big update: added reactions, groups, media share

server/internal/api/api.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"messenger/internal/auth"
+	"messenger/internal/media"
 	"messenger/internal/platform/config"
 	"messenger/internal/realtime"
 	"messenger/internal/store"
@@ -17,17 +18,19 @@ type apiHandler struct {
 	hub    *realtime.Hub
 	log    *slog.Logger
 	secure bool
+	media  media.Storage
 }
 
 // NewHandler builds the /api/v1 route tree with all middleware applied.
 // static, when non-nil, serves the built frontend for non-API paths.
-func NewHandler(st *store.Store, tm *auth.TokenManager, hub *realtime.Hub, log *slog.Logger, cfg *config.Config, static http.Handler) http.Handler {
+func NewHandler(st *store.Store, tm *auth.TokenManager, hub *realtime.Hub, log *slog.Logger, cfg *config.Config, ms media.Storage, static http.Handler) http.Handler {
 	h := &apiHandler{
 		store:  st,
 		tokens: tm,
 		hub:    hub,
 		log:    log,
 		secure: cfg.Environment == "production",
+		media:  ms,
 	}
 
 	mux := http.NewServeMux()
@@ -50,9 +53,18 @@ func NewHandler(st *store.Store, tm *auth.TokenManager, hub *realtime.Hub, log *
 	mux.Handle("DELETE /api/v1/contacts/{user_id}", requireAuth(tm, h.removeContact))
 
 	mux.Handle("GET /api/v1/conversations", requireAuth(tm, h.listConversations))
-	mux.Handle("POST /api/v1/conversations", requireAuth(tm, h.createDM))
+	mux.Handle("POST /api/v1/conversations", requireAuth(tm, h.createConversation))
+	mux.Handle("GET /api/v1/conversations/{id}/members", requireAuth(tm, h.listMembers))
+	mux.Handle("POST /api/v1/conversations/{id}/members", requireAuth(tm, h.addMember))
+	mux.Handle("DELETE /api/v1/conversations/{id}/members/{user_id}", requireAuth(tm, h.removeMember))
 	mux.Handle("GET /api/v1/conversations/{id}/messages", requireAuth(tm, h.listMessages))
 	mux.Handle("POST /api/v1/conversations/{id}/messages", requireAuth(tm, h.sendMessage))
+	mux.Handle("PUT /api/v1/conversations/{id}/messages/{msg_id}/reactions", requireAuth(tm, h.addReaction))
+	mux.Handle("DELETE /api/v1/conversations/{id}/messages/{msg_id}/reactions/{emoji}", requireAuth(tm, h.removeReaction))
+
+	mux.Handle("POST /api/v1/media", requireAuth(tm, h.uploadMedia))
+	mux.Handle("GET /api/v1/media/{id}", requireAuth(tm, h.downloadMedia))
+	mux.Handle("GET /api/v1/media/{id}/thumb", requireAuth(tm, h.downloadThumb))
 
 	mux.Handle("GET /ws", authHandler)
 

server/internal/api/conversations.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"net/http"
 	"strconv"
+	"strings"
 	"time"
 
 	"messenger/internal/realtime"
@@ -13,19 +14,34 @@ import (
 type conversationJSON struct {
 	ID          int64        `json:"id"`
 	Type        string       `json:"type"`
+	Name        string       `json:"name"`
+	Avatar      string       `json:"avatar"`
 	CreatedAt   time.Time    `json:"created_at"`
 	LastMessage *messageJSON `json:"last_message,omitempty"`
 	UnreadCount int64        `json:"unread_count"`
 }
 
+type memberJSON struct {
+	User     userJSON  `json:"user"`
+	Role     string    `json:"role"`
+	JoinedAt time.Time `json:"joined_at"`
+}
+
 type messageJSON struct {
-	ID             int64      `json:"id"`
-	ConversationID int64      `json:"conversation_id"`
-	SenderID       int64      `json:"sender_id"`
-	Body           string     `json:"body"`
-	CreatedAt      time.Time  `json:"created_at"`
-	EditedAt       *time.Time `json:"edited_at,omitempty"`
-	DeletedAt      *time.Time `json:"deleted_at,omitempty"`
+	ID             int64          `json:"id"`
+	ConversationID int64          `json:"conversation_id"`
+	SenderID       int64          `json:"sender_id"`
+	Body           string         `json:"body"`
+	Reactions      []reactionJSON `json:"reactions"`
+	Media          *mediaJSON     `json:"media,omitempty"`
+	CreatedAt      time.Time      `json:"created_at"`
+	EditedAt       *time.Time     `json:"edited_at,omitempty"`
+	DeletedAt      *time.Time     `json:"deleted_at,omitempty"`
+}
+
+type reactionJSON struct {
+	Emoji  string `json:"emoji"`
+	UserID int64  `json:"user_id"`
 }
 
 func toMessageJSON(m *store.Message) messageJSON {
@@ -34,12 +50,25 @@ func toMessageJSON(m *store.Message) messageJSON {
 		ConversationID: m.ConversationID,
 		SenderID:       m.SenderID,
 		Body:           m.Body,
+		Reactions:      []reactionJSON{},
 		CreatedAt:      m.CreatedAt,
 		EditedAt:       m.EditedAt,
 		DeletedAt:      m.DeletedAt,
 	}
 }
 
+func attachReactions(msgs []messageJSON, reactions []store.Reaction) {
+	byMessage := make(map[int64][]reactionJSON)
+	for _, r := range reactions {
+		byMessage[r.MessageID] = append(byMessage[r.MessageID], reactionJSON{Emoji: r.Emoji, UserID: r.UserID})
+	}
+	for i := range msgs {
+		if rs, ok := byMessage[msgs[i].ID]; ok {
+			msgs[i].Reactions = rs
+		}
+	}
+}
+
 func (h *apiHandler) listConversations(w http.ResponseWriter, r *http.Request) {
 	userID, _ := userIDFrom(r.Context())
 	summaries, err := h.store.ListConversationsForUser(r.Context(), userID)
@@ -52,6 +81,8 @@ func (h *apiHandler) listConversations(w http.ResponseWriter, r *http.Request) {
 		item := conversationJSON{
 			ID:          s.ID,
 			Type:        s.Type,
+			Name:        s.Name,
+			Avatar:      s.Avatar,
 			CreatedAt:   s.CreatedAt,
 			UnreadCount: s.UnreadCount,
 		}
@@ -64,12 +95,27 @@ func (h *apiHandler) listConversations(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, out)
 }
 
