Golang OpenFile O_APPEND 不尊重 Seek

Question

当我以这样的模式打开文件时:

file, _ := os.OpenFile("/path/to/my/file", os.O_RDWR|os.O_APPEND, os.FileMode(0666))
file.Seek(start, os.SEEK_SET)
io.CopyN(file, resp.Body, length)

io.CopyN 不尊重我寻求的位置。它似乎只是 append 到文件的尾部。相反，如果我像这样打开文件:

file, _ := os.OpenFile("/path/to/my/file", os.O_RDWR, os.FileMode(0666))
file.Seek(start, os.SEEK_SET)
io.CopyN(file, resp.Body, length)

它按我预期的那样工作。 io.CopyN 从我寻找的“开始”点写入文件。不确定这是功能还是错误？

Answer 1

这绝对是一个功能 (http://man7.org/linux/man-pages/man2/open.2.html)，它由底层操作系统控制，而不是 golang 运行时。

O_APPEND
          The file is opened in append mode.  Before each write(2), the
          file offset is positioned at the end of the file, as if with
          lseek(2).  O_APPEND may lead to corrupted files on NFS
          filesystems if more than one process appends data to a file at
          once.  This is because NFS does not support appending to a
          file, so the client kernel has to simulate it, which can't be
          done without a race condition.