exp/sql{,/driver}: new database packages

R=gustavo, rsc, borman, dave, kevlar, nigeltao, dvyukov, kardianos, fw, r, r, david.crawshaw
CC=golang-dev
https://golang.org/cl/4973055

src/pkg/Makefile

@@ -82,6 +82,8 @@ DIRS=\
 	exp/gui\
 	exp/gui/x11\
 	exp/norm\
+	exp/sql\
+	exp/sql/driver\
 	exp/template/html\
 	expvar\
 	flag\
@@ -202,6 +204,7 @@ NOTEST+=\
 	crypto/x509/pkix\
 	exp/gui\
 	exp/gui/x11\
+	exp/sql/driver\
 	go/ast\
 	go/doc\
 	go/token\

src/pkg/exp/sql/Makefile

+# Copyright 2011 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=exp/sql
+GOFILES=\
+	convert.go\
+	sql.go\
+
+include ../../../Make.pkg

src/pkg/exp/sql/convert.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Type conversions for Scan.
+
+package sql
+
+import (
+	"fmt"
+	"os"
+	"reflect"
+	"strconv"
+)
+
+// convertAssign copies to dest the value in src, converting it if possible.
+// An error is returned if the copy would result in loss of information.
+// dest should be a pointer type.
+func convertAssign(dest, src interface{}) os.Error {
+	// Common cases, without reflect.  Fall through.
+	switch s := src.(type) {
+	case string:
+		switch d := dest.(type) {
+		case *string:
+			*d = s
+			return nil
+		}
+	case []byte:
+		switch d := dest.(type) {
+		case *string:
+			*d = string(s)
+			return nil
+		case *[]byte:
+			*d = s
+			return nil
+		}
+	}
+
+	sv := reflect.ValueOf(src)
+
+	switch d := dest.(type) {
+	case *string:
+		switch sv.Kind() {
+		case reflect.Bool,
+			reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
+			reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
+			reflect.Float32, reflect.Float64:
+			*d = fmt.Sprintf("%v", src)
+			return nil
+		}
+	}
+
+	if scanner, ok := dest.(ScannerInto); ok {
+		return scanner.ScanInto(src)
+	}
+
+	dpv := reflect.ValueOf(dest)
+	if dpv.Kind() != reflect.Ptr {
+		return os.NewError("destination not a pointer")
+	}
+
+	dv := reflect.Indirect(dpv)
+	if dv.Kind() == sv.Kind() {
+		dv.Set(sv)
+		return nil
+	}
+
+	switch dv.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		if s, ok := asString(src); ok {
+			i64, err := strconv.Atoi64(s)
+			if err != nil {
+				return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
+			}
+			if dv.OverflowInt(i64) {
+				return fmt.Errorf("string %q overflows %s", s, dv.Kind())
+			}
+			dv.SetInt(i64)
+			return nil
+		}
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		if s, ok := asString(src); ok {
+			u64, err := strconv.Atoui64(s)
+			if err != nil {
+				return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
+			}
+			if dv.OverflowUint(u64) {
+				return fmt.Errorf("string %q overflows %s", s, dv.Kind())
+			}
+			dv.SetUint(u64)
+			return nil
+		}
+	}
+
+	return fmt.Errorf("unsupported driver -> Scan pair: %T -> %T", src, dest)
+}
+
+func asString(src interface{}) (s string, ok bool) {
+	switch v := src.(type) {
+	case string:
+		return v, true
+	case []byte:
+		return string(v), true
+	}
+	return "", false
+}