-func (h *apiHandler) createDM(w http.ResponseWriter, r *http.Request) {
+type createConversationRequest struct {
+	Type      string  `json:"type"`
+	UserID    int64   `json:"user_id"`
+	Name      string  `json:"name"`
+	MemberIDs []int64 `json:"member_ids"`
+}
+
+func (h *apiHandler) createConversation(w http.ResponseWriter, r *http.Request) {
 	userID, _ := userIDFrom(r.Context())
-	var req struct {
-		UserID int64 `json:"user_id"`
+	var req createConversationRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid json")
+		return
 	}
-	if err := json.NewDecoder(r.Body).Decode(&req); err != nil || req.UserID <= 0 {
+
+	if req.Type == "group" || req.Name != "" {
+		h.createGroup(w, r, userID, req)
+		return
+	}
+
+	if req.UserID <= 0 {
 		writeError(w, http.StatusBadRequest, "invalid user_id")
 		return
 	}
@@ -82,7 +128,148 @@ func (h *apiHandler) createDM(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}
-	writeJSON(w, http.StatusCreated, conversationJSON{ID: conv.ID, Type: conv.Type, CreatedAt: conv.CreatedAt})
+	writeJSON(w, http.StatusCreated, conversationJSON{
+		ID: conv.ID, Type: conv.Type, Name: conv.Name, Avatar: conv.Avatar, CreatedAt: conv.CreatedAt,
+	})
+}
+
+func (h *apiHandler) createGroup(w http.ResponseWriter, r *http.Request, userID int64, req createConversationRequest) {
+	name := strings.TrimSpace(req.Name)
+	if name == "" || len(name) > 64 {
+		writeError(w, http.StatusBadRequest, "name must be 1-64 chars")
+		return
+	}
+	for _, uid := range req.MemberIDs {
+		if uid == userID {
+			continue
+		}
+		if _, err := h.store.GetUserByID(r.Context(), uid); err != nil {
+			writeError(w, http.StatusBadRequest, "invalid member_id")
+			return
+		}
+	}
+	conv, err := h.store.CreateGroup(r.Context(), userID, name, req.MemberIDs)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	h.hub.Subscribe(userID, conv.ID)
+	for _, uid := range req.MemberIDs {
+		if uid == userID {
+			continue
+		}
+		h.hub.Subscribe(uid, conv.ID)
+		h.hub.SendToUser(uid, realtime.EventConversationAdded, realtime.ConversationChanged{ConversationID: conv.ID})
+	}
+	writeJSON(w, http.StatusCreated, conversationJSON{
+		ID: conv.ID, Type: conv.Type, Name: conv.Name, Avatar: conv.Avatar, CreatedAt: conv.CreatedAt,
+	})
+}
+
+func (h *apiHandler) listMembers(w http.ResponseWriter, r *http.Request) {
+	userID, _ := userIDFrom(r.Context())
+	convID, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
+	if err != nil || convID <= 0 {
+		writeError(w, http.StatusBadRequest, "invalid conversation id")
+		return
+	}
+	if member, err := h.store.IsMember(r.Context(), convID, userID); err != nil || !member {
+		writeError(w, http.StatusForbidden, "not a member")
+		return
+	}
+	members, err := h.store.ListMembers(r.Context(), convID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	out := make([]memberJSON, 0, len(members))
+	for _, m := range members {
+		out = append(out, memberJSON{User: toUserJSON(&m.User), Role: m.Role, JoinedAt: m.JoinedAt})
+	}
+	writeJSON(w, http.StatusOK, out)
+}
+
+func (h *apiHandler) addMember(w http.ResponseWriter, r *http.Request) {
+	userID, _ := userIDFrom(r.Context())
+	convID, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
+	if err != nil || convID <= 0 {
+		writeError(w, http.StatusBadRequest, "invalid conversation id")
+		return
+	}
+	if member, err := h.store.IsMember(r.Context(), convID, userID); err != nil || !member {
+		writeError(w, http.StatusForbidden, "not a member")
+		return
+	}
+	conv, err := h.store.GetConversationByID(r.Context(), convID)
+	if err != nil {
+		writeError(w, http.StatusNotFound, "conversation not found")
+		return
+	}
+	if conv.Type != "group" {
+		writeError(w, http.StatusBadRequest, "only groups support members")
+		return
+	}
+	var req struct {
+		UserID int64 `json:"user_id"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil || req.UserID <= 0 {
+		writeError(w, http.StatusBadRequest, "invalid user_id")
+		return
+	}
+	if _, err := h.store.GetUserByID(r.Context(), req.UserID); err != nil {
+		writeError(w, http.StatusNotFound, "user not found")
+		return
+	}
+	if err := h.store.AddMember(r.Context(), convID, req.UserID); err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	h.hub.Subscribe(req.UserID, convID)
+	h.hub.SendToUser(req.UserID, realtime.EventConversationAdded, realtime.ConversationChanged{ConversationID: convID})
+	h.hub.PublishMemberChanged(convID, req.UserID, true)
+	writeJSON(w, http.StatusCreated, map[string]string{"status": "ok"})
+}
+
+func (h *apiHandler) removeMember(w http.ResponseWriter, r *http.Request) {
+	userID, _ := userIDFrom(r.Context())
+	convID, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
+	if err != nil || convID <= 0 {
+		writeError(w, http.StatusBadRequest, "invalid conversation id")
+		return
+	}
+	targetID, err := strconv.ParseInt(r.PathValue("user_id"), 10, 64)
+	if err != nil || targetID <= 0 {
+		writeError(w, http.StatusBadRequest, "invalid user_id")
+		return
+	}
+
+	requesterRole, err := h.store.MemberRole(r.Context(), convID, userID)
+	if err != nil {
+		writeError(w, http.StatusForbidden, "not a member")
+		return
+	}
+	targetRole, err := h.store.MemberRole(r.Context(), convID, targetID)
+	if err != nil {
+		writeError(w, http.StatusNotFound, "member not found")
+		return
+	}
+	if targetRole == "owner" {
+		writeError(w, http.StatusBadRequest, "cannot remove the owner")
+		return
+	}
+	if userID != targetID && requesterRole != "owner" {
+		writeError(w, http.StatusForbidden, "only the owner can remove others")
+		return
+	}
+
+	if err := h.store.RemoveMember(r.Context(), convID, targetID); err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	h.hub.Unsubscribe(targetID, convID)
+	h.hub.SendToUser(targetID, realtime.EventConversationRemoved, realtime.ConversationChanged{ConversationID: convID})
+	h.hub.PublishMemberChanged(convID, targetID, false)
+	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
 }
 
 func (h *apiHandler) listMessages(w http.ResponseWriter, r *http.Request) {
@@ -115,15 +302,46 @@ func (h *apiHandler) listMessages(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	out := make([]messageJSON, 0, len(messages))
+	msgIDs := make([]int64, 0, len(messages))
+	mediaIDs := make(map[int64]struct{})
 	for i := range messages {
 		out = append(out, toMessageJSON(&messages[i]))
+		msgIDs = append(msgIDs, messages[i].ID)
+		if messages[i].MediaID != nil {
+			mediaIDs[*messages[i].MediaID] = struct{}{}
+		}
+	}
+	reactions, err := h.store.ReactionsForMessages(r.Context(), msgIDs)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	attachReactions(out, reactions)
+
+	mediaByID := make(map[int64]mediaJSON)
+	for id := range mediaIDs {
+		m, err := h.store.GetMediaByID(r.Context(), id)
+		if err == nil {
+			mediaByID[id] = toMediaJSON(m)
+		}
+	}
+	for i := range out {
+		for j := range messages {
+			if messages[j].ID == out[i].ID && messages[j].MediaID != nil {
+				if md, ok := mediaByID[*messages[j].MediaID]; ok {
+					out[i].Media = &md
+				}
+				break
+			}
+		}
 	}
 	writeJSON(w, http.StatusOK, out)
 }
 
 type sendMessageRequest struct {
-	Body   string `json:"body"`
-	TempID string `json:"temp_id"`
+	Body    string `json:"body"`
+	TempID  string `json:"temp_id"`
+	MediaID *int64 `json:"media_id,omitempty"`
 }
 
 func (h *apiHandler) sendMessage(w http.ResponseWriter, r *http.Request) {
@@ -144,8 +362,8 @@ func (h *apiHandler) sendMessage(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "invalid json")
 		return
 	}
-	if req.Body == "" {
-		writeError(w, http.StatusBadRequest, "body is required")
+	if req.Body == "" && req.MediaID == nil {
+		writeError(w, http.StatusBadRequest, "body or media_id is required")
 		return
 	}
 	if len(req.Body) > 4000 {
@@ -153,20 +371,50 @@ func (h *apiHandler) sendMessage(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	msg, err := h.store.InsertMessage(r.Context(), convID, userID, req.Body)
+	var attached *store.Media
+	if req.MediaID != nil {
+		attached, err = h.store.GetMediaByID(r.Context(), *req.MediaID)
+		if err != nil || attached.UploaderID != userID {
+			writeError(w, http.StatusBadRequest, "invalid media_id")
+			return
+		}
+	}
+
+	msg, err := h.store.InsertMessage(r.Context(), convID, userID, req.Body, req.MediaID)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "internal server error")
 		return
 	}
 
-	h.hub.PublishMessageCreated(convID, realtime.MessageCreated{
+	wsEvent := realtime.MessageCreated{
 		TempID:         req.TempID,
 		ConversationID: convID,
 		MessageID:      msg.ID,
 		SenderID:       userID,
 		Body:           msg.Body,
 		CreatedAt:      msg.CreatedAt,
-	})
+	}
+	if attached != nil {
+		wsEvent.MediaID = &attached.ID
+		info := toRealtimeMedia(attached)
+		wsEvent.Media = &info
+	}
+	h.hub.PublishMessageCreated(convID, wsEvent)
 
