Don't embed the execution.Storer interface into a runner

Previously, the execution.Storer interface was embedded in the Runner interface.
However, this resulted in calls like runner.Add(...) to add an execution to the
store which is kind of ugly. Thus, we decided to add only the required functions to
the runner interface and make the execution.Storer a field of the implementation.

internal/api/websocket.go

@@ -8,7 +8,6 @@ import (
 	"github.com/gorilla/websocket"
 	"gitlab.hpi.de/codeocean/codemoon/poseidon/internal/runner"
 	"gitlab.hpi.de/codeocean/codemoon/poseidon/pkg/dto"
-	"gitlab.hpi.de/codeocean/codemoon/poseidon/pkg/execution"
 	"io"
 	"net/http"
 	"sync"
@@ -299,9 +298,8 @@ func (wp *webSocketProxy) writeMessage(messageType int, data []byte) error {
 // connectToRunner is the endpoint for websocket connections.
 func (r *RunnerController) connectToRunner(writer http.ResponseWriter, request *http.Request) {
 	targetRunner, _ := runner.FromContext(request.Context())
-	executionID := execution.ID(request.URL.Query().Get(ExecutionIDKey))
-	executionRequest, ok := targetRunner.Pop(executionID)
-	if !ok {
+	executionID := request.URL.Query().Get(ExecutionIDKey)
+	if !targetRunner.ExecutionExists(executionID) {
 		writeNotFound(writer, ErrUnknownExecutionID)
 		return
 	}
@@ -317,7 +315,11 @@ func (r *RunnerController) connectToRunner(writer http.ResponseWriter, request *
 	}
 
 	log.WithField("runnerId", targetRunner.ID()).WithField("executionID", executionID).Info("Running execution")
-	exit, cancel := targetRunner.ExecuteInteractively(executionRequest, proxy.Stdin, proxy.Stdout, proxy.Stderr)
+	exit, cancel, err := targetRunner.ExecuteInteractively(executionID, proxy.Stdin, proxy.Stdout, proxy.Stderr)
+	if err != nil {
+		proxy.closeWithError(fmt.Sprintf("execution failed with: %v", err))
+		return
+	}
 
 	proxy.waitForExit(exit, cancel)
 }