src/pkg/exp/sql/convert_test.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sql
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+type conversionTest struct {
+	s, d interface{} // source and destination
+
+	// following are used if they're non-zero
+	wantint  int64
+	wantuint uint64
+	wantstr  string
+	wanterr  string
+}
+
+// Target variables for scanning into.
+var (
+	scanstr    string
+	scanint    int
+	scanint8   int8
+	scanint16  int16
+	scanint32  int32
+	scanuint8  uint8
+	scanuint16 uint16
+)
+
+var conversionTests = []conversionTest{
+	// Exact conversions (destination pointer type matches source type)
+	{s: "foo", d: &scanstr, wantstr: "foo"},
+	{s: 123, d: &scanint, wantint: 123},
+
+	// To strings
+	{s: []byte("byteslice"), d: &scanstr, wantstr: "byteslice"},
+	{s: 123, d: &scanstr, wantstr: "123"},
+	{s: int8(123), d: &scanstr, wantstr: "123"},
+	{s: int64(123), d: &scanstr, wantstr: "123"},
+	{s: uint8(123), d: &scanstr, wantstr: "123"},
+	{s: uint16(123), d: &scanstr, wantstr: "123"},
+	{s: uint32(123), d: &scanstr, wantstr: "123"},
+	{s: uint64(123), d: &scanstr, wantstr: "123"},
+	{s: 1.5, d: &scanstr, wantstr: "1.5"},
+
+	// Strings to integers
+	{s: "255", d: &scanuint8, wantuint: 255},
+	{s: "256", d: &scanuint8, wanterr: `string "256" overflows uint8`},
+	{s: "256", d: &scanuint16, wantuint: 256},
+	{s: "-1", d: &scanint, wantint: -1},
+	{s: "foo", d: &scanint, wanterr: `converting string "foo" to a int: parsing "foo": invalid argument`},
+}
+
+func intValue(intptr interface{}) int64 {
+	return reflect.Indirect(reflect.ValueOf(intptr)).Int()
+}
+
+func uintValue(intptr interface{}) uint64 {
+	return reflect.Indirect(reflect.ValueOf(intptr)).Uint()
+}
+
+func TestConversions(t *testing.T) {
+	for n, ct := range conversionTests {
+		err := convertAssign(ct.d, ct.s)
+		errstr := ""
+		if err != nil {
+			errstr = err.String()
+		}
+		errf := func(format string, args ...interface{}) {
+			base := fmt.Sprintf("convertAssign #%d: for %v (%T) -> %T, ", n, ct.s, ct.s, ct.d)
+			t.Errorf(base+format, args...)
+		}
+		if errstr != ct.wanterr {
+			errf("got error %q, want error %q", errstr, ct.wanterr)
+		}
+		if ct.wantstr != "" && ct.wantstr != scanstr {
+			errf("want string %q, got %q", ct.wantstr, scanstr)
+		}
+		if ct.wantint != 0 && ct.wantint != intValue(ct.d) {
+			errf("want int %d, got %d", ct.wantint, intValue(ct.d))
+		}
+		if ct.wantuint != 0 && ct.wantuint != uintValue(ct.d) {
+			errf("want uint %d, got %d", ct.wantuint, uintValue(ct.d))
+		}
+	}
+}
+
+func TestNullableString(t *testing.T) {
+	var ns NullableString
+	convertAssign(&ns, []byte("foo"))
+	if !ns.Valid {
+		t.Errorf("expecting not null")
+	}
+	if ns.String != "foo" {
+		t.Errorf("expecting foo; got %q", ns.String)
+	}
+	convertAssign(&ns, nil)
+	if ns.Valid {
+		t.Errorf("expecting null on nil")
+	}
+	if ns.String != "" {
+		t.Errorf("expecting blank on nil; got %q", ns.String)
+	}
+}

src/pkg/exp/sql/doc.txt

+Goals of the sql and sql/driver packages:
+
+* Provide a generic database API for a variety of SQL or SQL-like
+  databases.  There currently exist Go libraries for SQLite, MySQL,
+  and Postgres, but all with a very different feel, and often
+  a non-Go-like feel.
+
+* Feel like Go.
+
+* Care mostly about the common cases. Common SQL should be portable.
+  SQL edge cases or db-specific extensions can be detected and
+  conditionally used by the application.  It is a non-goal to care
+  about every particular db's extension or quirk.
+
+* Separate out the basic implementation of a database driver
+  (implementing the sql/driver interfaces) vs the implementation
+  of all the user-level types and convenience methods.
+  In a nutshell:
+
+  User Code ---> sql package (concrete types) ---> sql/driver (interfaces)
+  Database Driver -> sql (to register) + sql/driver (implement interfaces)
+
+* Make type casting/conversions consistent between all drivers. To
+  achieve this, most of the conversions are done in the db package,
+  not in each driver. The drivers then only have to deal with a
+  smaller set of types.
+
+* Be flexible with type conversions, but be paranoid about silent
+  truncation or other loss of precision.
+
+* Handle concurrency well.  Users shouldn't need to care about the
+  database's per-connection thread safety issues (or lack thereof),
+  and shouldn't have to maintain their own free pools of connections.
+  The 'db' package should deal with that bookkeeping as needed.  Given
+  an *sql.DB, it should be possible to share that instance between
+  multiple goroutines, without any extra synchronization.
+
+* Push complexity, where necessary, down into the sql+driver packages,
+  rather than exposing it to users. Said otherwise, the sql package
+  should expose an ideal database that's not finnicky about how it's
+  accessed, even if that's not true.
+
+* Provide optional interfaces in sql/driver for drivers to implement
+  for special cases or fastpaths.  But the only party that knows about
+  those is the sql package.  To user code, some stuff just might start
+  working or start working slightly faster.

src/pkg/exp/sql/driver/Makefile

+# Copyright 2011 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../../Make.inc
+
+TARG=exp/sql/driver
+GOFILES=\
+	driver.go\
+	types.go\
+
+include ../../../../Make.pkg

