Add MinLen validator

ui/options.go

@@ -138,11 +138,17 @@ func WithValidateFunc(fn func(string) error) Option {
 }
 
 // WithValidateNotEmpty adds a custom validation function to a prompt that
-// checks that the propted string is not empty.
+// checks that the prompted string is not empty.
 func WithValidateNotEmpty() Option {
 	return WithValidateFunc(NotEmpty())
 }
 
+// WithValidateMinLen adds a custom validation function to a prompt that
+// checks the input string meets the minimum length requirement.
+func WithValidateMinLength(minLength int) Option {
+	return WithValidateFunc(MinLength(minLength))
+}
+
 // WithValidateYesNo adds a custom validation function to a prompt for a Yes/No
 // prompt.
 func WithValidateYesNo() Option {
@@ -167,6 +173,6 @@ func WithValidateRegexp(re string) Option {
 		if rx.MatchString(s) {
 			return nil
 		}
-		return fmt.Errorf("%s does not match the regular expresion %s", s, re)
+		return fmt.Errorf("%s does not match the regular expression %s", s, re)
 	})
 }

ui/validators.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"strings"
+	"unicode"
 
 	"github.com/manifoldco/promptui"
 )
@@ -73,3 +74,17 @@ func YesNo() promptui.ValidateFunc {
 		}
 	}
 }
+
+// MinLength is a validation function that checks for a minimum length.
+// An input length <= 0 indicates that the check should not be performed.
+func MinLength(minLength int) promptui.ValidateFunc {
+	return func(s string) error {
+		if minLength <= 0 {
+			return nil
+		}
+		if len(strings.TrimRightFunc(s, unicode.IsSpace)) < minLength {
+			return fmt.Errorf("input does not meet minimum length requirement; must be at least %v characters", minLength)
+		}
+		return nil
+	}
+}

ui/validators_test.go

@@ -90,3 +90,63 @@ func TestDNS(t *testing.T) {
 		})
 	}
 }
+
+func TestMinLength(t *testing.T) {
+	tests := []struct {
+		name    string
+		length  int
+		input   string
+		wantErr bool
+	}{
+		{
+			name:    "negative",
+			length:  -5,
+			input:   "foobar",
+			wantErr: false,
+		},
+		{
+			name:    "zero",
+			length:  0,
+			input:   "localhost",
+			wantErr: false,
+		},
+		{
+			name:    "greater-than-min-length",
+			length:  5,
+			input:   "foobar",
+			wantErr: false,
+		},
+		{
+			name:    "equal-min-length",
+			length:  6,
+			input:   "foobar",
+			wantErr: false,
+		},
+		{
+			name:    "less-than-min-length",
+			length:  8,
+			input:   "foobar",
+			wantErr: true,
+		},
+		{
+			name:    "ignore-post-whitespace-characters",
+			length:  7,
+			input:   "  pass  ",
+			wantErr: true,
+		},
+		{
+			name:    "ignore-post-whitespace-characters-ok",
+			length:  6,
+			input:   "  pass  ",
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotErr := MinLength(tt.length)(tt.input) != nil
+			if gotErr != tt.wantErr {
+				t.Errorf("MinLength(%v)(%s) = %v, want %v", tt.length, tt.input, gotErr, tt.wantErr)
+			}
+		})
+	}
+}