I'm learning ccnp and encounter concept "window size " .it in TCP Header segment.Could you do me favor with this question?. I been searching for it function and the ideals of it.But it seem very less information provided
How it work and what is that?.Give me an example is perfect.
Related
I'm creating zip files on the fly for download, I don't know how big they are going to turn out exactly but I can give a pretty good guess. I added it for the sake of client side fluff since the downloads are pretty big but having a progress bar isn't essential. https://www.rfc-editor.org/rfc/rfc7230#section-3.3.2 says Content-Length is for "anticipated size" which can be interpreted as either exact or approximate.
So far all the browsers I've tried don't have a problem with an approximate content size header but are there any out there that do?
Read it completely!
If you are using HTTP/1.1, and do not use chunked encoding, the content-length absolutely needs to be precise; it's needed for the message framing.
I've put a lot of time and research into finding a reliable solution for my problem. I am attempting to modify values in packets sent to and from my Iphone, of course I can't directly view and tamper with packets directly from my phone. So I've connected my phone via proxy to my computer (windows) so I could attempt to modify the packets their. Now I can successfully view and save packets but I can't seem to find a way to modify them on the fly.
I've followed many suggestions posted here such as scapy and other tools like it yet I can't seem to get them to work on windows at all, also i'm not sure these tools are even right for my end goal. I am familiar with modifying live packets on programs like WPE Pro, but I don't think that's the right tool for the job.
My question is this, is this the right path for accomplishing my goal? If so do you have a suggestion for tools that may help? If not, where should I begin looking for different solution?
Edit: Specifically I am aiming to alter hex code in the packet. In the http 1.1 packets I want to alter, I know the exact position of a certain group of hex values that translate to a plain text number. For example, say on line 80 is some hex equaling "value:12345". I want to alter that "12345" part to different numbers, keeping everything else the same so my phone will process that different value instead.
I've been doing some work in VB.Net with Directshow over the past 3-4 weeks. I'm creating an application to keep tags on a video and eventually want to be able to extract the tagged parts of the video to a new file. In a video that is 2 hours long I might want to extract say 50 10-15 second "clips" up to 15 times (event tagging). This will be for a free application.
I've found it brilliant (and easy) to render / seek / play clips, etc on XP-Win7 with no issues. I've "discovered" the joys of GraphEdit, creating graphs, the issues with COM in VB.NET, GMFBridge, ....etc.
Now I need some advice. Am I using the right technology. Directshow seems to be very resistant to the idea of "open video", "seek to clip", "write clip to file", .....repeat for all clips, close file. I can sort of do this already if I visibly render the video but would need to do it as a background task faster than realtime render speed.
Things that seem to be missing are:
- an example of anyone doing anything similar (export multiple clips to a single file)
- no easily available 64bit compressors (lots of 32bit stuff around)
- all the references and examples I do find are VERY old
- VB.NET is not the first "port of call" for DirectShow developers
So, the question is, should I be using something else?
If not, has anyone done anything similar before. I'm not looking for their code, I just want some guidelines as it takes ages to figure things out in DirectShow and VB.Net just using trial & error (and Google).
I've looked at AFORGE (no sound), FFMPEG (command line toolset), Media Foundation (reluctant to throw away XP) and a variety of commercial helper libraries but not really getting any further.
Apologies for the length but I wanted readers to understand the background.
All help appreciated.
To output clips to a single file Microsoft had created the "DirectShow Editing Services". Sometimes it works, sometimes not. We use it in our software to create videos from clips like you. With a little bit work you can also include effects to the video.
It is also possible to use AviSynth. It's a scripting system and frameserver for DirectShow.
As I know, with MediaFoundation you can also create a video from multiple clips, but I never tried this.
Is there a way to determine if the request coming to a handler (lets assume the handler responds to get and post) is being performed by a real browser versus a programmatic client?
I already know that it is easy to spoof things like the User Agent and the Referrer, but are there other headers that are more difficult to spoof? Maybe headers that are not commonly available in classes like .net's HttpWebRequest?
The other path that I looked at is maybe using the Encrypted View State to send a value to the browser that gets validated on the server side, though couldn't that value simply be scraped from the previous response and added as a post parameter to the next request?
