asn1: decode Counter64 as unsigned so values >= 2^63 are not rejected (#36) - #37
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asn1: decode Counter64 as unsigned so values >= 2^63 are not rejected (#36)#37youdie006 wants to merge 1 commit into
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Counter64 is an unsigned INTEGER (0..2^64-1). A value with bit 63 set is BER-encoded with a leading 0x00 sign octet and therefore occupies 9 octets. read_snmp_counter64 decoded it through the signed decode_i64, which rejects anything longer than 8 octets with AsnIntOverflow. Because Varbinds treats a decode error as the end of the sequence, the offending varbind and every varbind after it were silently dropped from the response. Decode Counter64 through a dedicated unsigned path that accepts up to 8 octets, or 9 octets when the extra leading octet is the 0x00 sign pad. Add regression tests for 2^63 and u64::MAX. Fixes roboplc#36
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Fixes #36.
Problem
Counter64is an unsignedINTEGER (0..2^64-1)(RFC 2578). A value with bit 63 set is BER-encoded with a leading0x00sign octet, so it occupies 9 octets.read_snmp_counter64decoded it through the signedread_i64_type/decode_i64, which rejects anything longer than 8 octets withAsnIntOverflow.Worse,
Varbinds::nexttreats any decode failure as the end of the sequence, so the failingCounter64varbind and every varbind after it are silently dropped. A response whose only highCounter64is at the end returns zero varbinds; au64::MAXcounter in the middle of a 3-varbind response yields just one.Fix
Decode
Counter64through a dedicated unsigned path (decode_u64) that accepts up to 8 octets, or 9 octets when the extra leading octet is the0x00sign pad. This is scoped to the value-decode bug; the broaderVarbinds::next"treat error as end-of-sequence" behavior is left as a separate concern (as suggested in the issue).Test
Added
read_counter64_large_valuescovering a small value,2^63, andu64::MAX. Red-green verified withcargo test: before the change the2^63/u64::MAXcases fail withAsnIntOverflow; after, they decode correctly. The full test suite passes (11 lib + 6 integration), andcargo fmt --check/cargo clippyare clean.Disclosure: I used AI assistance (Claude) while preparing this change. I verified the encoding against RFC 2578, ran the tests (red-green) and the full suite, and take responsibility for the contribution.