commit e81de212db6614b74865a8c2219be2844fb4b9dc
Author: ek-dyoder <dyoder@emberkom.com>
Date:   Tue Mar 3 13:58:06 2026 -0500

    Initial commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..0c97a15
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+# Build outputs
+bin/
+
+# IDE files
+.idea/
\ No newline at end of file
diff --git a/dataprep.go b/dataprep.go
new file mode 100644
index 0000000..d543ad8
--- /dev/null
+++ b/dataprep.go
@@ -0,0 +1,133 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+var startPattern = "DNSHelper <<-> START CONFIG"
+var endPattern = "DNSHelper <->> END CONFIG"
+
+func extractLinesToEdit(data *workingData) error {
+	startIndex := 0
+	endIndex := 0
+	for i, line := range data.DefaultContent {
+		if strings.Contains(line, startPattern) {
+			startIndex = i
+			continue
+		}
+		if strings.Contains(line, endPattern) {
+			endIndex = i
+			break
+		}
+	}
+	var fileModified bool
+	var fileCorrupted bool
+	switch {
+	case startIndex == 0 && endIndex == 0:
+		fileModified = false
+		fileCorrupted = false
+	case startIndex > 0 && endIndex > startIndex:
+		fileModified = true
+		fileCorrupted = false
+	default:
+		fileModified = true
+		fileCorrupted = true
+	}
+
+	if fileCorrupted == true {
+		return errors.New("content has been corrupted")
+	}
+
+	if fileModified == true {
+		data.PrefixContent = data.DefaultContent[:startIndex]
+		data.PostfixContent = data.DefaultContent[endIndex+1:]
+		data.ExistingContent = data.DefaultContent[startIndex+1 : endIndex]
+	} else {
+		data.PrefixContent = data.DefaultContent
+		data.PostfixContent = make([]string, 0)
+		data.ExistingContent = make([]string, 0)
+	}
+	data.NewContent = make([]string, 0)
+	//fmt.Println("PrefixContent:")
+	//for _, line := range data.PrefixContent {
+	//	fmt.Println(line)
+	//}
+	//fmt.Println("ExistingContent:")
+	//for _, line := range data.ExistingContent {
+	//	fmt.Println(line)
+	//}
+	//fmt.Println("PostfixContent:")
+	//for _, line := range data.PostfixContent {
+	//	fmt.Println(line)
+	//}
+	return nil
+}
+
+func removeHostsFromExistingContent(data *workingData) {
+	var updatedContent []string
+	for _, host := range data.Hosts {
+		for _, line := range data.ExistingContent {
+			if !strings.Contains(line, host) {
+				updatedContent = append(updatedContent, line)
+			}
+		}
+	}
+	data.NewContent = updatedContent
+}
+
+func addHostsToWorkingData(data *workingData, hosts *string) {
+	hostToAddList := strings.Split(*hosts, ",")
+	var newHosts []string
+	for _, host := range hostToAddList {
+		newHosts = append(newHosts, host)
+	}
+	data.Hosts = newHosts
+}
+
+func addResolversToWorkingData(data *workingData, resolvers *string) {
+	resolverToAddList := strings.Split(*resolvers, ",")
+	var newResolvers []string
+	for _, resolver := range resolverToAddList {
+		newResolvers = append(newResolvers, resolver)
+	}
+	data.Resolvers = newResolvers
+}
+
+func addNameToIPMappingsToNewContent(data *workingData) {
+	for _, host := range data.Hosts {
+		for _, resolver := range data.Resolvers {
+			ips := lookupIP(host, resolver)
+			if len(ips) > 0 {
+				for _, ip := range ips {
+					data.NewContent = append(data.NewContent, fmt.Sprintf("%s\t%s", ip, host))
+				}
+			}
+		}
+	}
+}
+
