listing: improve listing of encrypted objects (#14667)

This commit improves the listing of encrypted objects:
 - Use `etag.Format` and `etag.Decrypt`
 - Detect SSE-S3 single-part objects in a single iteration
 - Fix batch size to `250`
 - Pass request context to `DecryptAll` to not waste resources
   when a client cancels the operation.

Signed-off-by: Andreas Auernhammer <hi@aead.dev>

internal/kms/kms.go

@@ -18,12 +18,11 @@
 package kms
 
 import (
+	"context"
 	"encoding"
 	"encoding/json"
-	"strconv"
 
 	jsoniter "github.com/json-iterator/go"
-	"github.com/minio/pkg/env"
 )
 
 // KMS is the generic interface that abstracts over
@@ -57,19 +56,7 @@ type KMS interface {
 	// DecryptAll decrypts all ciphertexts with the key referenced
 	// by the key ID. The contexts must match the context value
 	// used to generate the ciphertexts.
-	DecryptAll(keyID string, ciphertext [][]byte, context []Context) ([][]byte, error)
-}
-
-// BatchSize returns the size of the batches that should be used during
-// KES bulk decryption API calls.
-func BatchSize() int {
-	const DefaultBatchSize = 500
-	v := env.Get("MINIO_KMS_KES_BULK_API_BATCH_SIZE", strconv.Itoa(DefaultBatchSize))
-	n, err := strconv.Atoi(v)
-	if err != nil {
-		return DefaultBatchSize
-	}
-	return n
+	DecryptAll(ctx context.Context, keyID string, ciphertext [][]byte, context []Context) ([][]byte, error)
 }
 
 // Status describes the current state of a KMS.