vt: simplify ghostty_type_json to return null-terminated string

The function previously took a size_t* out-parameter for the string
length. Since the JSON blob is now null-terminated, the len parameter
is unnecessary. Remove it from the Zig implementation, C header, and
the WASM example consumer which no longer needs to allocate and free
a usize just to read the length.

example/wasm-vt/index.html

@@ -138,12 +138,11 @@
                 wasmMemory = wasmInstance.exports.memory;
 
                 // Load the type layout JSON from the library
-                const lenPtr = wasmInstance.exports.ghostty_wasm_alloc_usize();
+                const jsonPtr = wasmInstance.exports.ghostty_type_json();
-                const jsonPtr = wasmInstance.exports.ghostty_type_json(lenPtr);
+                const jsonStr = new TextDecoder().decode(
-                const jsonLen = new DataView(wasmMemory.buffer).getUint32(lenPtr, true);
+                    new Uint8Array(wasmMemory.buffer, jsonPtr, wasmMemory.buffer.byteLength - jsonPtr)
-                wasmInstance.exports.ghostty_wasm_free_usize(lenPtr);
+                ).split('\0')[0];
-                const jsonBytes = new Uint8Array(wasmMemory.buffer, jsonPtr, jsonLen);
+                typeLayout = JSON.parse(jsonStr);
-                typeLayout = JSON.parse(new TextDecoder().decode(jsonBytes));
 
                 return true;
             } catch (e) {

include/ghostty/vt/types.h

@@ -84,8 +84,8 @@ typedef struct {
   ((type){ .size = sizeof(type) })
 
 /**
- * Return a pointer to a JSON string describing the layout of every
+ * Return a pointer to a null-terminated JSON string describing the
- * C API struct for the current target.
+ * layout of every C API struct for the current target.
  *
  * This is primarily useful for language bindings that can't easily
  * set C struct fields and need to do so via byte offsets. For example,
@@ -113,12 +113,9 @@ typedef struct {
  * @endcode
  *
  * The returned pointer is valid for the lifetime of the process.
- * The length of the string (excluding any null terminator) is
- * written to @p len.
  *
- * @param[out] len Receives the length of the returned string in bytes.
+ * @return Pointer to the null-terminated JSON string.
- * @return Pointer to the JSON string.
  */
-const char *ghostty_type_json(size_t *len);
+const char *ghostty_type_json(void);
 
 #endif /* GHOSTTY_VT_TYPES_H */

src/terminal/c/types.zig

@@ -2,7 +2,7 @@
 //! extern structs for the current target.
 //!
 //! This is embedded in the binary as a const string and exposed via
-//! `ghostty_struct_meta` so that WASM (and other FFI) consumers can
+//! `ghostty_type_json` so that WASM (and other FFI) consumers can
 //! build structs without hardcoding byte offsets.
 const std = @import("std");
 const lib = @import("../lib.zig");
@@ -28,23 +28,22 @@ pub const structs: std.StaticStringMap(StructInfo) = .initComptime(.{
 });
 
 /// The comptime-generated JSON string of all structs.
-pub const json: []const u8 = json: {
+pub const json: [:0]const u8 = json: {
     @setEvalBranchQuota(50000);
     var counter: std.Io.Writer.Discarding = .init(&.{});
     jsonWriteAll(&counter.writer) catch unreachable;
 
-    var buf: [counter.count]u8 = undefined;
+    var buf: [counter.count:0]u8 = undefined;
     var writer: std.Io.Writer = .fixed(&buf);
     jsonWriteAll(&writer) catch unreachable;
     const final = buf;
-    break :json final[0..writer.end];
+    break :json final[0..writer.end :0];
 };
 
 /// Returns a pointer to the comptime-generated JSON string describing
 /// the layout of all C API extern structs, and writes its length to `len`.
 /// Exported as `ghostty_type_json` for FFI consumers.
-pub fn get_json(len: *usize) callconv(lib.calling_conv) [*]const u8 {
+pub fn get_json() callconv(lib.calling_conv) [*:0]const u8 {
-    len.* = json.len;
     return json.ptr;
 }