¿Cómo PUBLICAR datos JSON con PHP cURL?

Aquí está mi código

$url = 'url_to_post';
$data = array(
    "first_name" => "First name",
    "last_name" => "last name",
    "email"=>"email@gmail.com",
    "addresses" => array (
        "address1" => "some address",
        "city" => "city",
        "country" => "CA",
        "first_name" =>  "Mother",
        "last_name" =>  "Lastnameson",
        "phone" => "555-1212",
        "province" => "ON",
        "zip" => "123 ABC"
    )
);
$data_string = json_encode($data);
$ch=curl_init($url);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS, array("customer"=>$data_string));
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER,
    array(
        'Content-Type:application/json',
        'Content-Length: ' . strlen($data_string)
    )
);

$result = curl_exec($ch);
curl_close($ch);

Y en otra página, estoy recuperando datos de publicaciones.

    print_r ($_POST);

La salida es

HTTP/1.1 200 OK
Date: Mon, 18 Jun 2012 07:58:11 GMT
Server: Apache
X-Powered-By: PHP/5.3.6
Vary: Accept-Encoding
Connection: close
Content-Type: text/html

Array ( ) 

Por lo tanto, no obtengo los datos adecuados ni siquiera en mi propio servidor, es una matriz vacía. Quiero implementar REST usando json como en http://docs.shopify.com/api/customer#create

Está PUBLICANDO el json de forma incorrecta, pero incluso si fuera correcto, no podría realizar la prueba usando print_r($_POST)( lea por qué aquí ). En cambio, en su segunda página, puede atrapar la solicitud entrante usando file_get_contents("php://input"), que contendrá el json POSTed . Para ver los datos recibidos en un formato más legible, intente esto:

echo '<pre>'.print_r(json_decode(file_get_contents("php://input")),1).'</pre>';

En su código, está indicando Content-Type:application/json, pero no está codificando json todos los datos POST, solo el valor del campo POST "cliente". En cambio, haz algo como esto:

$ch = curl_init( $url );
# Setup request to send json via POST.
$payload = json_encode( array( "customer"=> $data ) );
curl_setopt( $ch, CURLOPT_POSTFIELDS, $payload );
curl_setopt( $ch, CURLOPT_HTTPHEADER, array('Content-Type:application/json'));
# Return response instead of printing.
curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
# Send request.
$result = curl_exec($ch);
curl_close($ch);
# Print response.
echo "<pre>$result</pre>";

Nota al margen: puede beneficiarse al usar una biblioteca de terceros en lugar de interactuar directamente con la API de Shopify.

$url = 'url_to_post';
$data = array("first_name" => "First name","last_name" => "last name","email"=>"email@gmail.com","addresses" => array ("address1" => "some address" ,"city" => "city","country" => "CA", "first_name" =>  "Mother","last_name" =>  "Lastnameson","phone" => "555-1212", "province" => "ON", "zip" => "123 ABC" ) );

$postdata = json_encode($data);

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $postdata);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));
$result = curl_exec($ch);
curl_close($ch);
print_r ($result);

Este código me funcionó. Puedes probar...

Reemplazar

curl_setopt($ch, CURLOPT_POSTFIELDS, array("customer"=>$data_string));

con:

$data_string = json_encode(array("customer"=>$data));
//Send blindly the json-encoded string.
//The server, IMO, expects the body of the HTTP request to be in JSON
curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);

No entiendo lo que quieres decir con "otra página", espero que sea la página en: 'url_to_post'. Si esa página está escrita en PHP, el JSON que acaba de publicar arriba se leerá de la siguiente manera:

$jsonStr = file_get_contents("php://input"); //read the HTTP body.
$json = json_decode($jsonStr);

Por favor, intente este código: -

$url = 'url_to_post';

$data = array("first_name" => "First name","last_name" => "last name","email"=>"email@gmail.com","addresses" => array ("address1" => "some address" ,"city" => "city","country" => "CA", "first_name" =>  "Mother","last_name" =>  "Lastnameson","phone" => "555-1212", "province" => "ON", "zip" => "123 ABC" ) );

$data_string = json_encode(array("customer" =>$data));

$ch = curl_init($url);

curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);

curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type:application/json'));

curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

$result = curl_exec($ch);

curl_close($ch);

echo "$result";

Prueba este ejemplo.

<?php 
 $url = 'http://localhost/test/page2.php';
    $data = array("first_name" => "First name","last_name" => "last name","email"=>"email@gmail.com","addresses" => array ("address1" => "some address" ,"city" => "city","country" => "CA", "first_name" =>  "Mother","last_name" =>  "Lastnameson","phone" => "555-1212", "province" => "ON", "zip" => "123 ABC" ) );
    $ch=curl_init($url);
    $data_string = urlencode(json_encode($data));
    curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
    curl_setopt($ch, CURLOPT_POSTFIELDS, array("customer"=>$data_string));


    $result = curl_exec($ch);
    curl_close($ch);

    echo $result;
?>

Su código page2.php

<?php
$datastring = $_POST['customer'];
$data = json_decode( urldecode( $datastring));

?>

Intenta así:

$url = 'url_to_post';
// this is only part of the data you need to sen
$customer_data = array("first_name" => "First name","last_name" => "last name","email"=>"email@gmail.com","addresses" => array ("address1" => "some address" ,"city" => "city","country" => "CA", "first_name" =>  "Mother","last_name" =>  "Lastnameson","phone" => "555-1212", "province" => "ON", "zip" => "123 ABC" ) );
// As per your API, the customer data should be structured this way
$data = array("customer" => $customer_data);
// And then encoded as a json string
$data_string = json_encode($data);
$ch=curl_init($url);

curl_setopt_array($ch, array(
    CURLOPT_POST => true,
    CURLOPT_POSTFIELDS => $data_string,
    CURLOPT_HEADER => true,
    CURLOPT_HTTPHEADER => array('Content-Type:application/json', 'Content-Length: ' . strlen($data_string)))
));

$result = curl_exec($ch);
curl_close($ch);

La clave que olvidó fue json_encode sus datos. Pero también puede resultarle conveniente utilizar curl_setopt_array para configurar todas las opciones de curva a la vez pasando una matriz.