chore: log where and after how many bytes a file transfer breaks

internal/agent/fsstream.go

@@ -5,11 +5,13 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"os"
 	"path/filepath"
 	"strconv"
 	"syscall"
+	"time"
 
 	"github.com/x-grk/longpolling-remote-access/internal/proto"
 )
@@ -62,6 +64,7 @@ func (a *Agent) doFSUpload(ctx context.Context, env proto.TaskEnvelope) proto.Ta
 	}
 	n, err := io.Copy(tmp, io.LimitReader(resp.Body, proto.FSFileCap+1))
 	if err != nil {
+		log.Printf("fs receive %s: broke after %d of %d bytes: %v", args.Path, n, args.Size, err)
 		return proto.TaskResult{Error: "загрузка прервана: " + err.Error()}
 	}
 	if n > proto.FSFileCap {
@@ -123,13 +126,16 @@ func (a *Agent) doFSGet(ctx context.Context, env proto.TaskEnvelope) proto.TaskR
 	req.ContentLength = info.Size()
 	req.Header.Set("X-Size", strconv.FormatInt(info.Size(), 10))
 	a.authHeaders(req)
+	start := time.Now()
 	resp, err := a.stream.Do(req)
 	if err != nil {
+		log.Printf("fs send %s (%d bytes): failed after %s: %v", args.Path, info.Size(), time.Since(start).Round(time.Millisecond), err)
 		return proto.TaskResult{Error: err.Error()}
 	}
 	io.Copy(io.Discard, resp.Body)
 	resp.Body.Close()
 	if resp.StatusCode != http.StatusNoContent {
+		log.Printf("fs send %s (%d bytes): server answered %d after %s", args.Path, info.Size(), resp.StatusCode, time.Since(start).Round(time.Millisecond))
 		return proto.TaskResult{Error: "браузер не дочитал файл"}
 	}
 	data, _ := json.Marshal(map[string]any{"path": args.Path, "size": info.Size()})