Promise Precedence when Trying to Upload File to Google Storage

Question

I am uploading a file to Google Cloud. On complete, I want to return the file URL and some metadata. I am trying to do it like this:

blobStream.on('finish', () => {

                var fileSize;
                var fileCreated;

                fileUpload.getMetadata()
                    .then(metadata => { 
                        const mObj = metadata[0];
                        fileSize = mObj.size;
                        fileCreated = mObj.timeCreated;
                });

                fileUpload.getSignedUrl({
                    action: 'read',
                    expires: '03-09-2491'
                }).then(signedUrl => {
                    let response = {};
                        response.name = newFileName;
                        response.size = fileSize;
                        response.created = fileCreated;
                        response.url = signedUrl[0];
                    resolve(response);
                }).catch(error => {
                    reject(error);  
                });

            });

The problem is, the getSignedUrl method always fires first and "fileSize" + "fileCreated" are never populated.

I believe I need to chain the events so getMetadata happens first but am relatively new to Node (and Promises) and could use some suggestions.

EDITED PER BERGI'S REPLY: (The Below Method Works)

uploadFileToStorage(file) {

    let utils = new Utils();
    let newFileName = `${utils._guid()}-${Date.now()}`;
    let bucket = admin.storage().bucket();
    let filePath = url.format('audioFiles/' + newFileName);
    let fileUpload = bucket.file(filePath);

    let prom = new Promise(function(resolve, reject) {

        if (!file) {
            reject('No file provided');
            return;
        }

        const blobStream = fileUpload.createWriteStream({
            metadata: {
                contentType: file.mimetype
            }
        });

        blobStream.on('error', (error) => {
            reject('Something is wrong! Unable to upload at the moment.');
            return;
         });

        blobStream.on('finish', resolve);

        blobStream.end(file.buffer);

      }).then(() => { 

        return Promise.all([
            fileUpload.getMetadata(),
            fileUpload.getSignedUrl({
                action: 'read',
                expires: '03-09-2491'
            }),
        ]);

    }).then(([metadata, signedUrl]) => {

        const fileSize = metadata[0].size;
        const fileCreated = metadata[0].timeCreated;
        const response = {
            name: newFileName,
            size: fileSize,
            created: fileCreated,
            url: signedUrl[0],
        };

        return response;

    });

    return prom;

}

If you need more, let me know how can I improve this question? — Peter, Jun 07 '18 at 21:08
One option is to move getSignedUrl into where you receive your metadata. Or, chain another .then() after the getMetadata().then(). — Frank Natividad, Jun 07 '18 at 21:21

score 2 · Accepted Answer · answered Jun 07 '18 at 21:39

2

Don't create two independent promises, and don't use outer-scope variables that you never know when they are going to be assigned. Instead, use Promise.all to wait for multiple promises:

new Promise(resolve => {
    blobStream.on('finish', resolve);
}).then(() => {
    return Promise.all([
        fileUpload.getMetadata(),
        fileUpload.getSignedUrl({
            action: 'read',
            expires: '03-09-2491'
        }),
    ]);
}).then(([metadata, signedUrl]) => {
    const fileSize = metadata[0].size;
    const fileCreated = metadata[0].timeCreated;
    const response = {
        name: newFileName,
        size: fileSize,
        created: fileCreated,
        url: signedUrl[0],
    });
    return response;
});

Also avoid using further promises inside the Promise constructor!

answered Jun 07 '18 at 21:39

Bergi

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Thanks Bergi. I have posted my entire method above. I am currently getting "TypeError: Cannot read property 'then' of undefined" – Peter Jun 08 '18 at 14:30
@Peter In the `if (!file)` condition, you will want to `return` from the function after rejecting. Also, the complete `uploadFileToStorage` function doesn't `return` the result of the promise chaining - so in `uploadFileToStorage().then(…)` usage it produces `undefined`. – Bergi Jun 08 '18 at 14:33
Thanks a lot, @Bergi. I really appreciate it. I worked it through and posted the final version in my original post. Thanks so much! – Peter Jun 08 '18 at 16:11

Promise Precedence when Trying to Upload File to Google Storage

1 Answers1