-	writeJSON(w, http.StatusCreated, toMessageJSON(msg))
+	out := toMessageJSON(msg)
+	if attached != nil {
+		md := toMediaJSON(attached)
+		out.Media = &md
+	}
+	writeJSON(w, http.StatusCreated, out)
+}
+
+func toRealtimeMedia(m *store.Media) realtime.MediaInfo {
+	return realtime.MediaInfo{
+		ID:          m.ID,
+		Filename:    m.Filename,
+		ContentType: m.ContentType,
+		Size:        m.Size,
+		URL:         "/api/v1/media/" + strconv.FormatInt(m.ID, 10),
+	}
 }

server/internal/api/media.go

@@ -0,0 +1,172 @@
+package api
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"mime"
+	"net/http"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"messenger/internal/media"
+	"messenger/internal/store"
+)
+
+const maxUploadBytes = 25 << 20 // 25 MiB
+
+type mediaJSON struct {
+	ID          int64  `json:"id"`
+	Filename    string `json:"filename"`
+	ContentType string `json:"content_type"`
+	Size        int64  `json:"size"`
+	URL         string `json:"url"`
+	ThumbURL    string `json:"thumb_url,omitempty"`
+}
+
+func toMediaJSON(m *store.Media) mediaJSON {
+	out := mediaJSON{
+		ID:          m.ID,
+		Filename:    m.Filename,
+		ContentType: m.ContentType,
+		Size:        m.Size,
+		URL:         fmt.Sprintf("/api/v1/media/%d", m.ID),
+	}
+	if m.ThumbKey != "" {
+		out.ThumbURL = fmt.Sprintf("/api/v1/media/%d/thumb", m.ID)
+	}
+	return out
+}
+
+// uploadMedia accepts a multipart file and stores it, generating a thumbnail
+// for images. Media is accessible to any authenticated user; conversation
+// membership checks are a documented family-scale simplification.
+func (h *apiHandler) uploadMedia(w http.ResponseWriter, r *http.Request) {
+	userID, _ := userIDFrom(r.Context())
+	r.Body = http.MaxBytesReader(w, r.Body, maxUploadBytes+1<<20)
+
+	file, header, err := r.FormFile("file")
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "missing file field")
+		return
+	}
+	defer file.Close()
+
+	data, err := io.ReadAll(file)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "failed to read file")
+		return
+	}
+	if len(data) == 0 {
+		writeError(w, http.StatusBadRequest, "empty file")
+		return
+	}
+	if len(data) > maxUploadBytes {
+		writeError(w, http.StatusBadRequest, "file too large (max 25 MiB)")
+		return
+	}
+
+	contentType := header.Header.Get("Content-Type")
+	if contentType == "" || strings.HasPrefix(contentType, "application/octet-stream") {
+		contentType = http.DetectContentType(data)
+	}
+
+	id := randomHex(16)
+	ext := filepath.Ext(header.Filename)
+	storageKey := fmt.Sprintf("u%d/%s%s", userID, id, ext)
+	if err := h.media.Save(r.Context(), storageKey, bytes.NewReader(data)); err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to store file")
+		return
+	}
+
+	thumbKey := ""
+	if media.IsImage(contentType) {
+		thumb, err := media.Generate(r.Context(), bytes.NewReader(data), contentType, 512)
+		if err != nil {
+			writeError(w, http.StatusInternalServerError, "failed to generate thumbnail")
+			return
+		}
+		if thumb != nil {
+			thumbKey = fmt.Sprintf("u%d/%s_thumb.jpg", userID, id)
+			if err := h.media.Save(r.Context(), thumbKey, bytes.NewReader(thumb)); err != nil {
+				writeError(w, http.StatusInternalServerError, "failed to store thumbnail")
+				return
+			}
+		}
+	}
+
+	created, err := h.store.CreateMedia(r.Context(), store.Media{
+		UploaderID:  userID,
+		Filename:    header.Filename,
+		ContentType: contentType,
+		Size:        int64(len(data)),
+		StorageKey:  storageKey,
+		ThumbKey:    thumbKey,
+	})
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	writeJSON(w, http.StatusCreated, toMediaJSON(created))
+}
+
+func (h *apiHandler) downloadMedia(w http.ResponseWriter, r *http.Request) {
+	h.serveStoredFile(w, r, func(m *store.Media) (string, string, int64) {
+		return m.StorageKey, m.ContentType, m.Size
+	})
+}
+
+func (h *apiHandler) downloadThumb(w http.ResponseWriter, r *http.Request) {
+	h.serveStoredFile(w, r, func(m *store.Media) (string, string, int64) {
+		if m.ThumbKey == "" {
+			return "", "", 0
+		}
+		return m.ThumbKey, "image/jpeg", 0
+	})
+}
+
+func (h *apiHandler) serveStoredFile(w http.ResponseWriter, r *http.Request, pick func(*store.Media) (key, contentType string, size int64)) {
+	id, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
+	if err != nil || id <= 0 {
+		writeError(w, http.StatusBadRequest, "invalid media id")
+		return
+	}
+	m, err := h.store.GetMediaByID(r.Context(), id)
+	if err != nil {
+		writeError(w, http.StatusNotFound, "media not found")
+		return
+	}
+	key, contentType, size := pick(m)
+	if key == "" {
+		writeError(w, http.StatusNotFound, "thumbnail not available")
+		return
+	}
+	rc, err := h.media.Open(r.Context(), key)
+	if err != nil {
+		writeError(w, http.StatusNotFound, "file not found")
+		return
+	}
+	defer rc.Close()
+
+	w.Header().Set("Content-Type", contentType)
+	w.Header().Set("Cache-Control", "private, max-age=31536000, immutable")
+	if ext := filepath.Ext(m.Filename); ext != "" {
+		if cd := mime.TypeByExtension(ext); cd == "" {
+			w.Header().Set("Content-Disposition", fmt.Sprintf("inline; filename=%q", m.Filename))
+		}
+	}
+	if size > 0 {
+		w.Header().Set("Content-Length", strconv.FormatInt(size, 10))
+	}
+	w.WriteHeader(http.StatusOK)
+	_, _ = io.Copy(w, rc)
+}
+
+func randomHex(n int) string {
+	buf := make([]byte, n)
+	_, _ = rand.Read(buf)
+	return hex.EncodeToString(buf)
+}

server/internal/api/reactions.go

@@ -0,0 +1,93 @@
+package api
+
+import (
+	"encoding/json"
+	"net/http"
+	"strconv"
+)
+
+func (h *apiHandler) addReaction(w http.ResponseWriter, r *http.Request) {
+	userID, _ := userIDFrom(r.Context())
+	convID, msgID, ok := h.parseMessagePath(w, r)
+	if !ok {
+		return
+	}
+	var req struct {
+		Emoji string `json:"emoji"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid json")
+		return
+	}
+	if len(req.Emoji) == 0 || len(req.Emoji) > 32 {
+		writeError(w, http.StatusBadRequest, "emoji must be 1-32 chars")
+		return
+	}
+
+	if err := h.store.AddReaction(r.Context(), msgID, userID, req.Emoji); err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	h.hub.PublishReactionChanged(convID, msgID, userID, req.Emoji, true)
+	h.writeMessageWithReactions(w, r, convID, msgID)
+}
+
+func (h *apiHandler) removeReaction(w http.ResponseWriter, r *http.Request) {
+	userID, _ := userIDFrom(r.Context())
+	convID, msgID, ok := h.parseMessagePath(w, r)
+	if !ok {
+		return
+	}
+	emoji := r.PathValue("emoji")
+	if emoji == "" {
+		writeError(w, http.StatusBadRequest, "emoji is required")
+		return
+	}
+
+	if err := h.store.RemoveReaction(r.Context(), msgID, userID, emoji); err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	h.hub.PublishReactionChanged(convID, msgID, userID, emoji, false)
+	h.writeMessageWithReactions(w, r, convID, msgID)
+}
+
+func (h *apiHandler) parseMessagePath(w http.ResponseWriter, r *http.Request) (convID, msgID int64, ok bool) {
+	userID, _ := userIDFrom(r.Context())
+	convID, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
+	if err != nil || convID <= 0 {
+		writeError(w, http.StatusBadRequest, "invalid conversation id")
+		return 0, 0, false
+	}
+	msgID, err = strconv.ParseInt(r.PathValue("msg_id"), 10, 64)
+	if err != nil || msgID <= 0 {
+		writeError(w, http.StatusBadRequest, "invalid message id")
+		return 0, 0, false
+	}
+	if member, err := h.store.IsMember(r.Context(), convID, userID); err != nil || !member {
+		writeError(w, http.StatusForbidden, "not a member")
+		return 0, 0, false
+	}
+	belongs, err := h.store.MessageBelongsToConversation(r.Context(), convID, msgID)
+	if err != nil || !belongs {
+		writeError(w, http.StatusNotFound, "message not found")
+		return 0, 0, false
+	}
+	return convID, msgID, true
+}
+
+func (h *apiHandler) writeMessageWithReactions(w http.ResponseWriter, r *http.Request, convID, msgID int64) {
+	msg, err := h.store.GetMessageByID(r.Context(), msgID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	msgs := []messageJSON{toMessageJSON(msg)}
+	reactions, err := h.store.ReactionsForMessages(r.Context(), []int64{msgID})
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "internal server error")
+		return
+	}
+	attachReactions(msgs, reactions)
+	writeJSON(w, http.StatusOK, msgs[0])
+}

