fix: reset lastIndex before testing global/sticky content-type RegExp parsers - #6846
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climba03003 merged 1 commit intoAug 8, 2026
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… parsers A content-type parser registered with a g- or y-flagged RegExp keeps a mutable lastIndex between calls, so getParser's .test() could skip part of the next content type and match inconsistently. Reset lastIndex before each test.
climba03003
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Jul 15, 2026
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The fixes LGTM.
But I do not think both g and y flag should be used in Content-Type matching.
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yeah fair, those flags come from user regexps tho, fastify never sets them itself. happy to just strip g/y at registration instead if you prefer that over resetting lastIndex |
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We may check the Independently by the fix, (maybe) we are changing the dev's intentions |
climba03003
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Aug 8, 2026
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npm run testandnpm run benchmarkWhat this does
ContentTypeParser.getParserwalksparserRegExpListand callsparserRegExp.test(ct)to find a matching custom parser. When a parser is registered with a RegExp that carries thegoryflag,RegExp.prototype.testis stateful: it advanceslastIndexon a match and resumes from there on the next call. So the same parser RegExp can match one request and then miss (or partially match) a later one for the same content type, depending on wherelastIndexwas left.The fix resets
parserRegExp.lastIndex = 0before eachtest(), which makes matching independent of previous calls. Parsers registered with non-global RegExps (the common case) are unaffected, sincelastIndexis not used there.Added a regression test that registers a global-flagged content-type RegExp and sends two matching requests; it fails before this change (the second request misses the parser) and passes after.