Make sure to not use a client connection multiple times in parallel.

[sysdb/webui.git] / server / server.go

diff --git a/server/server.go b/server/server.go
index 995f2558c7bd118854ba6db28e0f9c5fb63db2f3..706dac2492a86ab2882b1714d991571fef9f4094 100644 (file)
--- a/server/server.go
+++ b/server/server.go
@@ -44,8 +44,11 @@ import (
 
 // A Config specifies configuration values for a SysDB web server.
 type Config struct {
-       // Conn specifies a connection to a SysDB server instance.
-       Conn *client.Conn
+       // Conns is a slice of connections to a SysDB server instance. The number of
+       // elements specifies the maximum number of parallel queries to the backend.
+       // Note that a client connection is not thread-safe but multiple idle
+       // connections don't impose any load on the server.
+       Conns []*client.Conn
 
        // TemplatePath specifies the relative or absolute location of template files.
        TemplatePath string
@@ -56,7 +59,7 @@ type Config struct {
 
 // A Server implements an http.Handler that serves the SysDB user interface.
 type Server struct {
-       c *client.Conn
+       conns chan *client.Conn
 
        // Templates:
        main    *template.Template
@@ -68,7 +71,17 @@ type Server struct {
 
 // New constructs a new SysDB web server using the specified configuration.
 func New(cfg Config) (*Server, error) {
-       s := &Server{c: cfg.Conn, results: make(map[string]*template.Template)}
+       if len(cfg.Conns) == 0 {
+               return nil, errors.New("need at least one client connection")
+       }
+
+       s := &Server{
+               conns:   make(chan *client.Conn, len(cfg.Conns)),
+               results: make(map[string]*template.Template),
+       }
+       for _, c := range cfg.Conns {
+               s.conns <- c
+       }
 
        var err error
        s.main, err = cfg.parse("main.tmpl")
@@ -251,16 +264,19 @@ func html(s string) template.HTML {
 }
 
 func (s *Server) query(cmd string) (interface{}, error) {
+       c := <-s.conns
+       defer func() { s.conns <- c }()
+
        m := &proto.Message{
                Type: proto.ConnectionQuery,
                Raw:  []byte(cmd),
        }
-       if err := s.c.Send(m); err != nil {
+       if err := c.Send(m); err != nil {
                return nil, fmt.Errorf("Query %q: %v", cmd, err)
        }
 
        for {
-               m, err := s.c.Receive()
+               m, err := c.Receive()
                if err != nil {
                        return nil, fmt.Errorf("Failed to receive server response: %v", err)
                }