json: disallow overlong and out-of-range UTF-8 #4097
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Fixes ziglang#2379 = Overlong (non-shortest) sequences UTF-8's unique encoding scheme allows for some Unicode codepoints to be represented in multiple ways. For any of these characters, the spec forbids all but the shortest form. These disallowed longer sequences are called "overlong". As an interesting side effect of this rule, the bytes C0 and C1 never appear in valid UTF-8. = Codepoint range UTF-8 disallows representation of codepoints beyond U+10FFFF, which is the highest character which can be encoded in UTF-16. Because a 4-byte sequence is capable of resulting in such characters, they must be explicitly rejected. This rule also has an interesting side effect, which is that bytes F5 to FF never appear. = References Detecting an overlong version of a codepoint could get gnarly, but luckily The Unicode Consortium did the hard work by creating this handy table of valid byte sequences: https://unicode.org/versions/corrigendum1.html I thought this mapped nicely to the parser's state machine, so I rearranged the relevant states to make use of it.
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Regarding the naming convention in tests, these correspond to the tests found in this repository: https://github.com/nst/JSONTestSuite |
Ahhh, I see, thanks. I'm happy to rename the tests or move them to std/json.zig if you'd prefer. |
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I think it is fine to add these to the existing file. A few have already been done. A comment indicating what part of the spec they refer to would be more than enough. |
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Fixes #2379
Today we done learn a thing or two about UTF-8 and JSON! If you are curious about the encoding-related details, please see my commit message 💀 🔨
Changes
Notes
and preëmption of awkward feels
\uDEADcase in std.json failing test cases #2379 was already intentionally being allowed. See my comment on that issue for details, and investigate handling of windows file paths which are invalid utf-16le #1774, Windows paths allow unpaired surrogates #2565 for related discussion.--emit asmshows me that0x80...0xBF =>adds 10-ish instructions over a bitwise op, but I figured an optimizing stage2 will take care of that someday. I addedsequence_first_byteinstead of reusing an existing field. I'm open to changing any of that.