src/pkg/exp/sql/driver/driver.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package driver defines interfaces to be implemented by database
+// drivers as used by package sql.
+//
+// Code simply using databases should use package sql.
+//
+// Drivers only need to be aware of a subset of Go's types.  The db package
+// will convert all types into one of the following:
+//
+//   int64
+//   float64
+//   bool
+//   nil
+//   []byte
+//   string   [*] everywhere except from Rows.Next.
+//
+package driver
+
+import (
+	"os"
+)
+
+// Driver is the interface that must be implemented by a database
+// driver.
+type Driver interface {
+	// Open returns a new or cached connection to the database.
+	// The name is a string in a driver-specific format.
+	//
+	// The returned connection is only used by one goroutine at a
+	// time.
+	Open(name string) (Conn, os.Error)
+}
+
+// Execer is an optional interface that may be implemented by a Driver
+// or a Conn.
+//
+// If a Driver does not implement Execer, the sql package's DB.Exec
+// method first obtains a free connection from its free pool or from
+// the driver's Open method. Execer should only be implemented by
+// drivers that can provide a more efficient implementation.
+//
+// If a Conn does not implement Execer, the db package's DB.Exec will
+// first prepare a query, execute the statement, and then close the
+// statement.
+//
+// All arguments are of a subset type as defined in the package docs.
+type Execer interface {
+	Exec(query string, args []interface{}) (Result, os.Error)
+}
+
+// Conn is a connection to a database. It is not used concurrently
+// by multiple goroutines.
+//
+// Conn is assumed to be stateful.
+type Conn interface {
+	// Prepare returns a prepared statement, bound to this connection.
+	Prepare(query string) (Stmt, os.Error)
+
+	// Close invalidates and potentially stops any current
+	// prepared statements and transactions, marking this
+	// connection as no longer in use.  The driver may cache or
+	// close its underlying connection to its database.
+	Close() os.Error
+
+	// Begin starts and returns a new transaction.
+	Begin() (Tx, os.Error)
+}
+
+// Result is the result of a query execution.
+type Result interface {
+	// LastInsertId returns the database's auto-generated ID
+	// after, for example, an INSERT into a table with primary
+	// key.
+	LastInsertId() (int64, os.Error)
+
+	// RowsAffected returns the number of rows affected by the
+	// query.
+	RowsAffected() (int64, os.Error)
+}
+
+// Stmt is a prepared statement. It is bound to a Conn and not
+// used by multiple goroutines concurrently.
+type Stmt interface {
+	// Close closes the statement.
+	Close() os.Error
+
+	// NumInput returns the number of placeholder parameters.
+	NumInput() int
+
+	// Exec executes a query that doesn't return rows, such
+	// as an INSERT or UPDATE.  The args are all of a subset
+	// type as defined above.
+	Exec(args []interface{}) (Result, os.Error)
+
+	// Exec executes a query that may return rows, such as a
+	// SELECT.  The args of all of a subset type as defined above.
+	Query(args []interface{}) (Rows, os.Error)
+}
+
+// ColumnConverter may be optionally implemented by Stmt if the
+// the statement is aware of its own columns' types and can
+// convert from any type to a driver subset type.
+type ColumnConverter interface {
+	// ColumnConverter returns a ValueConverter for the provided
+	// column index.  If the type of a specific column isn't known
+	// or shouldn't be handled specially, DefaultValueConverter
+	// can be returned.
+	ColumnConverter(idx int) ValueConverter
+}
+
+// Rows is an iterator over an executed query's results.
+type Rows interface {
+	// Columns returns the names of the columns. The number of
+	// columns of the result is inferred from the length of the
+	// slice.  If a particular column name isn't known, an empty
+	// string should be returned for that entry.
+	Columns() []string
+
+	// Close closes the rows iterator.
+	Close() os.Error
+
+	// Next is called to populate the next row of data into
+	// the provided slice. The provided slice will be the same
+	// size as the Columns() are wide.
+	//
+	// The dest slice may be populated with only with values
+	// of subset types defined above, but excluding string.
+	// All string values must be converted to []byte.
+	Next(dest []interface{}) os.Error
+}
+
+// Tx is a transaction.
+type Tx interface {
+	Commit() os.Error
+	Rollback() os.Error
+}
+
+// RowsAffected implements Result for an INSERT or UPDATE operation
+// which mutates a number of rows.
+type RowsAffected int64
+
+var _ Result = RowsAffected(0)
+
+func (RowsAffected) LastInsertId() (int64, os.Error) {
+	return 0, os.NewError("no LastInsertId available")
+}
+
+func (v RowsAffected) RowsAffected() (int64, os.Error) {
+	return int64(v), nil
+}
+
+// DDLSuccess is a pre-defined Result for drivers to return when a DDL
+// command succeeds.
+var DDLSuccess ddlSuccess
+
+type ddlSuccess struct{}
+
+var _ Result = ddlSuccess{}
+
+func (ddlSuccess) LastInsertId() (int64, os.Error) {
+	return 0, os.NewError("no LastInsertId available after DDL statement")
+}
+
+func (ddlSuccess) RowsAffected() (int64, os.Error) {
+	return 0, os.NewError("no RowsAffected available after DDL statement")
+}

