This challenge allows you to practice the concepts and techniques learned over
the past week and apply them in a concrete project. This Sprint explored
learning about the HTTP protocol, web servers, and caching. In your challenge
this week, you will demonstrate proficiency by creating an application that
performs web requests and prints the results on stdout.
Read these instructions carefully. Understand exactly what is expected before starting this Sprint Challenge.
This is an individual assessment. All work must be your own. Your challenge score is a measure of your ability to work independently using the material covered through this sprint. You need to demonstrate proficiency in the concepts and objectives introduced and practiced in preceding days.
You are not allowed to collaborate during the Sprint Challenge. However, you are encouraged to follow the twenty-minute rule and seek support from your PM and Instructor in your cohort help channel on Slack. Your work reflects your proficiency with networking and the HTTP protocol and your command of the concepts and techniques in the C Web Server module.
You have three hours to complete this challenge. Plan your time accordingly.
Commit your code regularly and meaningfully. This helps both you (in case you ever need to return to old code for any number of reasons and your project manager.
For this sprint challenge, you'll be implementing a barebones web retrieval client that will run from the command line.
cURL, which stands for "Client URL", is a command line tool that can make requests to servers, just like browsers can. You may have been using cURL in order to test your web server implementation.
If you've never played around with cURL, open up a terminal window and type in
curl -D - www.google.comWhen that command gets executed, you'll see that you get back an HTTP response with a whole bunch of HTML in the body. You just requested Google's home page, but since cURL is just a command line tool, it isn't capable of taking the HTML in the response and rendering it.
Your program for the Sprint Challenge will be a stripped down version of cURL
that can only make GET requests. Your MVP implementation will need to be able to
accept a URL as input, make a GET request, receive the response and print it all
to stdout.
As part of the web server sprint, you had to construct the server's response to a given request, and these took the form:
HTTP/1.1 200 OK
Date: Wed Dec 20 13:05:11 PST 2017
Connection: close
Content-Length: 41749
Content-Type: text/html
<!DOCTYPE html><html><head><title>Lambda School ...Now that we're implementing a client, our client will instead need to construct requests.
For this sprint challenge, all your code should be implemented in the client.c
file. Whenever you update your code, rerun make in order to compile a new
executable.
The steps that your client will need to execute are the following:
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Parse the input URL.
-
Your client should be able to handle URLs such as
localhost:3490/d20andwww.google.com:80/. Input URLs need to be broken down intohostname,port, andpath. Thehostnameis everything before the colon (but doesn't includehttp://orhttps://if either are present), theportis the number after the colon ending at the slash, and thepathis everything after the slash. -
Implement the
parse_url()function, which receives the input URL and tokenizes it intohostname,port, andpathstrings. Assign each of these to the appropriate field in theurlinfo_tstruct and return it from theparse_url()function. -
You can use the
strchrfunction to look for specific characters in a string. You can also use thestrstrfunction to look for specific substrings in a string.
-
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Construct the HTTP request.
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Just like in the web server, use
sprintfin order to construct the request from thehostname,port, andpath. Requests should look like the following:GET /path HTTP/1.1 Host: hostname:port Connection: close
The connection should be closed, otherwise some servers will simply hang and not return a response, since they're expecting more data from our client.
-
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Connect to the server.
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All of the networking logic that you'll need to connect to an arbitrary server is provided in the
lib.handlib.cfiles. All you have to do call theget_socket()function in order to get a socket that you can then send and receive data from using thesendandrecvsystem calls. -
Make sure that your web server implementation (built during project days 1 & 2 from Web Server I) is running in another terminal window when testing local requests.
-
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Send the request string down the socket.
- Hopefully that's pretty self-explanatory.
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Receive the response from the server and print it to
stdout.-
The main hurdle that needs to be overcome when receiving data from a server is that we have no idea how large of a response we're going to get back. So to overcome this, we'll just keep calling
recv, which will return back data from the server up to a maximum specified byte length on each iteration. We'll just continue doing this in a loop untilrecvreturns back no more data from the server:while ((numbytes = recv(sockfd, buf, BUFSIZE - 1, 0)) > 0) { // print the data we got back to stdout }
-
-
Clean up.
