add code comments for package migrate

migrate.go

@@ -1,3 +1,7 @@
+// Package migrate reads migrations from sources and runs them against databases.
+// Sources are defined by the `source.Driver` and databases by the `database.Driver`
+// interface. The driver interfaces are kept "dump", all migration logic is kept
+// in this package.
 package migrate
 
 import (
@@ -10,6 +14,11 @@ import (
 	"github.com/mattes/migrate/source"
 )
 
+// DefaultPrefetchMigrations sets the number of migrations to pre-read
+// from the source. This is helpful if the source is remote, but has little
+// effect for a local source (i.e. file system).
+// Please note that this setting has a major impact on the memory usage,
+// since each pre-read migration is buffered in memory. See DefaultBufferSize.
 var DefaultPrefetchMigrations = uint(10)
 
 var (
@@ -18,10 +27,13 @@ var (
 	ErrLocked     = fmt.Errorf("database locked")
 )
 
+// ErrShortLimit is an error returned when not enough migrations
+// can be returned by a source for a given limit.
 type ErrShortLimit struct {
 	Short uint
 }
 
+// Error implements the error interface.
 func (e ErrShortLimit) Error() string {
 	return fmt.Sprintf("limit %v short", e.Short)
 }
@@ -32,17 +44,25 @@ type Migrate struct {
 	databaseName string
 	databaseDrv  database.Driver
 
+	// Log accepts a Logger interface
 	Log Logger
 
+	// GracefulStop accepts `true` and will stop executing migrations
+	// as soon as possible at a safe break point, so that the database
+	// is not corrpupted.
 	GracefulStop   chan bool
 	isGracefulStop bool
 
 	isLockedMu *sync.Mutex
 	isLocked   bool
 
+	// PrefetchMigrations defaults to DefaultPrefetchMigrations,
+	// but can be set per Migrate instance.
 	PrefetchMigrations uint
 }
 
+// New returns a new Migrate instance from a source URL and a database URL.
+// The URL scheme is defined by each driver.
 func New(sourceUrl, databaseUrl string) (*Migrate, error) {
 	m := newCommon()
 
@@ -73,6 +93,10 @@ func New(sourceUrl, databaseUrl string) (*Migrate, error) {
 	return m, nil
 }
 
+// NewWithDatabaseInstance returns a new Migrate instance from a source URL
+// and an existing database instance. The source URL scheme is defined by each driver.
+// Use any string that can serve as an identifier during logging as databaseName.
+// You are responsible for closing the underlying database client if necessary.
 func NewWithDatabaseInstance(sourceUrl string, databaseName string, databaseInstance database.Driver) (*Migrate, error) {
 	m := newCommon()
 
@@ -95,6 +119,10 @@ func NewWithDatabaseInstance(sourceUrl string, databaseName string, databaseInst
 	return m, nil
 }
 
+// NewWithSourceInstance returns a new Migrate instance from an existing source instance
+// and a database URL. The database URL scheme is defined by each driver.
+// Use any string that can serve as an identifier during logging as sourceName.
+// You are responsible for closing the underlying source client if necessary.
 func NewWithSourceInstance(sourceName string, sourceInstance source.Driver, databaseUrl string) (*Migrate, error) {
 	m := newCommon()
 
@@ -117,6 +145,10 @@ func NewWithSourceInstance(sourceName string, sourceInstance source.Driver, data
 	return m, nil
 }
 
+// NewWithInstance returns a new Migrate instance from an existing source and
+// database instance. Use any string that can serve as an identifier during logging
+// as sourceName and databaseName. You are responsible for closing down
+// the underlying source and database client if necessary.
 func NewWithInstance(sourceName string, sourceInstance source.Driver, databaseName string, databaseInstance database.Driver) (*Migrate, error) {
 	m := newCommon()
 
@@ -137,6 +169,7 @@ func newCommon() *Migrate {
 	}
 }
 
+// Close closes the the source and the database.
 func (m *Migrate) Close() (sourceErr error, databaseErr error) {
 	databaseSrvClose := make(chan error)
 	sourceSrvClose := make(chan error)
@@ -152,6 +185,8 @@ func (m *Migrate) Close() (sourceErr error, databaseErr error) {
 	return <-sourceSrvClose, <-databaseSrvClose
 }
 
