internal/impl: add runtime support for *[]byte unknown representation
This CL adds runtime support for unknown fields to be represented
as *[]byte in addition to the current representation as []byte.
This CL does not change generated code to use *[]byte.
Comparison between using *[]byte and []byte:
• Every message supports unknown fields, so use of []byte
expands a message size by 24B (for 64-bit systems).
In contrast, *[]byte only expands a message by 8B.
This has significant memory implications for small messages.
• If unknown fields are encountered, *[]byte has extra overhead
allocating the 24B slice header. However, it is assumed
that messages rarely see any unknown fields at runtime,
or generally do so for a temporary period of time.
Change-Id: I81935e4ea7394166e61ff4579f76f59fa792dfc9
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/244937
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/decode.go b/internal/impl/decode.go
index 2dcbdec..949dc49 100644
--- a/internal/impl/decode.go
+++ b/internal/impl/decode.go
@@ -175,7 +175,7 @@
return out, errDecode
}
if !opts.DiscardUnknown() && mi.unknownOffset.IsValid() {
- u := p.Apply(mi.unknownOffset).Bytes()
+ u := mi.mutableUnknownBytes(p)
*u = protowire.AppendTag(*u, num, wtyp)
*u = append(*u, b[:n]...)
}