src/pkg/exp/sql/driver/types.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package driver
+
+import (
+	"fmt"
+	"os"
+	"reflect"
+	"strconv"
+)
+
+// ValueConverter is the interface providing the ConvertValue method.
+type ValueConverter interface {
+	// ConvertValue converts a value to a restricted subset type.
+	ConvertValue(v interface{}) (interface{}, os.Error)
+}
+
+// Bool is a ValueConverter that converts input values to bools.
+//
+// The conversion rules are:
+//  - .... TODO(bradfitz): TBD
+var Bool boolType
+
+type boolType struct{}
+
+var _ ValueConverter = boolType{}
+
+func (boolType) ConvertValue(v interface{}) (interface{}, os.Error) {
+	return nil, fmt.Errorf("TODO(bradfitz): bool conversions")
+}
+
+// Int32 is a ValueConverter that converts input values to int64,
+// respecting the limits of an int32 value.
+var Int32 int32Type
+
+type int32Type struct{}
+
+var _ ValueConverter = int32Type{}
+
+func (int32Type) ConvertValue(v interface{}) (interface{}, os.Error) {
+	rv := reflect.ValueOf(v)
+	switch rv.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		i64 := rv.Int()
+		if i64 > (1<<31)-1 || i64 < -(1<<31) {
+			return nil, fmt.Errorf("sql/driver: value %d overflows int32", v)
+		}
+		return i64, nil
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		u64 := rv.Uint()
+		if u64 > (1<<31)-1 {
+			return nil, fmt.Errorf("sql/driver: value %d overflows int32", v)
+		}
+		return int64(u64), nil
+	case reflect.String:
+		i, err := strconv.Atoi(rv.String())
+		if err != nil {
+			return nil, fmt.Errorf("sql/driver: value %q can't be converted to int32", v)
+		}
+		return int64(i), nil
+	}
+	return nil, fmt.Errorf("sql/driver: unsupported value %v (type %T) converting to int32", v, v)
+}
+
+// String is a ValueConverter that converts its input to a string.
+// If the value is already a string or []byte, it's unchanged.
+// If the value is of another type, conversion to string is done
+// with fmt.Sprintf("%v", v).
+var String stringType
+
+type stringType struct{}
+
+func (stringType) ConvertValue(v interface{}) (interface{}, os.Error) {
+	switch v.(type) {
+	case string, []byte:
+		return v, nil
+	}
+	return fmt.Sprintf("%v", v), nil
+}
+
+// IsParameterSubsetType reports whether v is of a valid type for a
+// parameter. These types are:
+//
+//   int64
+//   float64
+//   bool
+//   nil
+//   []byte
+//   string
+//
+// This is the ame list as IsScanSubsetType, with the addition of
+// string.
+func IsParameterSubsetType(v interface{}) bool {
+	if IsScanSubsetType(v) {
+		return true
+	}
+	if _, ok := v.(string); ok {
+		return true
+	}
+	return false
+}
+
+// IsScanSubsetType reports whether v is of a valid type for a
+// value populated by Rows.Next. These types are:
+//
+//   int64
+//   float64
+//   bool
+//   nil
+//   []byte
+//
+// This is the same list as IsParameterSubsetType, without string.
+func IsScanSubsetType(v interface{}) bool {
+	if v == nil {
+		return true
+	}
+	switch v.(type) {
+	case int64, float64, []byte, bool:
+		return true
+	}
+	return false
+}
+
+// DefaultParameterConverter is the default implementation of
+// ValueConverter that's used when a Stmt doesn't implement
+// ColumnConverter.
+//
+// DefaultParameterConverter returns the given value directly if
+// IsSubsetType(value).  Otherwise integer type are converted to
+// int64, floats to float64, and strings to []byte.  Other types are
+// an error.
+var DefaultParameterConverter defaultConverter
+
+type defaultConverter struct{}
+
+var _ ValueConverter = defaultConverter{}
+
+func (defaultConverter) ConvertValue(v interface{}) (interface{}, os.Error) {
+	if IsParameterSubsetType(v) {
+		return v, nil
+	}
+
+	rv := reflect.ValueOf(v)
+	switch rv.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return rv.Int(), nil
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32:
+		return int64(rv.Uint()), nil
+	case reflect.Uint64:
+		u64 := rv.Uint()
+		if u64 >= 1<<63 {
+			return nil, fmt.Errorf("uint64 values with high bit set are not supported")
+		}
+		return int64(u64), nil
+	case reflect.Float32, reflect.Float64:
+		return rv.Float(), nil
+	}
+	return nil, fmt.Errorf("unsupported type %s", rv.Kind())
+}

