automagic sql db migrations (#461)

* adds migrations

closes #57

migrations only run if the database is not brand new. brand new
databases will contain all the right fields when CREATE TABLE is called,
this is for readability mostly more than efficiency (do not want to have
to go through all of the database migrations to ascertain what columns a table
has). upon startup of a new database, the migrations will be analyzed and the
highest version set, so that future migrations will be run. this should also
avoid running through all the migrations, which could bork db's easily enough
(if the user just exits from impatience, say).

otherwise, all migrations that a db has not yet seen will be run against it
upon startup, this should be seamless to the user whether they had a db that
had 0 migrations run on it before or N. this means users will not have to
explicitly run any migrations on their dbs nor see any errors when we upgrade
the db (so long as things go well). if migrations do not go so well, users
will have to manually repair dbs (this is the intention of the `migrate`
library and it seems sane), this should be rare, and I'm unsure myself how
best to resolve not having gone through this myself, I would assume it will
require running down migrations and then manually updating the migration
field; in any case, docs once one of us has to go through this.

migrations are written to files and checked into version control, and then use
go-bindata to generate those files into go code and compiled in to be consumed
by the migrate library (so that we don't have to put migration files on any
servers) -- this is also in vcs. this seems to work ok. I don't like having to
use the separate go-bindata tool but it wasn't really hard to install and then
go generate takes care of the args. adding migrations should be relatively
rare anyway, but tried to make it pretty painless.

1 migration to add created_at to the route is done here as an example of how
to do migrations, as well as testing these things ;) -- `created_at` will be
`0001-01-01T00:00:00.000Z` for any existing routes after a user runs this
version. could spend the extra time adding 'today's date to any outstanding
records, but that's not really accurate, the main thing is nobody will have to
nuke their db with the migrations in place & we don't have any prod clusters
really to worry about. all future routes will correctly have `created_at` set,
and plan to add other timestamps but wanted to keep this patch as small as
possible so only did routes.created_at.

there are tests that a spankin new db will work as expected as well as a db
after running all down & up migrations works. the latter tests only run on mysql
and postgres, since sqlite3 does not like ALTER TABLE DROP COLUMN; up
migrations will need to be tested manually for sqlite3 only, but in theory if
they are simple and work on postgres and mysql, there is a good likelihood of
success; the new migration from this patch works on sqlite3 fine.

for now, we need to use `github.com/rdallman/migrate` to move forward, as
getting integrated into upstream is proving difficult due to
`github.com/go-sql-driver/mysql` being broken on master (yay dependencies).
Fortunately for us, we vendor a version of the `mysql` bindings that actually
works, thus, we are capable of using the `mattes/migrate` library with success
due to that. this also will require go1.9 to use the new `database/sql.Conn`
type, CI has been updated accordingly.

some doc fixes too from testing.. and of course updated all deps.

anyway, whew. this should let us add fields to the db without busting
everybody's dbs. open to feedback on better ways, but this was overall pretty
simple despite futzing with mysql.