+// Migrate looks at the currently active migration version,
+// then migrates either up or down to the specified version.
 func (m *Migrate) Migrate(version uint) error {
 	if err := m.lock(); err != nil {
 		return err
@@ -168,6 +203,8 @@ func (m *Migrate) Migrate(version uint) error {
 	return m.unlockErr(m.runMigrations(ret))
 }
 
+// Steps looks at the currently active migration version.
+// It will migrate up if n > 0, and down if n < 0.
 func (m *Migrate) Steps(n int) error {
 	if n == 0 {
 		return ErrNoChange
@@ -193,6 +230,8 @@ func (m *Migrate) Steps(n int) error {
 	return m.unlockErr(m.runMigrations(ret))
 }
 
+// Up looks at the currently active migration version
+// and will migrate all the way up (applying all up migrations).
 func (m *Migrate) Up() error {
 	if err := m.lock(); err != nil {
 		return err
@@ -209,6 +248,8 @@ func (m *Migrate) Up() error {
 	return m.unlockErr(m.runMigrations(ret))
 }
 
+// Down looks at the currently active migration version
+// and will migrate all the way down (applying all down migrations).
 func (m *Migrate) Down() error {
 	if err := m.lock(); err != nil {
 		return err
@@ -224,6 +265,7 @@ func (m *Migrate) Down() error {
 	return m.unlockErr(m.runMigrations(ret))
 }
 
+// Drop deletes everyting in the database.
 func (m *Migrate) Drop() error {
 	if err := m.lock(); err != nil {
 		return err
@@ -234,6 +276,8 @@ func (m *Migrate) Drop() error {
 	return m.unlock()
 }
 
+// Version returns the currently active migration version.
+// If no migration has been applied, yet, it will return ErrNilVersion.
 func (m *Migrate) Version() (uint, error) {
 	v, err := m.databaseDrv.Version()
 	if err != nil {
@@ -247,6 +291,10 @@ func (m *Migrate) Version() (uint, error) {
 	return suint(v), nil
 }
 
+// read reads either up or down migrations from source `from` to `to`.
+// Each migration is then written to the ret channel.
+// If an error occurs during reading, that error is written to the ret channel, too.
+// Once read is done reading it will close the ret channel.
 func (m *Migrate) read(from int, to int, ret chan<- interface{}) {
 	defer close(ret)
 
@@ -354,6 +402,11 @@ func (m *Migrate) read(from int, to int, ret chan<- interface{}) {
 	}
 }
 
+// readUp reads up migrations from `from` limitted by `limit`.
+// limit can be -1, implying no limit and reading until there are no more migrations.
+// Each migration is then written to the ret channel.
+// If an error occurs during reading, that error is written to the ret channel, too.
+// Once readUp is done reading it will close the ret channel.
 func (m *Migrate) readUp(from int, limit int, ret chan<- interface{}) {
 	defer close(ret)
 
@@ -441,6 +494,11 @@ func (m *Migrate) readUp(from int, limit int, ret chan<- interface{}) {
 	}
 }
 
+// readDown reads down migrations from `from` limitted by `limit`.
+// limit can be -1, implying no limit and reading until there are no more migrations.
+// Each migration is then written to the ret channel.
+// If an error occurs during reading, that error is written to the ret channel, too.
+// Once readDown is done reading it will close the ret channel.
 func (m *Migrate) readDown(from int, limit int, ret chan<- interface{}) {
 	defer close(ret)
 
@@ -518,7 +576,12 @@ func (m *Migrate) readDown(from int, limit int, ret chan<- interface{}) {
 	}
 }
 
-// ret chan expects *Migration or error
+// runMigrations reads *Migration and error from a channel. Any other type
+// sent on this channel will result in a panic. Each migration is then
+// proxied to the database driver and run against the database.
+// Before running a newly received migration it will check if it's supposed
+// to stop execution because it might have received a stop signal on the
+// GracefulStop channel.
 func (m *Migrate) runMigrations(ret <-chan interface{}) error {
 	for r := range ret {
 
@@ -566,6 +629,8 @@ func (m *Migrate) runMigrations(ret <-chan interface{}) error {
 	return nil
 }
 
+// versionExists checks the source if either the up or down migration for
+// the specified migration version exists.
 func (m *Migrate) versionExists(version uint) error {
 	// try up migration first
 	up, _, err := m.sourceDrv.ReadUp(version)
@@ -592,6 +657,9 @@ func (m *Migrate) versionExists(version uint) error {
 	return os.ErrNotExist
 }
 
