Go port for local provider networking

environs/local/network.go

+package local
+
+import (
+        "encoding/xml"
+        "io/ioutil"
+        "os"
+        "os/exec"
+        "strings"
+        "text/template"
+)
+
+// networks represents a local virtual network.

[niemeyer, 2012/05/24 16:31:35]

s/networks/network/

+type network struct {
+        XMLName xml.Name `xml:"network"`
+        Name    string   `xml:"name"`
+        Bridge  bridge   `xml:"bridge"`
+        Ip      ip       `xml:"ip"`
+        Subnet  int
+}
+
+// ip represents an ip with the given address and netmask.
+type ip struct {
+        Ip   string `xml:"address,attr"`
+        Mask string `xml:"netmask,attr"`
+}
+
+// bridge represents a briddge with the given name.
+type bridge struct {
+        Name string `xml:"name,attr"`
+}
+
+// newNetwork returns a started network.
+func newNetwork(name string, subnet int) (*network, error) {
+        n := network{Name: name, Subnet: subnet}
+        err := n.start()
+        if err != nil {
+                return nil, err
+        }
+        err = n.loadAttributes()
+        if err != nil {
+                return nil, err
+        }
+        return &n, nil
+}
+
+// loadAttributes loads the attributes for a network.
+func (n *network) loadAttributes() error {
+        output, err := exec.Command("virsh", "net-dumpxml", n.Name).Output()
+        if err != nil {
+                return err
+        }
+        return xml.Unmarshal(output, &n)
+}
+
+// running returns true if network name is in the
+// list of networks and is active.
+func (n *network) running() (bool, error) {
+        networks, err := listNetworks()
+        if err != nil {
+                return false, err
+        }
+        return networks[n.Name], nil
+}
+
+// exists returns true if network name is in the
+// list of networks.
+func (n *network) exists() (bool, error) {
+        networks, err := listNetworks()
+        if err != nil {
+                return false, err
+        }
+        _, exists := networks[n.Name]
+        return exists, nil
+}
+
+// virsh replaces %d with an auto increment
+// number to make the bridge name unique
+var libVirtNetworkTemplate = template.Must(template.New("").Parse(`
+<network>
+  <name>{{.Name}}</name>
+  <bridge name='vbr-{{.Name}}-%d' />
+  <forward/>
+  <ip address='192.168.{{.Subnet}}.1' netmask='255.255.255.0'>
+    <dhcp>
+      <range start='192.168.{{.Subnet}}.2' end='192.168.{{.Subnet}}.254' />
+    </dhcp>
+  </ip>
+</network>
+`))
+
+// start ensures that the network is started.
+// If network name does not exist, it is created.

[rog, 2012/05/24 14:07:04]

s/network/the network/

+func (n *network) start() error {
+        exists, err := n.exists()
+        if err != nil {
+                return err
+        }
+        if exists {
+                running, err := n.running()
+                if err != nil {
+                        return err
+                }
+                if running {
+                        return nil
+                }
+                return exec.Command("virsh", "net-start", n.Name).Run()
+        }
+        file, err := ioutil.TempFile(os.TempDir(), "network")
+        if err != nil {
+                return err
+        }
+        defer file.Close()
+        defer os.Remove(file.Name())
+        err = libVirtNetworkTemplate.Execute(file, n)
+        if err != nil {
+                return err
+        }
+        err = exec.Command("virsh", "net-define", file.Name()).Run()
+        if err != nil {
+                return err
+        }
+        return exec.Command("virsh", "net-start", n.Name).Run()
+}
+
+// listNetworks returns a map from network name to active status.
+func listNetworks() (map[string]bool, error) {
+        output, err := exec.Command("virsh", "net-list", "--all").Output()
+        if err != nil {
+                return nil, err
+        }
+        // Remove the header.
+        networks := map[string]bool{}
+        lines := strings.Split(string(output), "\n")
+        if len(lines) < 3 {
+                return networks, nil
+        }
+        lines = lines[2:]
+        for _, line := range lines {
+                if line == "" {
+                        continue
+                }
+                fields := strings.Fields(line)
+                if len(fields) > 2 {
+                        networks[fields[0]] = fields[1] == "active"
+                }
+        }
+        return networks, nil
+}