ots 0.1.3

Please do not use this. Use opentimestamps instead.
Documentation 
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

// OpenTimestamps Library
// Written in 2017 by
//   Andrew Poelstra <rust-ots@wpsoftware.net>
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// You should have received a copy of the CC0 Public Domain Dedication
// along with this software.
// If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
//

//! # Attestations
//!
//! An attestation is a claim that some data existed at some time. It
//! comes from some server or from a blockchain.
//!

use std::fmt;
use std::io::{Read, Write};

use error::Error;
use hex::Hexed;
use ser;

/// Size in bytes of the tag identifying the attestation type
const TAG_SIZE: usize = 8;
/// Maximum length of a URI in a "pending" attestation
const MAX_URI_LEN: usize = 1000;

/// Tag indicating a Bitcoin attestation
const BITCOIN_TAG: &'static [u8] = b"\x05\x88\x96\x0d\x73\xd7\x19\x01";
/// Tag indicating a pending attestation
const PENDING_TAG: &'static [u8] = b"\x83\xdf\xe3\x0d\x2e\xf9\x0c\x8e";

/// An attestation that some data existed at some time
#[allow(missing_docs)]
#[derive(Clone, PartialEq, Eq, Debug)]
pub enum Attestation {
    /// An attestation from a Bitcoin blockheader. This consists of a blockheight
    /// and nothing more, it is expected that the current hash is equal to the
    /// Merkle root of the block at this height.
    Bitcoin {
        height: usize
    },
    /// An attestation from some server. It is commented at length in Peter Todd's
    /// `python-opentimestamps` that the server should be expected to keep anything
    /// it attests to, forever, and therefore the only thing we store locally is a
    /// single simple URI with a very restricted charset. (The restricted charset
    /// seems mainly to be to avoid the software being used for nefarious purposes,
    /// as it will fetch this URI under some circumstances.)
    Pending {
        uri: String
    },
    /// An unknown attestation that we just store straight
    Unknown {
        tag: Vec<u8>,
        data: Vec<u8>
    }
}

impl Attestation {
    /// Deserialize an arbitrary attestation
    pub fn deserialize<R: Read>(deser: &mut ser::Deserializer<R>) -> Result<Attestation, Error> {
        let tag = deser.read_fixed_bytes(TAG_SIZE)?;
        let len = deser.read_uint()?;

        if tag == BITCOIN_TAG {
            let height = deser.read_uint()?;
            Ok(Attestation::Bitcoin {
                height: height
            })
        } else if tag == PENDING_TAG {
            // This validation logic copied from python-opentimestamps. Peter comments
            // that he is deliberately avoiding ?, &, @, etc., to "keep us out of trouble"
            let uri_bytes = deser.read_bytes(0, MAX_URI_LEN)?;
            let uri_string = String::from_utf8(uri_bytes)?;
            for ch in uri_string.chars() {
                match ch {
                    'a'...'z' => {}
                    'A'...'Z' => {}
                    '0'...'9' => {}
                    '.' | '-' | '_' | '/' | ':' => {},
                    x => return Err(Error::InvalidUriChar(x))
                }
            }
            Ok(Attestation::Pending {
                uri: uri_string
            })
        } else {
            Ok(Attestation::Unknown {
                tag: tag,
                data: deser.read_fixed_bytes(len)?
            })
        }
    }

    /// Serialize an attestation
    pub fn serialize<W: Write>(&self, ser: &mut ser::Serializer<W>) -> Result<(), Error> {
        let mut byte_ser = ser::Serializer::new(vec![]);
        match *self {
            Attestation::Bitcoin { height } => {
                ser.write_fixed_bytes(BITCOIN_TAG)?;
                byte_ser.write_uint(height)?;
                ser.write_bytes(&byte_ser.into_inner())
            }
            Attestation::Pending { ref uri } => {
                ser.write_fixed_bytes(PENDING_TAG)?;
                byte_ser.write_bytes(uri.as_bytes())?;
                ser.write_bytes(&byte_ser.into_inner())
            }
            Attestation::Unknown { ref tag, ref data } => {
                ser.write_fixed_bytes(tag)?;
                ser.write_bytes(data)
            }
        }
    }
}

impl fmt::Display for Attestation {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            Attestation::Bitcoin { height } => write!(f, "Bitcoin block {}", height),
            Attestation::Pending { ref uri } => write!(f, "Pending: update URI {}", uri),
            Attestation::Unknown { ref tag, ref data } => write!(f, "unknown attestation type {}: {}", Hexed(tag), Hexed(data)),
        }
    }
}