+// stop returns true if no more migrations should be run against the database
+// because a stop signal was received on the GracefulStop channel.
+// Calls are cheap and this function is not blocking.
 func (m *Migrate) stop() bool {
 	if m.isGracefulStop {
 		return true
@@ -607,6 +675,8 @@ func (m *Migrate) stop() bool {
 	}
 }
 
+// newMigration is a helper func that returns a *Migration for the
+// specified version and targetVersion.
 func (m *Migrate) newMigration(version uint, targetVersion int) (*Migration, error) {
 	var migr *Migration
 
@@ -660,6 +730,8 @@ func (m *Migrate) newMigration(version uint, targetVersion int) (*Migration, err
 	return migr, nil
 }
 
+// lock is a thread safe helper function to lock the database.
+// It should be called as late as possible when running migrations.
 func (m *Migrate) lock() error {
 	m.isLockedMu.Lock()
 	defer m.isLockedMu.Unlock()
@@ -675,13 +747,15 @@ func (m *Migrate) lock() error {
 	return ErrLocked
 }
 
+// unlock is a thread safe helper function to unlock the database.
+// It should be called as early as possible when no more migrations are
+// expected to be executed.
 func (m *Migrate) unlock() error {
 	m.isLockedMu.Lock()
 	defer m.isLockedMu.Unlock()
 
 	if err := m.databaseDrv.Unlock(); err != nil {
-		// can potentially create deadlock when never succeeds
-		// TODO: add timeout
+		// BUG: Can potentially create a deadlock. Add a timeout.
 		return err
 	}
 
@@ -689,18 +763,23 @@ func (m *Migrate) unlock() error {
 	return nil
 }
 
+// unlockErr calls unlock and returns a combined error
+// if a prevErr is not nil.
 func (m *Migrate) unlockErr(prevErr error) error {
 	if err := m.unlock(); err != nil {
 		return NewMultiError(prevErr, err)
 	}
 	return prevErr
 }
+
+// logPrintf writes to m.Log if not nil
 func (m *Migrate) logPrintf(format string, v ...interface{}) {
 	if m.Log != nil {
 		m.Log.Printf(format, v...)
 	}
 }
 
+// logVerbosePrintf writes to m.Log if not nil. Use for verbose logging output.
 func (m *Migrate) logVerbosePrintf(format string, v ...interface{}) {
 	if m.Log != nil && m.Log.Verbose() {
 		m.Log.Printf(format, v...)

migrate/direction/direction.go

@@ -1,3 +1,5 @@
+// Deprecated: package direction is deprecated.
+// Will be removed soon.
 package direction
 
 type Direction int

migrate/file/file.go

@@ -1,3 +1,5 @@
+// Deprecated: package file is deprecated.
+// Will be removed soon.
 package file
 
 import (

migrate/v1compat.go

@@ -1,4 +1,5 @@
-// Deprecated: package migrate is here to make sure v2 is downwards compatible with v1
+// Deprecated: package migrate makes this version backwards compatible.
+// Expect this to be removed very soon.
 package migrate
 
 import (

migrate_test.go

@@ -2,8 +2,10 @@ package migrate
 
 import (
 	"bytes"
+	"database/sql"
 	"fmt"
 	"io/ioutil"
+	"log"
 	"os"
 	"testing"
 
@@ -15,7 +17,6 @@ import (
 // u = up migration, d = down migration, n = version
 //  |  1  |  -  |  3  |  4  |  5  |  -  |  7  |
 //  | u d |  -  | u   | u d |   d |  -  | u d |
-// var sourceStubMigrations  = source.NewMigrations()
 
 var sourceStubMigrations *source.Migrations
 
@@ -54,6 +55,19 @@ func TestNew(t *testing.T) {
 	}
 }
 
+func ExampleNew() {
+	// Read migrations from /home/mattes/migrations and connect to a local postgres database.
+	m, err := New("file:///home/mattes/migrations", "postgres://mattes:secret@localhost:5432/database?sslmode=disable")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Migrate all the way up ...
+	if err := m.Up(); err != nil {
+		log.Fatal(err)
+	}
+}
+
 func TestNewWithDatabaseInstance(t *testing.T) {
 	dummyDb := &DummyInstance{"database"}
 	dbInst, err := dStub.WithInstance(dummyDb, &dStub.Config{})
@@ -81,6 +95,34 @@ func TestNewWithDatabaseInstance(t *testing.T) {
 	}
 }
 
