症状：php curl调用https出错
排查方法：在命令行中使用curl调用试试。
原因：服务器所在机房无法验证SSL证书。
解决办法：跳过SSL证书检查。
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);

症状：php curl调用curl_exec返回bool(false)，命令行curl调用正常。
排查方法：
var_dump(curl_error($ch));
返回：
string(23) "Empty reply from server"
再排查：
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, false);
返回：
HTTP/1.1 100 Continue
Connection: close
原因：php curl接收到HTTP 100就结束了，应该继续接收HTTP 200
解决方案：
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Expect:'));

PHP and cURL: Disabling 100-continue header
Published June 15th, 2006
I've been using cURL (through PHP) to build a sort of proxy for a project I'm working on. I need to parse the returned headers (to recover the HTTP status), so had included a very simple script to do so. It had worked fine in the past, but for some reason barfed in this case. A closer look at what was being returned revealed that for some reason, Apache was prepending the ‘normal' headers with an extra response header:

HTTP/1.1 100 Continue

HTTP/1.1 200 OK Date: Fri, 09 Jun 2006 15:23:42 GMT
Server: Apache
...A bit of Googling revealed that this was to do with a header that cURL sends by default:

Expect: 100-continue

…which in turns tells Apache to send the extra header. I poked around a fair bit but couldn't quite find a workable solution short of manually removing the header in PHP, which seemed a bit clumsy. Finally, on a hunch I tried this:

curl_setopt( $curl_handle, CURLOPT_HTTPHEADER, array( 'Expect:' ) );

…which basically overrides the original ‘Expect:' header with an empty one.

Hope this helps someone.