Allow detect whether it's in a database transaction for a context.Context (#21756)

Fix #19513

This PR introduce a new db method `InTransaction(context.Context)`,
and also builtin check on `db.TxContext` and `db.WithTx`.
There is also a new method `db.AutoTx` has been introduced but could be used by other PRs.

`WithTx` will always open a new transaction, if a transaction exist in context, return an error.
`AutoTx` will try to open a new transaction if no transaction exist in context.
That means it will always enter a transaction if there is no error.

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: 6543 <6543@obermui.de>

4 files changed, 87 insertions, 11 deletions

diff --git a/models/db/context.go b/models/db/context.go
index e90780e4e9..8c81469ebc 100644
--- a/models/db/context.go
+++ b/models/db/context.go
@@ -8,6 +8,7 @@ import (
 	"context"
 	"database/sql"
 
+	"xorm.io/xorm"
 	"xorm.io/xorm/schemas"
 )
 
@@ -86,7 +87,11 @@ type Committer interface {
 }
 
 // TxContext represents a transaction Context
-func TxContext() (*Context, Committer, error) {
+func TxContext(parentCtx context.Context) (*Context, Committer, error) {
+	if InTransaction(parentCtx) {
+		return nil, nil, ErrAlreadyInTransaction
+	}
+
 	sess := x.NewSession()
 	if err := sess.Begin(); err != nil {
 		sess.Close()
@@ -97,14 +102,24 @@ func TxContext() (*Context, Committer, error) {
 }
 
 // WithTx represents executing database operations on a transaction
-// you can optionally change the context to a parent one
-func WithTx(f func(ctx context.Context) error, stdCtx ...context.Context) error {
-	parentCtx := DefaultContext
-	if len(stdCtx) != 0 && stdCtx[0] != nil {
-		// TODO: make sure parent context has no open session
-		parentCtx = stdCtx[0]
+// This function will always open a new transaction, if a transaction exist in parentCtx return an error.
+func WithTx(parentCtx context.Context, f func(ctx context.Context) error) error {
+	if InTransaction(parentCtx) {
+		return ErrAlreadyInTransaction
+	}
+	return txWithNoCheck(parentCtx, f)
+}
+
+// AutoTx represents executing database operations on a transaction, if the transaction exist,
+// this function will reuse it otherwise will create a new one and close it when finished.
+func AutoTx(parentCtx context.Context, f func(ctx context.Context) error) error {
+	if InTransaction(parentCtx) {
+		return f(newContext(parentCtx, GetEngine(parentCtx), true))
 	}
+	return txWithNoCheck(parentCtx, f)
+}
 
+func txWithNoCheck(parentCtx context.Context, f func(ctx context.Context) error) error {
 	sess := x.NewSession()
 	defer sess.Close()
 	if err := sess.Begin(); err != nil {
@@ -180,3 +195,28 @@ func EstimateCount(ctx context.Context, bean interface{}) (int64, error) {
 	}
 	return rows, err
 }
+
+// InTransaction returns true if the engine is in a transaction otherwise return false
+func InTransaction(ctx context.Context) bool {
+	var e Engine
+	if engined, ok := ctx.(Engined); ok {
+		e = engined.Engine()
+	} else {
+		enginedInterface := ctx.Value(enginedContextKey)
+		if enginedInterface != nil {
+			e = enginedInterface.(Engined).Engine()
+		}
+	}
+	if e == nil {
+		return false
+	}
+
+	switch t := e.(type) {
+	case *xorm.Engine:
+		return false
+	case *xorm.Session:
+		return t.IsInTx()
+	default:
+		return false
+	}
+}
diff --git a/models/db/context_test.go b/models/db/context_test.go
new file mode 100644
index 0000000000..f00e7834ed
--- /dev/null
+++ b/models/db/context_test.go
@@ -0,0 +1,33 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package db_test
+
+import (
+	"context"
+	"testing"
+
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/models/unittest"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestInTransaction(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+	assert.False(t, db.InTransaction(db.DefaultContext))
+	assert.NoError(t, db.WithTx(db.DefaultContext, func(ctx context.Context) error {
+		assert.True(t, db.InTransaction(ctx))
+		return nil
+	}))
+
+	ctx, committer, err := db.TxContext(db.DefaultContext)
+	assert.NoError(t, err)
+	defer committer.Close()
+	assert.True(t, db.InTransaction(ctx))
+	assert.Error(t, db.WithTx(ctx, func(ctx context.Context) error {
+		assert.True(t, db.InTransaction(ctx))
+		return nil
+	}))
+}
diff --git a/models/db/error.go b/models/db/error.go
index 9577fa55db..85cba5c4e9 100644
--- a/models/db/error.go
+++ b/models/db/error.go
@@ -5,11 +5,14 @@
 package db
 
 import (
+	"errors"
 	"fmt"
 
 	"code.gitea.io/gitea/modules/util"
 )
 
+var ErrAlreadyInTransaction = errors.New("database connection has already been in a transaction")
+
 // ErrCancelled represents an error due to context cancellation
 type ErrCancelled struct {
 	Message string
diff --git a/models/db/index_test.go b/models/db/index_test.go
index 1ea30e2b60..cf777b9d38 100644
--- a/models/db/index_test.go
+++ b/models/db/index_test.go
@@ -59,7 +59,7 @@ func TestSyncMaxResourceIndex(t *testing.T) {
 	assert.EqualValues(t, 62, maxIndex)
 
 	// commit transaction
-	err = db.WithTx(func(ctx context.Context) error {
+	err = db.WithTx(db.DefaultContext, func(ctx context.Context) error {
 		err = db.SyncMaxResourceIndex(ctx, "test_index", 10, 73)
 		assert.NoError(t, err)
 		maxIndex, err = getCurrentResourceIndex(ctx, "test_index", 10)
@@ -73,7 +73,7 @@ func TestSyncMaxResourceIndex(t *testing.T) {
 	assert.EqualValues(t, 73, maxIndex)
 
 	// rollback transaction
-	err = db.WithTx(func(ctx context.Context) error {
+	err = db.WithTx(db.DefaultContext, func(ctx context.Context) error {
 		err = db.SyncMaxResourceIndex(ctx, "test_index", 10, 84)
 		maxIndex, err = getCurrentResourceIndex(ctx, "test_index", 10)
 		assert.NoError(t, err)
@@ -102,7 +102,7 @@ func TestGetNextResourceIndex(t *testing.T) {
 	assert.EqualValues(t, 2, maxIndex)
 
 	// commit transaction
-	err = db.WithTx(func(ctx context.Context) error {
+	err = db.WithTx(db.DefaultContext, func(ctx context.Context) error {
 		maxIndex, err = db.GetNextResourceIndex(ctx, "test_index", 20)
 		assert.NoError(t, err)
 		assert.EqualValues(t, 3, maxIndex)
@@ -114,7 +114,7 @@ func TestGetNextResourceIndex(t *testing.T) {
 	assert.EqualValues(t, 3, maxIndex)
 
 	// rollback transaction
-	err = db.WithTx(func(ctx context.Context) error {
+	err = db.WithTx(db.DefaultContext, func(ctx context.Context) error {
 		maxIndex, err = db.GetNextResourceIndex(ctx, "test_index", 20)
 		assert.NoError(t, err)
 		assert.EqualValues(t, 4, maxIndex)