+func ExampleNewWithDatabaseInstance() {
+	// Create and use an existing database instance.
+	db, err := sql.Open("postgres", "postgres://mattes:secret@localhost:5432/database?sslmode=disable")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer db.Close()
+
+	// Create driver instance from db.
+	// Check each driver if it supports the WithInstance function.
+	// `import "github.com/mattes/migrate/database/postgres"`
+	instance, err := dStub.WithInstance(db, &dStub.Config{})
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Read migrations from /home/mattes/migrations and connect to a local postgres database.
+	m, err := NewWithDatabaseInstance("file:///home/mattes/migrations", "postgres", instance)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Migrate all the way up ...
+	if err := m.Up(); err != nil {
+		log.Fatal(err)
+	}
+}
+
 func TestNewWithSourceInstance(t *testing.T) {
 	dummySource := &DummyInstance{"source"}
 	sInst, err := sStub.WithInstance(dummySource, &sStub.Config{})
@@ -108,6 +150,29 @@ func TestNewWithSourceInstance(t *testing.T) {
 	}
 }
 
+func ExampleNewWithSourceInstance() {
+	di := &DummyInstance{"think any client required for a source here"}
+
+	// Create driver instance from DummyInstance di.
+	// Check each driver if it support the WithInstance function.
+	// `import "github.com/mattes/migrate/source/stub"`
+	instance, err := sStub.WithInstance(di, &sStub.Config{})
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Read migrations from Stub and connect to a local postgres database.
+	m, err := NewWithSourceInstance("stub", instance, "postgres://mattes:secret@localhost:5432/database?sslmode=disable")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Migrate all the way up ...
+	if err := m.Up(); err != nil {
+		log.Fatal(err)
+	}
+}
+
 func TestNewWithInstance(t *testing.T) {
 	dummyDb := &DummyInstance{"database"}
 	dbInst, err := dStub.WithInstance(dummyDb, &dStub.Config{})
@@ -141,6 +206,10 @@ func TestNewWithInstance(t *testing.T) {
 	}
 }
 
+func ExampleNewWithInstance() {
+	// See NewWithDatabaseInstance and NewWithSourceInstance for an example.
+}
+
 func TestClose(t *testing.T) {
 	m, _ := New("stub://", "stub://")
 	sourceErr, databaseErr := m.Close()

migration.go

@@ -7,25 +7,65 @@ import (
 	"time"
 )
 
+// DefaultBufferSize sets the in memory buffer size (in Bytes) for every
+// pre-read migration (see DefaultPrefetchMigrations).
 var DefaultBufferSize = uint(100000)
 
+// Migration holds information about a migration.
+// It is initially created from data coming from the source and then
+// used when run against the database.
 type Migration struct {
-	Identifier    string
-	Version       uint
+	// Identifier can be any string to help identifying
+	// the migration in the source.
+	Identifier string
+
+	// Version is the version of this migration.
+	Version uint
+
+	// TargetVersion is the migration version after this migration
+	// has been applied to the database.
 	TargetVersion int
 
-	Body         io.ReadCloser
+	// Body holds an io.ReadCloser to the source.
+	Body io.ReadCloser
+
+	// BufferedBody holds an buffered io.Reader to the underlying Body.
 	BufferedBody io.Reader
-	BufferSize   uint
+
+	// BufferSize defaults to DefaultBufferSize
+	BufferSize uint
+
+	// bufferWriter holds an io.WriteCloser and pipes to BufferBody.
+	// It's an *Closer for flow control.
 	bufferWriter io.WriteCloser
 
-	Scheduled         time.Time
-	StartedBuffering  time.Time
+	// Scheduled is the time when the migration was scheduled/ queued.
+	Scheduled time.Time
+
+	// StartedBuffering is the time when buffering of the migration source started.
+	StartedBuffering time.Time
+
+	// FinishedBuffering is the time when buffering of the migration source finished.
 	FinishedBuffering time.Time
-	FinishedReading   time.Time
-	BytesRead         int64
+
+	// FinishedReading is the time when the migration source is fully read.
+	FinishedReading time.Time
+
+	// BytesRead holds the number of Bytes read from the migration source.
+	BytesRead int64
 }
 
