This article examines Xojo’s capabilities by building a simple web API service. You will learn to handle different HTTP methods, manage requests, and send meaningful responses. Xojo’s simplicity makes it an excellent choice for experienced developers transitioning from other languages, as well as those familiar with its user-friendly language.

Foundation: The HandleURL Function

Defining API Endpoints for GET Requests

GET requests are primarily used to retrieve data. To handle these requests effectively, let’s see how to define API endpoints that correspond to specific data or actions in the following code example:

If request.Method = "GET" Then
  Select Case request.Path
  Case "time"
    Var currentTime As String = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")
    response.Write("{""message"": """ + currentTime + """}")
    response.Status = 200
    Return True
  Case "hello"
    response.Write("{""message"": ""Hello, World!""}")
    response.Status = 200
    Return True
  End Select
End If

Here, we define two endpoints: /time and /hello.

A GET request to /time will return the current date and time in JSON format, while a request to /hello will return a friendly “Hello, World!” greeting.

The response.Status is set to 200, indicating a successful response. Learn more here about HTTP status codes.

Defining API Endpoints for POST Requests

While GET requests primarily retrieve data, POST requests submit data to the API for processing. Consider submitting a form online – you are sending data to the server via a POST request.

If request.Method = "POST" Then
  Select Case request.Path
  Case "some-data"
    Try
      Var jReceivedData As New JSONItem(request.Body)
      Response.Write(jReceivedData.ToString)
      Response.Status = 200
      Return True
    Catch e As JSONException
      response.Write("{""error"": ""Internal Server Error""}")
      response.Status = 500
      Return True
    End Try
  End Select
End If

In this example, a POST request to the /some-data endpoint expects to receive JSON data (request.Body) for processing.

If the data is successfully parsed, the API responds with the received data.

Otherwise, an error status and message are returned to the client.

Bringing it all Together

Now that you know how to manage “GET” and “POST” requests, you can start building more complex APIs, with different endpoints available for different methods. To further illustrate API endpoint development, consider the following detailed code example that can be used as template:

Function HandleURL(request As WebRequest, response As WebResponse) Handles HandleURL as Boolean
  response.MIMEType = "application/json"
  
  Try
    Select Case request.Method
    Case "GET"
      
      Select Case request.Path
      Case "time"
        Var currentTime As String = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")
        response.Write("{""message"": """ + currentTime + """}")
        response.Status = 200
        Return True
      Case "hello"
        response.Write("{""message"": ""Hello, World!""}")
        response.Status = 200
        Return True
      Else
        response.Write("{""error"": ""Not Found""}")
        response.Status = 404
        Return True
      End Select
      
    Case "POST"
      
      Select Case request.Path
      Case "some-data"
        Try
          Var jReceivedData As New JSONItem(request.Body)
          Response.Write(jReceivedData.ToString)
          Response.Status = 200
          Return True
        Catch e As JSONException
          response.Write("{""error"": ""Internal Server Error""}")
          response.Status = 500
          Return True
        End Try
      Else
        response.Write("{""error"": ""Not Found""}")
        response.Status = 404
        Return True
      End Select
      
    End Select
    
  Catch e As RuntimeException
    response.Write("{""error"": ""Internal Server Error""}")
    response.Status = 500
    Return True
  End Try
  
  response.Write("{""error"": ""Not Found""}")
  response.Status = 404
  Return True
  
End Function

Small note: observe the start line within the HandleURL function.

response.MIMEType = "application/json"

This line of code informs the client (browser, application) that the API service is responding using the JSON format. Setting the MIMEType to “application/json” is best practice and helps prevent any potential parsing errors on the client side.

Next Steps

You might notice that some code is repeating itself (hint: the error responses), so a good idea would be to create a helper method that deals with this particular type of code repetition. Additionally, consider moving the code from the HandleURL function to a separate method that is then invoked within the HandleURL function for improved organization. This restructuring will enhance code organization, making it easier to maintain, read, and improve the efficiency of the program.

P.S.: You should also check the article about microservices and their purpose to get a better idea of what kind of API interfaces you can create.

Gabriel is a digital marketing enthusiast who loves coding with Xojo to create cool software tools for any platform. He is always eager to learn and share new ideas!

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