* add migrate pkg to deps, update deps

use rdallman/migrate until we resolve in mattes land

* add README in migrations package

* add ref to mattes lib

vendor/github.com/mattes/migrate/database/cassandra/cassandra.go

@@ -0,0 +1,228 @@
+package cassandra
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	nurl "net/url"
+	"strconv"
+	"time"
+
+	"github.com/gocql/gocql"
+	"github.com/mattes/migrate/database"
+)
+
+func init() {
+	db := new(Cassandra)
+	database.Register("cassandra", db)
+}
+
+var DefaultMigrationsTable = "schema_migrations"
+var dbLocked = false
+
+var (
+	ErrNilConfig     = fmt.Errorf("no config")
+	ErrNoKeyspace    = fmt.Errorf("no keyspace provided")
+	ErrDatabaseDirty = fmt.Errorf("database is dirty")
+)
+
+type Config struct {
+	MigrationsTable string
+	KeyspaceName    string
+}
+
+type Cassandra struct {
+	session  *gocql.Session
+	isLocked bool
+
+	// Open and WithInstance need to guarantee that config is never nil
+	config *Config
+}
+
+func (p *Cassandra) Open(url string) (database.Driver, error) {
+	u, err := nurl.Parse(url)
+	if err != nil {
+		return nil, err
+	}
+
+	// Check for missing mandatory attributes
+	if len(u.Path) == 0 {
+		return nil, ErrNoKeyspace
+	}
+
+	migrationsTable := u.Query().Get("x-migrations-table")
+	if len(migrationsTable) == 0 {
+		migrationsTable = DefaultMigrationsTable
+	}
+
+	p.config = &Config{
+		KeyspaceName:    u.Path,
+		MigrationsTable: migrationsTable,
+	}
+
+	cluster := gocql.NewCluster(u.Host)
+	cluster.Keyspace = u.Path[1:len(u.Path)]
+	cluster.Consistency = gocql.All
+	cluster.Timeout = 1 * time.Minute
+
+	if len(u.Query().Get("username")) > 0 && len(u.Query().Get("password")) > 0 {
+		authenticator := gocql.PasswordAuthenticator{
+			Username: u.Query().Get("username"),
+			Password: u.Query().Get("password"),
+		}
+		cluster.Authenticator = authenticator
+	}
+
+	// Retrieve query string configuration
+	if len(u.Query().Get("consistency")) > 0 {
+		var consistency gocql.Consistency
+		consistency, err = parseConsistency(u.Query().Get("consistency"))
+		if err != nil {
+			return nil, err
+		}
+
+		cluster.Consistency = consistency
+	}
+	if len(u.Query().Get("protocol")) > 0 {
+		var protoversion int
+		protoversion, err = strconv.Atoi(u.Query().Get("protocol"))
+		if err != nil {
+			return nil, err
+		}
+		cluster.ProtoVersion = protoversion
+	}
+	if len(u.Query().Get("timeout")) > 0 {
+		var timeout time.Duration
+		timeout, err = time.ParseDuration(u.Query().Get("timeout"))
+		if err != nil {
+			return nil, err
+		}
+		cluster.Timeout = timeout
+	}
+
+	p.session, err = cluster.CreateSession()
+
+	if err != nil {
+		return nil, err
+	}
+
+	if err := p.ensureVersionTable(); err != nil {
+		return nil, err
+	}
+
+	return p, nil
+}
+
+func (p *Cassandra) Close() error {
+	p.session.Close()
+	return nil
+}
+
+func (p *Cassandra) Lock() error {
+	if dbLocked {
+		return database.ErrLocked
+	}
+	dbLocked = true
+	return nil
+}
+
+func (p *Cassandra) Unlock() error {
+	dbLocked = false
+	return nil
+}
+
+func (p *Cassandra) Run(migration io.Reader) error {
+	migr, err := ioutil.ReadAll(migration)
+	if err != nil {
+		return err
+	}
+	// run migration
+	query := string(migr[:])
+	if err := p.session.Query(query).Exec(); err != nil {
+		// TODO: cast to Cassandra error and get line number
+		return database.Error{OrigErr: err, Err: "migration failed", Query: migr}
+	}
+
+	return nil
+}
+
+func (p *Cassandra) SetVersion(version int, dirty bool) error {
+	query := `TRUNCATE "` + p.config.MigrationsTable + `"`
+	if err := p.session.Query(query).Exec(); err != nil {
+		return &database.Error{OrigErr: err, Query: []byte(query)}
+	}
+	if version >= 0 {
+		query = `INSERT INTO "` + p.config.MigrationsTable + `" (version, dirty) VALUES (?, ?)`
+		if err := p.session.Query(query, version, dirty).Exec(); err != nil {
+			return &database.Error{OrigErr: err, Query: []byte(query)}
+		}
+	}
+
+	return nil
+}
+
+// Return current keyspace version
+func (p *Cassandra) Version() (version int, dirty bool, err error) {
+	query := `SELECT version, dirty FROM "` + p.config.MigrationsTable + `" LIMIT 1`
+	err = p.session.Query(query).Scan(&version, &dirty)
+	switch {
+	case err == gocql.ErrNotFound:
+		return database.NilVersion, false, nil
+
+	case err != nil:
+		if _, ok := err.(*gocql.Error); ok {
+			return database.NilVersion, false, nil
+		}
+		return 0, false, &database.Error{OrigErr: err, Query: []byte(query)}
+
+	default:
+		return version, dirty, nil
+	}
+}
+
+func (p *Cassandra) Drop() error {
+	// select all tables in current schema
+	query := fmt.Sprintf(`SELECT table_name from system_schema.tables WHERE keyspace_name='%s'`, p.config.KeyspaceName[1:]) // Skip '/' character
+	iter := p.session.Query(query).Iter()
+	var tableName string
+	for iter.Scan(&tableName) {
+		err := p.session.Query(fmt.Sprintf(`DROP TABLE %s`, tableName)).Exec()
+		if err != nil {
+			return err
+		}
+	}
+	// Re-create the version table
+	if err := p.ensureVersionTable(); err != nil {
+		return err
+	}
+	return nil
+}
+
+// Ensure version table exists
+func (p *Cassandra) ensureVersionTable() error {
+	err := p.session.Query(fmt.Sprintf("CREATE TABLE IF NOT EXISTS %s (version bigint, dirty boolean, PRIMARY KEY(version))", p.config.MigrationsTable)).Exec()
+	if err != nil {
+		return err
+	}
+	if _, _, err = p.Version(); err != nil {
+		return err
+	}
+	return nil
+}
+
+// ParseConsistency wraps gocql.ParseConsistency
+// to return an error instead of a panicking.
+func parseConsistency(consistencyStr string) (consistency gocql.Consistency, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			var ok bool
+			err, ok = r.(error)
+			if !ok {
+				err = fmt.Errorf("Failed to parse consistency \"%s\": %v", consistencyStr, r)
+			}
+		}
+	}()
+	consistency = gocql.ParseConsistency(consistencyStr)
+
+	return consistency, nil
+}