Add optional sync between Macs with a shared 8-digit code

Notes and photos were stuck on one machine. A small Go/Postgres backend stores each group's payload under a code that doubles as the shared secret, so a second Mac just needs the code — no account or login. Applying a remote change must not push it straight back, otherwise the two Macs would bump the version back and forth forever, so payloads are fingerprinted and identical ones are skipped. 💘 Generated with Crush Assisted-by: Crush:kimi-k3
2026-10-08 09:56:08 +08:00
parent 4934ad916a
commit 15ad9f355c
11 changed files with 747 additions and 3 deletions
@@ -0,0 +1,5 @@
+module dev.tzgyn.prompt/server
+
+go 1.26
+
+require github.com/lib/pq v1.10.9
@@ -0,0 +1,2 @@
+github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
+github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
@@ -0,0 +1,186 @@
+// Prompt sync server. No authentication: a sync group is identified by an
+// 8-digit code (1234-5678) that acts as the shared secret. Whoever has the
+// code can read and overwrite the group's data.
+//
+// Endpoints:
+//
+//	POST /api/codes           -> {"code":"1234-5678"}        (create group)
+//	GET  /api/sync/{code}     -> {"version":N,"data":{...}}  (404 if unknown)
+//	PUT  /api/sync/{code}     -> {"version":N+1}             (upsert payload)
+//	GET  /healthz             -> 200
+//
+// Config:
+//
+//	PROMPT_SYNC_DATABASE_URL  (default postgres://localhost:5432/prompt_sync?sslmode=disable)
+//	PROMPT_SYNC_ADDR          (default :8080)
+package main
+
+import (
+	"crypto/rand"
+	"database/sql"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"regexp"
+	"time"
+
+	_ "github.com/lib/pq"
+)
+
+const schema = `
+CREATE TABLE IF NOT EXISTS sync_groups (
+    code       TEXT PRIMARY KEY,
+    version    BIGINT NOT NULL DEFAULT 0,
+    data       JSONB,
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
+)`
+
+var codePattern = regexp.MustCompile(`^\d{4}-\d{4}$`)
+
+type Server struct {
+	db *sql.DB
+}
+
+func main() {
+	dsn := os.Getenv("PROMPT_SYNC_DATABASE_URL")
+	if dsn == "" {
+		dsn = "postgres://localhost:5432/prompt_sync?sslmode=disable"
+	}
+	addr := os.Getenv("PROMPT_SYNC_ADDR")
+	if addr == "" {
+		addr = ":8080"
+	}
+
+	db, err := sql.Open("postgres", dsn)
+	if err != nil {
+		log.Fatalf("open database: %v", err)
+	}
+	defer db.Close()
+	if err := db.Ping(); err != nil {
+		log.Fatalf("connect to database: %v", err)
+	}
+	if _, err := db.Exec(schema); err != nil {
+		log.Fatalf("ensure schema: %v", err)
+	}
+
+	s := &Server{db: db}
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /api/codes", s.createCode)
+	mux.HandleFunc("GET /api/sync/{code}", s.getSync)
+	mux.HandleFunc("PUT /api/sync/{code}", s.putSync)
+	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	})
+
+	log.Printf("prompt-sync listening on %s", addr)
+	log.Fatal(http.ListenAndServe(addr, mux))
+}
+
+// createCode generates a unique 8-digit code, formats it as 1234-5678, and
+// inserts an empty group so the code exists before the first PUT.
+func (s *Server) createCode(w http.ResponseWriter, _ *http.Request) {
+	for range 10 {
+		code, err := newCode()
+		if err != nil {
+			writeError(w, http.StatusInternalServerError, "could not generate code")
+			return
+		}
+		var exists bool
+		err = s.db.QueryRow(`SELECT EXISTS(SELECT 1 FROM sync_groups WHERE code = $1)`, code).Scan(&exists)
+		if err != nil {
+			writeError(w, http.StatusInternalServerError, "database error")
+			return
+		}
+		if exists {
+			continue
+		}
+		if _, err := s.db.Exec(`INSERT INTO sync_groups (code) VALUES ($1)`, code); err != nil {
+			writeError(w, http.StatusInternalServerError, "database error")
+			return
+		}
+		writeJSON(w, http.StatusOK, map[string]string{"code": code})
+		return
+	}
+	writeError(w, http.StatusInternalServerError, "could not find a free code")
+}
+
+func (s *Server) getSync(w http.ResponseWriter, r *http.Request) {
+	code := r.PathValue("code")
+	if !codePattern.MatchString(code) {
+		writeError(w, http.StatusBadRequest, "code must look like 1234-5678")
+		return
+	}
+	var (
+		version   int64
+		data      []byte
+		updatedAt time.Time
+	)
+	err := s.db.QueryRow(
+		`SELECT version, data, updated_at FROM sync_groups WHERE code = $1`, code,
+	).Scan(&version, &data, &updatedAt)
+	if err == sql.ErrNoRows {
+		writeError(w, http.StatusNotFound, "unknown code")
+		return
+	}
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "database error")
+		return
+	}
+	if data == nil {
+		data = []byte("null")
+	}
+	w.Header().Set("Content-Type", "application/json")
+	fmt.Fprintf(w, `{"version":%d,"updatedAt":%q,"data":%s}`,
+		version, updatedAt.UTC().Format(time.RFC3339), data)
+}
+
+func (s *Server) putSync(w http.ResponseWriter, r *http.Request) {
+	code := r.PathValue("code")
+	if !codePattern.MatchString(code) {
+		writeError(w, http.StatusBadRequest, "code must look like 1234-5678")
+		return
+	}
+	body := http.MaxBytesReader(w, r.Body, 50<<20) // 50 MB ceiling (images inside)
+	defer body.Close()
+	var payload json.RawMessage
+	if err := json.NewDecoder(body).Decode(&payload); err != nil {
+		writeError(w, http.StatusBadRequest, "body must be JSON")
+		return
+	}
+	var version int64
+	err := s.db.QueryRow(`
+		INSERT INTO sync_groups (code, version, data, updated_at)
+		VALUES ($1, 1, $2, now())
+		ON CONFLICT (code) DO UPDATE
+		SET version = sync_groups.version + 1, data = $2, updated_at = now()
+		RETURNING version`, code, payload).Scan(&version)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "database error")
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]int64{"version": version})
+}
+
+func newCode() (string, error) {
+	var b [8]byte
+	if _, err := rand.Read(b[:]); err != nil {
+		return "", err
+	}
+	digits := make([]byte, 8)
+	for i, v := range b {
+		digits[i] = '0' + v%10
+	}
+	return fmt.Sprintf("%s-%s", digits[:4], digits[4:]), nil
+}
+
+func writeJSON(w http.ResponseWriter, status int, v any) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(v)
+}
+
+func writeError(w http.ResponseWriter, status int, message string) {
+	writeJSON(w, status, map[string]string{"error": message})
+}