Aspnetcore.docs: Document that [FromRoute] does not unescape %2F

[gldraphael]

Query string parameters are completely unescaped, but %2F from the route parameters are not unescaped to /. Not sure if this is the correct page, but this definitely needs to be documented somewhere.

Original discussion: aspnet/Mvc#4599

---

Document Details

⚠ Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.

• ID: 32374077-e02e-d6a6-1cea-05e58447b7cd
• Version Independent ID: 86aeab13-1c25-9fc1-4e56-0390cb40c242
• Content: Routing in ASP.NET Core
• Content Source: aspnetcore/fundamentals/routing.md
• Service: unspecified
• GitHub Login: @ardalis
• Microsoft Alias: riande

[Rick-Anderson]

Per @ryanbrandenburg

the guidance would be not to use [FromRoute] on any values which are likely to contain %2f (/)
and instead use [FromQuery] which will give you an entirely URL decoded string

@gldraphael is that your understanding of what should be added?

[gldraphael]

That's a good recommendation.
I think it's also important to state that %2Fs will not be unescaped to /, because there are other ways to handle it if [FromRoute] is desired.

[gldraphael]

I think the IIS behaviour must also be documented.

So

1. [FromRoute] does not decode (or unescape) %2F to /.
2. Exception: when the app is hosted in IIS, IIS decodes the %2Fs.

PS: I haven't tested the IIS behavior.

[Rick-Anderson]

@gldraphael we'd rather not document the exception.