+// NewMigration returns a new Migration and sets the body, identifier,
+// version and targetVersion. Body can be nil, which turns this migration
+// into a "NilMigration". If no identifier is provided, it will default to "<empty>".
+//
+// What is a NilMigration?
+// Usually each migration version coming from source is expected to have an
+// Up and Down migration. This is not a hard requirement though, leading to
+// a situation where only the Up or Down migration is present. So let's say
+// the user wants to migrate up to a version that doesn't have the actual Up
+// migration, in that case we still want to apply the version, but with an empty
+// body. We are calling that a NilMigration, a migration with an empty body.
 func NewMigration(body io.ReadCloser, identifier string, version uint, targetVersion int) (*Migration, error) {
 	tnow := time.Now()
 	m := &Migration{
@@ -54,10 +94,13 @@ func NewMigration(body io.ReadCloser, identifier string, version uint, targetVer
 	return m, nil
 }
 
+// String implements string.Stringer and is used in tests.
 func (m *Migration) String() string {
 	return fmt.Sprintf("%v [%v=>%v]", m.Identifier, m.Version, m.TargetVersion)
 }
 
+// StringLong returns a string describing this migration to humans.
+// TODO: rename to LogString()
 func (m *Migration) StringLong() string {
 	directionStr := "u"
 	if m.TargetVersion < int(m.Version) {
@@ -66,7 +109,8 @@ func (m *Migration) StringLong() string {
 	return fmt.Sprintf("%v/%v %v", m.Version, directionStr, m.Identifier)
 }
 
-// Buffer buffers up to BufferSize (blocking, call with goroutine)
+// Buffer buffers Body up to BufferSize.
+// Calling this function blocks. Call with goroutine.
 func (m *Migration) Buffer() error {
 	if m.Body == nil {
 		return nil

migration_test.go

@@ -0,0 +1,39 @@
+package migrate
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"strings"
+)
+
+func ExampleNewMigration() {
+	// Create a dummy migration body, this is coming from the source usually.
+	body := ioutil.NopCloser(strings.NewReader("dumy migration that creates users table"))
+
+	// Create a new Migration that represents version 1486686016.
+	// Once this migration has been applied to the database, the new
+	// migration version will be 1486689359.
+	migr, err := NewMigration(body, "create_users_table", 1486686016, 1486689359)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Print(migr.StringLong())
+	// Output:
+	// 1486686016/u create_users_table
+}
+
+func ExampleNewMigration_nilMigration() {
+	// Create a new Migration that represents a NilMigration.
+	// Once this migration has been applied to the database, the new
+	// migration version will be 1486689359.
+	migr, err := NewMigration(nil, "", 1486686016, 1486689359)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Print(migr.StringLong())
+	// Output:
+	// 1486686016/u <empty>
+}

source/github/github.go

@@ -36,6 +36,9 @@ type Github struct {
 	migrations *source.Migrations
 }
 
+type Config struct {
+}
+
 func (g *Github) Open(url string) (source.Driver, error) {
 	u, err := nurl.Parse(url)
 	if err != nil {
@@ -80,7 +83,7 @@ func (g *Github) Open(url string) (source.Driver, error) {
 	return gn, nil
 }
 
-func WithInstance(client *github.Client) (source.Driver, error) {
+func WithInstance(client *github.Client, config *Config) (source.Driver, error) {
 	gn := &Github{
 		client:     client,
 		migrations: source.NewMigrations(),

util.go

@@ -9,10 +9,12 @@ import (
 	"time"
 )
 
+// MultiError holds multiple errors.
 type MultiError struct {
 	Errs []error
 }
 
+// NewMultiError returns an error type holding multiple errors.
 func NewMultiError(errs ...error) MultiError {
 	compactErrs := make([]error, 0)
 	for _, e := range errs {
@@ -23,6 +25,7 @@ func NewMultiError(errs ...error) MultiError {
 	return MultiError{compactErrs}
 }
 
+// Error implements error. Mulitple errors are concatenated with 'and's.
 func (m MultiError) Error() string {
 	var strs = make([]string, 0)
 	for _, e := range m.Errs {
@@ -72,7 +75,7 @@ func (b *slowReader) Close() error {
 	return b.rx.Close()
 }
 
-var ErrNoName = fmt.Errorf("no name")
+var errNoName = fmt.Errorf("no name")
 
 func nameFromUrl(url string) (string, error) {
 	u, err := nurl.Parse(url)
@@ -81,7 +84,7 @@ func nameFromUrl(url string) (string, error) {
 	}
 
 	if len(u.Scheme) == 0 {
-		return "", ErrNoName
+		return "", errNoName
 	}
 
 	return u.Scheme, nil