Objective-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. Objective-C

#import <CkoStringBuilder.h>
#import <CkoHttpCurl.h>

BOOL success = NO;

// 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}}}'

CkoStringBuilder *sbCurl = [[CkoStringBuilder alloc] init];
[sbCurl AppendLn: @"curl -X POST https://api.example.com/messages \\"];
[sbCurl AppendLn: @"  -H \"Content-Type: application/json\" \\"];
[sbCurl AppendLn: @"  -d '{\"text\":\"{{message}}\"}'"];

CkoHttpCurl *curl = [[CkoHttpCurl alloc] init];

// In this example, the value we'll provide for the "message" variable
// will contain chars that require JSON escaping.
[curl SetVar: @"message" varValue: @"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.
CkoStringBuilder *sbRawRequest = [[CkoStringBuilder alloc] init];
success = [curl ToRawRequest: [sbCurl GetAsString] sb: sbRawRequest];
if (success == NO) {
    NSLog(@"%@",curl.LastErrorText);
    return;
}

NSLog(@"%@",[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!\""}