Also, can you SEND any header back? (return headers) when you run a web server?
Or, are headers limited?
Web pages are retrieved using the HTTP protocol. HTTP is text-based. Both, a client requesting and a server responding within a HTTP communication can add custom headers to the HTTP messages. Its up to the communicating parties how to process these. I would assume that an unknown header is dropped silently.
Related
When a web server receives a http(s) GET request from a client, it has access to some information such as:
The client IP
The request itself :
the headers (including the cookies)
the content
and... that's all ?
I am wondering if there is something else.
Indeed, I am trying to make a server that can access to a page where it can collect some information to update its database. The site denied access to my server but not to web browsers, even if I replicate the IP, the headers and the content.
Thanks for your help.
Yes, it's only what is contained in the request itself. The server cannot reach back to the client to "pull" information, it only has the information contained in the HTTP request and the underlying TCP/IP packet. That's:
the requesting IP address
the HTTP headers, including requested URL and HTTP method
the HTTP request body, if any
if it's HTTPS, any data exchanged during the TLS handshake, which is usually not very relevant for identifying anything significant
All of that information is voluntarily provided by the requesting client.
Just a quick question, and probably a stupid one.
But usually when a client connects to an http server, the server sends them the header and the html, correct?
I'm packet sniffing a realtime-chat, and attempting to reverse engineer a plain text protocol, and it's connected to a http server. This is why I ask, for verification.
Basically, this is correct. Anyways, you have to differentiate between for example GET and POST Requests.
While POST Requests normally have a "real" body with information that they are delivering to the Server, the body of GET Requests is empty for most of the time.
For the responses, your Claim is correct. The Header is sent to tell how big the response is, which MIME Type is used, etc.
Can the HTTP client send a request while receiving the HTTP response?
For example, a client sends HTTP request A to server. Then, the server starts to send HTTP response. Before the client finish to receive HTTP response A, the client sends additional request B. Can it be possible? or Does it follow the HTTP RFC?
I think that above scenario is different from the pipelining. What I know about the pipelining is the scenario that client send multiple request A,B,C then the server response A,B,C consecutively. However, in the above scenario, request B is issued while the processing the response A.
Thank you
With the same connection object you must read the whole response before you can send a new request to the server, because response provides access to the request headers, return type and the entity body, If you send new request before fully reading response, client may get confused with mismatched responses.
Again it totally depends upon client library you using. Library could allow asynchronous requests.
There are concepts like
AsyncTask in android, promis in Angularjs etc.
allow asynchronous request.
There is a issue raised by one of our client who is using our Rest based API that whenever he is sending a post request to our server without AcceptEncoding http header but he is getting Compressed content in return. I checked the IIS logs on our API server which addressed his request and the request received on the server has come with a Accept-Encoding(http header) as set to gzip. In between the client machine and our server sits intermediaries(proxies) and load balancer. which network tracing tool should I use for investigating as to where this http header is getting added.
One solution to avoid an HTTP message to be compressed is to add Cache-Control: no-transform to the request headers to avoid payload alteration by proxies as stated in RFC 7234 section 5.2.1.6.
Also, Via header may contain useful comments that can help when looking for what did each proxy add to the request.
How HTTP request works:(if i have mistake, please write)
user type in browser http://www.website.com
the server send him html page with links to images+css+js files
browser read html and where included images/css/js file send http request to get the file
where browser send request to get file, does he waiting for response or he send request for next file?
Thanks
Most browsers will have an internal queue of requests which are handled as follows:
Request the first item. If a fresh copy is in the cache, this will mean a request to the cache. If a stale copy with validation information (last-mod and/or e-tag) this will be a conditional request (the server or proxy may return a 304 indicating the stale copy is actually still fresh). Otherwise an unconditional request.
As rendering of the entity returned requires other entities, these will be put into a queue of needed requests.
Requests in the queue that have already been in that same queue (e.g. if a page uses the same image more than once) will have the same entity immediately used (hence if a URI returns a random image, but you use it more than once in the same page, you will get the same image used).
Requests will be processed immediately, so in the case of a webserver, images, css, etc. will begin downloading before the HTML has finished rendering or indeed, finished downloading.
Requests to the same domain with the same protocol (HTTP or HTTPS) will be pipelined, using a connection that has already been used, rather than opening a new one.
Requests are throttled in two ways: A maximum number of simultaneous requests to the same domain, and a total maximum number of simultaneous requests.
The browser usually initiate more than one socket to the target server, and thus getting content on more than one socket at the same time. This can be combined with HTTP Pipelining (what you are asking about), where the browser sends multiple requests on the same socket without waiting for each of their responses.
From Wikipedia page:
HTTP pipelining is a technique in
which multiple HTTP requests are
written out to a single socket without
waiting for the corresponding
responses. Pipelining is only
supported in HTTP/1.1, not in 1.0.