cdrop — 跨 OS 剪贴板与文件传输服务

Commilitia Drop：自托管的跨设备剪贴板同步与点对点文件传输。

- 后端 Go（chi / SQLite WAL / SSE Hub / WebRTC signaling + 状态机 / Relay ring buffer），编译进单个 distroless 镜像（前端 go:embed）。
- 前端 React + TanStack Router + Zustand，自实现 SSE + WebRTC P2P，NAT 受阻时回退服务端中继；聚珍（Juzhen）CJK 综合排版。
- 桌面端 Wails v2（macOS / Windows），瘦客户端复用 web。
- 鉴权 OIDC PKCE（自建 Casdoor 等），refresh_token 信封加密存系统密钥库；iOS Shortcut 用 HS256 scoped token。

架构文档与变更记录见 docs 分支（PROJECT_BRIEF / FRONTEND_DESIGN / CHANGELOG）。

本次为公开发布初始提交：完整开发历史（含部署细节）留存于私有归档，公开仓库自此干净起步。

internal/httpapi/signal.go

@@ -0,0 +1,63 @@
+package httpapi
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"commilitia.net/cdrop/internal/hub"
+	"commilitia.net/cdrop/internal/jwtauth"
+)
+
+// maxSignalBytes caps the signaling body. WebRTC SDP offers/answers and bundled
+// ICE candidates are at most a few KB; the payload is an opaque json.RawMessage
+// with no other length check, so without this a single request could stream an
+// unbounded body into memory (R4). 64 KiB leaves generous headroom for fat SDP.
+const maxSignalBytes = 64 * 1024
+
+type signalReq struct {
+	To      string          `json:"to"`
+	Payload json.RawMessage `json:"payload"`
+}
+
+// handleSignal forwards WebRTC offer/answer/ICE candidates between same-user devices.
+// Body: { to: deviceName, payload: any-json }
+// 204 if delivered to live SSE; 410 if peer offline.
+func (s *Server) handleSignal(w http.ResponseWriter, r *http.Request) {
+	claims, _ := jwtauth.ClaimsFromContext(r.Context())
+	from, _ := jwtauth.DeviceNameFromContext(r.Context())
+
+	r.Body = http.MaxBytesReader(w, r.Body, maxSignalBytes)
+	var req signalReq
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		var mbe *http.MaxBytesError
+		if errors.As(err, &mbe) {
+			writeJSON(w, http.StatusRequestEntityTooLarge,
+				map[string]string{"error": "signal payload too large"})
+			return
+		}
+		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid json"})
+		return
+	}
+	if req.To == "" {
+		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "missing 'to'"})
+		return
+	}
+	if req.To == from {
+		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "cannot signal self"})
+		return
+	}
+
+	delivered := s.hub.SendTo(claims.UserID, req.To, hub.Event{
+		Type: "signal",
+		Data: map[string]any{
+			"from":    from,
+			"payload": req.Payload,
+		},
+	})
+	if !delivered {
+		writeJSON(w, http.StatusGone, map[string]string{"error": "peer offline"})
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}