src/pkg/exp/sql/fakedb_test.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sql
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+
+	"exp/sql/driver"
+)
+
+var _ = log.Printf
+
+// fakeDriver is a fake database that implements Go's driver.Driver
+// interface, just for testing.
+//
+// It speaks a query language that's semantically similar to but
+// syntantically different and simpler than SQL.  The syntax is as
+// follows:
+//
+//   WIPE
+//   CREATE|<tablename>|<col>=<type>,<col>=<type>,...
+//     where types are: "string", [u]int{8,16,32,64}, "bool"
+//   INSERT|<tablename>|col=val,col2=val2,col3=?
+//   SELECT|<tablename>|projectcol1,projectcol2|filtercol=?,filtercol2=?
+//
+// When opening a a fakeDriver's database, it starts empty with no
+// tables.  All tables and data are stored in memory only.
+type fakeDriver struct {
+	mu        sync.Mutex
+	openCount int
+	dbs       map[string]*fakeDB
+}
+
+type fakeDB struct {
+	name string
+
+	mu     sync.Mutex
+	free   []*fakeConn
+	tables map[string]*table
+}
+
+type table struct {
+	mu      sync.Mutex
+	colname []string
+	coltype []string
+	rows    []*row
+}
+
+func (t *table) columnIndex(name string) int {
+	for n, nname := range t.colname {
+		if name == nname {
+			return n
+		}
+	}
+	return -1
+}
+
+type row struct {
+	cols []interface{} // must be same size as its table colname + coltype
+}
+
+func (r *row) clone() *row {
+	nrow := &row{cols: make([]interface{}, len(r.cols))}
+	copy(nrow.cols, r.cols)
+	return nrow
+}
+
+type fakeConn struct {
+	db *fakeDB // where to return ourselves to
+
+	currTx *fakeTx
+}
+
+type fakeTx struct {
+	c *fakeConn
+}
+
+type fakeStmt struct {
+	c *fakeConn
+	q string // just for debugging
+
+	cmd   string
+	table string
+
+	colName      []string      // used by CREATE, INSERT, SELECT (selected columns)
+	colType      []string      // used by CREATE
+	colValue     []interface{} // used by INSERT (mix of strings and "?" for bound params)
+	placeholders int           // used by INSERT/SELECT: number of ? params
+
+	whereCol []string // used by SELECT (all placeholders)
+
+	placeholderConverter []driver.ValueConverter // used by INSERT
+}
+
+var fdriver driver.Driver = &fakeDriver{}
+
+func init() {
+	Register("test", fdriver)
+}
+
+// Supports dsn forms:
+//    <dbname>
+//    <dbname>;wipe
+func (d *fakeDriver) Open(dsn string) (driver.Conn, os.Error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	d.openCount++
+	if d.dbs == nil {
+		d.dbs = make(map[string]*fakeDB)
+	}
+	parts := strings.Split(dsn, ";")
+	if len(parts) < 1 {
+		return nil, os.NewError("fakedb: no database name")
+	}
+	name := parts[0]
+	db, ok := d.dbs[name]
+	if !ok {
+		db = &fakeDB{name: name}
+		d.dbs[name] = db
+	}
+	return &fakeConn{db: db}, nil
+}
+
+func (db *fakeDB) wipe() {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+	db.tables = nil
+}
+
+func (db *fakeDB) createTable(name string, columnNames, columnTypes []string) os.Error {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+	if db.tables == nil {
+		db.tables = make(map[string]*table)
+	}
+	if _, exist := db.tables[name]; exist {
+		return fmt.Errorf("table %q already exists", name)
+	}
+	if len(columnNames) != len(columnTypes) {
+		return fmt.Errorf("create table of %q len(names) != len(types): %d vs %d",
+			len(columnNames), len(columnTypes))
+	}
+	db.tables[name] = &table{colname: columnNames, coltype: columnTypes}
+	return nil
+}
+
+// must be called with db.mu lock held
+func (db *fakeDB) table(table string) (*table, bool) {
+	if db.tables == nil {
+		return nil, false
+	}
+	t, ok := db.tables[table]
+	return t, ok
+}
+
+func (db *fakeDB) columnType(table, column string) (typ string, ok bool) {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+	t, ok := db.table(table)
+	if !ok {
+		return
+	}
+	for n, cname := range t.colname {
+		if cname == column {
+			return t.coltype[n], true
+		}
+	}
+	return "", false
+}
+
+func (c *fakeConn) Begin() (driver.Tx, os.Error) {
+	if c.currTx != nil {
+		return nil, os.NewError("already in a transaction")
+	}
+	c.currTx = &fakeTx{c: c}
+	return c.currTx, nil
+}
+
+func (c *fakeConn) Close() os.Error {
+	if c.currTx != nil {
+		return os.NewError("can't close; in a Transaction")
+	}
+	if c.db == nil {
+		return os.NewError("can't close; already closed")
