add transaction to context

This adds the transaction handling to the connection and context
handling.
It will raise an error and inform the client if anything is going wrong
with the transaction.

server.go

@@ -10,6 +10,7 @@ import (
 )
 
 const (
+	LevelFatal = `FATAL`
 	LevelError = `ERROR`
 	LevelInfo  = `INFO`
 )
@@ -35,7 +36,7 @@ type (
 		w   http.ResponseWriter
 
 		username string
-		tx       *sql.DB
+		tx       *sql.Tx
 	}
 
 	// Request contains the method name and parameters requested by the client.
@@ -46,6 +47,7 @@ type (
 
 	// Response can have messages and/or a result to return the to client.
 	Response struct {
+		ID       string                 `json:"id"`
 		Messages map[string][]string    `json:"messages,omitempty"`
 		Result   map[string]interface{} `json:"result,omitempty"`
 	}
@@ -95,10 +97,22 @@ func (s *Server) Handle(w http.ResponseWriter, r *http.Request) {
 
 	req := Request{}
 	res := &Response{
+		ID:       c.id,
 		Messages: map[string][]string{},
 		Result:   map[string]interface{}{},
 	}
 
+	tx, err := s.db.Begin()
+	if err != nil {
+		c.Logf(LevelError, "could not create transaction: %s", err)
+		w.WriteHeader(http.StatusInternalServerError)
+		res.AddMessage(LevelFatal, "database problems occured")
+		c.render(res)
+		return
+	}
+	defer tx.Rollback() // make a rollback, just in case something goes wrong
+	c.tx = tx
+
 	dec := json.NewDecoder(r.Body)
 	defer r.Body.Close()
 	if err := dec.Decode(&req); err != nil {
@@ -119,6 +133,10 @@ func (s *Server) Handle(w http.ResponseWriter, r *http.Request) {
 	if err := handler(c, req, res); err != nil {
 		c.Logf(LevelError, "method '%s' returned an error: %s", req.Method, err)
 	}
+	if err := tx.Commit(); err != nil {
+		c.Logf(LevelFatal, "could not commit changes: %s", err)
+		res.AddMessage(LevelError, "changes were not committed")
+	}
 	c.render(res)
 }