IF : Extra padding is added to the hs_bitset when constructing a quorum_certificate from a quorum_certificate_message

[systemzax]

Printing a quorum_certificate bitset when created :
Id : PVT_BLS_r4ZpChd87ooyzl6MIkw23k7PRX8xptp7TczLJHCIIW88h/hS finalizers 21 000000111111111111111

Printing a quorum_certificate bitset when received :
Id : PVT_BLS_/l7xzXANaB+GrlTsbZEuTiSOiWTtpBoog+TZnirxUUSaAfCo finalizers 32 00000000000000000111111111111111

The message format seems to (correctly) encode the bitset using the minimum required number of unsigned integers to represent the active finalizer set votes, but the decoding should also trim the extra leading zeroes.

[greg7mdp]

If I understand correctly, and the first bitset is for 21 finalizers and the second for 32 finalizers, I think the leading zeroes are meaningful, as the first output is exactly 21 binary digits and the second exactly 32, so in my opinion they should not be trimmed.

[heifner]

If I understand correctly, and the first bitset is for 21 finalizers and the second for 32 finalizers, I think the leading zeroes are meaningful, as the first output is exactly 21 binary digits and the second exactly 32, so in my opinion they should not be trimmed.

The issue is that the conversion to "block" form out of boost::dynamic_bitset is filling in the extra bits of our uint32_t with zeros. Then on the other end we create the boost::dynamic_bitset from that set of 32 bits making it now 32 instead of 21.

We either need to implicitly know the finalizer set size (seems like we should know that) or pass along in the message how many of the provided bits are relevant (21 vs 32).

[greg7mdp]

Oh thanks, I get it now. boost::dynamic_bitset does know its size, which appears to be lost when serialized, right?
It is because active_finalizers in quorum_certificate_message is defined as std::vector<unsigned_int> and not boost::dynamic_bitset (which fc probably does not know how to serialize).

[heifner]

Oh thanks, I get it now. boost::dynamic_bitset does know its size, which appears to be lost when serialized, right?

Correct.

[heifner]

Change boost::dynamic_bitset to use uint8_t to be less wasteful and to avoid zigzag encoding.