Parsing Request Bodies

Interactive Web applications typically require some type of user input (whether that user is a human, machine, or otherwise is irrelevant). Angel3 features built-in support for parsing request bodies with the following content types:

  • application/x-www-form-urlencoded

  • application/json

  • multipart/form-data

Body Parsing

All you need to do to parse a request body is call RequestContext.parseBody. This method is idempotent, and only ever performs the body-parsing logic once, so it is recommended to call it any time you access the request body, unless you are 100% sure that it has been parsed before.

You can access the body as a Map, List, or Object, depending on your use case:'/my_form', (req, res) async {
    // Parse the body, if it has not already been parsed.
    await req.parseBody();

    // Access fields from the body, which is the most common use case.
    var userId = req.bodyAsMap['user_id'] as String;

    // If the user posted a List, i.e., through JSON:
    var count = req.bodyAsList.length;

    // To access the body, regardless of its runtime type:
    var objectBody = req.bodyAsObject as SomeType;

Handling File Uploads

In the case of multipart/form-data, Angel will also populate the uploadedFiles field. The UploadedFile wrapper class provides mechanisms for reading content types, metadata, and accessing the contents of an uploaded file as a Stream<List<int>>:'/upload', (req, res) async {
    await req.parseBody();

    var file = req.uploadedFiles.first;

    if (file.contentType.type == 'video') {
        // Write directly to a file.

Custom Body Parsing

You can handle other content types by manually parsing the body. You can set bodyAsObject, bodyAsMap, or bodyAsList exactly once:

Future<void> unzipPlugin(Angel app) async {
    app.fallback((req, res) async {
        if (!req.hasParsedBody
            && req.contentType.mimeType == 'application/zip') {
            var archive = await decodeZip(req.body);
            var fields = <String, dynamic>{};

            for (var file in archive.files) {
                fields[file.path] = file.mode;

            req.bodyAsMap = fields;

        return true;

If the user did not provide a content-type header when parseBody is called, a 400 Bad Request error will be thrown.

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