| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/base64-0.21.2/src/engine/general_purpose/decode_suffix.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>decode_suffix.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../../normalize.css"><link rel="stylesheet" href="../../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../../ayu.css" disabled><link rel="stylesheet" href="../../../../dark.css" disabled><link rel="stylesheet" href="../../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../../storage.js"></script><script defer src="../../../../source-script.js"></script><script defer src="../../../../source-files.js"></script><script defer src="../../../../main.js"></script><noscript><link rel="stylesheet" href="../../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../../base64/index.html"><div class="logo-container"><img class="rust-logo" src="../../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../../base64/index.html"><img class="rust-logo" src="../../../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="kw">use crate</span>::{ |
| engine::{general_purpose::INVALID_VALUE, DecodeMetadata, DecodePaddingMode}, |
| DecodeError, PAD_BYTE, |
| }; |
| |
| <span class="doccomment">/// Decode the last 1-8 bytes, checking for trailing set bits and padding per the provided |
| /// parameters. |
| /// |
| /// Returns the decode metadata representing the total number of bytes decoded, including the ones |
| /// indicated as already written by `output_index`. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>decode_suffix( |
| input: <span class="kw-2">&</span>[u8], |
| input_index: usize, |
| output: <span class="kw-2">&mut </span>[u8], |
| <span class="kw-2">mut </span>output_index: usize, |
| decode_table: <span class="kw-2">&</span>[u8; <span class="number">256</span>], |
| decode_allow_trailing_bits: bool, |
| padding_mode: DecodePaddingMode, |
| ) -> <span class="prelude-ty">Result</span><DecodeMetadata, DecodeError> { |
| <span class="comment">// Decode any leftovers that aren't a complete input block of 8 bytes. |
| // Use a u64 as a stack-resident 8 byte buffer. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>leftover_bits: u64 = <span class="number">0</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>morsels_in_leftover = <span class="number">0</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>padding_bytes = <span class="number">0</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>first_padding_index: usize = <span class="number">0</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>last_symbol = <span class="number">0_u8</span>; |
| <span class="kw">let </span>start_of_leftovers = input_index; |
| |
| <span class="kw">for </span>(i, <span class="kw-2">&</span>b) <span class="kw">in </span>input[start_of_leftovers..].iter().enumerate() { |
| <span class="comment">// '=' padding |
| </span><span class="kw">if </span>b == PAD_BYTE { |
| <span class="comment">// There can be bad padding bytes in a few ways: |
| // 1 - Padding with non-padding characters after it |
| // 2 - Padding after zero or one characters in the current quad (should only |
| // be after 2 or 3 chars) |
| // 3 - More than two characters of padding. If 3 or 4 padding chars |
| // are in the same quad, that implies it will be caught by #2. |
| // If it spreads from one quad to another, it will be an invalid byte |
| // in the first quad. |
| // 4 - Non-canonical padding -- 1 byte when it should be 2, etc. |
| // Per config, non-canonical but still functional non- or partially-padded base64 |
| // may be treated as an error condition. |
| |
| </span><span class="kw">if </span>i % <span class="number">4 </span>< <span class="number">2 </span>{ |
| <span class="comment">// Check for case #2. |
| </span><span class="kw">let </span>bad_padding_index = start_of_leftovers |
| + <span class="kw">if </span>padding_bytes > <span class="number">0 </span>{ |
| <span class="comment">// If we've already seen padding, report the first padding index. |
| // This is to be consistent with the normal decode logic: it will report an |
| // error on the first padding character (since it doesn't expect to see |
| // anything but actual encoded data). |
| // This could only happen if the padding started in the previous quad since |
| // otherwise this case would have been hit at i % 4 == 0 if it was the same |
| // quad. |
| </span>first_padding_index |
| } <span class="kw">else </span>{ |
| <span class="comment">// haven't seen padding before, just use where we are now |
| </span>i |
| }; |
| <span class="kw">return </span><span class="prelude-val">Err</span>(DecodeError::InvalidByte(bad_padding_index, b)); |
| } |
| |
| <span class="kw">if </span>padding_bytes == <span class="number">0 </span>{ |
| first_padding_index = i; |
| } |
| |
| padding_bytes += <span class="number">1</span>; |
| <span class="kw">continue</span>; |
| } |
| |
| <span class="comment">// Check for case #1. |
| // To make '=' handling consistent with the main loop, don't allow |
| // non-suffix '=' in trailing chunk either. Report error as first |
| // erroneous padding. |
| </span><span class="kw">if </span>padding_bytes > <span class="number">0 </span>{ |
| <span class="kw">return </span><span class="prelude-val">Err</span>(DecodeError::InvalidByte( |
