feat(router): optimize playground delivery, add concurrency_limit to config

[df-wg]

Motivation and Context

Previously, we were recomputing this template every time and loading it into memory every time you accessed the endpoint. This should fix that, and ensure we only compute it once.

Checklist

• I have discussed my proposed changes in an issue and have received approval to proceed.
• I have followed the coding standards of the project.
• Tests or benchmarks have been added or updated.
• Documentation has been updated on https://github.com/wundergraph/cosmo-docs.
• I have read the Contributors Guide.

[github-actions]

Router image scan passed

✅ No security vulnerabilities found in image:

ghcr.io/wundergraph/cosmo/router:sha-7c7f9c73d5aed98edd0df422d873b602dc7f378b

[jensneuse]

One minor.
Last thing, can you add a simple e2e test to the router-tests to ensure that the playground is returning HTML when configured with defaults?
I think we're currently not testing this.

[df-wg]

One minor. Last thing, can you add a simple e2e test to the router-tests to ensure that the playground is returning HTML when configured with defaults? I think we're currently not testing this.

@jensneuse isn't that present here?

cosmo/router/internal/graphiql/playgroundhandler_test.go

Lines 11 to 30 in e21577a

	func TestHealthCheckHandler(t *testing.T) {
	handler := NewPlayground(&PlaygroundOptions{
	Html: "test {{graphqlURL}}",
	GraphqlURL: "/",
	})
	rec := httptest.NewRecorder()
	th := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusOK)
	w.Write([]byte("test"))
	})
	req := test.NewRequest(http.MethodGet, "/html")
	req.Header.Set("Accept", "text/html")
	handler(th).ServeHTTP(rec, req)
	assert.Equal(t, http.StatusOK, rec.Code)
	assert.Equal(t, "text/html; charset=utf-8", rec.Header().Get("Content-Type"))
	assert.Equal(t, "test /", rec.Body.String())
	}

[Noroth]

@jensneuse I recently added a test for the playground

cosmo/router-tests/graphql_over_get_test.go

Lines 151 to 182 in e21577a

	t.Run("Should serve both graphql and playground on the same path", func(t *testing.T) {
	t.Parallel()
	testenv.Run(t, &testenv.Config{
	OverrideGraphQLPath: "/", // Default playground handler path
	}, func(t *testing.T, xEnv *testenv.Environment) {
	// We could see that successful graphql queries have been made in the previous tests
	res, err := xEnv.MakeGraphQLRequestOverGET(testenv.GraphQLRequest{
	OperationName: []byte(`Employees`),
	Query: `query Employees { employees { id } }`,
	})
	require.NoError(t, err)
	require.Equal(t, http.StatusOK, res.Response.StatusCode)
	require.Equal(t, `{"data":{"employees":[{"id":1},{"id":2},{"id":3},{"id":4},{"id":5},{"id":7},{"id":8},{"id":10},{"id":11},{"id":12}]}}`, res.Body)
	// If the graphql path and the playground path is the same, the playground will be mounted as a middleware and served based on the Accept header
	// The accept header must be text/html to get the playground
	header := http.Header{
	"Accept": {"text/html; charset=utf-8"}, // simulate simplified browser request
	}
	httpRes, err := xEnv.MakeRequest(http.MethodGet, "/", header, nil)
	require.NoError(t, err)
	require.Equal(t, http.StatusOK, httpRes.StatusCode)
	defer func() { _ = httpRes.Body.Close() }()
	_, err = html.Parse(httpRes.Body)
	require.NoError(t, err)
	})
	})
	}