fix: IMEI/IMEISV validation and test cases

nasConvert/MobileIdentity5GS.go

@@ -7,6 +7,7 @@ import (
 	"math/bits"
 	"strconv"
 	"strings"
+	"unicode"
 
 	"github.com/free5gc/nas/logger"
 	"github.com/free5gc/nas/nasMessage"
@@ -282,5 +283,52 @@ func PeiToStringWithError(buf []byte) (string, error) {
 		digitStr = digitStr[:len(digitStr)-1] // remove the last digit
 	}
 
+	if prefix == "imei-" {
+        // Validate IMEI before returning
+		if len(digitStr) != 15 {
+            return "", fmt.Errorf("invalid IMEI length: expected 15 digits, got %d", len(digitStr))
+        }
+        valid, err := ValidateIMEI(digitStr)
+        if err != nil {
+            return "", fmt.Errorf("IMEI validation error: %w", err)
+        }
+        if !valid {
+            return "", fmt.Errorf("invalid IMEI checksum")
+        }
+    } else{
+		if len(digitStr) != 16 {
+            return "", fmt.Errorf("invalid IMEISV length: expected 16 digits, got %d", len(digitStr))
+        }
+	}
+
 	return prefix + digitStr, nil
 }
+
+func ValidateIMEI(imei string) (bool, error) {
+    // Remove any non-digit characters
+    cleanIMEI := strings.ReplaceAll(imei, "-", "")
+    cleanIMEI = strings.ReplaceAll(cleanIMEI, " ", "")
+
+    // Check if all characters are digits
+    for _, char := range cleanIMEI {
+        if !unicode.IsDigit(char) {
+            return false, fmt.Errorf("IMEI contains non-digit character: %c", char)
+        }
+    }
+
+    // Luhn algorithm validation
+    sum := 0
+    for i := len(cleanIMEI) - 1; i >= 0; i-- {
+        digit := int(cleanIMEI[i] - '0')
+
+        if (len(cleanIMEI)-i)%2 == 0 {
+            digit *= 2
+            if digit > 9 {
+                digit = digit/10 + digit%10
+            }
+        }
+        sum += digit
+    }
+
+    return sum%10 == 0, nil
+}

nasConvert/MobileIdentity5GS_test.go

@@ -311,40 +311,53 @@ func TestPeiToStringWithError(t *testing.T) {
 		wantErr bool
 	}{
 		{
-			name: "PEI-IMEI-even",
-			args: args{
-				buf: []byte{0x3, 0xf1},
-			},
-			want:    "imei-01",
-			wantErr: false,
-		},
+            name: "Complete-Valid-IMEI",
+            args: args{
+                // Example encoding for a valid 15-digit IMEI
+                buf: []byte{
+					0x4b, 0x09, 0x51, 0x24, 0x30, 0x32, 0x57, 0x81,
+				},
+            },
+            want:    "imei-490154203237518",
+            wantErr: false,
+        },
 		{
-			name: "PEI-IMEISV-odd",
+            name: "Complete-Ivalid-IMEI",
+            args: args{
+                // Example encoding for a valid 15-digit IMEI
+                buf: []byte{
+					0x4b, 0x09, 0x51, 0x24, 0x30, 0x32, 0x57, 0x82,
+				},
+            },
+            wantErr: true,
+        },
+		{
+			name: "Complete-Valid-IMEISV",
 			args: args{
-				buf: []byte{0xd, 0x21},
+				buf: []byte{
+					0x90, 0x87, 0x65, 0x43, 0x21, 0x01, 0x23, 0x45, 0x60,
+				},
 			},
-			want:    "imeisv-012",
+			want:    "imeisv-9785634121032540",
 			wantErr: false,
 		},
 		{
-			name:    "PEI-nil",
-			wantErr: true,
-		},
-		{
-			name: "PEI-IMEI-len1",
+			name: "IMEI-TooLong",
 			args: args{
-				buf: []byte{0xb},
+				buf: []byte{
+					0x4b, 0x09, 0x51, 0x24, 0x30, 0x32, 0x57, 0x81, 0x20,
+				},
 			},
-			want:    "imei-0",
-			wantErr: false,
+			wantErr: true,
 		},
 		{
-			name: "PEI-IMEI-len0",
+			name: "IMEI-TooShort",
 			args: args{
-				buf: []byte{0x3},
+				buf: []byte{
+					0x4b, 0x09, 0x51, 0x24, 0x30, 0x32,
+				},
 			},
-			want:    "imei-",
-			wantErr: false,
+			wantErr: true,
 		},
 	}
 	for _, tt := range tests {