+	}
+	c.db = nil
+	return nil
+}
+
+func errf(msg string, args ...interface{}) os.Error {
+	return os.NewError("fakedb: " + fmt.Sprintf(msg, args...))
+}
+
+// parts are table|selectCol1,selectCol2|whereCol=?,whereCol2=?
+// (note that where where columns must always contain ? marks,
+//  just a limitation for fakedb)
+func (c *fakeConn) prepareSelect(stmt *fakeStmt, parts []string) (driver.Stmt, os.Error) {
+	if len(parts) != 3 {
+		return nil, errf("invalid SELECT syntax with %d parts; want 3", len(parts))
+	}
+	stmt.table = parts[0]
+	stmt.colName = strings.Split(parts[1], ",")
+	for n, colspec := range strings.Split(parts[2], ",") {
+		nameVal := strings.Split(colspec, "=")
+		if len(nameVal) != 2 {
+			return nil, errf("SELECT on table %q has invalid column spec of %q (index %d)", stmt.table, colspec, n)
+		}
+		column, value := nameVal[0], nameVal[1]
+		_, ok := c.db.columnType(stmt.table, column)
+		if !ok {
+			return nil, errf("SELECT on table %q references non-existent column %q", stmt.table, column)
+		}
+		if value != "?" {
+			return nil, errf("SELECT on table %q has pre-bound value for where column %q; need a question mark",
+				stmt.table, column)
+		}
+		stmt.whereCol = append(stmt.whereCol, column)
+		stmt.placeholders++
+	}
+	return stmt, nil
+}
+
+// parts are table|col=type,col2=type2
+func (c *fakeConn) prepareCreate(stmt *fakeStmt, parts []string) (driver.Stmt, os.Error) {
+	if len(parts) != 2 {
+		return nil, errf("invalid CREATE syntax with %d parts; want 2", len(parts))
+	}
+	stmt.table = parts[0]
+	for n, colspec := range strings.Split(parts[1], ",") {
+		nameType := strings.Split(colspec, "=")
+		if len(nameType) != 2 {
+			return nil, errf("CREATE table %q has invalid column spec of %q (index %d)", stmt.table, colspec, n)
+		}
+		stmt.colName = append(stmt.colName, nameType[0])
+		stmt.colType = append(stmt.colType, nameType[1])
+	}
+	return stmt, nil
+}
+
+// parts are table|col=?,col2=val
+func (c *fakeConn) prepareInsert(stmt *fakeStmt, parts []string) (driver.Stmt, os.Error) {
+	if len(parts) != 2 {
+		return nil, errf("invalid INSERT syntax with %d parts; want 2", len(parts))
+	}
+	stmt.table = parts[0]
+	for n, colspec := range strings.Split(parts[1], ",") {
+		nameVal := strings.Split(colspec, "=")
+		if len(nameVal) != 2 {
+			return nil, errf("INSERT table %q has invalid column spec of %q (index %d)", stmt.table, colspec, n)
+		}
+		column, value := nameVal[0], nameVal[1]
+		ctype, ok := c.db.columnType(stmt.table, column)
+		if !ok {
+			return nil, errf("INSERT table %q references non-existent column %q", stmt.table, column)
+		}
+		stmt.colName = append(stmt.colName, column)
+
+		if value != "?" {
+			var subsetVal interface{}
+			// Convert to driver subset type
+			switch ctype {
+			case "string":
+				subsetVal = []byte(value)
+			case "int32":
+				i, err := strconv.Atoi(value)
+				if err != nil {
+					return nil, errf("invalid conversion to int32 from %q", value)
+				}
+				subsetVal = int64(i) // int64 is a subset type, but not int32
+			default:
+				return nil, errf("unsupported conversion for pre-bound parameter %q to type %q", value, ctype)
+			}
+			stmt.colValue = append(stmt.colValue, subsetVal)
+		} else {
+			stmt.placeholders++
+			stmt.placeholderConverter = append(stmt.placeholderConverter, converterForType(ctype))
+			stmt.colValue = append(stmt.colValue, "?")
+		}
+	}
+	return stmt, nil
+}
+
+func (c *fakeConn) Prepare(query string) (driver.Stmt, os.Error) {
+	if c.db == nil {
+		panic("nil c.db; conn = " + fmt.Sprintf("%#v", c))
+	}
+	parts := strings.Split(query, "|")
+	if len(parts) < 1 {
+		return nil, errf("empty query")
+	}
+	cmd := parts[0]
+	parts = parts[1:]
+	stmt := &fakeStmt{q: query, c: c, cmd: cmd}
+	switch cmd {
+	case "WIPE":
+		// Nothing
+	case "SELECT":
+		return c.prepareSelect(stmt, parts)
+	case "CREATE":
+		return c.prepareCreate(stmt, parts)
+	case "INSERT":
+		return c.prepareInsert(stmt, parts)
+	default:
+		return nil, errf("unsupported command type %q", cmd)
+	}
+	return stmt, nil
+}
+
+func (s *fakeStmt) ColumnConverter(idx int) driver.ValueConverter {
+	return s.placeholderConverter[idx]
+}
+
+func (s *fakeStmt) Close() os.Error {
+	return nil
+}
+
+func (s *fakeStmt) Exec(args []interface{}) (driver.Result, os.Error) {
