From 23873a2be16fdbf0c68dba2ea11e11b94a0302cf Mon Sep 17 00:00:00 2001
From: Ulric Qin <ulric.qin@gmail.com>
Date: Tue, 31 May 2022 16:53:21 +0800
Subject: [PATCH] refactor code: get hostname

---
 agent/reader.go    |  2 +-
 config/config.go   | 52 +++++++++++++++++++---------------------
 config/hostname.go | 59 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+), 29 deletions(-)
 create mode 100644 config/hostname.go

diff --git a/agent/reader.go b/agent/reader.go
index 2cf9ec66..32d989ed 100644
--- a/agent/reader.go
+++ b/agent/reader.go
@@ -186,7 +186,7 @@ func convert(item *types.Sample) *prompb.TimeSeries {
 	// add label: agent_hostname
 	if _, has := item.Labels[agentHostnameLabelKey]; !has {
 		if !config.Config.Global.OmitHostname {
-			item.Labels[agentHostnameLabelKey] = config.Config.Global.Hostname
+			item.Labels[agentHostnameLabelKey] = config.Config.GetHostname()
 		}
 	}
 
diff --git a/config/config.go b/config/config.go
index be10ebd2..cbc649b6 100644
--- a/config/config.go
+++ b/config/config.go
@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"net"
-	"os"
 	"path"
 	"strings"
 	"time"
@@ -16,6 +15,7 @@ import (
 type Global struct {
 	PrintConfigs bool              `toml:"print_configs"`
 	Hostname     string            `toml:"hostname"`
+	IP           string            `toml:"-"`
 	OmitHostname bool              `toml:"omit_hostname"`
 	Labels       map[string]string `toml:"labels"`
 	Precision    string            `toml:"precision"`
@@ -67,7 +67,11 @@ func InitConfig(configDir string, debugMode bool, testMode bool) error {
 		return fmt.Errorf("failed to load configs of dir: %s", configDir)
 	}
 
-	if err := Config.fillHostname(); err != nil {
+	if err := Config.fillIP(); err != nil {
+		return err
+	}
+
+	if err := InitHostname(); err != nil {
 		return err
 	}
 
@@ -79,36 +83,32 @@ func InitConfig(configDir string, debugMode bool, testMode bool) error {
 	return nil
 }
 
-func (c *ConfigType) fillHostname() error {
-	if c.Global.Hostname == "" {
-		name, err := GetHostname()
-		if err != nil {
-			return err
-		}
-
-		c.Global.Hostname = name
+func (c *ConfigType) fillIP() error {
+	if !strings.Contains(c.Global.Hostname, "$ip") {
 		return nil
 	}
 
-	if strings.Contains(c.Global.Hostname, "$hostname") {
-		name, err := GetHostname()
-		if err != nil {
-			return err
-		}
-
-		c.Global.Hostname = strings.Replace(c.Global.Hostname, "$hostname", name, -1)
+	ip, err := GetOutboundIP()
+	if err != nil {
+		return err
 	}
 
-	if strings.Contains(c.Global.Hostname, "$ip") {
-		ip, err := GetOutboundIP()
-		if err != nil {
-			return err
-		}
+	c.Global.IP = fmt.Sprint(ip)
+	return nil
+}
 
-		c.Global.Hostname = strings.Replace(c.Global.Hostname, "$ip", fmt.Sprint(ip), -1)
+func (c *ConfigType) GetHostname() string {
+	ret := c.Global.Hostname
+
+	name := Hostname.Get()
+	if ret == "" {
+		return name
 	}
 
-	return nil
+	ret = strings.Replace(ret, "$hostname", name, -1)
+	ret = strings.Replace(ret, "$ip", c.Global.IP, -1)
+
+	return ret
 }
 
 func GetInterval() time.Duration {
@@ -119,10 +119,6 @@ func GetInterval() time.Duration {
 	return time.Duration(Config.Global.Interval)
 }
 
-func GetHostname() (string, error) {
-	return os.Hostname()
-}
-
 // Get preferred outbound ip of this machine
 func GetOutboundIP() (net.IP, error) {
 	conn, err := net.Dial("udp", "8.8.8.8:80")
diff --git a/config/hostname.go b/config/hostname.go
new file mode 100644
index 00000000..b5215414
--- /dev/null
+++ b/config/hostname.go
@@ -0,0 +1,59 @@
+package config
+
+import (
+	"log"
+	"os"
+	"sync"
+	"time"
+)
+
+type HostnameCache struct {
+	name string
+	sync.RWMutex
+}
+
+var Hostname *HostnameCache
+
+func (c *HostnameCache) Get() string {
+	c.RLock()
+	n := c.name
+	c.RUnlock()
+	return n
+}
+
+func (c *HostnameCache) Set(name string) {
+	if name == c.Get() {
+		return
+	}
+
+	c.Lock()
+	c.name = name
+	c.Unlock()
+}
+
+func InitHostname() error {
+	hostname, err := os.Hostname()
+	if err != nil {
+		return err
+	}
+
+	Hostname = &HostnameCache{
+		name: hostname,
+	}
+
+	go loopUpdateHostname()
+
+	return nil
+}
+
+func loopUpdateHostname() {
+	for {
+		time.Sleep(time.Second)
+		name, err := os.Hostname()
+		if err != nil {
+			log.Println("E! failed to get hostname:", err)
+		} else {
+			Hostname.Set(name)
+		}
+	}
+}