refactor(netxlite): hide details without breaking the rest of the tree (#454)

## Description

This PR continues the refactoring of `netx` under the following principles:

1. do not break the rest of the tree and do not engage in extensive tree-wide refactoring yet
2. move under `netxlite` clearly related subpackages (e.g., `iox`, `netxmocks`)
3. move into `internal/netxlite/internal` stuff that is clearly private of `netxlite`
4. hide implementation details in `netxlite` pending new factories
5. refactor `tls` code in `netxlite` to clearly separate `crypto/tls` code from `utls` code

After each commit, I run `go test -short -race ./...` locally. Each individual commit explains what it does. I will squash, but this operation will preserve the original commit titles, so this will give further insight on each step.

## Commits

* refactor: rename netxmocks -> netxlite/mocks

Part of https://github.com/ooni/probe/issues/1591

* refactor: rename quicx -> netxlite/quicx

See https://github.com/ooni/probe/issues/1591

* refactor: rename iox -> netxlite/iox

Regenerate sources and make sure the tests pass.

See https://github.com/ooni/probe/issues/1591.

* refactor(iox): move MockableReader to netxlite/mocks

See https://github.com/ooni/probe/issues/1591

* refactor(netxlite): generator is an implementation detail

See https://github.com/ooni/probe/issues/1591

* refactor(netxlite): separate tls and utls code

See https://github.com/ooni/probe/issues/1591

* refactor(netxlite): hide most types but keep old names as legacy

With this change we avoid breaking the rest of the tree, but we start
hiding some implementation details a bit. Factories will follow.

See https://github.com/ooni/probe/issues/1591

internal/netxlite/iox/example_test.go

@@ -0,0 +1,21 @@
+package iox_test
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"strings"
+
+	"github.com/ooni/probe-cli/v3/internal/netxlite/iox"
+)
+
+func ExampleReadAllContext() {
+	r := strings.NewReader("deadbeef")
+	ctx := context.Background()
+	out, err := iox.ReadAllContext(ctx, r)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%d\n", len(out))
+	// Output: 8
+}

internal/netxlite/iox/iox.go

@@ -0,0 +1,58 @@
+// Package iox contains io extensions.
+package iox
+
+import (
+	"context"
+	"io"
+)
+
+// ReadAllContext is like io.ReadAll but reads r in a
+// background goroutine. This function will return
+// earlier if the context is cancelled. In which case
+// we will continue reading from r in the background
+// goroutine, and we will discard the result. To stop
+// the long-running goroutine, you need to close the
+// connection bound to the r reader, if possible.
+func ReadAllContext(ctx context.Context, r io.Reader) ([]byte, error) {
+	datach, errch := make(chan []byte, 1), make(chan error, 1) // buffers
+	go func() {
+		data, err := io.ReadAll(r)
+		if err != nil {
+			errch <- err
+			return
+		}
+		datach <- data
+	}()
+	select {
+	case data := <-datach:
+		return data, nil
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case err := <-errch:
+		return nil, err
+	}
+}
+
+// CopyContext is like io.Copy but may terminate earlier
+// when the context expires. This function has the same
+// caveats of ReadAllContext regarding the temporary leaking
+// of the background goroutine used to do I/O.
+func CopyContext(ctx context.Context, dst io.Writer, src io.Reader) (int64, error) {
+	countch, errch := make(chan int64, 1), make(chan error, 1) // buffers
+	go func() {
+		count, err := io.Copy(dst, src)
+		if err != nil {
+			errch <- err
+			return
+		}
+		countch <- count
+	}()
+	select {
+	case count := <-countch:
+		return count, nil
+	case <-ctx.Done():
+		return 0, ctx.Err()
+	case err := <-errch:
+		return 0, err
+	}
+}

internal/netxlite/iox/iox_test.go

@@ -0,0 +1,134 @@
+package iox
+
+import (
+	"context"
+	"errors"
+	"io"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/netxlite/mocks"
+)
+
+func TestReadAllContextCommonCase(t *testing.T) {
+	r := strings.NewReader("deadbeef")
+	ctx := context.Background()
+	out, err := ReadAllContext(ctx, r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(out) != 8 {
+		t.Fatal("not the expected number of bytes")
+	}
+}
+
+func TestReadAllContextWithError(t *testing.T) {
+	expected := errors.New("mocked error")
+	r := &mocks.Reader{
+		MockRead: func(b []byte) (int, error) {
+			return 0, expected
+		},
+	}
+	ctx := context.Background()
+	out, err := ReadAllContext(ctx, r)
+	if !errors.Is(err, expected) {
+		t.Fatal("not the error we expected", err)
+	}
+	if len(out) != 0 {
+		t.Fatal("not the expected number of bytes")
+	}
+}
+
+func TestReadAllContextWithCancelledContext(t *testing.T) {
+	r := strings.NewReader("deadbeef")
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // fail immediately
+	out, err := ReadAllContext(ctx, r)
+	if !errors.Is(err, context.Canceled) {
+		t.Fatal("not the error we expected", err)
+	}
+	if len(out) != 0 {
+		t.Fatal("not the expected number of bytes")
+	}
+}
+
+func TestReadAllContextWithErrorAndCancelledContext(t *testing.T) {
+	expected := errors.New("mocked error")
+	r := &mocks.Reader{
+		MockRead: func(b []byte) (int, error) {
+			time.Sleep(time.Millisecond)
+			return 0, expected
+		},
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // fail immediately
+	out, err := ReadAllContext(ctx, r)
+	if !errors.Is(err, context.Canceled) {
+		t.Fatal("not the error we expected", err)
+	}
+	if len(out) != 0 {
+		t.Fatal("not the expected number of bytes")
+	}
+}
+
+func TestCopyContextCommonCase(t *testing.T) {
+	r := strings.NewReader("deadbeef")
+	ctx := context.Background()
+	out, err := CopyContext(ctx, io.Discard, r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if out != 8 {
+		t.Fatal("not the expected number of bytes")
+	}
+}
+
+func TestCopyContextWithError(t *testing.T) {
+	expected := errors.New("mocked error")
+	r := &mocks.Reader{
+		MockRead: func(b []byte) (int, error) {
+			return 0, expected
+		},
+	}
+	ctx := context.Background()
+	out, err := CopyContext(ctx, io.Discard, r)
+	if !errors.Is(err, expected) {
+		t.Fatal("not the error we expected", err)
+	}
+	if out != 0 {
+		t.Fatal("not the expected number of bytes")
+	}
+}
+
+func TestCopyContextWithCancelledContext(t *testing.T) {
+	r := strings.NewReader("deadbeef")
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // fail immediately
+	out, err := CopyContext(ctx, io.Discard, r)
+	if !errors.Is(err, context.Canceled) {
+		t.Fatal("not the error we expected", err)
+	}
+	if out != 0 {
+		t.Fatal("not the expected number of bytes")
+	}
+}
+
+func TestCopyContextWithErrorAndCancelledContext(t *testing.T) {
+	expected := errors.New("mocked error")
+	r := &mocks.Reader{
+		MockRead: func(b []byte) (int, error) {
+			time.Sleep(time.Millisecond)
+			return 0, expected
+		},
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // fail immediately
+	out, err := CopyContext(ctx, io.Discard, r)
+	if !errors.Is(err, context.Canceled) {
+		t.Fatal("not the error we expected", err)
+	}
+	if out != 0 {
+		t.Fatal("not the expected number of bytes")
+	}
+}