+	db := s.c.db
+	switch s.cmd {
+	case "WIPE":
+		db.wipe()
+		return driver.DDLSuccess, nil
+	case "CREATE":
+		if err := db.createTable(s.table, s.colName, s.colType); err != nil {
+			return nil, err
+		}
+		return driver.DDLSuccess, nil
+	case "INSERT":
+		return s.execInsert(args)
+	}
+	fmt.Printf("EXEC statement, cmd=%q: %#v\n", s.cmd, s)
+	return nil, fmt.Errorf("unimplemented statement Exec command type of %q", s.cmd)
+}
+
+func (s *fakeStmt) execInsert(args []interface{}) (driver.Result, os.Error) {
+	db := s.c.db
+	if len(args) != s.placeholders {
+		panic("error in pkg db; should only get here if size is correct")
+	}
+	db.mu.Lock()
+	t, ok := db.table(s.table)
+	db.mu.Unlock()
+	if !ok {
+		return nil, fmt.Errorf("fakedb: table %q doesn't exist", s.table)
+	}
+
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	cols := make([]interface{}, len(t.colname))
+	argPos := 0
+	for n, colname := range s.colName {
+		colidx := t.columnIndex(colname)
+		if colidx == -1 {
+			return nil, fmt.Errorf("fakedb: column %q doesn't exist or dropped since prepared statement was created", colname)
+		}
+		var val interface{}
+		if strvalue, ok := s.colValue[n].(string); ok && strvalue == "?" {
+			val = args[argPos]
+			argPos++
+		} else {
+			val = s.colValue[n]
+		}
+		cols[colidx] = val
+	}
+
+	t.rows = append(t.rows, &row{cols: cols})
+	return driver.RowsAffected(1), nil
+}
+
+func (s *fakeStmt) Query(args []interface{}) (driver.Rows, os.Error) {
+	db := s.c.db
+	if len(args) != s.placeholders {
+		panic("error in pkg db; should only get here if size is correct")
+	}
+
+	db.mu.Lock()
+	t, ok := db.table(s.table)
+	db.mu.Unlock()
+	if !ok {
+		return nil, fmt.Errorf("fakedb: table %q doesn't exist", s.table)
+	}
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	colIdx := make(map[string]int) // select column name -> column index in table
+	for _, name := range s.colName {
+		idx := t.columnIndex(name)
+		if idx == -1 {
+			return nil, fmt.Errorf("fakedb: unknown column name %q", name)
+		}
+		colIdx[name] = idx
+	}
+
+	mrows := []*row{}
+rows:
+	for _, trow := range t.rows {
+		// Process the where clause, skipping non-match rows. This is lazy
+		// and just uses fmt.Sprintf("%v") to test equality.  Good enough
+		// for test code.
+		for widx, wcol := range s.whereCol {
+			idx := t.columnIndex(wcol)
+			if idx == -1 {
+				return nil, fmt.Errorf("db: invalid where clause column %q", wcol)
+			}
+			tcol := trow.cols[idx]
+			if bs, ok := tcol.([]byte); ok {
+				// lazy hack to avoid sprintf %v on a []byte
+				tcol = string(bs)
+			}
+			if fmt.Sprintf("%v", tcol) != fmt.Sprintf("%v", args[widx]) {
+				continue rows
+			}
+		}
+		mrow := &row{cols: make([]interface{}, len(s.colName))}
+		for seli, name := range s.colName {
+			mrow.cols[seli] = trow.cols[colIdx[name]]
+		}
+		mrows = append(mrows, mrow)
+	}
+
+	cursor := &rowsCursor{
+		pos:  -1,
+		rows: mrows,
+		cols: s.colName,
+	}
+	return cursor, nil
+}
+
+func (s *fakeStmt) NumInput() int {
+	return s.placeholders
+}
+
+func (tx *fakeTx) Commit() os.Error {
+	tx.c.currTx = nil
+	return nil
+}
+
+func (tx *fakeTx) Rollback() os.Error {
+	tx.c.currTx = nil
+	return nil
+}
+
+type rowsCursor struct {
+	cols   []string
+	pos    int
+	rows   []*row
+	closed bool
+}
+
+func (rc *rowsCursor) Close() os.Error {
+	rc.closed = true
+	return nil
+}
+
+func (rc *rowsCursor) Columns() []string {
+	return rc.cols
+}
+
+func (rc *rowsCursor) Next(dest []interface{}) os.Error {
+	if rc.closed {
+		return os.NewError("fakedb: cursor is closed")
+	}
+	rc.pos++
+	if rc.pos >= len(rc.rows) {
+		return os.EOF // per interface spec
+	}
+	for i, v := range rc.rows[rc.pos].cols {
+		// TODO(bradfitz): convert to subset types? naah, I
+		// think the subset types should only be input to
+		// driver, but the db package should be able to handle
+		// a wider range of types coming out of drivers. all
+		// for ease of drivers, and to prevent drivers from
+		// messing up conversions or doing them differently.
+		dest[i] = v
+	}
+	return nil
+}
+
+func converterForType(typ string) driver.ValueConverter {
+	switch typ {
+	case "bool":
+		return driver.Bool
+	case "int32":
+		return driver.Int32
+	case "string":
+		return driver.String
+	}
+	panic("invalid fakedb column type of " + typ)
+}

