Delphi DLL Requires Chilkat v11.5.0+

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. Delphi DLL

var
success: Boolean;
sbCurl: HCkStringBuilder;
curl: HCkHttpCurl;
sbRawRequest: HCkStringBuilder;

begin
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}}}'

sbCurl := CkStringBuilder_Create();
CkStringBuilder_AppendLn(sbCurl,'curl -X POST https://api.example.com/messages \");
CkStringBuilder_AppendLn(sbCurl,'  -H "Content-Type: application/json" \");
CkStringBuilder_AppendLn(sbCurl,'  -d ''{"text":"{{message}}"}''');

curl := CkHttpCurl_Create();

//  In this example, the value we'll provide for the "message" variable
//  will contain chars that require JSON escaping.
CkHttpCurl_SetVar(curl,'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.
sbRawRequest := CkStringBuilder_Create();
success := CkHttpCurl_ToRawRequest(curl,CkStringBuilder__getAsString(sbCurl),sbRawRequest);
if (success = False) then
  begin
    Memo1.Lines.Add(CkHttpCurl__lastErrorText(curl));
    Exit;
  end;

Memo1.Lines.Add(CkStringBuilder__getAsString(sbRawRequest));

//  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!\""}

CkStringBuilder_Dispose(sbCurl);
CkHttpCurl_Dispose(curl);
CkStringBuilder_Dispose(sbRawRequest);