In this module, we will explore how to use APIs (Application Programming Interfaces) within Control Language (CL) programs. APIs allow CL programs to interact with other software components, services, or systems, enabling a wide range of functionalities and integrations.

An API is a set of rules and protocols for building and interacting with software applications. It defines the methods and data formats that applications can use to communicate with each other. APIs are essential for enabling software components to interact and share data.

• Endpoint: A specific URL where an API can be accessed.
• Request: The act of asking for data or action from an API.
• Response: The data or action returned by the API.
• HTTP Methods: Common methods include GET (retrieve data), POST (send data), PUT (update data), and DELETE (remove data).

Before you can use APIs in your CL programs, ensure that your environment is properly set up:

1. Network Configuration: Ensure your system can access the internet or the network where the API is hosted.
2. API Credentials: Obtain any necessary API keys or authentication tokens required to access the API.

CL does not natively support HTTP requests, so you will typically use external programs or utilities to make API calls. One common approach is to use the QSH (QShell) command to execute curl commands.

Here is an example of how to make a GET request to an API using CL:

1. Declare Variables: Define the URL and a variable to store the response.
2. QSH Command: Use the QSH command to execute a curl command that makes the GET request and saves the response to a temporary file.
3. Retrieve Response: Read the response from the file and store it in a variable.
4. Send Program Message: Display the response.

Write a CL program that makes a POST request to an API to send data.

Requirements:

• The API endpoint is https://api.example.com/submit.
• The data to be sent is in JSON format: {"name": "John Doe", "email": "[email protected]"}.
• Save the response to a file and display it.

1. Declare Variables: Define the URL, data to be sent, and a variable to store the response.
2. QSH Command: Use the QSH command to execute a curl command that makes the POST request with the JSON data and saves the response to a temporary file.
3. Retrieve Response: Read the response from the file and store it in a variable.
4. Send Program Message: Display the response.

• Incorrect URL: Ensure the URL is correct and accessible.
• Missing Headers: Some APIs require specific headers (e.g., Content-Type).
• Authentication: Ensure you include any necessary API keys or tokens.

• Use Variables: Store URLs, data, and other parameters in variables for easier management.
• Error Handling: Implement error handling to manage failed API calls gracefully.
• Logging: Log API requests and responses for debugging and auditing purposes.

In this section, we learned how to use APIs within CL programs by making HTTP requests using the QSH command and curl. We covered both GET and POST requests, providing practical examples and exercises to reinforce the concepts. Understanding how to interact with APIs opens up a wide range of possibilities for integrating CL programs with other systems and services.

Next, we will explore how to interface with databases in the following module.