| start_of_leftovers + first_padding_index, |
| PAD_BYTE, |
| )); |
| } |
| |
| last_symbol = b; |
| |
| <span class="comment">// can use up to 8 * 6 = 48 bits of the u64, if last chunk has no padding. |
| // Pack the leftovers from left to right. |
| </span><span class="kw">let </span>shift = <span class="number">64 </span>- (morsels_in_leftover + <span class="number">1</span>) * <span class="number">6</span>; |
| <span class="kw">let </span>morsel = decode_table[b <span class="kw">as </span>usize]; |
| <span class="kw">if </span>morsel == INVALID_VALUE { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(DecodeError::InvalidByte(start_of_leftovers + i, b)); |
| } |
| |
| leftover_bits |= (morsel <span class="kw">as </span>u64) << shift; |
| morsels_in_leftover += <span class="number">1</span>; |
| } |
| |
| <span class="kw">match </span>padding_mode { |
| DecodePaddingMode::Indifferent => { <span class="comment">/* everything we care about was already checked */ </span>} |
| DecodePaddingMode::RequireCanonical => { |
| <span class="kw">if </span>(padding_bytes + morsels_in_leftover) % <span class="number">4 </span>!= <span class="number">0 </span>{ |
| <span class="kw">return </span><span class="prelude-val">Err</span>(DecodeError::InvalidPadding); |
| } |
| } |
| DecodePaddingMode::RequireNone => { |
| <span class="kw">if </span>padding_bytes > <span class="number">0 </span>{ |
| <span class="comment">// check at the end to make sure we let the cases of padding that should be InvalidByte |
| // get hit |
| </span><span class="kw">return </span><span class="prelude-val">Err</span>(DecodeError::InvalidPadding); |
| } |
| } |
| } |
| |
| <span class="comment">// When encoding 1 trailing byte (e.g. 0xFF), 2 base64 bytes ("/w") are needed. |
| // / is the symbol for 63 (0x3F, bottom 6 bits all set) and w is 48 (0x30, top 2 bits |
| // of bottom 6 bits set). |
| // When decoding two symbols back to one trailing byte, any final symbol higher than |
| // w would still decode to the original byte because we only care about the top two |
| // bits in the bottom 6, but would be a non-canonical encoding. So, we calculate a |
| // mask based on how many bits are used for just the canonical encoding, and optionally |
| // error if any other bits are set. In the example of one encoded byte -> 2 symbols, |
| // 2 symbols can technically encode 12 bits, but the last 4 are non canonical, and |
| // useless since there are no more symbols to provide the necessary 4 additional bits |
| // to finish the second original byte. |
| |
| </span><span class="kw">let </span>leftover_bits_ready_to_append = <span class="kw">match </span>morsels_in_leftover { |
| <span class="number">0 </span>=> <span class="number">0</span>, |
| <span class="number">2 </span>=> <span class="number">8</span>, |
| <span class="number">3 </span>=> <span class="number">16</span>, |
| <span class="number">4 </span>=> <span class="number">24</span>, |
| <span class="number">6 </span>=> <span class="number">32</span>, |
| <span class="number">7 </span>=> <span class="number">40</span>, |
| <span class="number">8 </span>=> <span class="number">48</span>, |
| <span class="comment">// can also be detected as case #2 bad padding above |
| </span><span class="kw">_ </span>=> <span class="macro">unreachable!</span>( |
| <span class="string">"Impossible: must only have 0 to 8 input bytes in last chunk, with no invalid lengths" |
| </span>), |
| }; |
| |
| <span class="comment">// if there are bits set outside the bits we care about, last symbol encodes trailing bits that |
| // will not be included in the output |
| </span><span class="kw">let </span>mask = !<span class="number">0 </span>>> leftover_bits_ready_to_append; |
| <span class="kw">if </span>!decode_allow_trailing_bits && (leftover_bits & mask) != <span class="number">0 </span>{ |
| <span class="comment">// last morsel is at `morsels_in_leftover` - 1 |
| </span><span class="kw">return </span><span class="prelude-val">Err</span>(DecodeError::InvalidLastSymbol( |
| start_of_leftovers + morsels_in_leftover - <span class="number">1</span>, |
| last_symbol, |
| )); |
| } |
| |
| <span class="comment">// TODO benchmark simply converting to big endian bytes |
| </span><span class="kw">let </span><span class="kw-2">mut </span>leftover_bits_appended_to_buf = <span class="number">0</span>; |
| <span class="kw">while </span>leftover_bits_appended_to_buf < leftover_bits_ready_to_append { |
| <span class="comment">// `as` simply truncates the higher bits, which is what we want here |
| </span><span class="kw">let </span>selected_bits = (leftover_bits >> (<span class="number">56 </span>- leftover_bits_appended_to_buf)) <span class="kw">as </span>u8; |
| output[output_index] = selected_bits; |
| output_index += <span class="number">1</span>; |
| |
| leftover_bits_appended_to_buf += <span class="number">8</span>; |
| } |
| |
| <span class="prelude-val">Ok</span>(DecodeMetadata::new( |
| output_index, |
| <span class="kw">if </span>padding_bytes > <span class="number">0 </span>{ |
| <span class="prelude-val">Some</span>(input_index + first_padding_index) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">None |
| </span>}, |
| )) |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../../" data-current-crate="base64" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
