new: [dev] utils for d4 config files

config/config.go

@@ -0,0 +1,99 @@
+package config
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"os"
+	"regexp"
+	"strings"
+)
+
+// IsNet checks whether the string host is a valid
+// IPv6 or IPv4 address
+func IsNet(host string) (bool, string) {
+	// DNS regex
+	validDNS := regexp.MustCompile(`^(([a-zA-Z]{1})|([a-zA-Z]{1}[a-zA-Z]{1})|([a-zA-Z]{1}[0-9]{1})|([0-9]{1}[a-zA-Z]{1})|([a-zA-Z0-9][a-zA-Z0-9-_]{1,61}[a-zA-Z0-9]))\.([a-zA-Z]{2,6}|[a-zA-Z0-9-]{2,30}\.[a-zA-Z
+ ]{2,3})$`)
+	// Check ipv6
+	if strings.HasPrefix(host, "[") {
+		// Parse an IP-Literal in RFC 3986 and RFC 6874.
+		// E.g., "[fe80::1]:80".
+		i := strings.LastIndex(host, "]")
+		if i < 0 {
+			log.Fatal("Unmatched [ in destination config")
+			return false, ""
+		}
+		if !validPort(host[i+1:]) {
+			log.Fatal("No valid port specified")
+			return false, ""
+		}
+		// trim brackets
+		if net.ParseIP(strings.Trim(host[:i+1], "[]")) != nil {
+			log.Fatal(fmt.Sprintf("Server IP: %s, Server Port: %s\n", host[:i+1], host[i+1:]))
+			return true, host
+		}
+	} else {
+		// Ipv4 or DNS name
+		ss := strings.Split(string(host), ":")
+		if len(ss) > 1 {
+			if !validPort(":" + ss[1]) {
+				log.Fatal("No valid port specified")
+				return false, ""
+			}
+			if net.ParseIP(ss[0]) != nil {
+				log.Fatal(fmt.Sprintf("Server IP: %s, Server Port: %s\n", ss[0], ss[1]))
+				return true, host
+			} else if validDNS.MatchString(ss[0]) {
+				log.Fatal(fmt.Sprintf("DNS: %s, Server Port: %s\n", ss[0], ss[1]))
+				return true, host
+			}
+		}
+	}
+	return false, host
+}
+
+// validPort reports whether port is either an empty string
+// or matches /^:\d*$/
+func validPort(port string) bool {
+	if port == "" {
+		return false
+	}
+	if port[0] != ':' {
+		return false
+	}
+	for _, b := range port[1:] {
+		if b < '0' || b > '9' {
+			return false
+		}
+	}
+	return true
+}
+
+// ReadConfigFile takes two argument: folder and fileName.
+// It reads its content, trims\n, and return []byte
+// All errors are Fatal.
+func ReadConfigFile(folder string, fileName string) []byte {
+	f, err := os.OpenFile("./"+folder+"/"+fileName, os.O_RDWR|os.O_CREATE, 0666)
+	defer f.Close()
+	if err != nil {
+		log.Fatal(err)
+	}
+	data := make([]byte, 100)
+	count, err := f.Read(data)
+	if err != nil {
+		if err != io.EOF {
+			log.Fatal(err)
+		}
+	}
+	if count == 0 {
+		log.Fatal(fileName + " is empty.")
+	}
+	if err := f.Close(); err != nil {
+		log.Fatal(err)
+	}
+	// trim \n if present
+	return bytes.TrimSuffix(data[:count], []byte("\n"))
+}