php脚本返回值，尽管既没有“echo”也没有“print”，也没有使用“printf”？

Question

I've created this php script a while ago that is working well.

UPDATE

(Removed a lot of text that turns out not relevant for this problem.)

Only thing: I don't know why it is working. (returns $result and I don't know how)

UPDATE

Due to request here the original (sensible info replaced) script in question:

<?php

    $http_origin = $_SERVER['HTTP_ORIGIN'];

    if ($http_origin == "https://some.domains.tld" ||
        $http_origin == "https://some.domains.tld" ||
        $http_origin == "https://some.domains.tld" ||
        $http_origin == "https://some.domains.tld" ||
        $http_origin == "https://some.domains.tld")
    {
      header("Access-Control-Allow-Origin: ".$http_origin);
    }

    ### global variables
    $curl; $mode = $_POST['mode'];

    ### init logging
    $file = fopen('error.txt', 'w');

    ### log request source
    #fwrite($file, "request from: ".$http_origin."
");

    ### create variable parameters
    $api_key='mysecretkey';

    ###Init curl
    #fwrite($file, "Ok, try to include curl..."."
");

    try{
        $curl = curl_init();
    }catch(Exception $e){
        fwrite($file, "curl init failed. Look: "."
".$e."
");
        return null;
    }

    switch ($mode) {
        case 'alldatas':
            alldatas();
            break;

        case 'adata':
            adata();
            break;

        case 'register':
            register();
            break;

        default:
            return;
    }

    ###Get list of all datas
    function alldatas()
    {
        global $curl;
        global $api_key;
        global $file;
        $result;

        $params = ['api_key' => $api_key];

        try{
            curl_setopt($curl, CURLOPT_URL, "https://some.third-party.service/api/v2/ever/webinars");
            curl_setopt($curl, CURLOPT_POST, true);
            curl_setopt($curl, CURLOPT_POSTFIELDS, $params);

            $result = curl_exec($curl);

        }catch(Exception $e){
            fwrite($file, "data list failed. Look: "."
".$e."
");
            return null;
        }

        return $result;
    }

    ###Get a data
    function adata()
    {
        global $curl;
        global $api_key;
        global $file;
        $result;

        $data_id = $_POST['data_id'];

        if($data_id){

            $params = [
                'api_key' => $api_key,
                'data_id' => $data_id
            ];

            try{
                curl_setopt($curl, CURLOPT_URL, "https://some.third-party.service/api/v2/ever/webinar");
                curl_setopt($curl, CURLOPT_POST, true);
                curl_setopt($curl, CURLOPT_POSTFIELDS, $params);

                $result = curl_exec($curl);

            }catch(Exception $e){
                fwrite($file, "webinar fetch failed, man. Look: "."
".$e."
");
                return null;
            }

            return $result;

        }

    }

    ###Register user to a datas
    function register(){

        global $curl;
        global $api_key;
        global $file;
        $result;

        $data_id = $_POST['data_id'];
        $name = $_POST['name'];
        $email = $_POST['email'];
        $schedule = $_POST['schedule'];
        $timezone = $_POST['timezone'];

        if($data_id && $name && $email && $schedule && $timezone){

            $params = [
                'api_key'=>$api_key,
                'data_id'=>$data_id,
                'name'=>$name,
                'email'=>$email,
                'schedule'=>$schedule,
                'timezone'=>$timezone
            ];

            try{
                curl_setopt($curl, CURLOPT_URL, "https://some.third-party.service/api/v2/ever/register");
                curl_setopt($curl, CURLOPT_POST, true);
                curl_setopt($curl, CURLOPT_POSTFIELDS, $params);

                $result = curl_exec($curl);

            }catch(Exception $e){
                fwrite($file, "data list failed. Look: "."
".$e."
");
                return null;
            }

        }
        return $result;
    }

?>

Answer 1

You are not setting CURLOPT_RETURNTRANSFER in your curl_setopt(). What that means is that when curl_exec() is called, the result of the cURL transfer is echoed out! That's where your returned data is coming from.

When CURLOPT_RETURNTRANSFER is TRUE, then curl_exec() returns the data and echos nothing. But, when CURLOPT_RETURNTRANSFER is FALSE (or unset), then curl_exec() echos the data and returns TRUE.