feat: add message formatter

src/cbor.zig

@@ -897,8 +897,11 @@ pub fn extract_cbor(dest: *[]const u8) CborExtractor {
 }
 
 pub fn JsonStream(comptime T: type) type {
+    return JsonStreamWriter(T.Writer);
+}
+
+pub fn JsonStreamWriter(comptime Writer: type) type {
     return struct {
-        const Writer = T.Writer;
         const JsonWriter = json.WriteStream(Writer, .{ .checked_to_fixed_depth = 256 });
 
         fn jsonWriteArray(w: *JsonWriter, iter: *[]const u8, minor: u5) !void {
@@ -954,6 +957,12 @@ pub fn toJson(cbor_buf: []const u8, json_buf: []u8) (JsonEncodeError || error{No
     return fbs.getWritten();
 }
 
+pub fn toJsonWriter(cbor_buf: []const u8, writer: anytype, options: std.json.StringifyOptions) !void {
+    var s = json.writeStream(writer, options);
+    var iter: []const u8 = cbor_buf;
+    try JsonStreamWriter(@TypeOf(writer)).jsonWriteValue(&s, &iter);
+}
+
 pub fn toJsonAlloc(a: std.mem.Allocator, cbor_buf: []const u8) (JsonEncodeError)![]const u8 {
     var buf = std.ArrayList(u8).init(a);
     defer buf.deinit();

src/thespian.zig

@@ -207,6 +207,10 @@ pub const message = struct {
     pub fn match(self: Self, m: anytype) error{Exit}!bool {
         return if (cbor.match(self.buf, m)) |ret| ret else |e| exit_error(e, @errorReturnTrace());
     }
+
+    pub fn format(self: @This(), comptime _: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
+        return cbor.toJsonWriter(self.buf, writer, .{});
+    }
 };
 
 pub fn exit_message(e: anytype, stack_trace: ?*std.builtin.StackTrace) message {