Module encoder 

A cached-size, single-pass encoder for [WalEntry].

Why

prost does not cache message sizes the way protobuf-C++ does. When WalEntry::encode_to_vec runs, the encode pass recomputes the encoded_len of every nested message each time it needs a length delimiter. For the deep WAL tree (WalEntry → Mutation → Rows → Row → Value) the length of a leaf Value ends up being recomputed roughly once per ancestor level — i.e. ~5 times. Microbenchmarks show ~87% of encode_to_vec is spent in these repeated length walks, not in writing bytes.

How

This encoder walks the tree once to compute and cache the body length of every length-delimited message node (in pre-order into a flat sizes vector), then walks it a second time to write bytes, reading each cached length back via a cursor. Every node’s length is computed exactly once.

Leaf messages whose sizing is not recursively redundant (ColumnSchema, Value, WriteHint, BulkWalEntry) are delegated to prost’s own encoded_len/encode_raw, but their (single) computed length is still cached so the encode pass never recomputes it.

The output is byte-for-byte identical to WalEntry::encode_to_vec; this is asserted in tests and must hold to preserve WAL replay compatibility.

Maintenance

This encoder hard-codes the wire layout (field tags and field order) of WalEntry, Mutation, Rows and Row. If any of these messages change in greptime-proto, this file MUST be updated to match:

• Adding or removing a field is caught at compile time: every one of these messages is destructured exhaustively (no ..), so a changed field set fails to compile here.
• Changing a field’s tag number or type is caught by the byte-for-byte equality tests against prost (which populate all fields). Keep those tests exhaustive when adding fields.

Leaf messages are delegated to prost, so changes to them need no update here.

Structs

WalEntryEncoder

A reusable encoder that caches message body sizes between its size pass and its encode pass.

Constants

BULK_ENTRY_TAG 🔒

MUTATION_TAG 🔒

OP_TYPE_TAG 🔒

ROWS_TAG 🔒

ROW_TAG 🔒

SCHEMA_TAG 🔒

SEQUENCE_TAG 🔒

VALUE_TAG 🔒

WRITE_HINT_TAG 🔒

Functions

msg_field_len 🔒

Length contribution of a length-delimited message field: key + length varint + body.