Unicode C

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. Unicode C

#include <C_CkStringBuilderW.h>
#include <C_CkHttpCurlW.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkStringBuilderW sbCurl;
    HCkHttpCurlW curl;
    HCkStringBuilderW sbRawRequest;

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

    curl = CkHttpCurlW_Create();

    //  In this example, the value we'll provide for the "message" variable
    //  will contain chars that require JSON escaping.
    CkHttpCurlW_SetVar(curl,L"message",L"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 = CkStringBuilderW_Create();
    success = CkHttpCurlW_ToRawRequest(curl,CkStringBuilderW_getAsString(sbCurl),sbRawRequest);
    if (success == FALSE) {
        wprintf(L"%s\n",CkHttpCurlW_lastErrorText(curl));
        CkStringBuilderW_Dispose(sbCurl);
        CkHttpCurlW_Dispose(curl);
        CkStringBuilderW_Dispose(sbRawRequest);
        return;
    }

    wprintf(L"%s\n",CkStringBuilderW_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!\""}


    CkStringBuilderW_Dispose(sbCurl);
    CkHttpCurlW_Dispose(curl);
    CkStringBuilderW_Dispose(sbRawRequest);

    }