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encoding/proto: enable use cached size option #8569

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Merged
merged 4 commits into from
Sep 15, 2025
Merged

encoding/proto: enable use cached size option #8569

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19a8cef
proto: enable use cached size option
rs-unity Sep 10, 2025
188bece
proto: move MarshalOptions closer to size call and add comment clarif…
rs-unity Sep 11, 2025
50dfe64
proto: revert import sort
rs-unity Sep 11, 2025
ec0c47e
proto: improve comment
rs-unity Sep 11, 2025
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9 changes: 5 additions & 4 deletions encoding/proto/proto.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,10 +23,11 @@ package proto
import (
"fmt"

"google.golang.org/grpc/encoding"
"google.golang.org/grpc/mem"
"google.golang.org/protobuf/proto"
"google.golang.org/protobuf/protoadapt"

"google.golang.org/grpc/encoding"
"google.golang.org/grpc/mem"
)

// Name is the name registered for the proto compressor.
Expand All @@ -48,15 +49,15 @@ func (c *codecV2) Marshal(v any) (data mem.BufferSlice, err error) {

size := proto.Size(vv)
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@arjan-bal arjan-bal Sep 11, 2025

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Since this seems to rely on a runtime behaviour of calling proto.Size(vv) before using the cached size (please correct me if I'm wrong), we should call this out in a code comment just above this to serve as a warning for future code authors.

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@arjan-bal arjan-bal Sep 11, 2025

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I think if we don't call proto.Size(vv) here, we could end up using a stale cached size.

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@rs-unity rs-unity Sep 11, 2025 •
edited
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Would this be cleaner? rs-unity@188bece rs-unity@ec0c47e

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@easwars easwars Sep 11, 2025

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The docstring of UseCachedSize does say the following:

	// UseCachedSize indicates that the result of a previous Size call
	// may be reused.****

And that if that condition is not met, bad things might happen.

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@rs-unity rs-unity Sep 11, 2025

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I just want to flag an edge case that normally shouldn’t happen: if another part of the stack keeps a reference to the proto message and it’s shared across multiple Go routines, one routine might modify the message while another is marshaling it through this codec. In that situation, enabling UseCachedSize becomes risky.

That said, the issue I’m describing would still cause (other) problems even if UseCachedSize isn’t enabled.

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@rs-unity rs-unity Sep 11, 2025

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I've updated the comment: rs-unity@ec0c47e

if mem.IsBelowBufferPoolingThreshold(size) {
buf, err := proto.Marshal(vv)
buf, err := proto.MarshalOptions{UseCachedSize: true}.Marshal(vv)
if err != nil {
return nil, err
}
data = append(data, mem.SliceBuffer(buf))
} else {
pool := mem.DefaultBufferPool()
buf := pool.Get(size)
if _, err := (proto.MarshalOptions{}).MarshalAppend((*buf)[:0], vv); err != nil {
if _, err := (proto.MarshalOptions{UseCachedSize: true}).MarshalAppend((*buf)[:0], vv); err != nil {
pool.Put(buf)
return nil, err
}
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