(VBScript) curl with Variable Substitution in a JSON Request Body

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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.

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Dim fso, outFile
Set fso = CreateObject("Scripting.FileSystemObject")
'Create a Unicode (utf-16) output text file.
Set outFile = fso.CreateTextFile("output.txt", True, True)

success = 0

' 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}}}'

set sbCurl = CreateObject("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}}""}'")

set curl = CreateObject("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.
set sbRawRequest = CreateObject("Chilkat.StringBuilder")
success = curl.ToRawRequest(sbCurl.GetAsString(),sbRawRequest)
If (success = 0) Then
    outFile.WriteLine(curl.LastErrorText)
    WScript.Quit
End If

outFile.WriteLine(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!\""}

outFile.Close