fix(mem): free preserve_chars before overwriting on repeated -P/--preserve

The C FFI CLI (strdup x3) and the Zig CLI (allocator.dupe x4) overwrote
opts.preserve_chars on each -P/--preserve without freeing the prior allocation,
leaking when the flag was given more than once. Free the previous value first
(free(NULL)/optional-unwrap are safe). Lua/Node are GC'd, so N/A there.

Author: pmarreck

src/printable_binary_ffi_main.c

@@ -227,6 +227,7 @@ static options_t parse_options(int argc, char *argv[]) {
             if (strncmp(name, "format=", 7) == 0) {
                 parse_format_spec(&opts, name + 7);
             } else if (strncmp(name, "preserve=", 9) == 0) {
+                free(opts.preserve_chars);
                 opts.preserve_chars = strdup(name + 9);
             } else if (strcmp(name, "decode") == 0) {
                 opts.decode_mode = true;
@@ -340,9 +341,11 @@ static options_t parse_options(int argc, char *argv[]) {
                         break;
                     case 'P':
                         if (arg[j + 1]) {
+                            free(opts.preserve_chars);
                             opts.preserve_chars = strdup(arg + j + 1);
                             j = strlen(arg) - 1;
                         } else if (i + 1 < argc) {
+                            free(opts.preserve_chars);
                             opts.preserve_chars = strdup(argv[++i]);
                         } else {
                             fprintf(stderr, "Error: -P requires a value\n");

src/zig/main.zig

@@ -220,11 +220,13 @@ fn parseArgs(allocator: std.mem.Allocator, args: []const []const u8) !Options {
                 opts.format_group = parsed.group;
                 opts.format_groups_per_line = parsed.per_line;
             } else if (std.mem.startsWith(u8, name, "preserve=")) {
+                if (opts.preserve_chars) |old| allocator.free(old);
                 opts.preserve_chars = try allocator.dupe(u8, name[9..]);
             } else if (std.mem.eql(u8, name, "preserve")) {
                 // --preserve CHARS (space-separated)
                 if (i + 1 < args.len) {
                     i += 1;
+                    if (opts.preserve_chars) |old| allocator.free(old);
                     opts.preserve_chars = try allocator.dupe(u8, args[i]);
                 } else {
                     return error.MissingValue;
@@ -327,10 +329,12 @@ fn parseArgs(allocator: std.mem.Allocator, args: []const []const u8) !Options {
                     },
                     'P' => {
                         if (j + 1 < arg.len) {
+                            if (opts.preserve_chars) |old| allocator.free(old);
                             opts.preserve_chars = try allocator.dupe(u8, arg[j + 1 ..]);
                             break;
                         } else if (i + 1 < args.len) {
                             i += 1;
+                            if (opts.preserve_chars) |old| allocator.free(old);
                             opts.preserve_chars = try allocator.dupe(u8, args[i]);
                         } else {
                             return error.MissingValue;