der: accept the documented maximum nesting depth - #2424
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`Position::split_nested` checks `depth < MAX_DEPTH` after incrementing a counter that starts at zero, so the 64th nested SEQUENCE is rejected with `ErrorKind::NestingDepth` while `MAX_DEPTH` is 64 and the test module describes 64 as the expected maximum. Against master this decodes 63 levels and fails on 64. Comparing with `<=` makes exactly `MAX_DEPTH` levels decode, and `MAX_DEPTH + 1` still fails. The nesting test only asserted that `MAX_DEPTH + 1` errors; nothing asserted that `MAX_DEPTH` itself succeeds, which is why this never surfaced. The message builder is now a shared helper and there is a second test for the boundary itself. That test fails on the previous code and passes with this change -- checked by running it both ways. Closes RustCrypto#2392
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Fixes the off-by-one from #2392.
Position::split_nestedincrements a counter that starts at 0 and then checksdepth < MAX_DEPTH, so the 64th nestedSEQUENCEis rejected withNestingDepthwhileMAX_DEPTHis 64 andtests/nesting.rscalls 64 "the expected maximum depth". Measured against master (7637997):Changes:
reader/position.rs:<→<=, so exactlyMAX_DEPTHlevels decode andMAX_DEPTH + 1still fails.tests/nesting.rs: the message builder is now a shared helper, and there's a new test for the boundary itself. The old test only checked that 65 errors; nothing checked that 64 succeeds, which is how this slipped through. The new test fails on the old code and passes with this change — I ran it both ways.I asked on the issue whether 64 is actually meant to be accepted (#2392 (comment)) and didn't want to sit on this waiting for an answer, so opening it now to cover both cases. If 63 is the intended ceiling, say so and I'll turn this into a comment/test fix instead of a code change.
Closes #2392