+func slicesEqual(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+func dedupeSlice(slice []string) []string {
+	newSlice := make([]string, 0, len(slice))
+	seen := make(map[string]bool)
+	for _, value := range slice {
+		if !seen[value] {
+			seen[value] = true
+			newSlice = append(newSlice, value)
+		}
+	}
+	return newSlice
+}
diff --git a/dns.go b/dns.go
new file mode 100644
index 0000000..b07f1f3
--- /dev/null
+++ b/dns.go
@@ -0,0 +1,57 @@
+package main
+
+import (
+	"fmt"
+	"github.com/miekg/dns"
+)
+
+func lookupIP(hostname string, resolver string) []string {
+	c := dns.Client{}
+	m := dns.Msg{}
+	m.SetQuestion(dns.Fqdn(hostname), dns.TypeA)
+	r, _, err := c.Exchange(&m, resolver+":53")
+	if err != nil {
+		return nil
+	}
+	if r.Rcode != dns.RcodeSuccess {
+		fmt.Println("Error: querying " + resolver + " for A record of " + hostname + " failed with code " + dns.RcodeToString[r.Rcode])
+		return nil
+	}
+	ips := make([]string, 0)
+	for _, ans := range r.Answer {
+		if rec, ok := ans.(*dns.A); ok {
+			ips = append(ips, rec.A.String())
+		}
+	}
+
+	if len(ips) > 0 {
+		return ips
+	}
+
+	c = dns.Client{}
+	m = dns.Msg{}
+	m.SetQuestion(dns.Fqdn(hostname), dns.TypeCNAME)
+	r, _, err = c.Exchange(&m, resolver+":53")
+	if err != nil {
+		return nil
+	}
+	if r.Rcode != dns.RcodeSuccess {
+		fmt.Println("Error: querying " + resolver + " for CNAME record of " + hostname + " failed with code " + dns.RcodeToString[r.Rcode])
+		return nil
+	}
+	for _, ans := range r.Answer {
+		if rec, ok := ans.(*dns.CNAME); ok {
+			ips = lookupIP(rec.Target, resolver)
+			for _, ip := range ips {
+				ips = append(ips, ip)
+			}
+		}
+	}
+
+	if len(ips) > 0 {
+		return ips
+	}
+
+	fmt.Println("Error: no IP addresses found for " + hostname)
+	return nil
+}
diff --git a/fileoperations.go b/fileoperations.go
new file mode 100644
index 0000000..2ba8a95
--- /dev/null
+++ b/fileoperations.go
@@ -0,0 +1,73 @@
+package main
+
+import (
+	"bufio"
+	"os"
+)
+
+func fileExists(path string) (bool, error) {
+	_, err := os.Stat(path)
+	if err == nil {
+		return true, nil
+	}
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	return false, err
+}
+
+func getFileContentLines(path string) ([]string, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	var lines []string
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		lines = append(lines, scanner.Text())
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+	return lines, nil
+}
+
+func writeOverContentInFile(path string, lines []string) error {
+	file, err := os.OpenFile(path, os.O_WRONLY|os.O_TRUNC, 0644)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+	writer := bufio.NewWriter(file)
+	for _, line := range lines {
+		_, err := writer.WriteString(line + "\n")
+		if err != nil {
+			return err
+		}
+	}
+	err = writer.Flush()
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func writeHostsFile(data *workingData) error {
+	var newFileContent []string
+	newFileContent = append(newFileContent, data.PrefixContent...)
+	if len(data.NewContent) > 0 {
+		data.NewContent = dedupeSlice(data.NewContent)
+		newFileContent = append(newFileContent, "# "+startPattern)
+		newFileContent = append(newFileContent, data.NewContent...)
+		newFileContent = append(newFileContent, "# "+endPattern)
+	}
+	newFileContent = append(newFileContent, data.PostfixContent...)
