Match multiple ocelot routes for given downstream endpoint

[satano]

Downstream paths are matched against all relevant Ocelot routes and used all routes that fit. Consider following downstream API:

• GET /api/test
• POST /api/test

Which is represented in OpenApi JSON as:

"paths": {
    "/api/test": {
        "get": {

        },
        "post": {

        }
    }
}

And this ocelot.json:

"Routes": [
    {
        "UpstreamPathTemplate": "/post/ocelot",
        "UpstreamHttpMethod": [ "POST" ],
        "DownstreamPathTemplate": "/api/test"
        "SwaggerKey": "test"
    },
    {
        "UpstreamPathTemplate": "/all/ocelot",
        "DownstreamPathTemplate": "/api/test"
        "SwaggerKey": "test"
    }
]

So both API endpoints are mapped to /all/ocelot route, but POST endpoint is also mapped to /post/ocelot.

Former implementation of generating Swagger JSON file worked this way

• Walked through all paths in downstream.
• For each path (in this case just /api/test) found first suitable Ocelot route, which was /post/ocelot.
• Then for processing path walked through all its methods (GET, POST in this case) and checked if matched route can handle these methods.
  • If method was not hanlded by Ocelot route, it was completely removed. In this example, GET method is not in the first route, so it was removed from downstream.
• If all methods was removed from processing path (meaning this path remained empty), the whole path was removed from downstrem.

New implementation in this PR

Key changes in implementation are:

• Not just paths, but every method in path is checked against Ocelot routes separately.
• All suitable Ocelot routes are used, not just first one.
• All original paths in downstream are removed and new ones are built based on matched Ocelot routes.

So the previous example works this way:

• All suitable Ocelot routes for GET /api/test are found.
  • Only second route /all/ocelot matches, because the first one is only for POST.
  • New downstream path /all/ocelot is created and GET method is added to it.
• All suitable Ocelot routes for POST /api/test are found.
  • Now both Ocelot routes match. First one is explicitly for POST, second one is for all methods.
  • Downstream path /all/ocelot/ is already created, so POST method is added to it.
  • New downstream path /post/ocelot is created and POST method is added to it.
• When all paths and their methods are processed:
  • All original paths are removed from downstream.
  • All new generated downstream paths with methods are added.

[update-docs[bot]]

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