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Paul WellsandClaude Opus 5
0da02c4717
Manifest matching runs a compiled regex per route over a linear scan, once per
candidate registration, on the serving path. At the 256-route cap that is up to
256 RE2 executions per replica per request.
The router compiles a manifest into a compressed trie instead. Starlette
selects the first route declared that matches, so the trie cannot resolve
static before wildcard the way net/http's does: every node carries the lowest
route index in its subtree, the walk tracks the lowest full match found and
prunes any subtree that cannot improve on it, and inserting in declaration
order leaves edges and leaves sorted by that index with no sort pass.
Params are not segment-aligned - starlette allows /f/{name}.{ext}, a {p:path}
anywhere, and a float whose fraction backtracks - so the walk must search. An
edge is single when nothing below it can start with a byte its own convertor
could have consumed, which is a property of the target node and so is settled
at build time; a single edge takes its greedy run and descends once. Templates
whose params are segment-aligned are entirely single and never search. What
remains is bounded by a step budget, and exhausting it returns ResultOverBudget
rather than a route the cut-short search cannot vouch for.
Templates parse without regexp. Scanning the grammar by hand keeps a brace that
opens nothing well-formed as an ordinary literal, which is what starlette's
finditer does. Anchoring is `\n?$` rather than `$`: python's '$' matches before
one trailing newline where Go's does not, and [^/] accepts a newline where .
refuses one, so the two convertors diverge in opposite directions on a decoded
%0A.
The regex implementation moves into the tests as an oracle, carrying its own
parser so it references the hand-rolled scanner as well as the trie.
FuzzMatchAgainstOracle generates a table and a request and asserts the two
agree on both the winning template and the result. Matching allocates nothing,
asserted by AllocsPerRun on hit, 405, miss and on the searching path.
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>