Most internet communications are made with web requests through HTTP protocol.
HTTP communication is consisted of client and server.
Default port: 80
URL
When we visit a website, we use Fully Qualified Domain Name(FQDN) as a Uniform Resource Locator (URL), like jadu101.github.io.
We access resource over HTTP through URL as such:
http://admin:password@carabinersec.com:80/login.php?login=true#status
Let’s break down above URL:
- Scheme → http:// → Identify protocol being accessed by the client.
- User Info → admin:password@
- Host → carabinersec.com → Resource location
- Port → :80
- Path → /login.php → Resource being accessed. Could be file or a folder
- Query String → ?login=true → Query string starts with
?.loginis a parameter.trueis a value.&is used for multiple parameters. - Fragments →
#status→ They are processed by the browsers on the client-side to locate sections within the primary resource.
When a user enters the URL (carabinersec.com), DNS server resolves the domain and gets the ip of carabinersec.com. Once the browser gets the IP address linked the requested domain, it sends a GET request to the default HTTP port. Web server receives the request and processes it.
cURL
cURL is a command line tool that supports HTTP along with many other protocols.
We send basic HTTP request as such:
yoon@yoon-XH695R:~$ curl www.google.com
<!doctype html><html itemscope="" itemtype="http://schema.org/WebPage" lang="ko"><head><meta content="text/html; charset=UTF-8" http-equiv="Content-Type"><meta content="/images/branding/googleg/1x/googleg_standard_color_128dp.png" itemprop="image"><title>Google</title><script nonce="3xYE5vRzZsI254P6YyzqPg">(functio
cURL doesn’t render HTML/JavaScript/CSS code unlike web browser, making it faster and more convenient than a web browser.
Using -O -o flag, we can download a page or a file into a file.
-O flag will automatically name the file as the remote file name:
yoon@yoon-XH695R:~$ curl -O carabinersec.com/index.html
yoon@yoon-XH695R:~$ ls
index.html
One more thing, -s silents the status.