C

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. C

#include <C_CkStringBuilder.h>
#include <C_CkHttpCurl.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkStringBuilder sbCurl;
    HCkHttpCurl curl;
    HCkStringBuilder 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 = 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) {
        printf("%s\n",CkHttpCurl_lastErrorText(curl));
        CkStringBuilder_Dispose(sbCurl);
        CkHttpCurl_Dispose(curl);
        CkStringBuilder_Dispose(sbRawRequest);
        return;
    }

    printf("%s\n",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);

    }