What is Common Gateway Interface (CGI)? How CGI works at a conceptual level

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Short Answer

The Common Gateway Interface (CGI) is a way for web servers to run programs. It helps make websites interactive by processing user data.

Here’s how CGI works?

  1. You visit a webpage and fill out a form.
  2. When you submit it, the server uses CGI to run a program.
  3. This program processes your data and might save it or create a webpage to show you.

The biggest downside of CGI is that it’s slow. Each time someone uses a CGI program, the server starts a new process. This can take a lot of time and resources, especially with many users.

Detailed Answer

The Common Gateway Interface, or CGI, is a standard protocol used to enable web servers to execute external programs, often referred to as CGI scripts. These scripts can be written in various programming languages such as Perl, Python, or C. CGI scripts are used to generate dynamic content on web pages or to handle form submissions.

How CGI works?

  1. User Action: A user interacts with a webpage by clicking a link or submitting a form.
  2. Web Server Request: The user’s browser sends a request to the web server.
  3. CGI Script Execution: The web server passes the request to a CGI script.
  4. Processing: The CGI script runs, processing the request. It might access databases or perform calculations.
  5. Response Creation: The script generates a response, often in HTML format.
  6. Server Response: The web server sends the script’s response back to the user’s browser.
  7. Display: The user’s browser displays the result.

CGI scripts act as a bridge between the web server and external applications. When a CGI script is called, the server creates a new process to execute the script, which then sends its output back to the server, and in turn, to the client’s browser.

The highest disadvantage of CGI is its performance impact. Since a new process is created for each CGI script execution, this can be resource-intensive. This means that for high-traffic websites, CGI can lead to slower response times and increased server load.

For example, if you have a survey form on your website, a CGI script can process the submitted data. When a user completes the form and hits submit, the CGI script will take the data, perhaps store it in a database, and then generate a thank you page.

In conclusion, CGI is a way for web servers to interact with external programs to provide dynamic content. However, due to its resource-heavy nature, creating a new process for each request, CGI can be inefficient for busy websites. This has led to the development of more efficient technologies like server-side scripting languages and frameworks that maintain persistent server processes.