From 9dc864fd0feefd907aba16ba98cf453dd16df694 Mon Sep 17 00:00:00 2001
From: Maksym Pavlenko <pavlenko.maksym@gmail.com>
Date: Thu, 19 Mar 2026 09:52:33 -0700
Subject: [PATCH] Switch to proto instead of json

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>
---
 api/runtime/bootstrap/v1/bootstrap.proto |  5 ----
 core/runtime/v2/shim.go                  | 32 +++++++++++++++++-------
 pkg/shim/shim.go                         |  7 +++---
 pkg/shim/util.go                         |  3 +--
 4 files changed, 27 insertions(+), 20 deletions(-)

diff --git a/api/runtime/bootstrap/v1/bootstrap.proto b/api/runtime/bootstrap/v1/bootstrap.proto
index 1cb27129f..c90aecc76 100644
--- a/api/runtime/bootstrap/v1/bootstrap.proto
+++ b/api/runtime/bootstrap/v1/bootstrap.proto
@@ -26,11 +26,6 @@
 //   3. shim initializes and writes BootstrapResult as JSON to stdout
 //   4. containerd connects to the address provided in BootstrapResult
 //
-// Note: JSON serialization is used to keep shim binaries small since the
-// encoding/json package is already part of the Go runtime. The proto
-// definition serves as the schema for detecting breaking changes and
-// maintaining forward/backward compatibility.
-//
 // This design enables:
 //   - Forward/backward compatibility via version field
 //   - Typed extensibility via google.protobuf.Any and Extension
diff --git a/core/runtime/v2/shim.go b/core/runtime/v2/shim.go
index 92dff55bd..7832444af 100644
--- a/core/runtime/v2/shim.go
+++ b/core/runtime/v2/shim.go
@@ -53,6 +53,7 @@ import (
 	"github.com/containerd/containerd/v2/pkg/dialer"
 	"github.com/containerd/containerd/v2/pkg/identifiers"
 	"github.com/containerd/containerd/v2/pkg/protobuf"
+	"github.com/containerd/containerd/v2/pkg/protobuf/proto"
 	ptypes "github.com/containerd/containerd/v2/pkg/protobuf/types"
 	client "github.com/containerd/containerd/v2/pkg/shim"
 	"github.com/containerd/containerd/v2/pkg/timeout"
@@ -221,20 +222,33 @@ type clientVersionDowngrader interface {
 }
 
 func parseStartResponse(response []byte) (*bootapi.BootstrapResult, error) {
-	var params bootapi.BootstrapResult
+	var result bootapi.BootstrapResult
 
-	if err := json.Unmarshal(response, &params); err != nil || params.Version < 2 {
-		// Use TTRPC for legacy shims
-		params.Address = string(response)
-		params.Protocol = "ttrpc"
-		params.Version = 2
+	if json.Valid(response) {
+		var params client.BootstrapParams
+		if err := json.Unmarshal(response, &params); err != nil || params.Version < 2 {
+			// Use TTRPC for legacy shims
+			params.Address = string(response)
+			params.Protocol = "ttrpc"
+			params.Version = 2
+		}
+
+		if params.Version > CurrentShimVersion {
+			return nil, fmt.Errorf("unsupported shim version (%d): %w", params.Version, errdefs.ErrNotImplemented)
+		}
+
+		return &bootapi.BootstrapResult{
+			Version:  int32(params.Version),
+			Address:  params.Address,
+			Protocol: params.Protocol,
+		}, nil
 	}
 
-	if params.Version > CurrentShimVersion {
-		return nil, fmt.Errorf("unsupported shim version (%d): %w", params.Version, errdefs.ErrNotImplemented)
+	if err := proto.Unmarshal(response, &result); err != nil {
+		return nil, fmt.Errorf("unable to read shim bootstrap response: %w", err)
 	}
 
-	return &params, nil
+	return &result, nil
 }
 
 // writeBootstrapParams writes shim's bootstrap configuration (e.g. how to connect, version, etc).
diff --git a/pkg/shim/shim.go b/pkg/shim/shim.go
index add38df00..3b45e8060 100644
--- a/pkg/shim/shim.go
+++ b/pkg/shim/shim.go
@@ -18,7 +18,6 @@ package shim
 
 import (
 	"context"
-	"encoding/json"
 	"errors"
 	"flag"
 	"fmt"
@@ -280,7 +279,7 @@ func run(ctx context.Context, manager Shim, config Config) error {
 		}
 
 		var params bootapi.BootstrapParams
-		if err := json.Unmarshal(input, &params); err != nil {
+		if err := proto.Unmarshal(input, &params); err != nil {
 			// TODO: Return error once the new API is stable
 			if err := readBootstrapParamsFromDeprecatedFields(input, &params); err != nil {
 				return err
@@ -292,9 +291,9 @@ func run(ctx context.Context, manager Shim, config Config) error {
 			return err
 		}
 
-		data, err := json.Marshal(result)
+		data, err := proto.Marshal(result)
 		if err != nil {
-			return fmt.Errorf("failed to marshal bootstrap params to json: %w", err)
+			return fmt.Errorf("failed to marshal bootstrap params: %w", err)
 		}
 
 		if _, err := os.Stdout.Write(data); err != nil {
diff --git a/pkg/shim/util.go b/pkg/shim/util.go
index 4c95859f3..c51166d9e 100644
--- a/pkg/shim/util.go
+++ b/pkg/shim/util.go
@@ -19,7 +19,6 @@ package shim
 import (
 	"bytes"
 	"context"
-	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -141,7 +140,7 @@ func Command(ctx context.Context, config *CommandConfig) (*exec.Cmd, error) {
 			}
 		}
 
-		data, err := json.Marshal(&params)
+		data, err := proto.Marshal(&params)
 		if err != nil {
 			return nil, fmt.Errorf("unable to marshal bootstrap params: %w", err)
 		}