Initial commit

awsutil/awsutil.go

@@ -0,0 +1,61 @@
+// Package awsutil provides utility functions for using Sonyflake on AWS.
+package awsutil
+
+import (
+	"errors"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"os/exec"
+	"regexp"
+	"strconv"
+	"time"
+)
+
+func amazonEC2PrivateIPv4() (net.IP, error) {
+	res, err := http.Get("http://169.254.169.254/latest/meta-data/local-ipv4")
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+
+	body, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	ip := net.ParseIP(string(body))
+	if ip == nil {
+		return nil, errors.New("invalid ip address")
+	}
+	return ip.To4(), nil
+}
+
+// AmazonEC2MachineID retrieves the private IP address of the Amazon EC2 instance
+// and returns its lower 16 bits.
+// It works correctly on Docker as well.
+func AmazonEC2MachineID() (uint16, error) {
+	ip, err := amazonEC2PrivateIPv4()
+	if err != nil {
+		return 0, err
+	}
+
+	return uint16(ip[2])<<8 + uint16(ip[3]), nil
+}
+
+// TimeDifference returns the time difference between the localhost and the given NTP server.
+func TimeDifference(server string) (time.Duration, error) {
+	output, err := exec.Command("/usr/sbin/ntpdate", "-q", server).CombinedOutput()
+	if err != nil {
+		return time.Duration(0), err
+	}
+
+	re, _ := regexp.Compile("offset (.*) sec")
+	submatched := re.FindSubmatch(output)
+	if len(submatched) != 2 {
+		return time.Duration(0), errors.New("invalid ntpdate output")
+	}
+
+	f, err := strconv.ParseFloat(string(submatched[1]), 64)
+	return time.Duration(f*1000) * time.Millisecond, nil
+}