Any help would be much appreciated,
Cheers,
There is no easy way to differentiate because in the end, a post programitically looks the same to the server as a post by a user from the browser.
As mentioned, captcha's can be used to control posting but are not perfect (as it is very hard but not impossible for a computer to solve them). They also can annoy users.
Another route is only allowing authenticated users to post, but this can also still be done programatically.
If you want to get a good feel for how people are going to try to abuse your site, then you may want to look at http://seleniumhq.org/
This is very similar to the famous Halting Problem in computer science. See some more on the proof, and Alan Turing here: http://webcache.googleusercontent.com/search?q=cache:HZ7CMq6XAGwJ:www-inst.eecs.berkeley.edu/~cs70/fa06/lectures/computability/lec30.ps+alan+turing+infinite+loop+compiler&cd=1&hl=en&ct=clnk&gl=us
The most common way is using captcha's. Of course captcha's have their own issues (users don't really care for them) but they do make it much more difficult to programatically post data. Doesn't really help with GETs though you can force them to solve a captcha before delivering content.
Many ways to do this, like dynamically generated XHR requests that can only be made with human tasks.
Here's a great article on NP-Hard problems. I can see a huge possibility here:
http://www.i-programmer.info/news/112-theory/3896-classic-nintendo-games-are-np-hard.html
One way: You could use some tricky JS to handle tokens on click. So your server issues token-id's to elements on the page during the backend render phase. Log these in a database or data file. Then, when users click around and submit, you can compare the id's sent via the onclick() function. There's plenty of ways around this, but you could apply some heuristics to determine if posts are too fast to be a human or not, that is, even if they scripted the hijacking of the token-ids and auto submitted, you could check that the time between click events appears automated. Signed up for a twitter account lately? They use passive human detection that while not 100% foolproof, it is slower and more difficult to break. Many if not all of the spam accounts there had to be human opened.
Another Way: http://areyouahuman.com/
As long as you are using encrypted methods verifying humanity without crappy CAPTCHA is possible.I mean, don't ignore your headers either. These are complimentary ways.
The key is to have enough complexity to make for an NP-Complete problem in terms of number of ways to solve the total number of problems is extraordinary. http://en.wikipedia.org/wiki/NP-complete
When the day comes when AI can solve multiple complex Human problems on their own, we will have other things to worry about than request tampering.
http://louisville.academia.edu/RomanYampolskiy/Papers/1467394/AI-Complete_AI-Hard_or_AI-Easy_Classification_of_Problems_in_Artificial
Another company doing interesting research is http://www.vouchsafe.com/play-games they actually use games designed to trick the RTT into training the RTT how to be more solvable by only humans!
I am trying to debug some problems with very picking/complex webservices where some of the clients that are theoretically making the same requests are getting different results. A debugging proxy like Charles helps a lot but since the requests are complex (lots of headers, cookies, query strings, form data, etc) and the clients create the headers in different orders (which should be perfectly acceptable), etc. it's an extremely tedious process to do manually.
I'm pondering writing something to do this myself but I was hoping someone else had already solved this problem?
As an aside does anyone know of any Charles-like debugging proxies that are completely opensource? If Charles were open source I would definitely contribute any work I did on this front back to the project. If there is something similar out there, I would much rather do this than write an separate program from scratch (especially since I imagine Charles or any analog already has all of the data structures I might need etc).
Edit:
Just to be clear -- text diffing will not work as the order of lines (e.g. headers at least) may be different and/or the order of values within lines (e.g. cookies at least) can be different and in both cases as long as the names and values and metadata are all the same, the different ordering should not cause requests that are otherwise the same to be considered different.
Fiddler has such an option, if you have WinDiff in your path. I don't know though if it will suit your needs, because at first glance it's jus doing text comparisions. But perhaps it normalizes the sessions before that, so I can't say.
If there's nothing purpose built for the job, you can use packet capture to get the message content saved to a text file (something that inserts itself in the IP stack like CommView). The you can text diff the results for different messages.
Can the open-source proxy Squid maybe help?