fix(imagepush): 推送与拉取共用一个 HTTP 客户端复用连接，出错时先读响应体再关闭，错误信息不再为空

internal/imagepush/push.go

@@ -240,10 +240,11 @@ func (p *Pusher) uploadBlob(ctx context.Context, r Ref, digest string, size int6
 	if err != nil {
 		return err
 	}
-	start.Body.Close()
 	if start.StatusCode != http.StatusAccepted {
+		defer start.Body.Close()
 		return statusError("start upload", start)
 	}
+	drainClose(start)
 	loc, err := start.Location()
 	if err != nil {
 		return fmt.Errorf("start upload: %w", err)
@@ -261,10 +262,11 @@ func (p *Pusher) uploadBlob(ctx context.Context, r Ref, digest string, size int6
 	if err != nil {
 		return err
 	}
-	put.Body.Close()
 	if put.StatusCode != http.StatusCreated {
+		defer put.Body.Close()
 		return statusError("upload", put)
 	}
+	drainClose(put)
 	p.logf("pushed  %s (%d bytes)", digest, size)
 	return nil
 }
@@ -311,13 +313,17 @@ func (p *Pusher) do(ctx context.Context, method, target string, body io.Reader,
 	}
 	c := p.Client
 	if c == nil {
-		// No overall timeout: a modpack layer can take minutes on a slow disk, and
-		// the Job's activeDeadlineSeconds is the real bound.
-		c = &http.Client{Transport: &http.Transport{ResponseHeaderTimeout: 2 * time.Minute}}
+		c = pushClient
 	}
 	return c.Do(req)
 }
 
+// pushClient is shared by every Pusher without its own Client, so a restore of
+// many images reuses keep-alive connections instead of opening one per
+// request. No overall timeout: a modpack layer can take minutes on a slow disk,
+// and the caller's deadline is the real bound.
+var pushClient = &http.Client{Transport: &http.Transport{ResponseHeaderTimeout: 2 * time.Minute}}
+
 // retry runs fn up to Attempts times, backing off between tries. A refusal the
 // registry will repeat (401/403/4xx other than 408/429) is returned at once. A 503
 // with Retry-After is waited out without using up an attempt, for as long as
@@ -394,6 +400,13 @@ func (e *StatusError) Error() string {
 	return fmt.Sprintf("%s: registry answered %d: %s", e.Op, e.Code, e.Body)
 }
 
+// drainClose reads what is left of a small response body so its connection
+// goes back to the pool.
+func drainClose(resp *http.Response) {
+	io.Copy(io.Discard, io.LimitReader(resp.Body, 64<<10))
+	resp.Body.Close()
+}
+
 func statusError(op string, resp *http.Response) error {
 	b, _ := io.ReadAll(io.LimitReader(resp.Body, 2048))
 	se := &StatusError{Op: op, Code: resp.StatusCode, Body: strings.TrimSpace(string(b))}