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Diffstat (limited to 'src/decode.rs')
| -rw-r--r-- | src/decode.rs | 224 |
1 files changed, 224 insertions, 0 deletions
diff --git a/src/decode.rs b/src/decode.rs new file mode 100644 index 0000000..8004f18 --- /dev/null +++ b/src/decode.rs @@ -0,0 +1,224 @@ +// Copyright 2019 Alexandros Frantzis +// +// This Source Code Form is subject to the terms of the Mozilla Public +// License, v. 2.0. If a copy of the MPL was not distributed with this +// file, You can obtain one at https://mozilla.org/MPL/2.0/. +// +// SPDX-License-Identifier: MPL-2.0 + +//! Base64 and quoted-printable decoding. + +use crate::Result; + +const PAD: u8 = 64; // The pseudo-index of the PAD character. +const INV: u8 = 99; // An invalid index. + +static BASE64_INDICES: &'static [u8] = &[ + // 0 1 2 3 4 5 6 7 8 9 A B C D E F +/* 0 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +/* 1 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +/* 2 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, 62, INV, INV, INV, 63, +/* 3 */ 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, INV, INV, INV, PAD, INV, INV, +/* 4 */ INV, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, +/* 5 */ 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, INV, INV, INV, INV, INV, +/* 6 */ INV, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, +/* 7 */ 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, INV, INV, INV, INV, INV, +/* 8 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +/* 9 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +/* A */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +/* B */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +/* C */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +/* D */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +/* E */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +/* F */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, +]; + +/// Decodes base64 encoded data, appending the decoded data to a Vec<u8>. +/// +/// During decoding all line breaks and invalid characters are ignored. +/// If an error is encountered during decoding, the already decoded data in the +/// output buffer is left intact. It's up to the caller to deal with the partial +/// decoded data in case of failure. +pub fn base64_decode_into_buf(input: &[u8], output: &mut Vec<u8>) -> Result<()> { + let mut num_chars = 0; + let mut cur_triplet = 0; + let mut valid_chars = 0; + + for c in input { + let ci = BASE64_INDICES[*c as usize]; + match ci { + // rfc2045: All line breaks or other characters not + // found in Table 1 must be ignored by decoding software. + INV => continue, + _ if ci < PAD => valid_chars += 1, + _ => {} + } + + cur_triplet = cur_triplet << 6 | ((ci & 0x3f) as u32); + num_chars += 1; + + if num_chars == 4 { + match valid_chars { + 2 => output.push((cur_triplet >> 16) as u8), + 3 => output.extend( + &[(cur_triplet >> 16) as u8, (cur_triplet >> 8) as u8] + ), + 4 => output.extend( + &[(cur_triplet >> 16) as u8, + (cur_triplet >> 8) as u8, + cur_triplet as u8 + ] + ), + _ => return Err("Invalid base64 encoding".into()), + } + + cur_triplet = 0; + num_chars = 0; + valid_chars = 0; + } + } + + // rfc2045: A full encoding quantum is always completed at the end of a body. + if num_chars != 0 { + return Err("Unpadded input".into()); + } + + Ok(()) +} + +/// Converts an ascii byte representing a hex digit to it's numerical value. +fn hexdigit_to_num(mut a: u8) -> Option<u8> { + if a.is_ascii_digit() { + return Some(a - b'0'); + } + + a.make_ascii_lowercase(); + + if a >= b'a' && a <= b'f' { + return Some(a - b'a' + 10); + } + + None +} + +/// Decodes quoted-printable encoded data, appending the decoding data to a +/// Vec<u8>. +/// +/// During decoding all line breaks and invalid characters are ignored. +/// If an error is encountered during decoding, the already decoded data in the +/// output buffer is left intact. It's up to the caller to deal with the partial +/// decoded data in case of failure. +pub fn qp_decode_into_buf(input: &[u8], output: &mut Vec<u8>) -> Result<()> { + let mut iter = input.iter().peekable(); + + 'outer: loop { + loop { + match iter.next() { + Some(b'=') => break, + Some(c) => output.push(*c), + None => break 'outer, + } + } + + // At this point we have encountered a '=', so check + // to see what follows. + if let Some(&first) = iter.next() { + // A CRLF/LF after '=' marks a line continuation, and + // is effectively dropped. + if first == b'\r' { + if iter.peek() == Some(&&b'\n') { + iter.next(); + continue; + } + } else if first == b'\n' { + continue; + } else if let Some(first_num) = hexdigit_to_num(first) { + // A valid pair of hexdigits represent the raw byte value. + if let Some(&&second) = iter.peek() { + if let Some(second_num) = hexdigit_to_num(second) { + output.push(first_num * 16 + second_num); + iter.next(); + continue; + } + } + } + + // Emit the raw sequence if it's not one of the special + // special cases checked above. + output.extend(&[b'=', first]); + } else { + // Last character in the input was an '=', just emit it. + output.push(b'='); + } + } + + + Ok(()) +} + +#[cfg(test)] +mod test_base64 { + use crate::decode::base64_decode_into_buf; + + #[test] + fn decodes_full_length() { + let mut decoded = Vec::new(); + assert!(base64_decode_into_buf("YWJj".as_bytes(), &mut decoded).is_ok()); + assert_eq!(decoded, &[b'a', b'b', b'c']); + } + + #[test] + fn decodes_with_two_padding() { + let mut decoded = Vec::new(); + assert!(base64_decode_into_buf("YWJjZA==".as_bytes(), &mut decoded).is_ok()); + assert_eq!(decoded, &[b'a', b'b', b'c', b'd']); + } + + #[test] + fn decodes_with_one_padding() { + let mut decoded = Vec::new(); + assert!(base64_decode_into_buf("YWJjZGU=".as_bytes(), &mut decoded).is_ok()); + assert_eq!(decoded, &[b'a', b'b', b'c', b'd', b'e']); + } + + #[test] + fn error_with_invalid_paddings() { + let mut decoded = Vec::new(); + assert!(base64_decode_into_buf("YWJj====".as_bytes(), &mut decoded).is_err()); + assert!(base64_decode_into_buf("YWJjZ===".as_bytes(), &mut decoded).is_err()); + assert!(base64_decode_into_buf("====".as_bytes(), &mut decoded).is_err()); + } + + #[test] + fn error_with_unpadded_input() { + let mut decoded = Vec::new(); + assert!(base64_decode_into_buf("YWJjZA=".as_bytes(), &mut decoded).is_err()); + } +} + +#[cfg(test)] +mod test_qp { + use crate::decode::qp_decode_into_buf; + + #[test] + fn decodes_byte() { + let mut decoded = Vec::new(); + assert!(qp_decode_into_buf("a=62c=64".as_bytes(), &mut decoded).is_ok()); + assert_eq!(decoded, &[b'a', b'b', b'c', b'd']); + } + + #[test] + fn decodes_soft_break() { + let mut decoded = Vec::new(); + assert!(qp_decode_into_buf("a=\r\nb=\nc".as_bytes(), &mut decoded).is_ok()); + assert_eq!(decoded, &[b'a', b'b', b'c']); + } + + #[test] + fn invalid_sequences_are_untouched() { + let mut decoded = Vec::new(); + let invalid_sequence = "a=6t= c=".as_bytes(); + assert!(qp_decode_into_buf(invalid_sequence, &mut decoded).is_ok()); + assert_eq!(decoded, invalid_sequence); + } +} |