more work on porting rc command parsing to Go

tools/cmd/at/send_text.go

@@ -0,0 +1,60 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package at
+
+import (
+	"encoding/base64"
+	"errors"
+	"io"
+	"os"
+	"strings"
+)
+
+type generator_function func(io_data *rc_io_data) (bool, error)
+
+func parse_send_text(io_data *rc_io_data, args []string) error {
+	generators := make([]generator_function, 0, 1)
+	var payload send_text_json_type = io_data.rc.Payload.(send_text_json_type)
+
+	if len(args) > 0 {
+		text := strings.Join(args, " ")
+		text_gen := func(io_data *rc_io_data) (bool, error) {
+			payload.Data = "text:" + text[:2048]
+			text = text[2048:]
+			return len(text) == 0, nil
+		}
+		generators = append(generators, text_gen)
+	}
+
+	if options_send_text.from_file != "" {
+		f, err := os.Open(options_send_text.from_file)
+		if err != nil {
+			return err
+		}
+		chunk := make([]byte, 2048)
+		file_gen := func(io_data *rc_io_data) (bool, error) {
+			n, err := f.Read(chunk)
+			if err != nil && !errors.Is(err, io.EOF) {
+				return false, err
+			}
+			payload.Data = "base64:" + base64.StdEncoding.EncodeToString(chunk[:n])
+			return n == 0, nil
+		}
+		generators = append(generators, file_gen)
+	}
+
+	io_data.multiple_payload_generator = func(io_data *rc_io_data) (bool, error) {
+		if len(generators) == 0 {
+			payload.Data = "text:"
+			return true, nil
+		}
+		finished, err := generators[0](io_data)
+		if finished {
+			generators = generators[1:]
+			finished = len(generators) == 0
+		}
+		return finished, err
+	}
+
+	return nil
+}