refactor: redesign how we import assets (#260)

* fix(pkg.go.dev): import a subpackage containing the assets

We're trying to fix this issue that pkg.go.dev does not build.

Thanks to @hellais for this very neat idea! Let's keep our
fingers crossed and see whether it fixes!

* feat: use embedded geoip databases

Closes https://github.com/ooni/probe/issues/1372.

Work done as part of https://github.com/ooni/probe/issues/1369.

* fix(assetsx): add tests

* feat: simplify and just vendor uncompressed DBs

* remove tests that seems not necessary anymore

* fix: run go mod tidy

* Address https://github.com/ooni/probe-cli/pull/260/files#r605181364

* rewrite a test in a better way

* fix: gently cleanup the legacy assetsdir

Do not remove the whole directory with brute force. Just zap the
files whose name we know. Then attempt to delete the legacy directory
as well. If not empty, just fail. This is fine because it means the
user has stored other files inside the directory.

* fix: create .miniooni if missing

internal/engine/legacy/assetsdir/assetsdir.go

@@ -0,0 +1,62 @@
+// Package assetsdir contains code to cleanup the assets dir. We removed
+// the assetsdir in the 3.9.0 development cycle.
+package assetsdir
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+)
+
+// ErrEmptyDir indicates that you passed to Cleanup an empty dir.
+var ErrEmptyDir = errors.New("empty assets directory")
+
+// Result is the result of a Cleanup run.
+type Result struct {
+	// ASNDatabaseErr is the error of deleting the
+	// file containing the old ASN database.
+	ASNDatabaseErr error
+
+	// CABundleErr is the error of deleting the file
+	// containing the old CA bundle.
+	CABundleErr error
+
+	// CountryDatabaseErr is the error of deleting the
+	// file containing the old country database.
+	CountryDatabaseErr error
+
+	// RmdirErr is the error of deleting the supposedly
+	// empty directory that contained assets.
+	RmdirErr error
+}
+
+// Cleanup removes data from the assetsdir. This function will
+// try to delete the known assets inside of dir. It then also
+// tries to delete the directory. If the directory is not empty,
+// this operation will fail. That means the user has put some
+// extra data in there and we don't want to remove it.
+//
+// Returns the Result of cleaning up the assets on success and
+// an error on failure. The only cause of error is passing to
+// this function an empty directory. The Result data structure
+// contains the result of each individual remove operation.
+func Cleanup(dir string) (*Result, error) {
+	return fcleanup(dir, os.Remove)
+}
+
+// fcleanup is a version of Cleanup where we can mock the real function
+// used for removing files and dirs, so we can write unit tests.
+func fcleanup(dir string, remove func(name string) error) (*Result, error) {
+	if dir == "" {
+		return nil, ErrEmptyDir
+	}
+	r := &Result{}
+	asndb := filepath.Join(dir, "asn.mmdb")
+	r.ASNDatabaseErr = os.Remove(asndb)
+	cabundle := filepath.Join(dir, "ca-bundle.pem")
+	r.CABundleErr = os.Remove(cabundle)
+	countrydb := filepath.Join(dir, "country.mmdb")
+	r.CountryDatabaseErr = os.Remove(countrydb)
+	r.RmdirErr = os.Remove(dir)
+	return r, nil
+}

internal/engine/legacy/assetsdir/assetsdir_test.go

@@ -0,0 +1,40 @@
+package assetsdir
+
+import (
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestCleanupNormalUsage(t *testing.T) {
+	result, err := Cleanup("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	// we expect a bunch of ENOENT because the directory does not exist.
+	isExpectedErr := func(err error) bool {
+		return err != nil && strings.HasSuffix(err.Error(), "no such file or directory")
+	}
+	if !isExpectedErr(result.ASNDatabaseErr) {
+		t.Fatal("unexpected error", result.ASNDatabaseErr)
+	}
+	if !isExpectedErr(result.CABundleErr) {
+		t.Fatal("unexpected error", result.CABundleErr)
+	}
+	if !isExpectedErr(result.CountryDatabaseErr) {
+		t.Fatal("unexpected error", result.CountryDatabaseErr)
+	}
+	if !isExpectedErr(result.RmdirErr) {
+		t.Fatal("unexpected error", result.RmdirErr)
+	}
+}
+
+func TestCleanupWithEmptyInput(t *testing.T) {
+	result, err := Cleanup("")
+	if !errors.Is(err, ErrEmptyDir) {
+		t.Fatal("unexpected error", err)
+	}
+	if result != nil {
+		t.Fatal("expected nil result")
+	}
+}