server/internal/media/local.go

@@ -0,0 +1,95 @@
+package media
+
+import (
+	"context"
+	"errors"
+	"io"
+	"os"
+	"path/filepath"
+)
+
+// Local stores objects as files under a base directory.
+type Local struct {
+	dir string
+}
+
+// NewLocal creates a Local store rooted at dir, creating it if needed.
+func NewLocal(dir string) (*Local, error) {
+	if err := os.MkdirAll(dir, 0o750); err != nil {
+		return nil, err
+	}
+	return &Local{dir: dir}, nil
+}
+
+func (l *Local) resolve(key string) (string, error) {
+	clean := filepath.Clean(filepath.Join(l.dir, key))
+	if !hasPrefix(clean, l.dir) {
+		return "", errors.New("media: invalid storage key")
+	}
+	return clean, nil
+}
+
+// Save writes the stream to disk atomically under the base directory.
+func (l *Local) Save(_ context.Context, key string, r io.Reader) error {
+	path, err := l.resolve(key)
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(path), 0o750); err != nil {
+		return err
+	}
+	tmp, err := os.CreateTemp(filepath.Dir(path), ".upload-*")
+	if err != nil {
+		return err
+	}
+	defer os.Remove(tmp.Name())
+
+	if _, err := io.Copy(tmp, r); err != nil {
+		tmp.Close()
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		return err
+	}
+	return os.Rename(tmp.Name(), path)
+}
+
+// Open returns a reader for the object or ErrNotFound.
+func (l *Local) Open(_ context.Context, key string) (io.ReadCloser, error) {
+	path, err := l.resolve(key)
+	if err != nil {
+		return nil, err
+	}
+	f, err := os.Open(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, ErrNotFound
+		}
+		return nil, err
+	}
+	return f, nil
+}
+
+// Delete removes the object; missing objects are not an error.
+func (l *Local) Delete(_ context.Context, key string) error {
+	path, err := l.resolve(key)
+	if err != nil {
+		return err
+	}
+	if err := os.Remove(path); err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	return nil
+}
+
+func hasPrefix(p, dir string) bool {
+	rel, err := filepath.Rel(dir, p)
+	if err != nil {
+		return false
+	}
+	return rel != ".." && !startsWithDotDot(rel)
+}
+
+func startsWithDotDot(rel string) bool {
+	return len(rel) >= 3 && rel[0] == '.' && rel[1] == '.' && (rel[2] == '/' || rel[2] == '\\')
+}

server/internal/media/storage.go

@@ -0,0 +1,19 @@
+// Package media provides file storage and image thumbnail generation
+// for attachments shared in conversations.
+package media
+
+import (
+	"context"
+	"errors"
+	"io"
+)
+
+// ErrNotFound is returned when a stored object does not exist.
+var ErrNotFound = errors.New("media: not found")
+
+// Storage is an S3-like object store for attachment bytes.
+type Storage interface {
+	Save(ctx context.Context, key string, r io.Reader) error
+	Open(ctx context.Context, key string) (io.ReadCloser, error)
+	Delete(ctx context.Context, key string) error
+}

server/internal/media/storage_test.go

@@ -0,0 +1,73 @@
+package media
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestLocalSaveOpenDelete(t *testing.T) {
+	ctx := context.Background()
+	store, err := NewLocal(t.TempDir())
+	if err != nil {
+		t.Fatalf("NewLocal: %v", err)
+	}
+
+	payload := []byte("hello attachment")
+	if err := store.Save(ctx, "a/b/file.txt", bytes.NewReader(payload)); err != nil {
+		t.Fatalf("Save: %v", err)
+	}
+
+	rc, err := store.Open(ctx, "a/b/file.txt")
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	got, err := io.ReadAll(rc)
+	rc.Close()
+	if err != nil {
+		t.Fatalf("ReadAll: %v", err)
+	}
+	if !bytes.Equal(got, payload) {
+		t.Fatalf("content = %q, want %q", got, payload)
+	}
+
+	if err := store.Delete(ctx, "a/b/file.txt"); err != nil {
+		t.Fatalf("Delete: %v", err)
+	}
+	if err := store.Delete(ctx, "a/b/file.txt"); err != nil {
+		t.Fatalf("Delete idempotent: %v", err)
+	}
+	if _, err := store.Open(ctx, "a/b/file.txt"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("Open after delete = %v, want ErrNotFound", err)
+	}
+}
+
+func TestLocalPathTraversalRejected(t *testing.T) {
+	store, err := NewLocal(t.TempDir())
+	if err != nil {
+		t.Fatalf("NewLocal: %v", err)
+	}
+	err = store.Save(context.Background(), "../../etc/evil", strings.NewReader("x"))
+	if err == nil {
+		t.Fatal("Save with traversal key = nil, want error")
+	}
+}
+
+func TestIsImage(t *testing.T) {
+	cases := map[string]bool{
+		"image/png":       true,
+		"image/jpeg":      true,
+		"image/gif":       true,
+		"image/webp":      true,
+		"application/pdf": false,
+		"text/plain":      false,
+	}
+	for ct, want := range cases {
+		if got := IsImage(ct); got != want {
+			t.Errorf("IsImage(%q) = %v, want %v", ct, got, want)
+		}
+	}
+}

server/internal/media/thumbnail.go

@@ -0,0 +1,82 @@
+package media
+
+import (
+	"bytes"
+	"context"
+	"image"
+	_ "image/gif"
+	"image/jpeg"
+	_ "image/png"
+
+	"golang.org/x/image/draw"
+	"golang.org/x/image/webp"
+)
+
+const maxUploadSize = 25 << 20 // 25 MiB
+
+// IsImage reports whether the content type is a decodable image format.
+func IsImage(contentType string) bool {
+	switch contentType {
+	case "image/jpeg", "image/png", "image/gif", "image/webp":
+		return true
+	default:
+		return false
+	}
+}
+
+// Generate returns a JPEG thumbnail of at most maxDim on its larger side.
+// It returns nil for non-images or when the source is already small enough.
+func Generate(ctx context.Context, r *bytes.Reader, contentType string, maxDim int) ([]byte, error) {
+	if !IsImage(contentType) {
+		return nil, nil
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
+	src, err := decodeImage(r, contentType)
+	if err != nil {
+		return nil, err
+	}
+	bounds := src.Bounds()
+	w, h := bounds.Dx(), bounds.Dy()
+	if w <= maxDim && h <= maxDim {
+		return nil, nil
+	}
+
+	scale := float64(maxDim) / float64(max(w, h))
+	nw, nh := int(float64(w)*scale), int(float64(h)*scale)
+	if nw < 1 {
+		nw = 1
+	}
+	if nh < 1 {
+		nh = 1
+	}
+
+	dst := image.NewRGBA(image.Rect(0, 0, nw, nh))
+	draw.BiLinear.Scale(dst, dst.Bounds(), src, bounds, draw.Over, nil)
+
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	var buf bytes.Buffer
+	if err := jpeg.Encode(&buf, dst, &jpeg.Options{Quality: 80}); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+func decodeImage(r *bytes.Reader, contentType string) (image.Image, error) {
+	if contentType == "image/webp" {
+		return webp.Decode(r)
+	}
+	img, _, err := image.Decode(r)
+	return img, err
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}

