Support request headers by hyperlinks

[blablabla1234678]

My old dream to use mongodb _id-s for cache etagging. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag https://orangematter.solarwinds.com/2019/12/22/what-is-mongodbs-id-field-and-how-to-use-it/ I want to think it through how to support this with a REST service. In general this means resource versioning.

[blablabla1234678]

Mongodb has a _id UUID which could be used in Etag. Etag is relative easy to understand, it is a version identifier of a resource. We can use if-match for POST, PUT, DELETE, PATCH and it will give 422 if the latest version is not matching the etag. We can use if-none-match for GET and the server returns 304 not modified if the resource has not changed since we grabbed the etag from the last request. So it is pretty useful. Though how do we know the etags to send?

[blablabla1234678]

We need to send the etags in the response. We can either send an etag header or include them into the body of the response. The first is the standard way. The only problem that we can have nested resources something like the following:

GET /a/123

{
    items: {
        b: {
            items: {c: 1, d:3},
            hyperlinks: {
                self: {
                    type: "readB",
                    id: 456
                }
            }
        }
    },
    hyperlinks: {
        self: {
            type: "readA",
            id: 123
        }
    }
}

[blablabla1234678]

Here we have two options.

• The nested resource B is a value object instead of an entity and it changes with A. Thus they have the same version identifier.
• The nested resource B has a separate version identifier. If so, then we need to include its etag if we add for example a PUT link.

[blablabla1234678]

{
    version: "sdghkg4352asgreh",
    items: {
        b: {
            version: "adg235hdfhg46a",
            items: {c: 1, d:3},
            hyperlinks: {
                self: {
                    type: "readB",
                    id: 456
                },
                edit: {
                    type: "updateB",
                    id: 456,
                    c: 1,
                    d: 3
                },
            }
        }
    },
    hyperlinks: {
        self: {
            type: "readA",
            id: 123
        }
    }
}

[blablabla1234678]

Another option is adding the version to each of the hyperlinks:

{
    items: {
        b: {
            items: {c: 1, d:3},
            hyperlinks: {
                self: {
                    version: "adg235hdfhg46a",
                    type: "readB",
                    id: 456
                },
                edit: {
                    version: "adg235hdfhg46a",
                    type: "updateB",
                    id: 456,
                    c: 1,
                    d: 3
                },
            }
        }
    },
    hyperlinks: {
        self: {
            version: "sdghkg4352asgreh",
            type: "readA",
            id: 123
        }
    }
}

[blablabla1234678]

I might prefer using the hyperlinks header part and send explicitly if-match. Since this is a general solution for headers I think the name of the issue can be changed.

[blablabla1234678]

Maybe using FlatObject for requests is not a good idea after all because it is hard to add additional metadata like headers.