What is the best way to design a HTTP request when somewhat complex parameters are needed?

Question

I have some web services that I am writing and I am trying to be as RESTful as possible. I am hosting these web services using a HTTPHandler running inside of IIS/ASP.NET/S

Answer 1

There's no perfect way to do this.

The correct HTTP/REST way would be to use a GET and have all your parameters in the URL as query arguments. You've identified two practical problems with this approach

1. Your server software is not correctly passing some characters to you, even if URL encoded. That surprises me, actually, and you should look more closely at what's going on that you can't even get a % through the URL. Does your framework give you raw access to PATH_INFO or otherwise unprocessed characters? That may give you a workaround.
2. Your query strings may be too long. You mention the 2083 byte limit in MSIE. That may or may not be a practical problem for you, depending on whether MSIE is a client of your API. (Ie: via Javascript making calls to a JSON API). But in my experience very long URLs will end up breaking mysteriously in several places; proxy caches along the path, even a stateful firewall. If you have absolute control over the clients and network path you can probably live with the dangers of long URLs. If it's a public API, forget it.

Hopefully you can make the straightforward GET work in your environment. You may even want to consider refactoring your API to make the query data smaller.

But what if you can't make the GET work? You propose several alternatives. I would immediately dismiss two of them. Don't put content in the GET request body; too much software will break if you try that, and anyway it violates the very REST spirit you're trying to capture. And I wouldn't use base64 encoding. It may help you work around problem 1, your server not handling some characters in URLs right. But if applied wrong it will actually make your URLs longer, not shorter, compounding problem 2. Even if you do base64 right and include some compression it won't make URLs significantly shorter, and will make the client much more complicated.

Your most practical solution is probably option 3, an HTTP POST. This isn't RESTful; you should be using GETs for read-only queries. And you'll lose some advantages of the REST approach with caching of GETs and the like. On the other hand it will work correctly, and simply, with a large variety of Internet infrastructure and software libraries. You can then pass as much data you want in the POST body either via multipart/form-data encoding, JSON, or XML. (I've built two major public web services using SOAP, which is just XML on POSTs. It's ugly and not RESTful, but it does work reliably.)

REST is a great design paradigm. It's a guideline. If it doesn't fit your app, don't feel you need to stick with it. HTTP is not good at passing large amounts of data to the server with a GET. If you need have giant query parameters, do something else.