server/internal/media/thumbnail_test.go

@@ -0,0 +1,73 @@
+package media
+
+import (
+	"bytes"
+	"context"
+	"image"
+	"image/color"
+	"image/jpeg"
+	"image/png"
+	"testing"
+)
+
+func testPNG(t *testing.T, w, h int) []byte {
+	t.Helper()
+	img := image.NewRGBA(image.Rect(0, 0, w, h))
+	for x := 0; x < w; x++ {
+		for y := 0; y < h; y++ {
+			img.Set(x, y, color.RGBA{R: uint8(x % 256), G: uint8(y % 256), B: 120, A: 255})
+		}
+	}
+	var buf bytes.Buffer
+	if err := png.Encode(&buf, img); err != nil {
+		t.Fatalf("png.Encode: %v", err)
+	}
+	return buf.Bytes()
+}
+
+func TestGenerateSkipsSmallImage(t *testing.T) {
+	data := testPNG(t, 64, 64)
+	out, err := Generate(context.Background(), bytes.NewReader(data), "image/png", 256)
+	if err != nil {
+		t.Fatalf("Generate: %v", err)
+	}
+	if out != nil {
+		t.Fatalf("small image produced thumbnail, want nil")
+	}
+}
+
+func TestGenerateResizesLargeImage(t *testing.T) {
+	data := testPNG(t, 512, 512)
+	out, err := Generate(context.Background(), bytes.NewReader(data), "image/png", 256)
+	if err != nil {
+		t.Fatalf("Generate: %v", err)
+	}
+	if out == nil {
+		t.Fatal("large image produced nil thumbnail")
+	}
+	img, err := jpeg.Decode(bytes.NewReader(out))
+	if err != nil {
+		t.Fatalf("thumbnail is not valid JPEG: %v", err)
+	}
+	b := img.Bounds()
+	if b.Dx() > 256 || b.Dy() > 256 {
+		t.Fatalf("thumbnail size = %dx%d, want <= 256x256", b.Dx(), b.Dy())
+	}
+}
+
+func TestGenerateNonImageReturnsNil(t *testing.T) {
+	out, err := Generate(context.Background(), bytes.NewReader([]byte("plain")), "text/plain", 256)
+	if err != nil {
+		t.Fatalf("Generate: %v", err)
+	}
+	if out != nil {
+		t.Fatal("non-image produced thumbnail, want nil")
+	}
+}
+
+func TestGenerateCorruptImageFails(t *testing.T) {
+	_, err := Generate(context.Background(), bytes.NewReader([]byte("not an image")), "image/png", 256)
+	if err == nil {
+		t.Fatal("corrupt image: Generate = nil error, want error")
+	}
+}

server/internal/platform/config/config.go

@@ -24,6 +24,8 @@ type Config struct {
 	DatabaseURL string
 	// JWTSecret signs access tokens. Must be set in production.
 	JWTSecret string
+	// MediaDir is the local disk location for uploaded attachments.
+	MediaDir string
 }
 
 // Load reads configuration from the environment, falling back to
@@ -35,6 +37,7 @@ func Load() (*Config, error) {
 		Environment: fromEnv("MESSENGER_ENV", "development"),
 		DatabaseURL: fromEnv("MESSENGER_DATABASE_URL", "postgres://messenger:messenger@localhost:5432/messenger?sslmode=disable"),
 		JWTSecret:   fromEnv("MESSENGER_JWT_SECRET", "dev-secret-change-me"),
+		MediaDir:    fromEnv("MESSENGER_MEDIA_DIR", "./media"),
 	}
 
 	for _, origin := range strings.Split(fromEnv("MESSENGER_ALLOWED_ORIGINS", ""), ",") {

server/internal/realtime/events.go

@@ -9,10 +9,16 @@ import (
 
 // Event type constants sent over the wire.
 const (
-	EventMessageCreated = "message.created"
-	EventTyping         = "typing"
-	EventPresence       = "presence"
-	EventRead           = "read"
+	EventMessageCreated      = "message.created"
+	EventTyping              = "typing"
+	EventPresence            = "presence"
+	EventRead                = "read"
+	EventConversationAdded   = "conversation.added"
+	EventConversationRemoved = "conversation.removed"
+	EventMemberAdded         = "member.added"
+	EventMemberRemoved       = "member.removed"
+	EventReactionAdded       = "reaction.added"
+	EventReactionRemoved     = "reaction.removed"
 )
 
 // Presence status values.
@@ -23,12 +29,24 @@ const (
 
 // MessageCreated is published when a message is stored.
 type MessageCreated struct {
-	TempID         string    `json:"temp_id,omitempty"`
-	ConversationID int64     `json:"conversation_id"`
-	MessageID      int64     `json:"message_id"`
-	SenderID       int64     `json:"sender_id"`
-	Body           string    `json:"body"`
-	CreatedAt      time.Time `json:"created_at"`
+	TempID         string     `json:"temp_id,omitempty"`
+	ConversationID int64      `json:"conversation_id"`
+	MessageID      int64      `json:"message_id"`
+	SenderID       int64      `json:"sender_id"`
+	Body           string     `json:"body"`
+	MediaID        *int64     `json:"media_id,omitempty"`
+	Media          *MediaInfo `json:"media,omitempty"`
+	CreatedAt      time.Time  `json:"created_at"`
+}
+
+// MediaInfo mirrors attachment metadata delivered with a message event.
+type MediaInfo struct {
+	ID          int64  `json:"id"`
+	Filename    string `json:"filename"`
+	ContentType string `json:"content_type"`
+	Size        int64  `json:"size"`
+	URL         string `json:"url"`
+	ThumbURL    string `json:"thumb_url,omitempty"`
 }
 
 // Typing is published when a user starts or stops typing in a conversation.
@@ -51,6 +69,25 @@ type Read struct {
 	MessageID      int64 `json:"message_id"`
 }
 
+// ConversationChanged is sent to a user when they gain or lose a conversation.
+type ConversationChanged struct {
+	ConversationID int64 `json:"conversation_id"`
+}
+
+// MemberChanged is published when a user joins or leaves a conversation.
+type MemberChanged struct {
+	ConversationID int64 `json:"conversation_id"`
+	UserID         int64 `json:"user_id"`
+}
+
+// ReactionChanged is published when a reaction is added to or removed from a message.
+type ReactionChanged struct {
+	ConversationID int64  `json:"conversation_id"`
+	MessageID      int64  `json:"message_id"`
+	UserID         int64  `json:"user_id"`
+	Emoji          string `json:"emoji"`
+}
+
 // envelope is the wire format for every message, both inbound and outbound.
 type envelope struct {
 	Type string          `json:"type"`

server/internal/realtime/hub.go

@@ -84,6 +84,67 @@ func (h *Hub) PublishRead(conversationID, userID, messageID int64) {
 	h.sendToConversation(conversationID, envelope{Type: EventRead, Data: mustMarshal(evt)}, userID)
 }
 
