Refactor drivers into separate packages (#179)

`dbmate` package was starting to get a bit polluted. This PR migrates each driver into a separate package, with clean separation between each.

In addition:

* Drivers are now initialized with a URL, avoiding the need to pass `*url.URL` to every method
* Sqlite supports a cleaner syntax for relative paths
* Driver tests now load their test URL from environment variables

Public API of `dbmate` package has not changed (no changes to `main` package).

pkg/driver/sqlite/sqlite.go

@@ -0,0 +1,220 @@
+// +build cgo
+
+package sqlite
+
+import (
+	"bytes"
+	"database/sql"
+	"fmt"
+	"net/url"
+	"os"
+	"regexp"
+	"strings"
+
+	"github.com/amacneil/dbmate/pkg/dbmate"
+	"github.com/amacneil/dbmate/pkg/dbutil"
+
+	"github.com/lib/pq"
+	_ "github.com/mattn/go-sqlite3" // database/sql driver
+)
+
+func init() {
+	dbmate.RegisterDriver(NewDriver, "sqlite")
+	dbmate.RegisterDriver(NewDriver, "sqlite3")
+}
+
+// Driver provides top level database functions
+type Driver struct {
+	migrationsTableName string
+	databaseURL         *url.URL
+}
+
+// NewDriver initializes the driver
+func NewDriver(config dbmate.DriverConfig) dbmate.Driver {
+	return &Driver{
+		migrationsTableName: config.MigrationsTableName,
+		databaseURL:         config.DatabaseURL,
+	}
+}
+
+// ConnectionString converts a URL into a valid connection string
+func ConnectionString(u *url.URL) string {
+	// duplicate URL and remove scheme
+	newURL := *u
+	newURL.Scheme = ""
+
+	// trim duplicate leading slashes
+	str := regexp.MustCompile("^//+").ReplaceAllString(newURL.String(), "/")
+
+	return str
+}
+
+// Open creates a new database connection
+func (drv *Driver) Open() (*sql.DB, error) {
+	return sql.Open("sqlite3", ConnectionString(drv.databaseURL))
+}
+
+// CreateDatabase creates the specified database
+func (drv *Driver) CreateDatabase() error {
+	fmt.Printf("Creating: %s\n", ConnectionString(drv.databaseURL))
+
+	db, err := drv.Open()
+	if err != nil {
+		return err
+	}
+	defer dbutil.MustClose(db)
+
+	return db.Ping()
+}
+
+// DropDatabase drops the specified database (if it exists)
+func (drv *Driver) DropDatabase() error {
+	path := ConnectionString(drv.databaseURL)
+	fmt.Printf("Dropping: %s\n", path)
+
+	exists, err := drv.DatabaseExists()
+	if err != nil {
+		return err
+	}
+	if !exists {
+		return nil
+	}
+
+	return os.Remove(path)
+}
+
+func (drv *Driver) schemaMigrationsDump(db *sql.DB) ([]byte, error) {
+	migrationsTable := drv.quotedMigrationsTableName()
+
+	// load applied migrations
+	migrations, err := dbutil.QueryColumn(db,
+		fmt.Sprintf("select quote(version) from %s order by version asc", migrationsTable))
+	if err != nil {
+		return nil, err
+	}
+
+	// build schema migrations table data
+	var buf bytes.Buffer
+	buf.WriteString("-- Dbmate schema migrations\n")
+
+	if len(migrations) > 0 {
+		buf.WriteString(
+			fmt.Sprintf("INSERT INTO %s (version) VALUES\n  (", migrationsTable) +
+				strings.Join(migrations, "),\n  (") +
+				");\n")
+	}
+
+	return buf.Bytes(), nil
+}
+
+// DumpSchema returns the current database schema
+func (drv *Driver) DumpSchema(db *sql.DB) ([]byte, error) {
+	path := ConnectionString(drv.databaseURL)
+	schema, err := dbutil.RunCommand("sqlite3", path, ".schema")
+	if err != nil {
+		return nil, err
+	}
+
+	migrations, err := drv.schemaMigrationsDump(db)
+	if err != nil {
+		return nil, err
+	}
+
+	schema = append(schema, migrations...)
+	return dbutil.TrimLeadingSQLComments(schema)
+}
+
+// DatabaseExists determines whether the database exists
+func (drv *Driver) DatabaseExists() (bool, error) {
+	_, err := os.Stat(ConnectionString(drv.databaseURL))
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	if err != nil {
+		return false, err
+	}
+
+	return true, nil
+}
+
+// CreateMigrationsTable creates the schema migrations table
+func (drv *Driver) CreateMigrationsTable(db *sql.DB) error {
+	_, err := db.Exec(
+		fmt.Sprintf("create table if not exists %s ", drv.quotedMigrationsTableName()) +
+			"(version varchar(255) primary key)")
+
+	return err
+}
+
+// SelectMigrations returns a list of applied migrations
+// with an optional limit (in descending order)
+func (drv *Driver) SelectMigrations(db *sql.DB, limit int) (map[string]bool, error) {
+	query := fmt.Sprintf("select version from %s order by version desc", drv.quotedMigrationsTableName())
+	if limit >= 0 {
+		query = fmt.Sprintf("%s limit %d", query, limit)
+	}
+	rows, err := db.Query(query)
+	if err != nil {
+		return nil, err
+	}
+
+	defer dbutil.MustClose(rows)
+
+	migrations := map[string]bool{}
+	for rows.Next() {
+		var version string
+		if err := rows.Scan(&version); err != nil {
+			return nil, err
+		}
+
+		migrations[version] = true
+	}
+
+	if err = rows.Err(); err != nil {
+		return nil, err
+	}
+
+	return migrations, nil
+}
+
+// InsertMigration adds a new migration record
+func (drv *Driver) InsertMigration(db dbutil.Transaction, version string) error {
+	_, err := db.Exec(
+		fmt.Sprintf("insert into %s (version) values (?)", drv.quotedMigrationsTableName()),
+		version)
+
+	return err
+}
+
+// DeleteMigration removes a migration record
+func (drv *Driver) DeleteMigration(db dbutil.Transaction, version string) error {
+	_, err := db.Exec(
+		fmt.Sprintf("delete from %s where version = ?", drv.quotedMigrationsTableName()),
+		version)
+
+	return err
+}
+
+// Ping verifies a connection to the database. Due to the way SQLite works, by
+// testing whether the database is valid, it will automatically create the database
+// if it does not already exist.
+func (drv *Driver) Ping() error {
+	db, err := drv.Open()
+	if err != nil {
+		return err
+	}
+	defer dbutil.MustClose(db)
+
+	return db.Ping()
+}
+
+func (drv *Driver) quotedMigrationsTableName() string {
+	return drv.quoteIdentifier(drv.migrationsTableName)
+}
+
+// quoteIdentifier quotes a table or column name
+// we fall back to lib/pq implementation since both use ansi standard (double quotes)
+// and mattn/go-sqlite3 doesn't provide a sqlite-specific equivalent
+func (drv *Driver) quoteIdentifier(s string) string {
+	return pq.QuoteIdentifier(s)
+}