Fix filer GET error caused by incorrect database connection management

This resolves errors like "Internal /buckets/XXX: find /buckets/XXX: context canceled", which was triggered when using SQL filer store. The *sql.DB uses ctx from http.Request to create new connection, and then put it back to the connection pool. That means connections inside the pool are mostly unhealthy because the request context are cancelled just after http request finished.

weed/filer/abstract_sql/abstract_sql_store.go

@@ -66,11 +66,27 @@ const (
 	DEFAULT_TABLE = "filemeta"
 )
 
-type TxOrDB interface {
+type TxOrDBWithoutClose interface {
 	ExecContext(ctx context.Context, query string, args ...interface{}) (sql.Result, error)
 	QueryRowContext(ctx context.Context, query string, args ...interface{}) *sql.Row
 	QueryContext(ctx context.Context, query string, args ...interface{}) (*sql.Rows, error)
 }
+type TxOrDB interface {
+	TxOrDBWithoutClose
+	Close() error
+}
+
+type TxOrDbWrapper struct {
+	TxOrDBWithoutClose
+	CloseFunc func() error
+}
+
+func (t *TxOrDbWrapper) Close() error {
+	if t.CloseFunc == nil {
+		return nil
+	}
+	return t.CloseFunc()
+}
 
 func (store *AbstractSqlStore) BeginTransaction(ctx context.Context) (context.Context, error) {
 	tx, err := store.DB.BeginTx(ctx, &sql.TxOptions{
@@ -102,9 +118,12 @@ func (store *AbstractSqlStore) getTxOrDB(ctx context.Context, fullpath util.Full
 	bucket = DEFAULT_TABLE
 
 	if tx, ok := ctx.Value("tx").(*sql.Tx); ok {
-		txOrDB = tx
+		txOrDB = &TxOrDbWrapper{tx, nil}
 	} else {
-		txOrDB = store.DB
+		txOrDB, err = store.DB.Conn(context.Background())
+		if err != nil {
+			return
+		}
 	}
 
 	if !store.SupportBucketTable {
@@ -155,6 +174,7 @@ func (store *AbstractSqlStore) InsertEntry(ctx context.Context, entry *filer.Ent
 	if err != nil {
 		return fmt.Errorf("findDB %s : %v", entry.FullPath, err)
 	}
+	defer db.Close()
 
 	dir, name := shortPath.DirAndName()
 	meta, err := entry.EncodeAttributesAndChunks()
@@ -191,6 +211,7 @@ func (store *AbstractSqlStore) UpdateEntry(ctx context.Context, entry *filer.Ent
 	if err != nil {
 		return fmt.Errorf("findDB %s : %v", entry.FullPath, err)
 	}
+	defer db.Close()
 
 	dir, name := shortPath.DirAndName()
 	meta, err := entry.EncodeAttributesAndChunks()
@@ -216,6 +237,7 @@ func (store *AbstractSqlStore) FindEntry(ctx context.Context, fullpath util.Full
 	if err != nil {
 		return nil, fmt.Errorf("findDB %s : %v", fullpath, err)
 	}
+	defer db.Close()
 
 	dir, name := shortPath.DirAndName()
 	row := db.QueryRowContext(ctx, store.GetSqlFind(bucket), util.HashStringToLong(dir), name, dir)
@@ -244,6 +266,7 @@ func (store *AbstractSqlStore) DeleteEntry(ctx context.Context, fullpath util.Fu
 	if err != nil {
 		return fmt.Errorf("findDB %s : %v", fullpath, err)
 	}
+	defer db.Close()
 
 	dir, name := shortPath.DirAndName()
 
@@ -266,6 +289,7 @@ func (store *AbstractSqlStore) DeleteFolderChildren(ctx context.Context, fullpat
 	if err != nil {
 		return fmt.Errorf("findDB %s : %v", fullpath, err)
 	}
+	defer db.Close()
 
 	if isValidBucket(bucket) && shortPath == "/" {
 		if err = store.deleteTable(ctx, bucket); err == nil {
@@ -297,6 +321,7 @@ func (store *AbstractSqlStore) ListDirectoryPrefixedEntries(ctx context.Context,
 	if err != nil {
 		return lastFileName, fmt.Errorf("findDB %s : %v", dirPath, err)
 	}
+	defer db.Close()
 
 	sqlText := store.GetSqlListExclusive(bucket)
 	if includeStartFile {