feat: complete contract-driven business development and MySQL integration

contract/file.go

@@ -0,0 +1,80 @@
+package contract
+
+import (
+	"errors"
+	"io"
+	"os"
+	"sync"
+)
+
+// File is a request-scoped upload, staged on disk using a bounded copy buffer.
+// Name and ContentType are untrusted client metadata. Open streams content;
+// readers and the temporary file are closed when the generated handler returns.
+// Persist wanted content before returning. Retaining File does not extend its lifetime.
+type File struct {
+	Name        string
+	ContentType string
+	Size        int64
+	state       *uploadState
+}
+type uploadState struct {
+	mu      sync.Mutex
+	path    string
+	closed  bool
+	readers map[*uploadReader]bool
+}
+type uploadReader struct {
+	file  *os.File
+	once  sync.Once
+	err   error
+	state *uploadState
+}
+
+// Present reports whether the optional upload was supplied.
+func (f File) Present() bool { return f.state != nil }
+
+func (f File) Open() (io.ReadCloser, error) {
+	if f.state == nil {
+		return nil, errors.New("upload file is absent")
+	}
+	s := f.state
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.closed {
+		return nil, errors.New("upload file is closed")
+	}
+	file, err := os.Open(s.path)
+	if err != nil {
+		return nil, err
+	}
+	r := &uploadReader{file: file, state: s}
+	s.readers[r] = true
+	return r, nil
+}
+func (r *uploadReader) Read(p []byte) (int, error) { return r.file.Read(p) }
+func (r *uploadReader) Close() error {
+	r.once.Do(func() { r.err = r.file.Close(); r.state.mu.Lock(); delete(r.state.readers, r); r.state.mu.Unlock() })
+	return r.err
+}
+func (f File) cleanup() error {
+	if f.state == nil {
+		return nil
+	}
+	s := f.state
+	s.mu.Lock()
+	if s.closed {
+		s.mu.Unlock()
+		return nil
+	}
+	s.closed = true
+	readers := make([]*uploadReader, 0, len(s.readers))
+	for r := range s.readers {
+		readers = append(readers, r)
+	}
+	s.mu.Unlock()
+	var err error
+	for _, r := range readers {
+		err = errors.Join(err, r.Close())
+	}
+	return errors.Join(err, os.Remove(s.path))
+}