protocol/aprs: refactored

protocol/aprs/message.go

@@ -0,0 +1,99 @@
+package aprs
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type Message struct {
+	ID            int    `json::"id"`
+	IsAcknowledge bool   `json:"is_ack"`
+	IsRejection   bool   `json:"is_rejection"`
+	IsBulletin    bool   `json:"is_bulletin"`
+	Recipient     string `json:"recipient"`
+	AnnoucementID byte   `json:"announcement_id,omitempty"`
+	Group         string `json:"group,omitempty"`
+	Severity      string `json:"severity,omitempty"`
+	Text          string `json:"text"`
+}
+
+func (msg *Message) String() string {
+	return fmt.Sprintf("%s: %q", msg.Recipient, msg.Text)
+}
+
+type messageDecoder struct{}
+
+func (messageDecoder) CanDecode(frame *Frame) bool {
+	var (
+		maybeMessage  = len(frame.Raw) >= 11 && frame.Raw[10] == ':'
+		maybeBulletin = len(frame.Raw) >= 10 && frame.Raw[9] == ':'
+	)
+	return frame.Raw.Type() == ':' && (maybeMessage || maybeBulletin)
+}
+
+func (messageDecoder) Decode(frame *Frame) (data Data, err error) {
+	var (
+		msg  = new(Message)
+		text string
+		size = len(text)
+	)
+	if len(frame.Raw) >= 10 && frame.Raw[9] == ':' {
+		msg.Recipient, text = strings.TrimSpace(string(frame.Raw[1:9])), string(frame.Raw[9:])
+	} else {
+		msg.Recipient, text = strings.TrimSpace(string(frame.Raw[1:10])), string(frame.Raw[10:])
+	}
+
+	switch {
+	case strings.HasPrefix(msg.Recipient, "BLN"):
+		// Bulletin
+		kind := msg.Recipient[3:]
+		if id, err := strconv.Atoi(kind); err == nil {
+			// General bulletin
+			msg.IsBulletin = true
+			msg.ID = id
+		} else if len(kind) >= 2 && isDigit(kind[0]) {
+			// Group Bulletin Format
+			msg.IsBulletin = true
+			msg.ID = int(kind[0] - '0')
+			msg.Group = kind[1:]
+		} else if len(kind) == 1 {
+			// Announcement
+			msg.IsBulletin = true
+			msg.AnnoucementID = kind[0]
+		}
+
+	case strings.HasPrefix(msg.Recipient, "NWS-"):
+		// National Weather Service Bulletins
+		msg.IsBulletin = true
+		msg.Severity = msg.Recipient[4:]
+
+	default:
+		if i := strings.LastIndexByte(text, '{'); i != -1 && i > (size-6) {
+			// Plain message ID: {XXXXX (where there are 1-5 X)
+			msg.ID, _ = strconv.Atoi(text[i+1:])
+			text = text[:i]
+		}
+
+		if i := strings.LastIndex(text, ":ack"); i != -1 && i > (size-9) {
+			// Message acknowledgement: :ackXXXXX (where there are 1-5 X)
+			msg.IsAcknowledge = true
+			msg.ID, _ = strconv.Atoi(text[i+4:])
+			text = text[:i]
+		}
+
+		if i := strings.LastIndex(text, ":rej"); i != -1 && i > (size-9) {
+			// Message acknowledgement: :rejXXXXX (where there are 1-5 X)
+			msg.IsRejection = true
+			msg.ID, _ = strconv.Atoi(text[i+4:])
+			text = text[:i]
+		}
+	}
+
+	if len(text) > 0 && text[0] == ':' {
+		text = text[1:]
+	}
+
+	msg.Text = text
+	return msg, nil
+}