wasi-shims: chunk get-random-bytes past the 64KiB getRandomValues quota - #50
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crypto.getRandomValues rejects a single request over 65536 bytes
(QuotaExceededError, verified on Deno), so get-random-bytes(len > 64KiB)
threw an unbranded host error -> trap. The WIT permits no shorter return
("Return `len` cryptographically-secure random or pseudo-random bytes",
random.wit `@since 0.2.0`) and callers (Rust getrandom, the Go runtime)
fill fixed-size buffers trusting the result length, so the fill is
chunked to exactly len bytes rather than clamped. Latent until now: no
consumer in the corpus requests more than a few hundred bytes per call.
Fail-on-pre-fix pin: random_test.ts spans three chunks plus a ragged
tail and asserts exact length plus per-chunk non-zero windows.
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Found while scoping the JSPI/blocking-profile work:
get-random-bytes(len > 65536)threwQuotaExceededErrorthrough the provider (unbranded host throw -> trap), because a singlecrypto.getRandomValuescall caps at 64KiB.The WIT allows no shorter return —
random.wit(@since 0.2.0): "Returnlencryptographically-secure random or pseudo-random bytes" — and real callers (Rustgetrandom, the Go runtime) fill fixed-size buffers trusting the returned length, so a clamp would silently under-randomize key buffers. The fill is chunked instead: exactlen, still synchronous per the WIT's must-not-block clause.Latent in practice (no corpus consumer requests >64KiB per call); pinned by a fail-on-pre-fix test spanning three chunks plus a ragged tail, asserting exact length and per-chunk non-zero windows.
Gates run locally:
just test-wasi-shims test-ct-runner(40 + 17 pass).