How do I go from io.ReadCloser to io.ReadSeeker? -
    i'm trying download file s3 , upload file bucket in s3.  copy api won't work here because i've been told not use it.   getting object s3 has response.body  that's io.readcloser  , upload file, payload takes body  that's io.readseeker .   the way can figure out saving response.body  file passing file io.readseeker .  require writing entire file disk first reading entire file disk sounds pretty wrong.   what is:   resp, _ := conn.getobject(&s3.getobjectinput{key: "bla"}) conn.putobject(&s3.putobjectinput{body: resp.body}) // resp.body io.readcloser , field type expects io.readseeker   question is, how go io.readcloser  io.readseeker  in efficient way possible?          io.readseeker  interface groups basic read()  , seek()  methods. definition of seek()  method:   seek(offset int64, whence int) (int64, error)   an implementation of seek()  method requires able seek anywhere  in source, requires all  source available or reproducible. file perfect ...