Answers for "what are http headers"

what is header

Header : exists in both request and response 
	is metadata about the request 
	It's a key value pair 

	few common header type is 
	Accept header to specify what format you want to get your result
		only if the api itself support 
	Content Type 
		in request header : 
		to specify what kind of data we are sending 
			to the server 
		in response header : 
			what was the contenttype we got as response

HTTP Header

$ curl -u my_client_id:my_client_secret https://api.github.com/user/repos
> HTTP/2 200
> Date: Mon, 01 Jul 2013 17:27:06 GMT
> X-RateLimit-Limit: 5000
> X-RateLimit-Remaining: 4966
> X-RateLimit-Reset: 1372700873

HTTP Header

new Date(1372700873 * 1000)
// => Mon Jul 01 2013 13:47:53 GMT-0400 (EDT)

Request header

$ curl -I https://api.github.com/user
> HTTP/2 200
> Cache-Control: private, max-age=60
> ETag: "644b5b0155e6404a9cc4bd9d8b1ae730"
> Last-Modified: Thu, 05 Jul 2012 15:31:30 GMT
> Vary: Accept, Authorization, Cookie
> X-RateLimit-Limit: 5000
> X-RateLimit-Remaining: 4996
> X-RateLimit-Reset: 1372700873

$ curl -I https://api.github.com/user -H 'If-None-Match: "644b5b0155e6404a9cc4bd9d8b1ae730"'
> HTTP/2 304
> Cache-Control: private, max-age=60
> ETag: "644b5b0155e6404a9cc4bd9d8b1ae730"
> Last-Modified: Thu, 05 Jul 2012 15:31:30 GMT
> Vary: Accept, Authorization, Cookie
> X-RateLimit-Limit: 5000
> X-RateLimit-Remaining: 4996
> X-RateLimit-Reset: 1372700873

$ curl -I https://api.github.com/user -H "If-Modified-Since: Thu, 05 Jul 2012 15:31:30 GMT"
> HTTP/2 304
> Cache-Control: private, max-age=60
> Last-Modified: Thu, 05 Jul 2012 15:31:30 GMT
> Vary: Accept, Authorization, Cookie
> X-RateLimit-Limit: 5000
> X-RateLimit-Remaining: 4996
> X-RateLimit-Reset: 1372700873

Request header

$ curl -I https://api.github.com -H "Origin: http://www.airnovaet.com"
HTTP/2 302
Access-Control-Allow-Origin: *
Access-Control-Expose-Headers: ETag, Link, X-GitHub-OTP, X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset, X-OAuth-Scopes, X-Accepted-OAuth-Scopes, X-Poll-Interval

HTTP Header

$ curl -IH 'User-Agent: ' https://api.github.com/meta
> HTTP/1.0 403 Forbidden
> Connection: close
> Content-Type: text/html

> Request forbidden by administrative rules.
> Please make sure your request has a User-Agent header.
> Check  for other possible causes.