Merge pull request #1047 from AaronJny/feat/discord-reply-context

feat(discord): support referenced messages and resolve channel/link references

pkg/channels/discord/discord.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"regexp"
 	"strings"
 	"sync"
 	"time"
@@ -26,6 +27,12 @@ const (
 	sendTimeout = 10 * time.Second
 )
 
+var (
+	// Pre-compiled regexes for resolveDiscordRefs (avoid re-compiling per call)
+	channelRefRe = regexp.MustCompile(`<#(\d+)>`)
+	msgLinkRe    = regexp.MustCompile(`https://(?:discord\.com|discordapp\.com)/channels/(\d+)/(\d+)/(\d+)`)
+)
+
 type DiscordChannel struct {
 	*channels.BaseChannel
 	session    *discordgo.Session
@@ -338,6 +345,24 @@ func (c *DiscordChannel) handleMessage(s *discordgo.Session, m *discordgo.Messag
 		content = c.stripBotMention(content)
 	}
 
+	// Resolve Discord refs in main content before concatenation to avoid
+	// double-expanding links that appear in the referenced message.
+	content = c.resolveDiscordRefs(s, content, m.GuildID)
+
+	// Prepend referenced (quoted) message content if this is a reply
+	if m.MessageReference != nil && m.ReferencedMessage != nil {
+		refContent := m.ReferencedMessage.Content
+		if refContent != "" {
+			refAuthor := "unknown"
+			if m.ReferencedMessage.Author != nil {
+				refAuthor = m.ReferencedMessage.Author.Username
+			}
+			refContent = c.resolveDiscordRefs(s, refContent, m.GuildID)
+			content = fmt.Sprintf("[quoted message from %s]: %s\n\n%s",
+				refAuthor, refContent, content)
+		}
+	}
+
 	senderID := m.Author.ID
 
 	mediaPaths := make([]string, 0, len(m.Attachments))
@@ -508,6 +533,51 @@ func applyDiscordProxy(session *discordgo.Session, proxyAddr string) error {
 	return nil
 }
 
+// resolveDiscordRefs resolves channel references (<#id> → #channel-name) and
+// expands Discord message links to show the linked message content.
+// Only links pointing to the same guild are expanded to prevent cross-guild leakage.
+func (c *DiscordChannel) resolveDiscordRefs(s *discordgo.Session, text string, guildID string) string {
+	// 1. Resolve channel references: <#id> → #channel-name
+	text = channelRefRe.ReplaceAllStringFunc(text, func(match string) string {
+		parts := channelRefRe.FindStringSubmatch(match)
+		if len(parts) < 2 {
+			return match
+		}
+		// Prefer session state cache to avoid API calls
+		if ch, err := s.State.Channel(parts[1]); err == nil {
+			return "#" + ch.Name
+		}
+		if ch, err := s.Channel(parts[1]); err == nil {
+			return "#" + ch.Name
+		}
+		return match
+	})
+
+	// 2. Expand Discord message links (max 3, same guild only)
+	matches := msgLinkRe.FindAllStringSubmatch(text, 3)
+	for _, m := range matches {
+		if len(m) < 4 {
+			continue
+		}
+		linkGuildID, channelID, messageID := m[1], m[2], m[3]
+		// Security: only expand links from the same guild
+		if linkGuildID != guildID {
+			continue
+		}
+		msg, err := s.ChannelMessage(channelID, messageID)
+		if err != nil || msg == nil || msg.Content == "" {
+			continue
+		}
+		author := "unknown"
+		if msg.Author != nil {
+			author = msg.Author.Username
+		}
+		text += fmt.Sprintf("\n[linked message from %s]: %s", author, msg.Content)
+	}
+
+	return text
+}
+
 // stripBotMention removes the bot mention from the message content.
 // Discord mentions have the format <@USER_ID> or <@!USER_ID> (with nickname).
 func (c *DiscordChannel) stripBotMention(text string) string {

pkg/channels/discord/discord_resolve_test.go

@@ -0,0 +1,98 @@
+package discord
+
+import (
+	"testing"
+)
+
+func TestChannelRefRegex(t *testing.T) {
+	tests := []struct {
+		name   string
+		input  string
+		wantID string
+		wantOK bool
+	}{
+		{"basic channel ref", "<#123456789>", "123456789", true},
+		{"long id", "<#9876543210123456>", "9876543210123456", true},
+		{"no match plain text", "hello world", "", false},
+		{"no match partial", "<#>", "", false},
+		{"no match letters", "<#abc>", "", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			matches := channelRefRe.FindStringSubmatch(tt.input)
+			if tt.wantOK {
+				if len(matches) < 2 || matches[1] != tt.wantID {
+					t.Errorf("channelRefRe(%q) = %v, want ID %q", tt.input, matches, tt.wantID)
+				}
+			} else {
+				if len(matches) >= 2 {
+					t.Errorf("channelRefRe(%q) should not match, got %v", tt.input, matches)
+				}
+			}
+		})
+	}
+}
+
+func TestMsgLinkRegex(t *testing.T) {
+	tests := []struct {
+		name      string
+		input     string
+		wantGuild string
+		wantChan  string
+		wantMsg   string
+		wantOK    bool
+	}{
+		{
+			"discord.com link",
+			"https://discord.com/channels/111/222/333",
+			"111", "222", "333", true,
+		},
+		{
+			"discordapp.com link",
+			"https://discordapp.com/channels/111/222/333",
+			"111", "222", "333", true,
+		},
+		{
+			"real world ids",
+			"check this https://discord.com/channels/9000000000000001/9000000000000002/9000000000000003 please",
+			"9000000000000001", "9000000000000002", "9000000000000003", true,
+		},
+		{"no match http", "http://discord.com/channels/1/2/3", "", "", "", false},
+		{"no match missing segment", "https://discord.com/channels/1/2", "", "", "", false},
+		{"no match plain text", "hello world", "", "", "", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			matches := msgLinkRe.FindStringSubmatch(tt.input)
+			if tt.wantOK {
+				if len(matches) < 4 {
+					t.Fatalf("msgLinkRe(%q) didn't match, want guild=%s chan=%s msg=%s",
+						tt.input, tt.wantGuild, tt.wantChan, tt.wantMsg)
+				}
+				if matches[1] != tt.wantGuild || matches[2] != tt.wantChan || matches[3] != tt.wantMsg {
+					t.Errorf("msgLinkRe(%q) = guild=%s chan=%s msg=%s, want %s/%s/%s",
+						tt.input, matches[1], matches[2], matches[3],
+						tt.wantGuild, tt.wantChan, tt.wantMsg)
+				}
+			} else {
+				if len(matches) >= 4 {
+					t.Errorf("msgLinkRe(%q) should not match, got %v", tt.input, matches)
+				}
+			}
+		})
+	}
+}
+
+func TestMsgLinkRegex_MultipleMatches(t *testing.T) {
+	input := "see https://discord.com/channels/1/2/3 and https://discord.com/channels/4/5/6 and https://discord.com/channels/7/8/9 and https://discord.com/channels/10/11/12"
+	matches := msgLinkRe.FindAllStringSubmatch(input, 3)
+	if len(matches) != 3 {
+		t.Fatalf("expected 3 matches (capped), got %d", len(matches))
+	}
+	// Verify the 3rd match is 7/8/9 (not 10/11/12)
+	if matches[2][1] != "7" || matches[2][2] != "8" || matches[2][3] != "9" {
+		t.Errorf("3rd match = %v, want guild=7 chan=8 msg=9", matches[2])
+	}
+}