(Xojo Plugin) curl with Variable Substitution in a JSON Request Body

See more CURL Examples

This example shows how to use variables inside a JSON request body using the {{variable_name}} syntax. When the HTTP request’s Content-Type indicates JSON, Chilkat automatically applies proper JSON escaping to each substituted value, ensuring the resulting JSON remains valid.

Note: This example requires Chilkat v11.5.0 or greater.

Chilkat Xojo Plugin Download

Xojo Plugin for Windows, Linux, Mac OS X, and ARM, ARM64

Dim success As Boolean
success = False

// Variable names are enclosed between {{ and }}
// Important: The variable {{var_name}} should be placed inside the quotes.

// This is correct:
// curl -X POST https://api.example.com/messages \
//   -H "Content-Type: application/json" \
//   -d '{"text":"{{message}}"}'

// This is incorrect:
//   -d '{"text":{{message}}}'

Dim sbCurl As New Chilkat.StringBuilder
success = sbCurl.AppendLn("curl -X POST https://api.example.com/messages \")
success = sbCurl.AppendLn("  -H ""Content-Type: application/json"" \")
success = sbCurl.AppendLn("  -d '{""text"":""{{message}}""}'")

Dim curl As New Chilkat.HttpCurl

// In this example, the value we'll provide for the "message" variable
// will contain chars that require JSON escaping.
curl.SetVar "message","He said ""Hello, world!"""

// To demonstrate how the variables are replaced, this example does not execute the curl command. 
// Instead, it generates the raw HTTP request that would be sent if the curl command were run.
Dim sbRawRequest As New Chilkat.StringBuilder
success = curl.ToRawRequest(sbCurl.GetAsString(),sbRawRequest)
If (success = False) Then
    System.DebugLog(curl.LastErrorText)
    Return
End If

System.DebugLog(sbRawRequest.GetAsString())

// The output is shown below.
// Notice that the quote chars around "Hello World!" are properly JSON escaped.

// POST /messages HTTP/1.1
// Host: api.example.com
// Content-Type: application/json
// Content-Length: 36
// 
// {"text":"He said \"Hello, world!\""}