+// Subscribe adds a user to a conversation's subscriber set so they receive its
+// events without reconnecting (used when a member is added to a group).
+func (h *Hub) Subscribe(userID, conversationID int64) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	if h.subs[conversationID] == nil {
+		h.subs[conversationID] = make(map[int64]struct{})
+	}
+	h.subs[conversationID][userID] = struct{}{}
+}
+
+// Unsubscribe removes a user from a conversation's subscriber set.
+func (h *Hub) Unsubscribe(userID, conversationID int64) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	users := h.subs[conversationID]
+	delete(users, userID)
+	if len(users) == 0 {
+		delete(h.subs, conversationID)
+	}
+}
+
+// SendToUser delivers an event to every connection of a single user.
+func (h *Hub) SendToUser(userID int64, evtType string, data any) {
+	payload, err := json.Marshal(envelope{Type: evtType, Data: mustMarshal(data)})
+	if err != nil {
+		slog.Error("ws: marshal direct event", "error", err)
+		return
+	}
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	for c := range h.conns[userID] {
+		c.enqueueRaw(payload)
+	}
+}
+
+// PublishMemberChanged tells a conversation's members that someone joined or left.
+func (h *Hub) PublishMemberChanged(conversationID, userID int64, added bool) {
+	evtType := EventMemberAdded
+	if !added {
+		evtType = EventMemberRemoved
+	}
+	evt := MemberChanged{ConversationID: conversationID, UserID: userID}
+	h.sendToConversation(conversationID, envelope{Type: evtType, Data: mustMarshal(evt)}, 0)
+}
+
+// PublishReactionChanged tells a conversation's members that a reaction changed.
+func (h *Hub) PublishReactionChanged(conversationID, messageID, userID int64, emoji string, added bool) {
+	evtType := EventReactionAdded
+	if !added {
+		evtType = EventReactionRemoved
+	}
+	evt := ReactionChanged{
+		ConversationID: conversationID,
+		MessageID:      messageID,
+		UserID:         userID,
+		Emoji:          emoji,
+	}
+	h.sendToConversation(conversationID, envelope{Type: evtType, Data: mustMarshal(evt)}, 0)
+}
+
 func (h *Hub) register(c *client, conversationIDs []int64) {
 	h.mu.Lock()
 	defer h.mu.Unlock()

server/internal/server/server.go

@@ -10,13 +10,14 @@ import (
 
 	"messenger/internal/api"
 	"messenger/internal/auth"
+	"messenger/internal/media"
 	"messenger/internal/platform/config"
 	"messenger/internal/realtime"
 	"messenger/internal/store"
 )
 
 // New builds an *http.Server with all routes and middleware applied.
-func New(cfg *config.Config, log *slog.Logger, st *store.Store, tm *auth.TokenManager, hub *realtime.Hub) *http.Server {
+func New(cfg *config.Config, log *slog.Logger, st *store.Store, tm *auth.TokenManager, hub *realtime.Hub, ms media.Storage) *http.Server {
 	mux := http.NewServeMux()
 
 	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
@@ -32,7 +33,7 @@ func New(cfg *config.Config, log *slog.Logger, st *store.Store, tm *auth.TokenMa
 		static = spaHandler{staticDir: cfg.StaticDir, log: log}
 	}
 
-	mux.Handle("/", api.NewHandler(st, tm, hub, log, cfg, static))
+	mux.Handle("/", api.NewHandler(st, tm, hub, log, cfg, ms, static))
 
 	handler := logRequests(log, recoverPanics(cors(cfg.AllowedOrigins, mux)))
 

server/internal/store/conversations.go

@@ -14,13 +14,13 @@ func (s *Store) CreateDM(ctx context.Context, userA, userB int64) (*Conversation
 	// Check existing DM
 	var conv Conversation
 	err := s.pool.QueryRow(ctx, `
-       SELECT c.id, c.type, c.created_at
+       SELECT c.id, c.type, c.name, c.avatar, c.created_at
        FROM conversations c
        JOIN conversation_members m1 ON m1.conversation_id=c.id AND m1.user_id=$1
        JOIN conversation_members m2 ON m2.conversation_id=c.id AND m2.user_id=$2
        WHERE c.type='dm'
        LIMIT 1
-   `, userA, userB).Scan(&conv.ID, &conv.Type, &conv.CreatedAt)
+   `, userA, userB).Scan(&conv.ID, &conv.Type, &conv.Name, &conv.Avatar, &conv.CreatedAt)
 	if err == nil {
 		return &conv, nil
 	}
@@ -42,8 +42,8 @@ func (s *Store) CreateDM(ctx context.Context, userA, userB int64) (*Conversation
 
 	err = tx.QueryRow(ctx, `
        INSERT INTO conversations(type) VALUES('dm')
-       RETURNING id, type, created_at
-   `).Scan(&conv.ID, &conv.Type, &conv.CreatedAt)
+       RETURNING id, type, name, avatar, created_at
+   `).Scan(&conv.ID, &conv.Type, &conv.Name, &conv.Avatar, &conv.CreatedAt)
 	if err != nil {
 		return nil, err
 	}
@@ -68,8 +68,8 @@ func (s *Store) CreateDM(ctx context.Context, userA, userB int64) (*Conversation
 func (s *Store) GetConversationByID(ctx context.Context, id int64) (*Conversation, error) {
 	var conv Conversation
 	err := s.pool.QueryRow(ctx, `
-       SELECT id, type, created_at FROM conversations WHERE id=$1
-   `, id).Scan(&conv.ID, &conv.Type, &conv.CreatedAt)
+       SELECT id, type, name, avatar, created_at FROM conversations WHERE id=$1
+   `, id).Scan(&conv.ID, &conv.Type, &conv.Name, &conv.Avatar, &conv.CreatedAt)
 	if err != nil {
 		if errors.Is(err, pgx.ErrNoRows) {
 			return nil, ErrNotFound
@@ -118,7 +118,7 @@ func (s *Store) ConversationIDsForUser(ctx context.Context, userID int64) ([]int
 // ListConversationsForUser returns summaries of conversations for a user.
 func (s *Store) ListConversationsForUser(ctx context.Context, userID int64) ([]ConversationSummary, error) {
 	rows, err := s.pool.Query(ctx, `
-       SELECT c.id, c.type, c.created_at,
+       SELECT c.id, c.type, c.name, c.avatar, c.created_at,
            m.id, m.conversation_id, m.sender_id, m.body, m.created_at, m.edited_at, m.deleted_at,
            uc.unread_count
        FROM conversation_members cm
@@ -156,7 +156,7 @@ func (s *Store) ListConversationsForUser(ctx context.Context, userID int64) ([]C
 			msgDeleted *time.Time
 		)
 		if err := rows.Scan(
-			&cs.ID, &cs.Type, &cs.CreatedAt,
+			&cs.ID, &cs.Type, &cs.Name, &cs.Avatar, &cs.CreatedAt,
 			&msgID, &msgConvID, &msgSender, &msgBody, &msgCreated, &msgEdited, &msgDeleted,
 			&cs.UnreadCount,
 		); err != nil {

server/internal/store/groups.go

@@ -0,0 +1,121 @@
+package store
+
+import (
+	"context"
+	"errors"
+
+	"github.com/jackc/pgx/v5"
+)
+
+// CreateGroup creates a group conversation with the creator as owner and
+// the given members added, returning the created conversation.
+func (s *Store) CreateGroup(ctx context.Context, creatorID int64, name string, memberIDs []int64) (*Conversation, error) {
+	conn, err := s.pool.Acquire(ctx)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Release()
+
+	tx, err := conn.Begin(ctx)
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback(ctx)
+
+	var conv Conversation
+	err = tx.QueryRow(ctx, `
+       INSERT INTO conversations(type, name) VALUES('group', $1)
+       RETURNING id, type, name, avatar, created_at
+   `, name).Scan(&conv.ID, &conv.Type, &conv.Name, &conv.Avatar, &conv.CreatedAt)
+	if err != nil {
+		return nil, err
+	}
+
+	if _, err := tx.Exec(ctx, `
+       INSERT INTO conversation_members(conversation_id, user_id, role)
+       VALUES($1, $2, 'owner')
+   `, conv.ID, creatorID); err != nil {
+		return nil, err
+	}
+
+	seen := map[int64]struct{}{creatorID: {}}
+	for _, uid := range memberIDs {
+		if _, ok := seen[uid]; ok {
+			continue
+		}
+		seen[uid] = struct{}{}
+		if _, err := tx.Exec(ctx, `
+           INSERT INTO conversation_members(conversation_id, user_id, role)
+           VALUES($1, $2, 'member')
+           ON CONFLICT (conversation_id, user_id) DO NOTHING
+       `, conv.ID, uid); err != nil {
+			return nil, err
+		}
+	}
+
+	if err := tx.Commit(ctx); err != nil {
+		return nil, err
+	}
+	return &conv, nil
+}
+
+// AddMember adds a user to a conversation; it is a no-op if already a member.
+func (s *Store) AddMember(ctx context.Context, conversationID, userID int64) error {
+	_, err := s.pool.Exec(ctx, `
+       INSERT INTO conversation_members(conversation_id, user_id, role)
+       VALUES($1, $2, 'member')
+       ON CONFLICT (conversation_id, user_id) DO NOTHING
+   `, conversationID, userID)
+	return err
+}
+
+// RemoveMember removes a user from a conversation; it is a no-op if absent.
+func (s *Store) RemoveMember(ctx context.Context, conversationID, userID int64) error {
+	_, err := s.pool.Exec(ctx, `
+       DELETE FROM conversation_members WHERE conversation_id=$1 AND user_id=$2
+   `, conversationID, userID)
+	return err
+}
+
+// MemberRole returns the role of a user in a conversation, or ErrNotFound.
+func (s *Store) MemberRole(ctx context.Context, conversationID, userID int64) (string, error) {
+	var role string
+	err := s.pool.QueryRow(ctx, `
+       SELECT role FROM conversation_members WHERE conversation_id=$1 AND user_id=$2
+   `, conversationID, userID).Scan(&role)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return "", ErrNotFound
+		}
+		return "", err
+	}
+	return role, nil
+}
+
+// ListMembers returns the members of a conversation with their profiles.
+func (s *Store) ListMembers(ctx context.Context, conversationID int64) ([]MemberInfo, error) {
+	rows, err := s.pool.Query(ctx, `
+       SELECT u.id, u.username, u.display_name, u.avatar, u.created_at, cm.role, cm.joined_at
+       FROM conversation_members cm
+       JOIN users u ON u.id = cm.user_id
+       WHERE cm.conversation_id = $1
+       ORDER BY cm.joined_at, u.id
+   `, conversationID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var members []MemberInfo
+	for rows.Next() {
+		var m MemberInfo
+		if err := rows.Scan(
+			&m.User.ID, &m.User.Username, &m.User.DisplayName, &m.User.Avatar, &m.User.CreatedAt,
+			&m.Role, &m.JoinedAt,
+		); err != nil {
+			return nil, err
+		}
+		members = append(members, m)
+	}
+	return members, nil
+}

