light-client-verifier: reuse sign_bytes buffer

[mina86]

Rather than allocating a new vector each time canonical vote is encoded, allocate a vector in NonAbsentCommitVotes once and then reuse it each time sign_bytes are needed. This saves on doing multiple allocations and deallocations.

For overly verbose description of the length calculation:

• CanonicalVote. Note that length prefix doesn’t count bytes used for encoding the length, e.g. if the CanonicalVote message is 127 bytes than the length prefix is one byte and thus sign_bytes is 128 bytes. The table assumes all fields are set.

  | | tag | value | |-----------------+-----+-------| | (length) | | 1–2 | 2 if (length) is > 127 | type | 1 | 1 | SignedMsgType is at most 32 | height | 1 | 8 | The field is sfixed64 | round | 1 | 8 | The field is sfixed64 | block_id | 1 | 73–77 | See CanonicalBlockId below | timestamp | 1 | 7—13 | See Timestamp below | chain_id | 1 | 1+N | Assuming N < 128 |-----------------+-----+-------| | (total) | 105–116+N | If N≤13 than (length) is | | | 1 byte and this is 115+N

• CanonicalBlockId.

  | | tag | value | |-----------------+-----+-------| | (length) | | 1 | | hash | 1 | 33 | Assuming 32-byte hash | part_set_header | 1 | 37–41 | See CanonicalPartSetHeader |-----------------+-----+-------| | (total) | 73–77 |

• CanonicalPartSetHeader.

  | | tag | value | |-----------------+-----+-------| | (length) | | 1 | | total | 1 | 1–5 | Varint of u32; at most 5 bytes | hash | 1 | 33 | Assuming 32-byte hash |-----------------+-----+-------| | (total) | 37–41 |

• Timestamp. In unlikely event vote was made exactly at a second, nanos is zero and thus the field is not present. Assuming uniform probability of the nanos, in a bit over 73% of cases the filed will occupy it’s maximum size.

  | | tag | value | |-----------------+-----+-------| | (length) | | 1 | | seconds | 1 | 5 | Assuming timestamps around now | nanos | 0–1 | 0–5 | |-----------------+-----+-------| | (total) | | 7–13 |

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• [ ] Referenced an issue explaining the need for the change
• [x] Updated all relevant documentation in docs
• [x] Updated all code comments where relevant
• [ ] Wrote tests
• [x] Added entry in .changelog/

[romac]

I will release all this in v0.36 later this week.