Creating mysqldump in node with dockerode is resulting in a file with wrong mime-type

Question

I'm creating an application that should do a mysqldump from mysql running in a docker container. The application i'm creating is build in node.

This is the script that i'm using.

const containerId = '71501a8ab0f8';
const database = 'my-db';
const exportPath = `${database}.sql`;

const docker = new Dockerode({socketPath: '/var/run/docker.sock'});
const container = docker.getContainer(containerId);

const exec = await container.exec({
{
    Cmd: [
        'mysqldump',
        '--single-transaction',
        database,
    ],
    AttachStdin: true,
    AttachStdout: true
}
});

const stream = await exec.start({
    hijack: true,
    stdin: false
});

const writeStream = fs.createWriteStream(exportPath);
stream.pipe(writeStream);

stream.on('end', () => {
    console.log('Database dump successfully saved!');
});

This creates the sql file with dump of the database, but it's not really readable. When I do a file -I my-db.sql I get the following result:

my-db.sql: application/octet-stream; charset=binary

When I open in in a text-editor (sublime) I see a random sequence of characters.

But when I open de file with for example nano I just see the (plain text) content of the mysqldump.

What I noticed is that every chuck that was added to the generated file starts with some random characters. When I remove them manually and do the file -I my-db.sql again the result is:

my-db.sql: text/plain; charset=us-ascii

Now I'm also able to open the file in my text editor and see the actual dump.

I tried to just writes the chunks to the file when data arrives, like:

stream.on('data', (chunk: Buffer) => {
    writeStream.write(chunk.toString());
});

But this results in the same issue.

Since the script has to able to make dumps of large databases I really want to use the stream and pipe it to a file.

How can I get rid of the "characters" that are added before each inserted chuck so the file mime-type will be text/plain.

Answer 1

Just found the anwser myself. The stream needed to be demux first.

const stream = await exec.start({
    hijack: true,
    stdin: false
});

const writeStream = fs.createWriteStream(path);

docker.modem.demuxStream(stream, writeStream, process.stderr);