feat: create working client

download.go

@@ -0,0 +1,71 @@
+package zw
+
+import (
+	"context"
+	"io"
+	"io/fs"
+	"sync"
+	"sync/atomic"
+)
+
+type downloadReader struct {
+	recv   func() ([]byte, error)
+	cancel context.CancelFunc
+
+	pending  []byte
+	terminal error
+
+	cancelOnce sync.Once
+	closed     atomic.Bool
+}
+
+func (r *downloadReader) Read(destination []byte) (int, error) {
+	if len(destination) == 0 {
+		return 0, nil
+	}
+
+	if r.closed.Load() {
+		return 0, fs.ErrClosed
+	}
+
+	if len(r.pending) > 0 {
+		n := copy(destination, r.pending)
+		r.pending = r.pending[n:]
+		return n, nil
+	}
+
+	if r.terminal != nil {
+		return 0, r.terminal
+	}
+
+	for {
+		chunk, err := r.recv()
+		if err != nil {
+			if r.closed.Load() {
+				return 0, fs.ErrClosed
+			}
+
+			if err == io.EOF {
+				r.terminal = io.EOF
+			} else {
+				r.terminal = convertRPCError(err)
+			}
+			r.cancelOnce.Do(r.cancel)
+			return 0, r.terminal
+		}
+
+		if len(chunk) == 0 {
+			continue
+		}
+
+		n := copy(destination, chunk)
+		r.pending = chunk[n:]
+		return n, nil
+	}
+}
+
+func (r *downloadReader) Close() error {
+	r.closed.Store(true)
+	r.cancelOnce.Do(r.cancel)
+	return nil
+}