How to avoid binary characters in the result of a docker engine api http exec call? - docker

Question

When running a
http://127.0.0.1:2375/exec/xxxxx/start
i get a response of type application/vnd.docker.raw-stream
with some binary chars in the response. so for example, when calling "date" inside a docker container, the response always looks like this (screenshot made from postman):
in joe (editor) I see: A######]Wed Dec 29 00:55:05 CET 2021
and vi (editor) shows A^#^#^#^#^#^#^]Wed Dec 29 00:55:05 CET 2021
I wasn´t able to find anything to control the output via docker.
So I want to ask, what is the best way to get rid of these binary characters? In the end, I want to parse the result via PHP, but maybe there is a way to avoid these characters in the first place because these characters are nearly everywhere.

Answer 1

First:
As far as I have seen, there is no way to tell the Docker Engine to get something else than a "stream" as a response, because it´s the nature of some Docker calls, for example, if you "attach" to a running container, the output can be endless so it´s not a "one call->wait 2 seconds->get response" - because containers can run forever, so the output can be endless long.
Secondly:
Removing the binary string with a simple regex is working like explained here.
Finally:
How to read the Stream with PHP?
Using Guzzle is in most cases the easiest way to handle HTTP calls with PHP.
<?php
$response = $client->request('POST', '/exec/' . $id . '/start', [
'json' => [
"Detach" => false,
"Tty" => false,
],
'stream' => true // <---------- THIS IS THE IMPORTANT PART HERE
]);
The Docker Engine Documentation clearly explains how to read the Stream:
The simplest way to implement this protocol is the following:
Read 8 bytes.
Choose stdout or stderr depending on the first byte.
Extract the frame size from the last four bytes.
Read the extracted size and output it on the correct output.
Goto 1.
So with the Help of an old PHP Package, that shows how it's done, I
was able to finally get a "clear" output:
$body = $response->getBody();
$str = '';
do {
$strToUnpack = $body->read(8);
if (strlen($strToUnpack)) {
$decoded = \unpack('C1type/C3/N1size', $strToUnpack);
if ($decoded) {
$str = $body->read($decoded['size']);
echo $str . "\n";
}
}
} while (!$body->of());