server/internal/store/integration_test.go

@@ -97,7 +97,7 @@ func TestIntegration(t *testing.T) {
 		t.Fatalf("ListConversationsForUser: %v, %v", sums, err)
 	}
 
-	msg, err := db.InsertMessage(ctx, conv.ID, u1.ID, "hello")
+	msg, err := db.InsertMessage(ctx, conv.ID, u1.ID, "hello", nil)
 	if err != nil {
 		t.Fatalf("InsertMessage: %v", err)
 	}
@@ -111,4 +111,74 @@ func TestIntegration(t *testing.T) {
 	if err := db.UpdateLastRead(ctx, conv.ID, u2.ID); err != nil {
 		t.Fatalf("UpdateLastRead: %v", err)
 	}
+
+	// Groups
+	u3, err := db.CreateUser(ctx, "user3", "User Three", "hash3")
+	if err != nil {
+		t.Fatalf("CreateUser u3: %v", err)
+	}
+	group, err := db.CreateGroup(ctx, u1.ID, "Family", []int64{u2.ID, u1.ID})
+	if err != nil {
+		t.Fatalf("CreateGroup: %v", err)
+	}
+	if group.Type != "group" || group.Name != "Family" {
+		t.Fatalf("CreateGroup result = %+v", group)
+	}
+	members, err := db.ListMembers(ctx, group.ID)
+	if err != nil {
+		t.Fatalf("ListMembers: %v", err)
+	}
+	if len(members) != 2 {
+		t.Fatalf("ListMembers len = %d, want 2", len(members))
+	}
+	role, err := db.MemberRole(ctx, group.ID, u1.ID)
+	if err != nil || role != "owner" {
+		t.Fatalf("MemberRole u1 = %q, %v; want owner", role, err)
+	}
+	if err := db.AddMember(ctx, group.ID, u3.ID); err != nil {
+		t.Fatalf("AddMember: %v", err)
+	}
+	if err := db.AddMember(ctx, group.ID, u3.ID); err != nil {
+		t.Fatalf("AddMember idempotent: %v", err)
+	}
+	members, _ = db.ListMembers(ctx, group.ID)
+	if len(members) != 3 {
+		t.Fatalf("ListMembers after add = %d, want 3", len(members))
+	}
+	if err := db.RemoveMember(ctx, group.ID, u3.ID); err != nil {
+		t.Fatalf("RemoveMember: %v", err)
+	}
+	members, _ = db.ListMembers(ctx, group.ID)
+	if len(members) != 2 {
+		t.Fatalf("ListMembers after remove = %d, want 2", len(members))
+	}
+
+	// Reactions
+	if err := db.AddReaction(ctx, msg.ID, u2.ID, "👍"); err != nil {
+		t.Fatalf("AddReaction: %v", err)
+	}
+	if err := db.AddReaction(ctx, msg.ID, u2.ID, "👍"); err != nil {
+		t.Fatalf("AddReaction idempotent: %v", err)
+	}
+	if err := db.AddReaction(ctx, msg.ID, u1.ID, "❤️"); err != nil {
+		t.Fatalf("AddReaction u1: %v", err)
+	}
+	reactions, err := db.ReactionsForMessages(ctx, []int64{msg.ID})
+	if err != nil {
+		t.Fatalf("ReactionsForMessages: %v", err)
+	}
+	if len(reactions) != 2 {
+		t.Fatalf("ReactionsForMessages len = %d, want 2", len(reactions))
+	}
+	if err := db.RemoveReaction(ctx, msg.ID, u2.ID, "👍"); err != nil {
+		t.Fatalf("RemoveReaction: %v", err)
+	}
+	reactions, _ = db.ReactionsForMessages(ctx, []int64{msg.ID})
+	if len(reactions) != 1 {
+		t.Fatalf("ReactionsForMessages after remove = %d, want 1", len(reactions))
+	}
+	belongs, err := db.MessageBelongsToConversation(ctx, conv.ID, msg.ID)
+	if err != nil || !belongs {
+		t.Fatalf("MessageBelongsToConversation = %v, %v; want true", belongs, err)
+	}
 }

server/internal/store/media.go

@@ -0,0 +1,62 @@
+package store
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"github.com/jackc/pgx/v5"
+)
+
+// Media stores metadata of an uploaded file. The file bytes live in the
+// media storage backend (see internal/media), referenced by StorageKey.
+type Media struct {
+	ID          int64
+	UploaderID  int64
+	Filename    string
+	ContentType string
+	Size        int64
+	StorageKey  string
+	ThumbKey    string
+	CreatedAt   time.Time
+}
+
+// CreateMedia inserts a media record and returns it with its ID.
+func (s *Store) CreateMedia(ctx context.Context, m Media) (*Media, error) {
+	err := s.pool.QueryRow(ctx, `
+       INSERT INTO media(uploader_id, filename, content_type, size, storage_key, thumb_key)
+       VALUES($1, $2, $3, $4, $5, $6)
+       RETURNING id, created_at
+   `, m.UploaderID, m.Filename, m.ContentType, m.Size, m.StorageKey, nullableString(m.ThumbKey)).Scan(&m.ID, &m.CreatedAt)
+	if err != nil {
+		return nil, err
+	}
+	return &m, nil
+}
+
+// GetMediaByID retrieves a media record or returns ErrNotFound.
+func (s *Store) GetMediaByID(ctx context.Context, id int64) (*Media, error) {
+	var m Media
+	var thumbKey *string
+	err := s.pool.QueryRow(ctx, `
+       SELECT id, uploader_id, filename, content_type, size, storage_key, thumb_key, created_at
+       FROM media WHERE id=$1
+   `, id).Scan(&m.ID, &m.UploaderID, &m.Filename, &m.ContentType, &m.Size, &m.StorageKey, &thumbKey, &m.CreatedAt)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, ErrNotFound
+		}
+		return nil, err
+	}
+	if thumbKey != nil {
+		m.ThumbKey = *thumbKey
+	}
+	return &m, nil
+}
+
+func nullableString(s string) *string {
+	if s == "" {
+		return nil
+	}
+	return &s
+}

server/internal/store/messages.go

@@ -8,14 +8,15 @@ import (
 )
 
