title: How to add file md5 checksum to a nginx HTTP response header?
body: <p>I would like to know how to add file md5 checksum to a nginx HTTP response header. The details is described below:</p>
  
  <p>I have a nginx server to serve some static files, these files are generated daily by other program, the old file will be overwritten when generating the new one.</p>
  
  <p>Sometimes the file content changed, sometimes not. But the modified time always changed.</p>
  
  <p>And I have an android app to download these files everyday, it should download only changed files.</p>
  
  <p>I cannot use etag because it was generated from file length and timestamp, and timestamp always changed.</p>
  
  <p>Thank you.</p>