Canary fields
"Judson Lester [email protected] [rest-discuss]" <[email protected]> Tue, 20 Jun 2017 20:59:14 +0000
| Newsgroups | gmane.comp.web.services.rest |
|---|---|
| Message-ID | <CAOpbp3cRS-z+13AjuOz=JVqs8jnvFf6kgeChRwXqXm+h1PE4Mg@mail.gmail.com> |
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I've just had a problem with serialization of JSON in Go that seems like it
would be a general problem. I don't know about the elegance of my solution
or its generality but I doubt I'm the only one who came to it, and further
than others must've come up with something similar.
The context is this: Go permissively deserializes JSON into structs -
attributes that don't correspond to a struct member are ignored silently,
and struct members without a corresponding JSON attribute are left with a
zero value. When the server is upgraded, if its versions of JSON resources
get new attributes, the client ignores them (nbd), but when the client does
a PUT with the intention of updating, it zeros out attributes of which it
is unaware. The solution to this problem was not difficult (and involved an
applicaiton of the concept of lenses in the Go context...).
The problem is: if the server receives an PUT update, how does it know that
the update is legitimate, or produced by a pre-lens client who may have
elided important fields?
My solution is that the server adds a JSON attribute on all resources whose
name is the Etag of the resource, and whose value is (unconditionally)
"canary." PUTs without this field intact are assumed not to know how to
properly do updates and return a 4xx status.
I dimly feel as if I'm reimplementing something I may have heard/read in
passing, but I'm wondering if the technique is well known? Perhaps it is
(or should be) deprecated - if so in favor of what?
Judson
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<p><div dir="ltr">I've just had a problem with serialization of JSON in Go that seems like it would be a general problem. I don't know about the elegance of my solution or its generality but I doubt I'm the only one who came to it, and further than others must've come up with something similar.<div><br></div><div>The context is this: Go permissively deserializes JSON into structs - attributes that don't correspond to a struct member are ignored silently, and struct members without a corresponding JSON attribute are left with a zero value. When the server is upgraded, if its versions of JSON resources get new attributes, the client ignores them (nbd), but when the client does a PUT with the intention of updating, it zeros out attributes of which it is unaware. The
solution to this problem was not difficult (and involved an applicaiton of the concept of lenses in the Go context...).</div><div><br></div><div>The problem is: if the server receives an PUT update, how does it know that the update is legitimate, or produced by a pre-lens client who may have elided important fields?</div><div><br></div><div>My solution is that the server adds a JSON attribute on all resources whose name is the Etag of the resource, and whose value is (unconditionally) "canary." PUTs without this field intact are assumed not to know how to properly do updates and return a 4xx status.</div><div><br></div><div>I dimly feel as if I'm reimplementing something I may have heard/read in passing, but I'm wondering if the technique is well known? Perhaps it is (o
r should be) deprecated - if so in favor of what?</div><div><br></div><div>Judson</div></div>
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