 // InsertMessage creates a new message in a conversation and returns it.
-func (s *Store) InsertMessage(ctx context.Context, conversationID, senderID int64, body string) (*Message, error) {
+// mediaID, when non-nil, attaches a previously uploaded media object.
+func (s *Store) InsertMessage(ctx context.Context, conversationID, senderID int64, body string, mediaID *int64) (*Message, error) {
 	var m Message
 	err := s.pool.QueryRow(ctx, `
-       INSERT INTO messages(conversation_id, sender_id, body)
-       VALUES($1, $2, $3)
-       RETURNING id, conversation_id, sender_id, body, created_at, edited_at, deleted_at
-   `, conversationID, senderID, body).Scan(
-		&m.ID, &m.ConversationID, &m.SenderID, &m.Body,
+       INSERT INTO messages(conversation_id, sender_id, body, media_id)
+       VALUES($1, $2, $3, $4)
+       RETURNING id, conversation_id, sender_id, body, media_id, created_at, edited_at, deleted_at
+   `, conversationID, senderID, body, mediaID).Scan(
+		&m.ID, &m.ConversationID, &m.SenderID, &m.Body, &m.MediaID,
 		&m.CreatedAt, &m.EditedAt, &m.DeletedAt,
 	)
 	if err != nil {
@@ -28,10 +29,10 @@ func (s *Store) InsertMessage(ctx context.Context, conversationID, senderID int6
 func (s *Store) GetMessageByID(ctx context.Context, id int64) (*Message, error) {
 	var m Message
 	err := s.pool.QueryRow(ctx, `
-       SELECT id, conversation_id, sender_id, body, created_at, edited_at, deleted_at
+       SELECT id, conversation_id, sender_id, body, media_id, created_at, edited_at, deleted_at
        FROM messages WHERE id=$1
    `, id).Scan(
-		&m.ID, &m.ConversationID, &m.SenderID, &m.Body,
+		&m.ID, &m.ConversationID, &m.SenderID, &m.Body, &m.MediaID,
 		&m.CreatedAt, &m.EditedAt, &m.DeletedAt,
 	)
 	if err != nil {
@@ -50,14 +51,14 @@ func (s *Store) ListMessages(ctx context.Context, conversationID int64, before i
 	var err error
 	if before > 0 {
 		rows, err = s.pool.Query(ctx, `
-           SELECT id, conversation_id, sender_id, body, created_at, edited_at, deleted_at
+           SELECT id, conversation_id, sender_id, body, media_id, created_at, edited_at, deleted_at
            FROM messages
            WHERE conversation_id=$1 AND id<$2
            ORDER BY id DESC LIMIT $3
        `, conversationID, before, limit)
 	} else {
 		rows, err = s.pool.Query(ctx, `
-           SELECT id, conversation_id, sender_id, body, created_at, edited_at, deleted_at
+           SELECT id, conversation_id, sender_id, body, media_id, created_at, edited_at, deleted_at
            FROM messages
            WHERE conversation_id=$1
            ORDER BY id DESC LIMIT $2
@@ -72,7 +73,7 @@ func (s *Store) ListMessages(ctx context.Context, conversationID int64, before i
 	for rows.Next() {
 		var m Message
 		if err := rows.Scan(
-			&m.ID, &m.ConversationID, &m.SenderID, &m.Body,
+			&m.ID, &m.ConversationID, &m.SenderID, &m.Body, &m.MediaID,
 			&m.CreatedAt, &m.EditedAt, &m.DeletedAt,
 		); err != nil {
 			return nil, err

server/internal/store/migrations/0002_groups.sql

@@ -0,0 +1,5 @@
+-- 0002_groups.sql
+ALTER TABLE conversations ADD COLUMN IF NOT EXISTS name TEXT NOT NULL DEFAULT '';
+ALTER TABLE conversations ADD COLUMN IF NOT EXISTS avatar TEXT NOT NULL DEFAULT '';
+ALTER TABLE conversation_members ADD COLUMN IF NOT EXISTS role TEXT NOT NULL DEFAULT 'member';
+CREATE INDEX IF NOT EXISTS idx_members_conversation ON conversation_members(conversation_id);

server/internal/store/migrations/0003_reactions.sql

@@ -0,0 +1,9 @@
+-- 0003_reactions.sql
+CREATE TABLE IF NOT EXISTS message_reactions (
+    message_id BIGINT NOT NULL REFERENCES messages(id) ON DELETE CASCADE,
+    user_id    BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    emoji      TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    PRIMARY KEY (message_id, user_id, emoji)
+);
+CREATE INDEX IF NOT EXISTS idx_reactions_message ON message_reactions(message_id);

server/internal/store/migrations/0004_media.sql

@@ -0,0 +1,14 @@
+-- 0004_media.sql
+CREATE TABLE IF NOT EXISTS media (
+    id           BIGSERIAL PRIMARY KEY,
+    uploader_id  BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    filename     TEXT NOT NULL,
+    content_type TEXT NOT NULL,
+    size         BIGINT NOT NULL,
+    storage_key  TEXT NOT NULL UNIQUE,
+    thumb_key    TEXT,
+    created_at   TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+CREATE INDEX IF NOT EXISTS idx_media_uploader ON media(uploader_id);
+
+ALTER TABLE messages ADD COLUMN IF NOT EXISTS media_id BIGINT REFERENCES media(id) ON DELETE SET NULL;

server/internal/store/reactions.go

@@ -0,0 +1,71 @@
+package store
+
+import (
+	"context"
+)
+
+// Reaction represents a single emoji reaction on a message.
+type Reaction struct {
+	MessageID int64
+	UserID    int64
+	Emoji     string
+}
+
+// AddReaction adds a reaction to a message; it is a no-op if it already exists.
+func (s *Store) AddReaction(ctx context.Context, messageID, userID int64, emoji string) error {
+	_, err := s.pool.Exec(ctx, `
+       INSERT INTO message_reactions(message_id, user_id, emoji)
+       VALUES($1, $2, $3)
+       ON CONFLICT (message_id, user_id, emoji) DO NOTHING
+   `, messageID, userID, emoji)
+	return err
+}
+
+// RemoveReaction removes a reaction from a message; it is a no-op if absent.
+func (s *Store) RemoveReaction(ctx context.Context, messageID, userID int64, emoji string) error {
+	_, err := s.pool.Exec(ctx, `
+       DELETE FROM message_reactions WHERE message_id=$1 AND user_id=$2 AND emoji=$3
+   `, messageID, userID, emoji)
+	return err
+}
+
+// ReactionsForMessages returns all reactions for the given message IDs.
+func (s *Store) ReactionsForMessages(ctx context.Context, messageIDs []int64) ([]Reaction, error) {
+	if len(messageIDs) == 0 {
+		return nil, nil
+	}
+	rows, err := s.pool.Query(ctx, `
+       SELECT message_id, user_id, emoji
+       FROM message_reactions
+       WHERE message_id = ANY($1)
+       ORDER BY message_id, created_at
+   `, messageIDs)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var reactions []Reaction
+	for rows.Next() {
+		var r Reaction
+		if err := rows.Scan(&r.MessageID, &r.UserID, &r.Emoji); err != nil {
+			return nil, err
+		}
+		reactions = append(reactions, r)
+	}
+	return reactions, nil
+}
+
+// MessageBelongsToConversation reports whether a message belongs to a conversation.
+func (s *Store) MessageBelongsToConversation(ctx context.Context, conversationID, messageID int64) (bool, error) {
+	var exists bool
+	err := s.pool.QueryRow(ctx, `
+       SELECT EXISTS(
+           SELECT 1 FROM messages WHERE id=$1 AND conversation_id=$2
+       )
+   `, messageID, conversationID).Scan(&exists)
+	if err != nil {
+		return false, err
+	}
+	return exists, nil
+}

server/internal/store/store.go

@@ -42,9 +42,18 @@ type Session struct {
 type Conversation struct {
 	ID        int64
 	Type      string
+	Name      string
+	Avatar    string
 	CreatedAt time.Time
 }
 
+// MemberInfo describes a conversation participant together with their profile.
+type MemberInfo struct {
+	User     User
+	Role     string
+	JoinedAt time.Time
+}
+
 // ConversationSummary provides a conversation with its last message and unread count.
 type ConversationSummary struct {
 	Conversation
@@ -58,6 +67,7 @@ type Message struct {
 	ConversationID int64
 	SenderID       int64
 	Body           string
+	MediaID        *int64
 	CreatedAt      time.Time
 	EditedAt       *time.Time
 	DeletedAt      *time.Time