Make it possible to validate a code.

src/main.zig

@@ -59,6 +59,13 @@ fn mainInternal() !void {
         const authenticator = try getAuthenticator(allocator, arg.show.?, arg.config_location);
         const code = try authenticator.code(allocator, std.time.timestamp);
         try std.io.getStdOut().writer().print("{s}\n", .{code});
+    } else if (arg.validateAuthenticator != null and arg.validateCode != null) {
+        const authenticator = try getAuthenticator(allocator, arg.validateAuthenticator.?, arg.config_location);
+        const matches = try authenticator.validate(allocator, arg.validateCode.?, std.time.timestamp);
+        if (!matches) {
+            std.process.exit(1);
+        }
+        std.process.exit(0);
     } else {
         printHelp();
     }
@@ -71,6 +78,7 @@ fn printHelp() void {
         \\Commands:
         \\  list                   List the configured authentiators
         \\  show NAME              Show the code for the authenticator with name NAME
+        \\  validate NAME CODE     Validate the code CODE for the authenticator with name NAME
         \\
         \\Options:
         \\  --bash                 Print script to set up Bash shell integration. Usage: add 
@@ -82,11 +90,7 @@ fn printHelp() void {
     std.debug.print("{s}", .{msg});
 }
 
-const Args = struct {
-    list: bool,
-    show: ?[]const u8,
-    config_location: []const u8,
-};
+const Args = struct { list: bool, show: ?[]const u8, config_location: []const u8, validateAuthenticator: ?[]const u8, validateCode: ?[]const u8 };
 
 const OtpAuthUrl = struct { name: []const u8, secretEncoded: []const u8, url: []const u8, period: u32, digits: u4, algorithm: []const u8 };
 
@@ -148,6 +152,12 @@ const Authenticator = struct {
         //debug("code as 0-padded string: {s} ({d})\n", .{ result, token });
         return result;
     }
+
+    fn validate(self: Authenticator, allocator: Allocator, expectedCode: []const u8, timeFunc: *const fn () i64) !bool {
+        const actualCode = try self.code(allocator, timeFunc);
+        defer allocator.free(actualCode);
+        return eql(u8, actualCode, expectedCode);
+    }
 };
 
 fn zeroPad(allocator: Allocator, digits: u4, x: anytype) ![]u8 {
@@ -176,11 +186,7 @@ fn zeroPad(allocator: Allocator, digits: u4, x: anytype) ![]u8 {
 const ArgumentError = error{ InvalidOtpAuthUrl, UnknownParameter, MissingConfigLocation, AuthenticatorNotFound, MissingAuthenticatorParam, FailedToOpenConfigFile, TooManyParsinErrors };
 
 fn parseArgs(allocator: Allocator, args: []const []const u8) !Args {
-    var result = Args{
-        .list = false,
-        .show = null,
-        .config_location = try configLocation(allocator),
-    };
+    var result = Args{ .list = false, .show = null, .config_location = try configLocation(allocator), .validateAuthenticator = null, .validateCode = null };
     var i: u17 = 1;
     while (i < args.len) : (i += 1) {
         const arg = args[i];
@@ -189,14 +195,17 @@ fn parseArgs(allocator: Allocator, args: []const []const u8) !Args {
             const msg =
                 \\_zig_totp_completions()
                 \\{
-                \\   if [ "${COMP_WORDS[$COMP_CWORD-1]}" = 'show' ]
+                \\   if [ "${COMP_WORDS[$COMP_CWORD-1]}" = 'show' ] || [ "${COMP_WORDS[$COMP_CWORD-1]}" = 'validate' ]
                 \\   then
                 \\      COMPREPLY=($(compgen -W "$(zig-totp list 2> /dev/null )" -- "${COMP_WORDS[$COMP_CWORD]}" ))
+                \\   elif [ "${COMP_WORDS[$COMP_CWORD-2]}" = 'validate' ]
+                \\   then
+                \\      COMPREPLY=($(compgen -W "CODE" -- "${COMP_WORDS[$COMP_CWORD]}"))
                 \\   elif [ "${COMP_WORDS[$COMP_CWORD-1]}" = '--config' ]
                 \\   then 
                 \\      COMPREPLY=($(compgen -A file -- "${COMP_WORDS[$COMP_CWORD]}" ))
                 \\   else 
-                \\      COMPREPLY=($(compgen -W "list show --bash --config" -- "${COMP_WORDS[$COMP_CWORD]}" ))
+                \\      COMPREPLY=($(compgen -W "list show validate --bash --config" -- "${COMP_WORDS[$COMP_CWORD]}" ))
                 \\   fi
                 \\}
                 \\complete -F _zig_totp_completions zig-totp
@@ -220,6 +229,14 @@ fn parseArgs(allocator: Allocator, args: []const []const u8) !Args {
                 return error.MissingAuthenticatorParam;
             }
             result.show = args[i];
+        } else if (eql(u8, "validate", arg)) {
+            i += 2;
+            if (i >= args.len) {
+                std.debug.print("expected two parameters for 'validate'. The name for an authenticator and a code to validate.\n", .{});
+                return error.MissingValidateParam;
+            }
+            result.validateAuthenticator = args[i - 1];
+            result.validateCode = args[i];
         } else {
             std.debug.print("unknown argument: {s}\n", .{arg});
             return ArgumentError.UnknownParameter;
@@ -577,3 +594,19 @@ test "secret is not Base32 - invalid character" {
     const actualError = authenticator.code(std.testing.allocator, _closure_return_1725695340);
     try std.testing.expectError(Base32Error.InvalidCharacter, actualError);
 }
+
+test "testcases for 'validate'" {
+    const secretForSha1 = "GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ"; // plain: "12345678901234567890"  hex: "3132333435363738393031323334353637383930"
+
+    try testValidate(OtpAuthUrl{ .name = "", .secretEncoded = secretForSha1, .url = "", .period = 30, .digits = 8, .algorithm = "SHA1" }, _closure_return_59, "94287082", true);
+
+    try testValidate(OtpAuthUrl{ .name = "", .secretEncoded = secretForSha1, .url = "", .period = 30, .digits = 8, .algorithm = "SHA1" }, _closure_return_1111111109, "07081804", true);
+
+    try testValidate(OtpAuthUrl{ .name = "", .secretEncoded = secretForSha1, .url = "", .period = 30, .digits = 8, .algorithm = "SHA1" }, _closure_return_1111111109, "12345678", false);
+}
+fn testValidate(otpAuthUrl: OtpAuthUrl, timeFunc: *const fn () i64, expected: []const u8, expectedMatch: bool) !void {
+    const authenticator = Authenticator{ .url = otpAuthUrl };
+
+    const match = try authenticator.validate(std.testing.allocator, expected, timeFunc);
+    try std.testing.expectEqual(expectedMatch, match);
+}