# view server response

response body:

    curl URL

response header (actual HEAD request):

    curl -I URL

response header and body:

    curl -i URL

to see request as well add `-v`, which adds extra info to stderr.
to make `-v` output cleaner pipe stdout to /dev/null and suppress progress meter:

    curl -vs URL > /dev/null

moar options:

    -A 'user agent'
    -u 'user:password'
    -k, --insecure    don't check cert validity
    -L  follow redirects


# measure connection times

    curl -s -w @.curl-format-times.txt -o /dev/null URL

# timeout
php guzzle `timeout` ought (*) to be the entire libcurl transfer operation, which should include
everything starting form name resolving, connection and data transfer. `connect_timeout` is only the
first part.
(*) according to someoine in the internet

# proxy

    http_proxy=<ip>:<port> curl <url>

# view certificate

    openssl s_client -servername DOMAIN -connect DOMAIN:PORT < /dev/null
    openssl s_client -servername DOMAIN -connect DOMAIN:PORT < /dev/null 2> /dev/null | openssl x509 -noout -dates

`-showcerts` displays sent intermediate certificates as well.