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Lawrence Aberba


A generalist full stack developer, open source contributor and an avid Linux user


Multiple file upload in vibe.d

Multiple files upload form

Previously, I did a demo on how to submit a form in vibe.d including a file upload. Now its time to demo multiple file upload which sometimes come in handy. This post serves as continuation so refer to it to catch up.

Similar to the previous post, we will create an upload function which will handle file uploads on the server side. However, I will only implement the multiple file upload functionality without boring you with textual data which I did previously. Create a new vibe.d project and build upon it to a point where you have the upload function (You may use code from the previous post).

So lets rock and roll ASAP, shall we. Multiple file input (of any number) can be specified in an HTML form by appending square brackets ("[]") to the value of the name property.

Using JavaScript, you can dynamically add file inputs to allow user to upload several file at a time.

The diet template code will be:

doctype html
head
    title File upload
body
    form(method='post',action='/upload',enctype='multipart/form-data')
        p
            label(for='picture[]') Select multiple pictures
            br
            input(name='picture[]', type='file')
            br
            input(name='picture[]', type='file')
        
        button(type='submit') Upload

The enctype='multipart/form-data' is necessary to submit files in a form as discussed in my previous post. As you can see, the value of the name property of all the file inputs is picture[]. This makes it easy to identify all those files, as we will see below, as belonging to the same category. This is particularly useful for uploading one or more of a certain file without having to give each file a unique name value for identification on the server side.

Within the upload function, add the following code:

void upload(HTTPServerRequest req, HTTPServerResponse res)
{
    import std.conv: to;
    import std.path: extension;

    foreach(nameAttr, picture; req.files) {

        // Extract file extension
        string ext = extension(to!string(picture.filename));

        // Sort files based on "name" attribute
        // Only files with name="picture[]" will be uploaded
        if (nameAttr == "picture[]" && (ext == ".png" || ext == ".jpg"))
        {
            import std.datetime: Clock;
            // Rename uploaded file using current timestamp to make it unique
            string newFileName = "image_" ~ to!string(Clock.currTime.toUnixTime) ~ ext;

            try {
                logInfo("Move successful!");
                moveFile(picture.tempPath, Path("./public/pictures/" ~ newFileName));
            } catch (Exception e) {
                logInfo("Exception thrown");
                copyFile(picture.tempPath, Path("./public/pictures/" ~ newFileName));
            }
        }
    }

    res.redirect("/");
}

The extension of each uploaded file is extracted using the extension function from std.path to be used in renaming. We then iterate over the submitted files in the form to filter out those that do not have a name value of picture[]. As common in file uploads, you may also choose to only allow files of certain extension (“.png”, “.jpg”, “.jpeg”, “.gif,”, “.pdf”, etc), which I implemented only for image files with either “.png” or “.jpg” extension.

Uploaded files may contain certain characters which are not allowed in some Operating Systems, and one approach is by giving each file a custom file name which you can guarantee will not cause any issues. I therefore renamed each file as "image_" appended with the current Unix timestamp and the file extension. The file is then moved to public/pictures/ or copied in-case an exception is thrown (who knows what else can happen).

Make sure you create the pictures directory in your public folder.

That’s all it takes to upload multiple files in vibe.d, I may demo how to implement the same functionality using the Web Interface of vibe.d but not until I write an introductory blog about it and why you really need to use it in most cases.

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