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age-core: Un-nest Base64 decoding in read::wrapped_encoded_data

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Instead of checking that each line is individually valid Base64, just
check line lengths. The no-padding-character check is moved to the end,
and the final Base64 decode is now load-bearing.

The parser structure has also been simplified using `nom` combinators.
This commit is contained in:
Jack Grigg 2021-08-07 22:14:43 +01:00
parent 7467e7b447
commit 7243768a61
1 changed files with 15 additions and 35 deletions
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50
age-core/src/format.rs
View file

@ -105,10 +105,10 @@ pub fn grease_the_joint() -> Stanza {
pub mod read {
use nom::{
branch::alt,
bytes::streaming::{tag, take_while, take_while1},
bytes::streaming::{tag, take, take_while1, take_while_m_n},
character::streaming::newline,
combinator::{map, map_opt, opt, verify},
multi::{many0, separated_list1},
multi::{many_till, separated_list1},
sequence::{pair, preceded, terminated},
IResult,
};
@ -126,21 +126,6 @@ pub mod read {
})(input)
}
/// Returns the slice of input up to (but not including) the first LF
/// character, if that slice is entirely Base64 characters
///
/// # Errors
///
/// - Returns Incomplete(1) if a LF is not found.
fn take_b64_line(input: &[u8]) -> IResult<&[u8], &[u8]> {
verify(take_while(|c| c != b'\n'), |bytes: &[u8]| {
// STANDARD_NO_PAD only differs from STANDARD during serialization; the base64
// crate always allows padding during parsing. We require canonical
// serialization, so we explicitly reject padding characters here.
base64::decode_config(bytes, base64::STANDARD_NO_PAD).is_ok() && !bytes.contains(&b'=')
})(input)
}
/// Returns the slice of input up to (but not including) the first LF
/// character, if that slice is entirely Base64 characters
///
@ -159,23 +144,11 @@ pub mod read {
fn wrapped_encoded_data(input: &[u8]) -> IResult<&[u8], Vec<u8>> {
map_opt(
pair(
many_till(
// Any body lines before the last MUST be full-length.
many0(map_opt(terminated(take_b64_line, newline), |chunk| {
if chunk.len() != 64 {
None
} else {
Some(chunk)
}
})),
terminated(take(64usize), newline),
// Last body line MUST be short (empty if necessary).
map_opt(terminated(take_b64_line, newline), |chunk| {
if chunk.len() < 64 {
Some(chunk)
} else {
None
}
}),
terminated(take_while_m_n(0, 63, |c| c != b'\n'), newline),
),
|(full_chunks, partial_chunk)| {
let data: Vec<u8> = full_chunks
@ -184,7 +157,11 @@ pub mod read {
.flatten()
.cloned()
.collect();
base64::decode_config(&data, base64::STANDARD_NO_PAD).ok()
if data.contains(&b'=') {
None
} else {
base64::decode_config(&data, base64::STANDARD_NO_PAD).ok()
}
},
)(input)
}
@ -277,8 +254,11 @@ pub mod read {
#[test]
fn base64_padding_rejected() {
assert!(take_b64_line(b"Tm8gcGFkZGluZyE\n").is_ok());
assert!(take_b64_line(b"Tm8gcGFkZGluZyE=\n").is_err());
assert!(wrapped_encoded_data(b"Tm8gcGFkZGluZyE\n").is_ok());
assert!(wrapped_encoded_data(b"Tm8gcGFkZGluZyE=\n").is_err());
// Internal padding is also rejected.
assert!(wrapped_encoded_data(b"SW50ZXJuYWwUGFk\n").is_ok());
assert!(wrapped_encoded_data(b"SW50ZXJuYWw=UGFk\n").is_err());
}
}
}