc1\\xc2\\xc3\\xc4\\xc5\\xc6\\xc7\
67             \\xc8\\xc9\\xca\\xcb\\xcc\\xcd\\xce\\xcf\
68             \\xd0\\xd1\\xd2\\xd3\\xd4\\xd5\\xd6\\xd7\
69             \\xd8\\xd9\\xda\\xdb\\xdc\\xdd\\xde\\xdf\
70             \\xe0\\xe1\\xe2\\xe3\\xe4\\xe5\\xe6\\xe7\
71             \\xe8\\xe9\\xea\\xeb\\xec\\xed\\xee\\xef\
72             \\xf0\\xf1\\xf2\\xf3\\xf4\\xf5\\xf6\\xf7\
73             \\xf8\\xf9\\xfa\\xfb\\xfc\\xfd\\xfe\\xff\"";
74 
75         assert_eq!(expected, format!("{:?}", BsDebug(&vec)));
76     }
77 }
78