Allow API call to be skipped in endpoints

[bbenligiray]

Sometimes you want Airnode to not make an API call and just use pre/post processing (for example, to generate a pseudo-random number). Both endpointId and templateId are hashes (endpointId only by convention), which means that they should never be zero. Then, we can use zero endpointId/templateId as a signal of omitting the API call.

@metobom mentioned to me that he wanted to contribute to Airnode and this may be an easy enough task. Also, it would be nice to have this in 0.10.0. @aTeoke for visibility.

[metobom]

Setting endpointId to zero will cause problems in configs with multiple OIS. How about changing "operation" and "fixedOperationParameters" to optional from required in the endpoint as an indicator?

[bbenligiray]

I and @bdrhn9 understood the above because we talked about this offline but I doubt this is clear to anyone else. So we want to be able to define an endpoint that skips the API call. If this is a regular endpoint that calls an API

{
          "name": "GET /last/stock/{symbol}",
          "operation": {
            "path": "/last/stock/{symbol}",
            "method": "get"
          },
          "parameters": [
            {
              "name": "symbol",
              "operationParameter": {
                "in": "path",
                "name": "symbol"
              }
            },
            {
              "name": "ts",
              "operationParameter": {
                "in": "query",
                "name": "ts"
              }
            }
          ],
          "reservedParameters": [
            {
              "name": "_type"
            },
            {
              "name": "_path"
            },
            {
              "name": "_times"
            }
          ],
          "fixedOperationParameters": []
        }

an endpoint that skips the API call could be

{
          "name": "GET /last/stock/{symbol}",
          "parameters": [
            {
              "name": "symbol",
              "operationParameter": {
                "in": "path",
                "name": "symbol"
              }
            },
            {
              "name": "ts",
              "operationParameter": {
                "in": "query",
                "name": "ts"
              }
            }
          ],
          "reservedParameters": [
            {
              "name": "_type"
            },
            {
              "name": "_path"
            },
            {
              "name": "_times"
            }
          ]
        }

The reasoning is that omitting the operation here implies that there is no API operation to be used, which also makes fixedOperationParameters redundant. We still need parameters because they may be used in pre/post-processing.

Another point here is that fixedOperationParameters should probably have been a field under operation as in

{
          "name": "GET /last/stock/{symbol}",
          "operation": {
            "path": "/last/stock/{symbol}",
            "method": "get",
             "fixedOperationParameters": []
          },
          "parameters": [
            {
              "name": "symbol",
              "operationParameter": {
                "in": "path",
                "name": "symbol"
              }
            },
            {
              "name": "ts",
              "operationParameter": {
                "in": "query",
                "name": "ts"
              }
            }
          ],
          "reservedParameters": [
            {
              "name": "_type"
            },
            {
              "name": "_path"
            },
            {
              "name": "_times"
            }
          ]
        }

I'm less convinced about this being an urgent enough need to be in 0.10.0 now.

[aquarat]

I looked into this some time back. About 6 months ago axios had the ability to load data from a data URI added. An example data URI call: axios.get('data:text/vnd-example+xyz;foo=bar;base64,R0lGODdh')

More info at MDN here

[bbenligiray]

The OIS will still need to specify that the API call is to be skipped without using axios-specific features, so I'm not sure how that helps this

[martinkolenic]

Hi, I have successfully tested this.

Steps: Clear the endpoint and only keep the relevant entries in the preprocessingSpecifications of the coingecko-pre-processing example. Then deploy Airnode and attempt making a request. Deploy the Airnode and attempt making a request
Expected result: Successful preprocessing without making an API call
Actual result: No API call was made but it did not return a meaningful response due to a fault in my test code (the pre-processed date value could not be cast to a string type which I set there thinking it would work). Nevertheless, I consider the test to be successful as the API cal was skipped and some tasks were carried out anyway, without a hitch on Airnode's side.