feat: implement security, discovery, history, file transfer, web UI (P0-P3)

internal/transfer/transfer.go

@@ -0,0 +1,83 @@
+// Package transfer handles binary content (images, files) transfer between
+// clip-sync peers. It is kept separate from the text clipboard path so that
+// text sync remains simple and safe; binary content is sent explicitly and is
+// written to disk on the receiving side only when enabled.
+package transfer
+
+import (
+	"encoding/base64"
+	"fmt"
+	"mime"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+// File is the wire payload for a transferred binary object.
+type File struct {
+	Name   string `json:"name"`
+	Mime   string `json:"mime"`
+	Data   string `json:"data"` // base64-encoded content
+	Ts     int64  `json:"ts"`
+	Origin string `json:"origin"`
+}
+
+// ReadFile reads a file from disk and encodes it as a transfer.File payload.
+func ReadFile(path, origin string) (*File, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	mimeType := mime.TypeByExtension(filepath.Ext(path))
+	if mimeType == "" {
+		mimeType = "application/octet-stream"
+	}
+
+	return &File{
+		Name:   filepath.Base(path),
+		Mime:   mimeType,
+		Data:   base64.StdEncoding.EncodeToString(data),
+		Ts:     time.Now().UnixNano(),
+		Origin: origin,
+	}, nil
+}
+
+// Decode returns the raw bytes of the file.
+func (f *File) Decode() ([]byte, error) {
+	if f.Data == "" {
+		return nil, fmt.Errorf("transfer: empty data")
+	}
+	return base64.StdEncoding.DecodeString(f.Data)
+}
+
+// SaveTo writes the decoded content to the given directory, sanitizing the
+// file name to avoid path traversal. It returns the written path.
+func (f *File) SaveTo(dir string) (string, error) {
+	data, err := f.Decode()
+	if err != nil {
+		return "", err
+	}
+
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return "", err
+	}
+
+	name := filepath.Base(f.Name)
+	if name == "." || name == "" || name == string(filepath.Separator) {
+		name = "received.bin"
+	}
+
+	// Avoid overwriting existing files: append a numeric suffix if needed.
+	dest := filepath.Join(dir, name)
+	for i := 1; ; i++ {
+		if _, err := os.Stat(dest); os.IsNotExist(err) {
+			break
+		}
+		ext := filepath.Ext(name)
+		base := name[:len(name)-len(ext)]
+		dest = filepath.Join(dir, fmt.Sprintf("%s (%d)%s", base, i, ext))
+	}
+
+	return dest, os.WriteFile(dest, data, 0644)
+}