Use switch statements for argument matching, use a map for removing disallowedCharacters, and set up worker pool for concurrent "chunk" generation of the password

main.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"math/big"
 	"os"
+	"runtime"
 	"strconv"
 	"strings"
 )
@@ -14,8 +15,9 @@ import (
 var allowedCharacters = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890`~!@#$%^&*()_+[]\\{}|;':,./<>?")
 
 const (
-	Version = "1.3.0"
-	symbols = "`~!@#$%^&*()_+[]\\{}|;':,./<>?"
+	Version   = "1.3.1"
+	symbols   = "`~!@#$%^&*()_+[]\\{}|;':,./<>?"
+	chunkSize = 16 // The size of each chunk of the password to be generated by the worker goroutines
 )
 
 func matchArguments(args []string) string {
@@ -26,11 +28,10 @@ func matchArguments(args []string) string {
 
 	// First argument is special, must be an integer, -v, or -h
 	var size = 0 // Password length
-	err := error(nil)
-	if size, err = strconv.Atoi(args[0]); err == nil { // If first argument is an integer
-	} else if args[0] == "-v" {
+	switch args[0] {
+	case "-v":
 		return "GoPass version " + Version
-	} else if args[0] == "-h" {
+	case "-h":
 		return "GoPass - A simple password generator written in Go\n" +
 			"Usage: gopass [length] [disallowed characters] [optional remove symbols -s]\n" +
 			"     Example: gopass 16\n" +
@@ -38,16 +39,23 @@ func matchArguments(args []string) string {
 			"     Example: gopass 16 -s\n" +
 			"\nFor help (this output): gopass -h\n" +
 			"For version: gopass -v\n"
+	default:
+		err := error(nil)
+		size, err = strconv.Atoi(args[0])
+		if err != nil {
+			return "Invalid first argument (\"" + args[0] + "\") supplied! (Type gopass -h for help)"
+		}
 	}
 
 	for i := 1; i < len(args); i++ {
 		v := args[i]
-		if v == "-s" {
+		switch {
+		case v == "-s":
 			removeDisallowed([]rune(symbols))
-		} else if strings.HasPrefix(v, "-r=") { // If argument starts with -r=
+		case strings.HasPrefix(v, "-r="):
 			// Remove all characters after the = until next whitespace
 			removeDisallowed([]rune(v[2:]))
-		} else {
+		default:
 			return "Invalid argument (\"" + v + "\") supplied! (Type gopass -h for help)"
 		}
 	}
@@ -61,28 +69,57 @@ func matchArguments(args []string) string {
 
 // Remove all disallowed characters from the allowedCharacters slice
 func removeDisallowed(disallowed []rune) {
+	disallowedMap := make(map[rune]bool, len(disallowed))
 	for _, r := range disallowed {
-		for i, v := range allowedCharacters {
-			if v == r {
-				allowedCharacters = append(allowedCharacters[:i], allowedCharacters[i+1:]...)
-			}
+		disallowedMap[r] = true
+	}
+
+	i := 0
+	for _, v := range allowedCharacters {
+		if !disallowedMap[v] {
+			allowedCharacters[i] = v
+			i++
 		}
 	}
+	allowedCharacters = allowedCharacters[:i]
 }
 
 func generatePassword(size int) string {
 	// Make empty array of runes with size of size
 	pass := make([]rune, size)
 
-	// Assign every slot of pass to a random allowedCharacter
-	for i := range pass {
-		// Generate a random int greater than 0 and not to exceed the length of allowedCharacters
-		index, err := rand.Int(rand.Reader, big.NewInt(int64(len(allowedCharacters))))
-		if err != nil {
-			println("Error securely generating random character!")
-			return ""
-		}
-		pass[i] = allowedCharacters[index.Int64()]
+	// Create a channel to receive chunks of the password
+	passChan := make(chan []rune)
+
+	// Determine the number of worker goroutines to use
+	numWorkers := runtime.NumCPU()
+
+	// Launch the worker goroutines
+	for i := 0; i < numWorkers; i++ {
+		go func() {
+			allowedLen := len(allowedCharacters)
+			for {
+				// Generate a chunk of the password
+				chunk := make([]rune, chunkSize)
+				for i := range chunk {
+					index, err := rand.Int(rand.Reader, big.NewInt(int64(allowedLen)))
+					if err != nil {
+						println("Error securely generating random character chunk!")
+						return
+					}
+					chunk[i] = allowedCharacters[index.Int64()]
+				}
+
+				// Send the chunk of the password to the main goroutine
+				passChan <- chunk
+			}
+		}()
+	}
+
+	// Collect the chunks of the password from the channel
+	for i := 0; i < size; i += chunkSize {
+		chunk := <-passChan
+		copy(pass[i:], chunk)
 	}
 
 	return string(pass)