Decoder registry: don't panic if multiple calls with same parameters to `RegisterInstructionDecoder` func

registry.go

@@ -20,6 +20,7 @@ package solana
 import (
 	"errors"
 	"fmt"
+	"reflect"
 	"sync"
 )
 
@@ -77,10 +78,20 @@ func (reg *decoderRegistry) RegisterIfNew(programID PublicKey, decoder Instructi
 }
 
 func RegisterInstructionDecoder(programID PublicKey, decoder InstructionDecoder) {
-	isNew := instructionDecoderRegistry.RegisterIfNew(programID, decoder)
-	if !isNew {
+	prev, has := instructionDecoderRegistry.Get(programID)
+	if has {
+		// If it's the same function, then OK (tollerate multiple calls with same params).
+		if isSameFunction(prev, decoder) {
+			return
+		}
+		// If it's another decoder for the same pubkey, then panic.
 		panic(fmt.Sprintf("unable to re-register instruction decoder for program %s", programID))
 	}
+	instructionDecoderRegistry.RegisterIfNew(programID, decoder)
+}
+
+func isSameFunction(f1 interface{}, f2 interface{}) bool {
+	return reflect.ValueOf(f1).Pointer() == reflect.ValueOf(f2).Pointer()
 }
 
 func DecodeInstruction(programID PublicKey, accounts []*AccountMeta, data []byte) (interface{}, error) {

registry_test.go

@@ -0,0 +1,27 @@
+package solana
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRegisterInstructionDecoder(t *testing.T) {
+
+	decoder := func(instructionAccounts []*AccountMeta, data []byte) (interface{}, error) {
+		return nil, nil
+	}
+	decoderAnother := func(instructionAccounts []*AccountMeta, data []byte) (interface{}, error) {
+		return nil, nil
+	}
+
+	assert.NotPanics(t, func() {
+		RegisterInstructionDecoder(BPFLoaderProgramID, decoder)
+	})
+	assert.NotPanics(t, func() {
+		RegisterInstructionDecoder(BPFLoaderProgramID, decoder)
+	})
+	assert.Panics(t, func() {
+		RegisterInstructionDecoder(BPFLoaderProgramID, decoderAnother)
+	})
+}