{"id":372,"date":"2016-09-27T21:59:20","date_gmt":"2016-09-27T20:59:20","guid":{"rendered":"http:\/\/www.troliver.com\/?p=372"},"modified":"2017-07-07T11:57:13","modified_gmt":"2017-07-07T10:57:13","slug":"uploading-data-to-a-webserver-part-1-cc-and-curl","status":"publish","type":"post","link":"https:\/\/www.troliver.com\/?p=372","title":{"rendered":"Uploading data to a webserver Part 1 – C\/C++ and CURL"},"content":{"rendered":"

Following on from the last post on the\u00a0topic of capturing packet data from a network<\/a>, this guide\u00a0demonstrates how you can use a cURL library to upload data from\u00a0an application written in C (or C++) to a webserver.\u00a0Although at times I refer to previous examples, you can use this in\u00a0any number of applications.<\/p>\n

This will touch on\u00a0a number of areas and require a little more\u00a0prep work\u00a0than previous examples, due to needing a few extra libraries and a server running PHP and SQL.\u00a0In a nutshell, you have to cobble together a string with all your data in, send it along to your\u00a0server with a request and then have that server do something with it.\u00a0The steps covered are:<\/p>\n

    \n
  1. (Setup) LAMP server and database<\/li>\n
  2. (Client)\u00a0Generate a URL string from variables in your program<\/li>\n
  3. (Client) Send a web request to the URL generated in step 1<\/li>\n
  4. (Server) Process the uploaded string to retrieve values from data<\/li>\n
  5. (Server) Store the data as a new record in a database<\/li>\n<\/ol>\n

    Finally, there are some really quick and horrible things that I do here, with minimal catching of errors, but the purpose is to show the process from start to finish as briefly as possible!<\/p>\n

    Environment<\/h2>\n

    First of all, its worth mentioning the set-up I am using for this system. Just to demonstrate, I have a\u00a0LAMP server<\/strong> running on Ubuntu<\/strong>\u00a0with\u00a0a\u00a0MySQL<\/strong>\u00a0database. <\/strong>I won’t cover how to actually get as far as having those running because there’s plenty of articles that explain how to do that. The only other thing you may want to use is phpMyAdmin<\/strong>, as this makes database management via a web UI much easier than just command line interaction. It also helps hugely to understand basics of HTML\/PHP – but you may well be able to stumble through this if you’ve never touched either before!<\/p>\n

    Setup<\/h2>\n

    Database Table<\/h3>\n

    The first thing to do\u00a0is to create a new table to store the records in. This may as well just be a spreadsheet at this point, but later on I will be talking about queries and combining\u00a0data from different tables. You can either create a new table with phpMyAdmin by selecting the appropriate settings from the code below or you can simply copy and paste the entire thing into an SQL query box and run it, which will create a new table for you.<\/p>\n

    CREATE TABLE inventory\r\n(\r\nhostName varchar(25) NOT NULL,\r\nhostIP varchar(25),\r\nhostMAC varchar(18),\r\nhostCreateDate timestamp DEFAULT CURRENT_TIMESTAMP,\r\nvlanID int(4),\r\nswitchPort varchar(32),\r\nswitchIP varchar(25),\r\nswitchName varchar(64),\r\nswitchPlatform varchar(64),\r\nUNIQUE (hostName)\r\n);<\/pre>\n
    This single table consists of host information (name, mac, ip), switch information (name, platform, IP, port) and a date that the entry was created. Note that this also adds the constraint to the hostName to ensure that it is unique (and stipulates that it can’t be empty). There is a logical argument that, perhaps, it should be the MAC address that is unique; but I am quite happy with my domain and that it won’t give me hostname duplication for this demo. Plus, the focus is on getting data of different types in, rather than necessarily what the data is.<\/em><\/p>\n
    PHP page\u00a0to process data<\/h3>\n
    This is the part that is going to bring it all together later. When we want to place data into the database, we need something that will take data sent to the server and process that into the database. This file is going to store the database credentials, so its really important that it\u00a0isn’t made available outside of your webserver. Since PHP files execute on the server, rather than the client, the file contents aren’t sent back when requested (unless the PHP service stops and breaks, in which case everything will be displayed in plaintext..). In fact, we really don’t have to – or necessarily want to – output anything with a PHP file; in this instance, it is simply used as a way to process data from clients to be stored in a database as follows:<\/p>\n
    The first thing to do is to specify some variables for the database\u00a0details. These are used to connect to the database (on the same server, in this case):<\/p>\n
    <?php\r\n\t$servername = \"localhost\";\r\n\t$username = \"user\";\r\n\t$password = \"Passw0rd\";\r\n\t$dbname = \"inventory\";\r\n\r\n\/\/Rest of the code goes here\r\n\r\n?><\/pre>\n
     <\/p>\n
    The next thing to do is to create a connection object that handles the connection to a MySQL database, passing it the above variables as parameters:<\/p>\n
    $conn = new mysqli($servername, $username, $password, $dbname);<\/pre>\n
    Before we can go any further, however, we need to actually have some data to process – or know what data we want to process. I’ll come back to this in a while, but first let’s generate the URL string.<\/p>\n
    Generate a URL string<\/h2>\n
    At this point, I am making an assumption that you already have variables that you want to send. The key thing is to prepare that data to be sent to the server.<\/p>\n
    There are a number of ways in which you could send data with a web request; HTTP GET<\/strong>\u00a0and\u00a0POST <\/strong>being probably the most suited.<\/p>\n