ngx.req.raw_header on SSL

For some reason on SSL connections, nginx is crashing when trying to get the raw headers using lua, on non ssl-connections it works fine.

local function get_req_headers(self)
    local req_headers = ngx.req.raw_header()
    return req_headers
end

local function get_sock()
    local host = ngx.var.upstream_host
    local http = http_lib:new()
    local port = get_port()
    local c, err = http:connect(host, port)
    if not c then
        log(ERR, "cannot connect origin.", err)
        http:close()
        return nil, err
    end

    return http, err
end

sock, err = get_sock()
if sock then 
    headers = get_req_headers()
end

Nginx 1.8
CentOS
ngx_lua

2016/07/21 03:00:28 [alert] 25628#0: worker process 29903 exited on signal 11
2016/07/21 03:00:34 [alert] 25628#0: worker process 30653 exited on signal 11
2016/07/21 03:01:06 [alert] 31550#0: worker process 31559 exited on signal 11
2016/07/21 03:01:07 [alert] 31550#0: worker process 31555 exited on signal 11
2016/07/21 03:01:15 [alert] 31550#0: worker process 31604 exited on signal 11

Start by reproducing the crash with the shown ngx.req.raw_header() call on an SSL connection using Nginx 1.8 on CentOS, then inspect the ngx.req.raw_header entry point and its SSL-specific path. Done means the request no longer exits the worker with signal 11 while raw headers are retrieved.