- Don't forget to
freeany allocated memory andcloseany open file descriptors.
- Don't forget to
In your solution, it is essential that you follow best practices and produce clean and professional results. Schedule time to review, refine, and assess your work and perform basic professional polishing including spell-checking and grammar-checking on your work. It is better to submit a challenge that meets MVP than one that attempts to much and does not.
Your cURL client will receive a 2 when it satisfies the following:
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Your client can successfully request any resource that your web server implementation (built during project days 1 & 2 from Web Server I) is capable of serving, i.e., it can successfully execute
./client localhost:3490/d20,./client localhost:3490/index.html, and any other URL that your web server implementation is capable of serving up. Don't forget to start up your web server implementation in another terminal window. Your client should print out the correct response tostdout, something like:HTTP/1.1 200 OK Date: Tue Oct 2 11:41:43 2018 Connection: close Content-Length: 3 Content-Type: text/plain 17
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Your client can successfully make a request to a non-local host, such as Google, Facebook, Reddit, etc. It doesn't necessarily need to successfully get back the HTML contents of the page, but your client should receive back a header response with some sort of HTTP status code and other metadata. For example, executing
./client www.google.com:80/should return back a 200 status code with all the HTML that makes up Google's homepage and print it all tostdout. The response header will look something like this:HTTP/1.1 200 OK Date: Tue, 02 Oct 2018 18:44:13 GMT Expires: -1 Cache-Control: private, max-age=0 Content-Type: text/html; charset=ISO-8859-1 P3P: CP="This is not a P3P policy! See g.co/p3phelp for more info." Server: gws X-XSS-Protection: 1; mode=block X-Frame-Options: SAMEORIGIN Set-Cookie: 1P_JAR=2018-10-02-18; expires=Thu, 01-Nov-2018 18:44:13 GMT; path=/; domain=.google.com Set-Cookie: NID=140=xQnQZhdVuKxdbMlSwuwPo-3Ii375x3h2c936Kcyk_JA8HAZTunEFW2L5F93UcSqDI-JtnHgl3r_qwZVxyJMFvMKYDKYZf4ab25QjziB5iFRNuNpjDEPKa8bn7ICeWNsH; expires=Wed, 03-Apr-2019 18:44:13 GMT; path=/; domain=.google.com; HttpOnly Accept-Ranges: none Vary: Accept-Encoding Connection: close
After finishing your required elements, you can push your work further. These goals may or may not be things you have learned in this module but they build on the material you just studied. Time allowing, stretch your limits and see if you can deliver on the following optional goals:
In order to earn a score of 3, complete at least one of the following stretch goals:
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Make the URL parsing logic more robust.
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The specified URL parsing logic is really brittle. The most glaring hole is the fact that oftentimes, URLs don't actually include the port number. In such cases, clients just assume a default port number of 80. Improve the URL parsing logic such that it can handle being passed a URL without a port number, such as
www.google.com/. -
Also improve the parsing logic so that it can receive URLs prepended with
http://orhttps://. Such URLs should not be treated any differently by the client, you'll just need to strip them off the input URL so that they don't become part of the hostname.
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Implement the ability for the client to follow redirects.
- If you execute
./client google.com:80/, you'll get back a response with a301 Moved Permanentlystatus. There's aLocationfield in the header as well as ahreftag in the body specifying where the client needs to be redirected. Augment your client such that when it encounters a 301 status, it will automatically follow the redirect link and issue another request for the correct location.
- If you execute
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Don't have the client print out the header.
- Let's make the printing of the header of the response optional. Implement
functionality such that the client can accept a
-hflag, and only when this flag is present do we print the response header as well. Otherwise, when printing a response, your client should just print the body of the response to stdout.
- Let's make the printing of the header of the response optional. Implement
functionality such that the client can accept a