Add -advertise flag.

This enables us to have a different advertise IP in /etc/hosts compared
to the local bind (via `-host`) flag.

This is useful when binding to 127.0.0.1 behind a web server but running
with a Pihole.

README.md

@@ -194,6 +194,9 @@ With this config, you can use the following queries:
 - `-config` - path to config file. Default is `./c.yml`
 - `-port` - port to bind to. Default is 8927. Use 80 in standalone mode.
 - `-host` - default is 127.0.0.1. Use 0.0.0.0 for a public server.
+- `-advertise` - which address to use when populating `/etc/hosts`. 
+ This is useful when running zap behind `dnsmasq`, so that the host bind and advertised address can differ.
+
 
 ### DNS management via /etc/hosts
 

cmd/main.go

@@ -24,7 +24,8 @@ func main() {
  var (
  configName = flag.String("config", "c.yml", "config file")
  port = flag.Int("port", 8927, "port to bind to")
- host = flag.String("host", "127.0.0.1", "host interface")
+ host = flag.String("host", "127.0.0.1", "host address to bind to")
+ advertise = flag.String("advertise", "127.0.0.1", "IP to advertise, used in /etc/hosts")
  v = flag.Bool("v", false, "print version info")
  validate = flag.Bool("validate", false, "load config file and check for errors")
  )
@@ -52,7 +53,7 @@ func main() {
  os.Exit(0)
  }
 
- context := &zap.Context{Config: c}
+ context := &zap.Context{Config: c, Advertise: *advertise}
  zap.UpdateHosts(context) // sync changes since last run.
 
  // Enable hot reload.

cmd/zap/config.go

@@ -152,7 +152,7 @@ func UpdateHosts(c *Context) {
  replacement.WriteString(delimStart)
  children := c.Config.ChildrenMap()
  for k := range children {
- replacement.WriteString(fmt.Sprintf("127.0.0.1 %s\n", k))
+ replacement.WriteString(fmt.Sprintf("%s %s\n", c.Advertise, k))
  }
  replacement.WriteString(delimEnd)
 

cmd/zap/structs.go

@@ -9,11 +9,14 @@ import (
 )
 
 type Context struct {
- // Json container with path configs
+ // Config is a Json container with path configs
  Config *gabs.Container
 
- // Enables safe hot reloading of Config.
+ // ConfigMtx Enables safe hot reloading of Config.
  ConfigMtx sync.Mutex
+
+ // Advertise IP, used in /etc/hosts in case bind address differs.
+ Advertise string
 }
 
 type CtxWrapper struct {