I have a problem. this error: "curl error 56: SSL read: error:00000000:lib(0):func(0):reason(0), errno 104"

[Cryin]

When I use human_curl make get request:https://www.sample.com ,test the site is reachable or not.
Then This error occurred：curlerror(56: SSL read: error:00000000:lib(0):func(0):reason(0), errno 104),error code:56

the python sourse code debug info output :log.debug('error when access %.256s, CurlError(%s), error code:%d', url, str(e), error_code)

When i use the system curl command it return 200:
`

curl -I https://www.sample.com/

HTTP/1.1 200 OK
Date: Fri, 16 Dec 2016 06:29:14 GMT
X-Frame-Options: SAMEORIGIN
Last-Modified: Thu, 04 Aug 2016 01:24:58 GMT
ETag: "1cc-53934d169ae80"
Accept-Ranges: bytes
Content-Length: 460
Content-Type: text/html
Connection: close
system curl version:
linux # curl --version
curl 7.21.4 (i686-pc-linux-gnu) libcurl/7.24.0 OpenSSL/1.0.1u zlib/1.2.5
Protocols: dict file ftp ftps gopher http https imap imaps pop3 pop3s rtsp smtp smtps telnet tftp
Features: IPv6 Largefile NTLM SSL libz
`
What means this error?