upstream: finish and cache requests even when the client cancels

internal/upstream/upstream.go

@@ -32,8 +32,9 @@ func New(client *http.Client) *Fetcher {
 
 // Get fetches the given url.
 func (f *Fetcher) Get(ctx context.Context, url string) (*Result, error) {
+	fetchCtx := context.WithoutCancel(ctx)
 	v, err, _ := f.group.Do(url, func() (any, error) {
-		return f.doGet(ctx, url)
+		return f.doGet(fetchCtx, url)
 	})
 	if err != nil {
 		return nil, err

internal/upstream/upstream_test.go

@@ -0,0 +1,48 @@
+// Copyright 2026 Edgeless Systems GmbH
+// SPDX-License-Identifier: BUSL-1.1
+
+package upstream
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestCallerCancellationDoesNotAbortFetch covers the case of a client disconnecting while the upstream request it triggered is still in flight.
+func TestCallerCancellationDoesNotAbortFetch(t *testing.T) {
+	release := make(chan struct{})
+	var hits int
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		hits++
+		<-release
+		select {
+		case <-r.Context().Done():
+			// The server saw the fetch get canceled; fail via an empty body below.
+			return
+		default:
+		}
+		_, _ = w.Write([]byte("collateral"))
+	}))
+	defer srv.Close()
+
+	f := New(srv.Client())
+
+	canceledCtx, cancel := context.WithCancel(context.Background())
+	var wg sync.WaitGroup
+	wg.Go(func() {
+		res, err := f.Get(canceledCtx, srv.URL)
+		require.NoError(t, err)
+		assert.Equal(t, "collateral", string(res.Body))
+	})
+
+	cancel()
+	close(release)
+	wg.Wait()
+	assert.Equal(t, 1, hits)
+}