refactor(oohelperd): better distinguish different helpers (#434)

Part of https://github.com/ooni/probe/issues/1733

internal/cmd/oohelperd/internal/webconnectivity/dns.go

@@ -0,0 +1,32 @@
+package webconnectivity
+
+import (
+	"context"
+	"sync"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/experiment/webconnectivity"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
+)
+
+// newfailure is a convenience shortcut to save typing
+var newfailure = archival.NewFailure
+
+// CtrlDNSResult is the result of the DNS check performed by
+// the Web Connectivity test helper.
+type CtrlDNSResult = webconnectivity.ControlDNSResult
+
+// DNSConfig configures the DNS check.
+type DNSConfig struct {
+	Domain   string
+	Out      chan CtrlDNSResult
+	Resolver netx.Resolver
+	Wg       *sync.WaitGroup
+}
+
+// DNSDo performs the DNS check.
+func DNSDo(ctx context.Context, config *DNSConfig) {
+	defer config.Wg.Done()
+	addrs, err := config.Resolver.LookupHost(ctx, config.Domain)
+	config.Out <- CtrlDNSResult{Failure: newfailure(err), Addrs: addrs}
+}