refactor(oohelperd): flatten package hierarchy (#834)

In https://github.com/ooni/probe-cli/pull/832's initial diff, I
mentioned it would be cool to flatten oohelperd's hier.

I'm doing this now, and just for the master branch.

This diff is mostly a mechanical refactoring with very light
and apparently rather safe manual changes.

internal/cmd/oohelperd/http_test.go

@@ -0,0 +1,136 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"sync"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/ooni/probe-cli/v3/internal/model"
+	"github.com/ooni/probe-cli/v3/internal/netxlite"
+)
+
+func TestHTTPDoWithInvalidURL(t *testing.T) {
+	ctx := context.Background()
+	wg := new(sync.WaitGroup)
+	httpch := make(chan ctrlHTTPResponse, 1)
+	wg.Add(1)
+	go httpDo(ctx, &httpConfig{
+		Headers:           nil,
+		MaxAcceptableBody: 1 << 24,
+		NewClient: func() model.HTTPClient {
+			return http.DefaultClient
+		},
+		Out: httpch,
+		URL: "http://[::1]aaaa",
+		Wg:  wg,
+	})
+	// wait for measurement steps to complete
+	wg.Wait()
+	resp := <-httpch
+	if resp.Failure == nil || *resp.Failure != "unknown_error" {
+		t.Fatal("not the failure we expected")
+	}
+}
+
+func TestHTTPDoWithHTTPTransportFailure(t *testing.T) {
+	expected := errors.New("mocked error")
+	ctx := context.Background()
+	wg := new(sync.WaitGroup)
+	httpch := make(chan ctrlHTTPResponse, 1)
+	wg.Add(1)
+	go httpDo(ctx, &httpConfig{
+		Headers:           nil,
+		MaxAcceptableBody: 1 << 24,
+		NewClient: func() model.HTTPClient {
+			return &http.Client{
+				Transport: FakeTransport{
+					Err: expected,
+				},
+			}
+		},
+		Out: httpch,
+		URL: "http://www.x.org",
+		Wg:  wg,
+	})
+	// wait for measurement steps to complete
+	wg.Wait()
+	resp := <-httpch
+	if resp.Failure == nil || *resp.Failure != "unknown_error" {
+		t.Fatal("not the error we expected")
+	}
+}
+
+func newErrWrapper(failure, operation string) error {
+	return &netxlite.ErrWrapper{
+		Failure:    failure,
+		Operation:  operation,
+		WrappedErr: nil, // should not matter
+	}
+}
+
+func newErrWrapperTopLevel(failure string) error {
+	return newErrWrapper(failure, netxlite.TopLevelOperation)
+}
+
+func Test_httpMapFailure(t *testing.T) {
+	tests := []struct {
+		name    string
+		failure error
+		want    *string
+	}{{
+		name:    "nil",
+		failure: nil,
+		want:    nil,
+	}, {
+		name:    "nxdomain",
+		failure: newErrWrapperTopLevel(netxlite.FailureDNSNXDOMAINError),
+		want:    stringPointerForString("dns_lookup_error"),
+	}, {
+		name:    "no answer",
+		failure: newErrWrapperTopLevel(netxlite.FailureDNSNoAnswer),
+		want:    stringPointerForString("dns_lookup_error"),
+	}, {
+		name:    "non recoverable failure",
+		failure: newErrWrapperTopLevel(netxlite.FailureDNSNonRecoverableFailure),
+		want:    stringPointerForString("dns_lookup_error"),
+	}, {
+		name:    "refused",
+		failure: newErrWrapperTopLevel(netxlite.FailureDNSRefusedError),
+		want:    stringPointerForString("dns_lookup_error"),
+	}, {
+		name:    "server misbehaving",
+		failure: newErrWrapperTopLevel(netxlite.FailureDNSServerMisbehaving),
+		want:    stringPointerForString("dns_lookup_error"),
+	}, {
+		name:    "temporary failure",
+		failure: newErrWrapperTopLevel(netxlite.FailureDNSTemporaryFailure),
+		want:    stringPointerForString("dns_lookup_error"),
+	}, {
+		name:    "timeout outside of dns lookup",
+		failure: newErrWrapperTopLevel(netxlite.FailureGenericTimeoutError),
+		want:    stringPointerForString(netxlite.FailureGenericTimeoutError),
+	}, {
+		name:    "timeout inside of dns lookup",
+		failure: newErrWrapper(netxlite.FailureGenericTimeoutError, netxlite.ResolveOperation),
+		want:    stringPointerForString("dns_lookup_error"),
+	}, {
+		name:    "connection refused",
+		failure: newErrWrapperTopLevel(netxlite.FailureConnectionRefused),
+		want:    stringPointerForString("connection_refused_error"),
+	}, {
+		name:    "anything else",
+		failure: newErrWrapperTopLevel(netxlite.FailureEOFError),
+		want:    stringPointerForString("unknown_error"),
+	}}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := httpMapFailure(tt.failure)
+			if diff := cmp.Diff(tt.want, got); diff != "" {
+				t.Fatal(diff)
+			}
+		})
+	}
+}