fix: truncate long activity fields to prevent Discord rejection (#18)

rpc.go

@@ -55,6 +55,30 @@ const (
 
 const heartbeatInterval = 41 // Heartbeat interval in seconds
 
+// Discord API field length limits
+const (
+	maxTextLength = 128 // Max characters for text fields (details, state, name, large_text)
+	maxURLLength  = 256 // Max characters for URL fields (details_url, state_url, etc.)
+)
+
+// truncateText truncates s to maxTextLength runes, appending "…" if truncated.
+func truncateText(s string) string {
+	runes := []rune(s)
+	if len(runes) <= maxTextLength {
+		return s
+	}
+	return string(runes[:maxTextLength-1]) + "…"
+}
+
+// truncateURL returns s unchanged if within maxURLLength, otherwise returns ""
+// (a truncated URL would be broken, so we omit it entirely).
+func truncateURL(s string) string {
+	if len(s) <= maxURLLength {
+		return s
+	}
+	return ""
+}
+
 // activity represents a Discord activity sent via Gateway opcode 3.
 type activity struct {
 	Name              string             `json:"name"`
@@ -200,6 +224,18 @@ func (r *discordRPC) processImage(imageURL, clientID, token string, ttl int64) (
 func (r *discordRPC) sendActivity(clientID, username, token string, data activity) error {
 	pdk.Log(pdk.LogInfo, fmt.Sprintf("Sending activity for user %s: %s - %s", username, data.Details, data.State))
 
+	// Truncate text fields to Discord's 128-character limit
+	data.Name = truncateText(data.Name)
+	data.Details = truncateText(data.Details)
+	data.State = truncateText(data.State)
+	data.Assets.LargeText = truncateText(data.Assets.LargeText)
+
+	// Omit URLs that exceed Discord's 256-character limit
+	data.DetailsURL = truncateURL(data.DetailsURL)
+	data.StateURL = truncateURL(data.StateURL)
+	data.Assets.LargeURL = truncateURL(data.Assets.LargeURL)
+	data.Assets.SmallURL = truncateURL(data.Assets.SmallURL)
+
 	// Try track artwork first, fall back to Navidrome logo
 	usingDefaultImage := false
 	processedImage, err := r.processImage(data.Assets.LargeImage, clientID, token, imageCacheTTL)