I can get curl_init() working, but not curl_multi_init() - php

Question

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Jonathon Philip Chambers wants to draw more attention to this question:
Even a clue or insight that leads me to discovering the correct answer on my own is worthy of the green tick.
This is my first time using curl_multi_init() so I'm probably misunderstanding something. Learning to use it properly is more important to me than solving my problem because this particular function will solve a lot of my problems in future.
This particular call is for uploading Etsy photos. Etsy documentation for this call here.
It works fine in Postman. The code snippet postman generates for "PHP - cURL" works fine. It keeps working fine even after my edits to it.
Trouble is, I've got well over a thousand high resolution images to upload, so running the entire snippet from start to finish, then looping it a thousand times will time out no matter how generous my php.ini settings.
So, line by line I merged the existing code with a synchronous snippet and, I must have done something wrong. This example is almost exactly the live code. I've just deleted/simplified irrelevant things and redacted personal information. (Hopefully I didn't delete/simplify the bug.):
<?php
include_once 'databaseStuff.php';
include_once 'EtsyTokenStuff.php';
$result = mysqli_query($conn, "SELECT product, listing_id, alt_text, dataStuff;");
$multiCurl = [];
$multiResult = [];
$multiHandle = curl_multi_init();
if (mysqli_num_rows($result) > 0){
while ($row = mysqli_fetch_assoc($result)){
for($image = 1; $image <=2; $image++){
$multiCurl[$row['product'] . "_" . $image] = curl_init();
curl_setopt_array($multiCurl[$row['product'] . "_" . $image],
array(
CURLOPT_URL => "https://openapi.etsy.com/v3/application/shops/$myShopNumber/listings/" . $row['listing_id'] . "/images",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => '',
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 0,
CURLOPT_FOLLOWLOCATION => true,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => 'POST',
CURLOPT_POSTFIELDS => array(
"image" => new CURLFILE(
[
1 => "img/imagePathStuff/" . $row['product'] . ".jpg",
2 => "img/differentImagePathStuff/" . $row['product'] . ".jpg"
][$image]
),
// "listing_image_id" =>,
"rank" => $image,
"overwrite" => true,
// "is_watermarked" =>,
"alt_text" => $row['alt_text']
),
CURLOPT_HTTPHEADER => array(
"x-api-key: $myAPIKey",
"authorization: Bearer {$etsyAccessToken}"
),
)
);
curl_multi_add_handle($multiHandle, $multiCurl[$row['product'] . "_" . $image]);
}
}
$index = null;
do {
curl_multi_exec($multiHandle, $index);
} while($index > 0);
foreach($multiCurl as $k => $curlHandle){
$multiResult[$k] = curl_multi_getcontent($curlHandle);
curl_multi_remove_handle($multiHandle, $curlHandle);
}
curl_multi_close($multiHandle);
}
Once it starts working I'll probably block it out into functions, but I prefer to edit broken code in this format and add the function calls later.
Having never worked with these functions before, I'm not sure how they're supposed to behave but the behaviour I've noticed:
All of the code executes, start to finish, no fatal errors.
The do-while loop executes once then loops once more. (Maybe it's supposed to or maybe it's supposed to loop once per photo. Couldn't get that clarified anywhere.)
It's supposed to update photos. Unfortunately the first test was on very minor edits, but trying again including a deliberately wrong photo I at least know that that particular photo didn't update, so probably none of them updated.
curl_multi_getcontent($curlHandle) always returns an empty string
curl_multi_exec($multiHandle, $index) always returns 0 (Previous claim that it was 1002 was incorrect. 1002 was actually the value of the second argument $index after running the function.)
This particular call normally has very detailed responses for 201 and at least returns the error for 400, 401, 403, 404, 409, and 500, but I don't think my code is even going far enough to make the call. I haven't even figured out how to get the response codes at all.
For a script that transfers well over one thousand high resolution images from my server to Etsy's server, it certainly executes very fast.
The $multiHandle seems to work as intended. At the very least, a var_dump($multiHandle) reveals all the correct file names in there.
I've lost an entire work day to this issue, but it wouldn't surprise me if it's a minor typo causing this. What is it?

Answer 1

This is just a bit of a guess, but if your problem is that your are timing out, then it seems that the following loop you coded may be the problem:
$index = null;
do {
curl_multi_exec($multiHandle, $index);
} while($index > 0);
You are making repeated calls to curl_multi_exec, which is burning up CPU all the while you are waiting for all of your uploads to complete. You should instead only periodically be checking the status of your uploads and going into a wait state in between. This should reduce your total CPU time:
while (TRUE) {
$status = curl_multi_exec($multiHandle, $activeCount);
if ($status == CURLM_OK && $activeCount) {
// Wait some time before checking again:
curl_multi_select($mh, $timeout=1.0);
}
else {
break;
}
}