Mysqld: capture mysqlbinlog std error output (#15278)

Signed-off-by: Shlomi Noach <2607934+shlomi-noach@users.noreply.github.com>

go/vt/mysqlctl/mysqld.go

@@ -1250,11 +1250,18 @@ func (mysqld *Mysqld) ApplyBinlogFile(ctx context.Context, req *mysqlctlpb.Apply
  if err != nil {
  return err
  }
+ var mysqlbinlogErrFile *os.File
  {
  name, err := binaryPath(dir, "mysqlbinlog")
  if err != nil {
  return err
  }
+ mysqlbinlogErrFile, err = os.CreateTemp("", "err-mysqlbinlog-")
+ if err != nil {
+ return err
+ }
+ defer os.Remove(mysqlbinlogErrFile.Name())
+
  args := []string{}
  if gtids := req.BinlogRestorePosition; gtids != "" {
  args = append(args,
@@ -1274,7 +1281,8 @@ func (mysqld *Mysqld) ApplyBinlogFile(ctx context.Context, req *mysqlctlpb.Apply
  mysqlbinlogCmd = exec.Command(name, args...)
  mysqlbinlogCmd.Dir = dir
  mysqlbinlogCmd.Env = env
- log.Infof("ApplyBinlogFile: running mysqlbinlog command: %#v", mysqlbinlogCmd)
+ mysqlbinlogCmd.Stderr = mysqlbinlogErrFile
+ log.Infof("ApplyBinlogFile: running mysqlbinlog command: %#v with errfile=%v", mysqlbinlogCmd, mysqlbinlogErrFile.Name())
  pipe, err = mysqlbinlogCmd.StdoutPipe() // to be piped into mysql
  if err != nil {
  return err
@@ -1344,6 +1352,12 @@ func (mysqld *Mysqld) ApplyBinlogFile(ctx context.Context, req *mysqlctlpb.Apply
  }
  // Wait for both to complete:
  if err := mysqlbinlogCmd.Wait(); err != nil {
+ if mysqlbinlogErrFile != nil {
+ errFileContent, _ := os.ReadFile(mysqlbinlogErrFile.Name())
+ if len(errFileContent) > 0 {
+ err = vterrors.Wrapf(err, "with error output: %s", string(errFileContent))
+ }
+ }
  return vterrors.Wrapf(err, "mysqlbinlog command failed")
  }
  if err := mysqlCmd.Wait(); err != nil {