Add mongo/runcmdopt

GODRIVER-272

Change-Id: Idd6ef1f97c55e0b4f270c42695c1cebb93a401a1

Author: Divjot Arora

mongo/database.go

@@ -19,6 +19,7 @@ import (
 	"github.com/mongodb/mongo-go-driver/core/writeconcern"
 	"github.com/mongodb/mongo-go-driver/mongo/collectionopt"
 	"github.com/mongodb/mongo-go-driver/mongo/dbopt"
+	"github.com/mongodb/mongo-go-driver/mongo/runcmdopt"
 )
 
 // Database performs operations on a given database.
@@ -88,16 +89,25 @@ func (db *Database) Collection(name string, opts ...collectionopt.Option) *Colle
 
 // RunCommand runs a command on the database. A user can supply a custom
 // context to this method, or nil to default to context.Background().
-func (db *Database) RunCommand(ctx context.Context, runCommand interface{}) (bson.Reader, error) {
+func (db *Database) RunCommand(ctx context.Context, runCommand interface{}, opts ...runcmdopt.Option) (bson.Reader, error) {
 
 	if ctx == nil {
 		ctx = context.Background()
 	}
 
+	runCmd, err := runcmdopt.BundleRunCmd(opts...).Unbundle()
+	if err != nil {
+		return nil, err
+	}
+	rp := runCmd.ReadPreference
+	if rp == nil {
+		rp = db.readPreference // inherit from db if nothing specified in options
+	}
+
 	cmd := command.Command{
 		DB:       db.Name(),
 		Command:  runCommand,
-		ReadPref: db.readPreference,
+		ReadPref: rp,
 	}
 	return dispatch.Command(ctx, cmd, db.client.topology, db.writeSelector)
 }

mongo/runcmdopt/runcmd_test.go

@@ -0,0 +1,69 @@
+package runcmdopt
+
+import (
+	"testing"
+
+	"github.com/mongodb/mongo-go-driver/core/readpref"
+	"github.com/mongodb/mongo-go-driver/internal/testutil/helpers"
+)
+
+var rpPrimary = readpref.Primary()
+var rpSeconadary = readpref.Secondary()
+
+func createNestedBundle1(t *testing.T) *RunCmdBundle {
+	nested := BundleRunCmd(ReadPreference(rpPrimary))
+	testhelpers.RequireNotNil(t, nested, "nested bundle was nil")
+
+	outer := BundleRunCmd(ReadPreference(rpSeconadary), nested)
+	testhelpers.RequireNotNil(t, nested, "nested bundle was nil")
+
+	return outer
+}
+
+func TestRunCmdOpt(t *testing.T) {
+	nilBundle := BundleRunCmd()
+	var nilRc = &RunCmd{}
+
+	var bundle1 *RunCmdBundle
+	bundle1 = bundle1.ReadPreference(rpSeconadary)
+	testhelpers.RequireNotNil(t, bundle1, "created bundle was nil")
+	bundle1Rc := &RunCmd{
+		ReadPreference: rpSeconadary,
+	}
+
+	bundle2 := BundleRunCmd(ReadPreference(rpPrimary))
+	testhelpers.RequireNotNil(t, bundle2, "created bundle was nil")
+	bundle2Rc := &RunCmd{
+		ReadPreference: rpPrimary,
+	}
+
+	nested1 := createNestedBundle1(t)
+	nested1Rc := &RunCmd{
+		ReadPreference: rpPrimary,
+	}
+
+	t.Run("Unbundle", func(t *testing.T) {
+		var cases = []struct {
+			name   string
+			bundle *RunCmdBundle
+			rc     *RunCmd
+		}{
+			{"NilBundle", nilBundle, nilRc},
+			{"Bundle1", bundle1, bundle1Rc},
+			{"Bundle2", bundle2, bundle2Rc},
+			{"Nested1", nested1, nested1Rc},
+		}
+
+		for _, tc := range cases {
+			t.Run(tc.name, func(t *testing.T) {
+				rc, err := tc.bundle.Unbundle()
+				testhelpers.RequireNil(t, err, "err unbundling rc: %s", err)
+
+				switch {
+				case rc.ReadPreference != tc.rc.ReadPreference:
+					t.Errorf("read preferences don't match")
+				}
+			})
+		}
+	})
+}

mongo/runcmdopt/runcmdopt.go

@@ -0,0 +1,120 @@
+package runcmdopt
+
+import (
+	"reflect"
+
+	"github.com/mongodb/mongo-go-driver/core/readpref"
+)
+
+var runCmdBundle = new(RunCmdBundle)
+
+// Option represents a RunCommand option.
+type Option interface {
+	runCmdOption()
+}
+
+// optionFunc adds the option to the RunCmd instance.
+type optionFunc func(*RunCmd) error
+
+// RunCmd represents a run command.
+type RunCmd struct {
+	ReadPreference *readpref.ReadPref
+}
+
+// RunCmdBundle is a bundle of RunCommand options.
+type RunCmdBundle struct {
+	option Option
+	next   *RunCmdBundle
+}
+
+func (*RunCmdBundle) runCmdOption() {}
+
+func (optionFunc) runCmdOption() {}
+
+// BundleRunCmd bundles RunCommand options
+func BundleRunCmd(opts ...Option) *RunCmdBundle {
+	head := runCmdBundle
+
+	for _, opt := range opts {
+		newBundle := RunCmdBundle{
+			option: opt,
+			next:   head,
+		}
+		head = &newBundle
+	}
+
+	return head
+}
+
+// ReadPreference sets the read preference.
+func (rcb *RunCmdBundle) ReadPreference(rp *readpref.ReadPref) *RunCmdBundle {
+	return &RunCmdBundle{
+		option: ReadPreference(rp),
+		next:   rcb,
+	}
+}
+
+// Unbundle unbundles the options, returning a RunCmd instance.
+func (rcb *RunCmdBundle) Unbundle() (*RunCmd, error) {
+	database := &RunCmd{}
+	err := rcb.unbundle(database)
+	if err != nil {
+		return nil, err
+	}
+
+	return database, nil
+}
+
+// Helper that recursively unwraps the bundle.
+func (rcb *RunCmdBundle) unbundle(database *RunCmd) error {
+	if rcb == nil {
+		return nil
+	}
+
+	for head := rcb; head != nil && head.option != nil; head = head.next {
+		var err error
+		switch opt := head.option.(type) {
+		case *RunCmdBundle:
+			err = opt.unbundle(database) // add all bundle's options to database
+		case optionFunc:
+			err = opt(database) // add option to database
+		default:
+			return nil
+		}
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// String implements the Stringer interface
+func (rcb *RunCmdBundle) String() string {
+	if rcb == nil {
+		return ""
+	}
+
+	str := ""
+	for head := rcb; head != nil && head.option != nil; head = head.next {
+		switch opt := head.option.(type) {
+		case *RunCmdBundle:
+			str += opt.String()
+		case optionFunc:
+			str += reflect.TypeOf(opt).String() + "\n"
+		}
+	}
+
+	return str
+}
+
+// ReadPreference sets the read preference.
+func ReadPreference(rp *readpref.ReadPref) Option {
+	return optionFunc(
+		func(rc *RunCmd) error {
+			if rc.ReadPreference == nil {
+				rc.ReadPreference = rp
+			}
+			return nil
+		})
+}