+	if slicesEqual(newFileContent, data.DefaultContent) == false {
+		err := writeOverContentInFile(data.HostsFileLocation, newFileContent)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
diff --git a/fileoperations_darwin.go b/fileoperations_darwin.go
new file mode 100644
index 0000000..5922e75
--- /dev/null
+++ b/fileoperations_darwin.go
@@ -0,0 +1,18 @@
+//go:build darwin
+
+package main
+
+import "errors"
+
+func getHostsFileLocation() (string, error) {
+	var hostsFileLocation string
+	hostsFileLocation = "/etc/hosts"
+	exists, err := fileExists(hostsFileLocation)
+	if err != nil {
+		term(err)
+	}
+	if exists == false {
+		term(errors.New("hosts file does not exist at " + hostsFileLocation))
+	}
+	return hostsFileLocation, nil
+}
diff --git a/fileoperations_linux.go b/fileoperations_linux.go
new file mode 100644
index 0000000..c85b8d4
--- /dev/null
+++ b/fileoperations_linux.go
@@ -0,0 +1,18 @@
+//go:build linux
+
+package main
+
+import "errors"
+
+func getHostsFileLocation() (string, error) {
+	var hostsFileLocation string
+	hostsFileLocation = "/etc/hosts"
+	exists, err := fileExists(hostsFileLocation)
+	if err != nil {
+		term(err)
+	}
+	if exists == false {
+		term(errors.New("hosts file does not exist at " + hostsFileLocation))
+	}
+	return hostsFileLocation, nil
+}
diff --git a/fileoperations_windows.go b/fileoperations_windows.go
new file mode 100644
index 0000000..96dd429
--- /dev/null
+++ b/fileoperations_windows.go
@@ -0,0 +1,27 @@
+//go:build windows
+
+package main
+
+import (
+	"errors"
+	"os"
+)
+
+func getHostsFileLocation() (string, error) {
+	//return "hosts", nil
+	var hostsFileLocation string
+	value, envExists := os.LookupEnv("SystemRoot")
+	if envExists {
+		hostsFileLocation = value + "\\System32\\drivers\\etc\\hosts"
+	} else {
+		hostsFileLocation = "C:\\Windows\\System32\\drivers\\etc\\hosts"
+	}
+	exists, err := fileExists(hostsFileLocation)
+	if err != nil {
+		return "", err
+	}
+	if exists == false {
+		return "", errors.New("file does not exist: " + hostsFileLocation)
+	}
+	return hostsFileLocation, nil
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..fdb2df1
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,11 @@
+module dns-helper
+
+go 1.18
+
+require (
+	github.com/miekg/dns v1.1.59 // indirect
+	golang.org/x/mod v0.16.0 // indirect
+	golang.org/x/net v0.22.0 // indirect
+	golang.org/x/sys v0.18.0 // indirect
+	golang.org/x/tools v0.19.0 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..31f195d
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,10 @@
+github.com/miekg/dns v1.1.59 h1:C9EXc/UToRwKLhK5wKU/I4QVsBUc8kE6MkHBkeypWZs=
+github.com/miekg/dns v1.1.59/go.mod h1:nZpewl5p6IvctfgrckopVx2OlSEHPRO/U4SYkRklrEk=
+golang.org/x/mod v0.16.0 h1:QX4fJ0Rr5cPQCF7O9lh9Se4pmwfwskqZfq5moyldzic=
+golang.org/x/mod v0.16.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/net v0.22.0 h1:9sGLhx7iRIHEiX0oAJ3MRZMUCElJgy7Br1nO+AMN3Tc=
+golang.org/x/net v0.22.0/go.mod h1:JKghWKKOSdJwpW2GEx0Ja7fmaKnMsbu+MWVZTokSYmg=
+golang.org/x/sys v0.18.0 h1:DBdB3niSjOA/O0blCZBqDefyWNYveAYMNF1Wum0DYQ4=
+golang.org/x/sys v0.18.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/tools v0.19.0 h1:tfGCXNR1OsFG+sVdLAitlpjAvD/I6dHDKnYrpEZUHkw=
+golang.org/x/tools v0.19.0/go.mod h1:qoJWxmGSIBmAeriMx19ogtrEPrGtDbPK634QFIcLAhc=
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..440f448
--- /dev/null
+++ b/main.go
@@ -0,0 +1,94 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+var fileName = filepath.Base(os.Args[0])
+
+func init() {
+	fmt.Println("DNSHelper v1.0")
+	fmt.Println("Copyright (c) 2024 Emberkom LLC")
+	fmt.Println("")
+	if len(os.Args) < 2 {
+		printUsage()
+		defer os.Exit(1)
+	}
+}
+
+func printUsage() {
+	fmt.Println("This utility will update the local hosts file with DNS entries obtained by the specified DNS server.")
