The symtom was one of these two on upload of files only * panic: d.nx != 0 in crypto/md5.(*digest).checkSum * read tcp: i/o timeout It turned out to be a combination of two upstream bugs * https://github.com/mreiferson/go-httpclient/commit/5a2187309eac92103d0329aaae48e06837f260fb * https://groups.google.com/forum/#!topic/golang-dev/0Nl6k5Sj6UU This commit contains a work-around for the second problem, I've fixed the first and had the change accepted upstream.