Part 3: Implementing the Number Server

Now that we've completed our walkthrough of the basics of the http-server library. It's time to use the library to create our own server.

The number-server needs handle 3 different routes:

  • /shownum

    This function responds to the client socket with the current value of num.

  • /increment

    This function increments the value of num by one and responds to the client with the new value of num.

  • /add?value=NNN

    This function increments the value of num by the value encoded in NNN (a decimal integer) and responds to the client with the new value of num

We'll walk you through the first one, then you can try the others on your own.

3.1 Getting started

Successful Responses

However, now that we're adding support for /shownum and friends, we need to be able to send back a successful response, not just a "page not found". The HTTP status code for success is 200, so a successful response would look something like this:

HTTP/1.1 200 OK
Content-Type: text/plain

... body of response ...

As a string literal, the response header would look like this:

"HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\n\r\n"

Path parsing:

We also need to ensure that our /shownum, /increment, and /add responses only trigger when the correct path is requested, a path like /badpath should still result in a 404 response. Using a function like strcmp or strstr can be useful to check if the path matches a given string.

Maintaining state

In the lab5 starter, num is a global int variable, so functions can read/write its value.

After completing the /shownum route, curl the route with:

curl localhost:<port>/shownum

You should see something like: 

Your number is 0

Congrats! You officially got a web server running! Now, you have all the tools to implement the other functions of number-server.

3.2 Query parameters:

This section might be useful once you start working on the /add endpoint.

When sending a GET request in HTTP, any data accompanying the request needs to be sent as part of the path. This data is encoded as query parameters which follow a ? in the path and usually take the form of

?keyA=foo&keyB=bar&...

For the case of the /add endpoint, we need to encode the amount to add as part of the query string. A valid request to /add looks like

/add?value=<number>

Parsing query parameters correctly can be tricky, but in this case we only have one parameter to worry about, which makes it easier.

Task:

  1. What string function could we use to scan through our path and extract the number?
  2. Try using this function to print out the number after value= from the url path
  3. Implement the /add endpoint for your number-server
  4. In your notes: Put a screenshot of your number-server working with the endpoints you implemented.
  5. In your notes: Think of a request you could make that would cause your numeric-server to crash.