+	fmt.Println("Usage: " + fileName + " [add|delete] -host hostname [-server dns.example.com]")
+	fmt.Println("Example:")
+	fmt.Println("       " + fileName + " add -host xyz.acme.com -server dns.example.com")
+	fmt.Println("         This will use dns.example.com to find and add all IP addresses for xyz.acme.com to the local hosts file.")
+	fmt.Println("       " + fileName + " delete -host hostname.example.com")
+	fmt.Println("         This will delete all entries for hostname.example.com from the local hosts file.")
+	fmt.Println("       " + fileName + " delete all")
+	fmt.Println("         This will delete all entries from the local hosts file that were added by this utility.")
+	fmt.Println("Note: Adding a hostname will first remove all entries in the hosts file that match the same hostname.")
+	fmt.Println("      This utility will only remove entries from the hosts file that it added.")
+}
+
+func term(err error) {
+	fmt.Println("Error: " + err.Error())
+	defer os.Exit(1)
+}
+
+func main() {
+	modePing := flag.NewFlagSet("ping", flag.ExitOnError)
+	modeAdd := flag.NewFlagSet("add", flag.ExitOnError)
+	hostToAdd := modeAdd.String("host", "", "Comma separated list of hostnames to add")
+	dnsResolver := modeAdd.String("server", "", "DNS resolver to use")
+	modeDelete := flag.NewFlagSet("delete", flag.ExitOnError)
+	hostToDelete := modeDelete.String("host", "", "Comma separated list of hostnames to delete")
+
+	data := new(workingData)
+
+	var err error
+	data.HostsFileLocation, err = getHostsFileLocation()
+	if err != nil {
+		term(err)
+	}
+
+	data.DefaultContent, err = getFileContentLines(data.HostsFileLocation)
+	if err != nil {
+		term(err)
+	}
+
+	if err = extractLinesToEdit(data); err != nil {
+		term(err)
+	}
+
+	switch strings.ToLower(os.Args[1]) {
+	case "a", "add":
+		err = modeAdd.Parse(os.Args[2:])
+		if err != nil {
+			term(err)
+		}
+		addHostsToWorkingData(data, hostToAdd)
+		addResolversToWorkingData(data, dnsResolver)
+		removeHostsFromExistingContent(data)
+		addNameToIPMappingsToNewContent(data)
+	case "d", "del", "delete":
+		err = modeDelete.Parse(os.Args[2:])
+		if err != nil {
+			term(err)
+		}
+		if strings.ToLower(*hostToDelete) != "all" && strings.ToLower(*hostToDelete) != "a" {
+			addHostsToWorkingData(data, hostToDelete)
+			removeHostsFromExistingContent(data)
+		}
+	default:
+		printUsage()
+	}
+
+	err = writeHostsFile(data)
+	if err != nil {
+		term(err)
+	}
+}
diff --git a/structs.go b/structs.go
new file mode 100644
index 0000000..ee9713d
--- /dev/null
+++ b/structs.go
@@ -0,0 +1,13 @@
+package main
+
+type workingData struct {
+	HostsFileLocation string
+	IsNew             bool
+	Hosts             []string
+	Resolvers         []string
+	DefaultContent    []string
+	PrefixContent     []string
+	NewContent        []string
+	ExistingContent   []string
+	PostfixContent    []string
+}