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vt: simplify ghostty_type_json to return null-terminated string

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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.
This commit is contained in:
Mitchell Hashimoto
2026-03-30 10:12:07 -07:00
parent 6479d90ca5
commit 0c38e8be60
3 changed files with 14 additions and 19 deletions
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11
example/wasm-vt/index.html
View File

@@ -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(lenPtr);
const jsonLen = new DataView(wasmMemory.buffer).getUint32(lenPtr, true);
wasmInstance.exports.ghostty_wasm_free_usize(lenPtr);
const jsonBytes = new Uint8Array(wasmMemory.buffer, jsonPtr, jsonLen);
typeLayout = JSON.parse(new TextDecoder().decode(jsonBytes));
const jsonPtr = wasmInstance.exports.ghostty_type_json();
const jsonStr = new TextDecoder().decode(
new Uint8Array(wasmMemory.buffer, jsonPtr, wasmMemory.buffer.byteLength - jsonPtr)
).split('\0')[0];
typeLayout = JSON.parse(jsonStr);
return true;
} catch (e) {

11
include/ghostty/vt/types.h
View File

@@ -84,8 +84,8 @@ typedef struct {
((type){ .size = sizeof(type) })
/**
* Return a pointer to a JSON string describing the layout of every
* C API struct for the current target.
* Return a pointer to a null-terminated JSON string describing the
* 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 JSON string.
* @return Pointer to the null-terminated JSON string.
*/
const char *ghostty_type_json(size_t *len);
const char *ghostty_type_json(void);
#endif /* GHOSTTY_VT_TYPES_H */

11
src/terminal/c/types.zig
View File

@@ -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 {
len.* = json.len;
pub fn get_json() callconv(lib.calling_conv) [*:0]const u8 {
return json.ptr;
}