Work on conversion of args parsing to go code

tools/cmd/at/set_window_logo.go

@@ -0,0 +1,54 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package at
+
+import (
+	"encoding/base64"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"strings"
+)
+
+func read_window_logo(path string) (func(io_data *rc_io_data) (bool, error), error) {
+	if strings.ToLower(path) == "none" {
+		return func(io_data *rc_io_data) (bool, error) {
+			io_data.rc.Payload = "-"
+			return true, nil
+		}, nil
+	}
+
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	buf := make([]byte, 2048)
+	n, err := f.Read(buf)
+	if err != nil && err != io.EOF {
+		f.Close()
+		return nil, err
+	}
+	buf = buf[:n]
+
+	if http.DetectContentType(buf) != "image/png" {
+		f.Close()
+		return nil, fmt.Errorf("%s is not a PNG image", path)
+	}
+
+	return func(io_data *rc_io_data) (bool, error) {
+		var payload set_window_logo_json_type = io_data.rc.Payload.(set_window_logo_json_type)
+		if len(buf) == 0 {
+			payload.Data = ""
+			return true, nil
+		}
+		payload.Data = base64.StdEncoding.EncodeToString(buf)
+		buf = buf[:cap(buf)]
+		n, err := f.Read(buf)
+		if err != nil && err != io.EOF {
+			return false, err
+		}
+		buf = buf[:n]
+		return n == 0, nil
+	}, nil
+}