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)

rpc_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"encoding/json"
 	"errors"
 	"strings"
 
@@ -435,6 +436,66 @@ var _ = Describe("discordRPC", func() {
 			})
 			Expect(err).ToNot(HaveOccurred())
 		})
+
+		It("truncates long text fields and omits long URLs", func() {
+			host.CacheMock.On("GetString", discordImageKey).Return("mp:cached/art", true, nil).Once()
+			host.CacheMock.On("GetString", discordImageKey).Return("mp:cached/logo", true, nil).Once()
+
+			longName := strings.Repeat("N", 200)
+			longTitle := strings.Repeat("T", 200)
+			longArtist := strings.Repeat("A", 200)
+			longAlbum := strings.Repeat("B", 200)
+			longURL := "https://example.com/" + strings.Repeat("x", 237)
+
+			truncatedName := strings.Repeat("N", 127) + "…"
+			truncatedTitle := strings.Repeat("T", 127) + "…"
+			truncatedArtist := strings.Repeat("A", 127) + "…"
+			truncatedAlbum := strings.Repeat("B", 127) + "…"
+
+			host.WebSocketMock.On("SendText", "testuser", mock.MatchedBy(func(msg string) bool {
+				var message struct {
+					D json.RawMessage `json:"d"`
+				}
+				if err := json.Unmarshal([]byte(msg), &message); err != nil {
+					return false
+				}
+				var presence presencePayload
+				if err := json.Unmarshal(message.D, &presence); err != nil {
+					return false
+				}
+				if len(presence.Activities) != 1 {
+					return false
+				}
+				act := presence.Activities[0]
+				return act.Name == truncatedName &&
+					act.Details == truncatedTitle &&
+					act.State == truncatedArtist &&
+					act.Assets.LargeText == truncatedAlbum &&
+					act.DetailsURL == "" &&
+					act.StateURL == "" &&
+					act.Assets.LargeURL == "" &&
+					act.Assets.SmallURL == ""
+			})).Return(nil)
+
+			err := r.sendActivity("client123", "testuser", "token123", activity{
+				Application: "client123",
+				Name:        longName,
+				Type:        2,
+				Details:     longTitle,
+				DetailsURL:  longURL,
+				State:       longArtist,
+				StateURL:    longURL,
+				Assets: activityAssets{
+					LargeImage: "https://example.com/art.jpg",
+					LargeText:  longAlbum,
+					LargeURL:   longURL,
+					SmallImage: navidromeLogoURL,
+					SmallText:  "Navidrome",
+					SmallURL:   longURL,
+				},
+			})
+			Expect(err).ToNot(HaveOccurred())
+		})
 	})
 
 	Describe("clearActivity", func() {
@@ -448,4 +509,55 @@ var _ = Describe("discordRPC", func() {
 			Expect(err).ToNot(HaveOccurred())
 		})
 	})
+
+	Describe("truncateText", func() {
+		It("returns short strings unchanged", func() {
+			Expect(truncateText("hello")).To(Equal("hello"))
+		})
+
+		It("returns exactly 128-char strings unchanged", func() {
+			s := strings.Repeat("a", 128)
+			Expect(truncateText(s)).To(Equal(s))
+		})
+
+		It("truncates strings over 128 chars to 127 + ellipsis", func() {
+			s := strings.Repeat("a", 200)
+			result := truncateText(s)
+			Expect([]rune(result)).To(HaveLen(128))
+			Expect(result).To(HaveSuffix("…"))
+		})
+
+		It("handles multi-byte characters correctly", func() {
+			// 130 Japanese characters — each is one rune but 3 bytes
+			s := strings.Repeat("あ", 130)
+			result := truncateText(s)
+			runes := []rune(result)
+			Expect(runes).To(HaveLen(128))
+			Expect(string(runes[127])).To(Equal("…"))
+		})
+
+		It("returns empty string unchanged", func() {
+			Expect(truncateText("")).To(Equal(""))
+		})
+	})
+
+	Describe("truncateURL", func() {
+		It("returns short URLs unchanged", func() {
+			Expect(truncateURL("https://example.com")).To(Equal("https://example.com"))
+		})
+
+		It("returns exactly 256-char URLs unchanged", func() {
+			u := "https://example.com/" + strings.Repeat("a", 236)
+			Expect(truncateURL(u)).To(Equal(u))
+		})
+
+		It("returns empty string for URLs over 256 chars", func() {
+			u := "https://example.com/" + strings.Repeat("a", 237)
+			Expect(truncateURL(u)).To(Equal(""))
+		})
+
+		It("returns empty string unchanged", func() {
+			Expect(truncateURL("")).To(Equal(""))
+		})
+	})
 })