[CAPPL-316] implement FetchFunc (#15424)

* feat: implement FetchFunc

* fix: generate ID based on the secretsURL

core/services/gateway/handlers/capabilities/handler.go

@@ -20,9 +20,10 @@ import (
 
 const (
 	// NOTE: more methods will go here. HTTP trigger/action/target; etc.
-	MethodWebAPITarget  = "web_api_target"
-	MethodWebAPITrigger = "web_api_trigger"
-	MethodComputeAction = "compute_action"
+	MethodWebAPITarget   = "web_api_target"
+	MethodWebAPITrigger  = "web_api_trigger"
+	MethodComputeAction  = "compute_action"
+	MethodWorkflowSyncer = "workflow_syncer"
 )
 
 type handler struct {

core/services/workflows/syncer/fetcher.go

@@ -0,0 +1,43 @@
+package syncer
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/smartcontractkit/chainlink/v2/core/capabilities/webapi"
+	"github.com/smartcontractkit/chainlink/v2/core/logger"
+	ghcapabilities "github.com/smartcontractkit/chainlink/v2/core/services/gateway/handlers/capabilities"
+)
+
+func NewFetcherFunc(
+	ctx context.Context,
+	lggr logger.Logger,
+	och *webapi.OutgoingConnectorHandler) FetcherFunc {
+	return func(ctx context.Context, url string) ([]byte, error) {
+		payloadBytes, err := json.Marshal(ghcapabilities.Request{
+			URL:    url,
+			Method: http.MethodGet,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("failed to marshal fetch request: %w", err)
+		}
+
+		messageID := strings.Join([]string{ghcapabilities.MethodWorkflowSyncer, url}, "/")
+		resp, err := och.HandleSingleNodeRequest(ctx, messageID, payloadBytes)
+		if err != nil {
+			return nil, err
+		}
+
+		lggr.Debugw("received gateway response", "resp", resp)
+		var payload ghcapabilities.Response
+		err = json.Unmarshal(resp.Body.Payload, &payload)
+		if err != nil {
+			return nil, err
+		}
+
+		return payload.Body, nil
+	}
+}

core/services/workflows/syncer/fetcher_test.go

@@ -0,0 +1,76 @@
+package syncer
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
+
+	"github.com/smartcontractkit/chainlink/v2/core/capabilities/webapi"
+	"github.com/smartcontractkit/chainlink/v2/core/logger"
+	"github.com/smartcontractkit/chainlink/v2/core/services/gateway/api"
+	gcmocks "github.com/smartcontractkit/chainlink/v2/core/services/gateway/connector/mocks"
+	ghcapabilities "github.com/smartcontractkit/chainlink/v2/core/services/gateway/handlers/capabilities"
+	"github.com/smartcontractkit/chainlink/v2/core/services/gateway/handlers/common"
+)
+
+func TestNewFetcherFunc(t *testing.T) {
+	ctx := context.Background()
+	lggr := logger.TestLogger(t)
+
+	config := webapi.ServiceConfig{
+		RateLimiter: common.RateLimiterConfig{
+			GlobalRPS:      100.0,
+			GlobalBurst:    100,
+			PerSenderRPS:   100.0,
+			PerSenderBurst: 100,
+		},
+	}
+
+	connector := gcmocks.NewGatewayConnector(t)
+	och, err := webapi.NewOutgoingConnectorHandler(connector, config, ghcapabilities.MethodComputeAction, lggr)
+	require.NoError(t, err)
+
+	url := "http://example.com"
+
+	msgID := strings.Join([]string{ghcapabilities.MethodWorkflowSyncer, url}, "/")
+
+	t.Run("OK-valid_request", func(t *testing.T) {
+		gatewayResp := gatewayResponse(t, msgID)
+		connector.EXPECT().SignAndSendToGateway(mock.Anything, "gateway1", mock.Anything).Run(func(ctx context.Context, gatewayID string, msg *api.MessageBody) {
+			och.HandleGatewayMessage(ctx, "gateway1", gatewayResp)
+		}).Return(nil).Times(1)
+		connector.EXPECT().DonID().Return("don-id")
+		connector.EXPECT().GatewayIDs().Return([]string{"gateway1", "gateway2"})
+
+		fetcher := NewFetcherFunc(ctx, lggr, och)
+
+		payload, err := fetcher(ctx, url)
+		require.NoError(t, err)
+
+		expectedPayload := []byte("response body")
+		require.Equal(t, expectedPayload, payload)
+	})
+}
+
+func gatewayResponse(t *testing.T, msgID string) *api.Message {
+	headers := map[string]string{"Content-Type": "application/json"}
+	body := []byte("response body")
+	responsePayload, err := json.Marshal(ghcapabilities.Response{
+		StatusCode:     200,
+		Headers:        headers,
+		Body:           body,
+		ExecutionError: false,
+	})
+	require.NoError(t, err)
+	return &api.Message{
+		Body: api.MessageBody{
+			MessageId: msgID,
+			Method:    ghcapabilities.MethodWebAPITarget,
+			Payload:   responsePayload,
+		},
+	}
+}