Status Code Forwarding

This repository demonstrates how to setup a coprocessor that forwards status codes from the subgraph to the client.

Running the Example

Note: To run this example, you will need a GraphOS Enterprise plan and must create /router/.env based on /router/.env.example which exports APOLLO_KEY and APOLLO_GRAPH_REF.

1. Run the subgraph from the /subgraph directory with npm run dev
2. Run the coprocessor from the /coprocessor directory with npm run dev.
3. In the /router directory, download the router by running ./download_router.sh
4. In the /router directory, compose the schema by running ./create_local_schema.sh (NOTE - the subgraph has to be running for this to work as this script relies on introspecting the subgraph schema)
5. In the /router directory, run the router by running ./start_router.sh

Now if you run this code in the browser (http://127.0.0.1:4000/), you will be able to query the router. You will be able to how the coprocessor transforms the context and control fields in the coprocessor's console output.

If you run the query below:

query Query {
  hello
}

you should see the response (with an error code 403 instead of 200):

{
  "data": {
    "hello": "Hello World!"
  },
  "errors": [
    {
      "message": "HTTP fetch failed from 'subgraph': 403: Forbidden",
      "path": [],
      "extensions": {
        "code": "SUBREQUEST_HTTP_ERROR",
        "service": "subgraph",
        "reason": "403: Forbidden",
        "http": {
          "status": 403
        }
      }
    }
  ]
}

How it works

The SubgraphResponseStage and SupergraphResponseStage are both part of the coprocessor. The coprocessor listens on one port for both of these stages and handles which one it evaluates based on the stage passed in the request to the coprocessor.

There are comments in the code for the subgraph, coprocessor and router config explaining what each part of the code is doing.

sequenceDiagram
    participant Client
    participant Router
    participant Subgraph
    participant SubgraphResponseStage
    participant SupergraphResponseStage
    Client->>Router: Request
    Router->>Subgraph: Fulfill Request
    Subgraph->>Router: Return Data with Status Code 403
    Router->>SubgraphResponseStage: Send context and status_code
    SubgraphResponseStage->>Router: Return context with 403 status code in its entries
    Router->>SupergraphResponseStage: Send context (which now includes status code)
    SupergraphResponseStage->>Router: Return control with a break for 403 status code
    Router->>Client: Return data and 403 status code

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