B4X Requires Chilkat v11.5.0+

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. B4X

Dim success As Boolean = 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 ChilkatStringBuilder
sbCurl.Initialize
sbCurl.AppendLn("curl -X POST https://api.example.com/messages \")
sbCurl.AppendLn("  -H " & Chr(34) & "Content-Type: application/json" & Chr(34) & " \")
sbCurl.AppendLn("  -d '{" & Chr(34) & "text" & Chr(34) & ":" & Chr(34) & "{{message}}" & Chr(34) & "}'")

Dim curl As ChilkatHttpCurl
curl.Initialize("curl")

'  In this example, the value we'll provide for the "message" variable
'  will contain chars that require JSON escaping.
curl.SetVar("message", "He said " & Chr(34) & "Hello, world!" & Chr(34))

'  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 ChilkatStringBuilder
sbRawRequest.Initialize
success = curl.ToRawRequest(sbCurl.GetAsString, sbRawRequest)
If success = False Then
    Log(curl.LastErrorText)
    Return
End If


Log(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!\""}