src/pkg/exp/sql/sql.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package sql provides a generic interface around SQL (or SQL-like)
+// databases.
+package sql
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+	"sync"
+
+	"exp/sql/driver"
+)
+
+var drivers = make(map[string]driver.Driver)
+
+// Register makes a database driver available by the provided name.
+// If Register is called twice with the same name or if driver is nil,
+// it panics.
+func Register(name string, driver driver.Driver) {
+	if driver == nil {
+		panic("db: Register driver is nil")
+	}
+	if _, dup := drivers[name]; dup {
+		panic("db: Register called twice for driver " + name)
+	}
+	drivers[name] = driver
+}
+
+// NullableString represents a string that may be null.
+// NullableString implements the ScannerInto interface so
+// it can be used as a scan destination:
+//
+//  var s NullableString
+//  err := db.QueryRow("SELECT name FROM foo WHERE id=?", id).Scan(&s)
+//  ...
+//  if s.Valid {
+//     // use s.String
+//  } else {
+//     // NULL value
+//  }
+//
+// TODO(bradfitz): add other types.
+type NullableString struct {
+	String string
+	Valid  bool // Valid is true if String is not NULL
+}
+
+// ScanInto implements the ScannerInto interface.
+func (ms *NullableString) ScanInto(value interface{}) os.Error {
+	if value == nil {
+		ms.String, ms.Valid = "", false
+		return nil
+	}
+	ms.Valid = true
+	return convertAssign(&ms.String, value)
+}
+
+// ScannerInto is an interface used by Scan.
+type ScannerInto interface {
+	// ScanInto assigns a value from a database driver.
+	//
+	// The value will be of one of the following restricted
+	// set of types:
+	//
+	//    int64
+	//    float64
+	//    bool
+	//    []byte
+	//    nil - for NULL values
+	//
+	// An error should be returned if the value can not be stored
+	// without loss of information.
+	ScanInto(value interface{}) os.Error
+}
+
+// ErrNoRows is returned by Scan when QueryRow doesn't return a
+// row. In such a case, QueryRow returns a placeholder *Row value that
+// defers this error until a Scan.
+var ErrNoRows = os.NewError("db: no rows in result set")
+
+// DB is a database handle. It's safe for concurrent use by multiple
+// goroutines.
+type DB struct {
+	driver driver.Driver
+	dsn    string
+
+	mu       sync.Mutex
+	freeConn []driver.Conn
+}
+
+// Open opens a database specified by its database driver name and a
+// driver-specific data source name, usually consisting of at least a
+// database name and connection information.
+//
+// Most users will open a database via a driver-specific connection
+// helper function that returns a *DB.
+func Open(driverName, dataSourceName string) (*DB, os.Error) {
+	driver, ok := drivers[driverName]
+	if !ok {
+		return nil, fmt.Errorf("db: unknown driver %q (forgotten import?)", driverName)
+	}
+	return &DB{driver: driver, dsn: dataSourceName}, nil
+}
+
+func (db *DB) maxIdleConns() int {
+	const defaultMaxIdleConns = 2
+	// TODO(bradfitz): ask driver, if supported, for its default preference
+	// TODO(bradfitz): let users override?
+	return defaultMaxIdleConns
+}
+
+// conn returns a newly-opened or cached driver.Conn
+func (db *DB) conn() (driver.Conn, os.Error) {
+	db.mu.Lock()
+	if n := len(db.freeConn); n > 0 {
+		conn := db.freeConn[n-1]
+		db.freeConn = db.freeConn[:n-1]
+		db.mu.Unlock()
+		return conn, nil
+	}
+	db.mu.Unlock()
+	return db.driver.Open(db.dsn)
+}
+
+func (db *DB) connIfFree(wanted driver.Conn) (conn driver.Conn, ok bool) {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+	for n, conn := range db.freeConn {
+		if conn == wanted {
+			db.freeConn[n] = db.freeConn[len(db.freeConn)-1]
+			db.freeConn = db.freeConn[:len(db.freeConn)-1]
+			return wanted, true
+		}
+	}
+	return nil, false
+}
+
+func (db *DB) putConn(c driver.Conn) {
+	if n := len(db.freeConn); n < db.maxIdleConns() {
+		db.freeConn = append(db.freeConn, c)
+		return
+	}
+	db.closeConn(c)
+}
+
+func (db *DB) closeConn(c driver.Conn) {
+	// TODO: check to see if we need this Conn for any prepared statements
+	// that are active.
+	c.Close()
+}
+
+// Prepare creates a prepared statement for later execution.
+func (db *DB) Prepare(query string) (*Stmt, os.Error) {
+	// TODO: check if db.driver supports an optional
+	// driver.Preparer interface and call that instead, if so,
+	// otherwise we make a prepared statement that's bound
+	// to a connection, and to execute this prepared statement
+	// we either need to use this connection (if it's free), else
+	// get a new connection + re-prepare + execute on that one.
+	ci, err := db.conn()
+	if err != nil {
+		return nil, err
+	}
+	defer db.putConn(ci)
+	si, err := ci.Prepare(query)
+	if err != nil {
+		return nil, err
+	}
+	stmt := &Stmt{
+		db:    db,
+		query: query,
+		css:   []connStmt{{ci, si}},
+	}
+	return stmt, nil
+}
+
+// Exec executes a query without returning any rows.
+func (db *DB) Exec(query string, args ...interface{}) (Result, os.Error) {
+	// Optional fast path, if the driver implements driver.Execer.
+	if execer, ok := db.driver.(driver.Execer); ok {
+		resi, err := execer.Exec(query, args)
+		if err != nil {
+			return nil, err
+		}
+		return result{resi}, nil
+	}
+
+	// If the driver does not implement driver.Execer, we need
+	// a connection.
+	conn, err := db.conn()
+	if err != nil {
+		return nil, err
+	}
+	defer db.putConn(conn)
+
+	if execer, ok := conn.(driver.Execer); ok {
+		resi, err := execer.Exec(query, args)
+		if err != nil {
+			return nil, err
+		}
+		return result{resi}, nil
+	}
+
+	sti, err := conn.Prepare(query)
+	if err != nil {
+		return nil, err
+	}
+	defer sti.Close()
+	resi, err := sti.Exec(args)
+	if err != nil {
+		return nil, err
+	}
+	return result{resi}, nil
+}
+
+// Query executes a query that returns rows, typically a SELECT.
+func (db *DB) Query(query string, args ...interface{}) (*Rows, os.Error) {
+	stmt, err := db.Prepare(query)
+	if err != nil {
+		return nil, err
+	}
+	defer stmt.Close()
+	return stmt.Query(args...)
+}
+
+// QueryRow executes a query that is expected to return at most one row.
+// QueryRow always return a non-nil value. Errors are deferred until
+// Row's Scan method is called.
+func (db *DB) QueryRow(query string, args ...interface{}) *Row {
+	rows, err := db.Query(query, args...)
+	if err != nil {
+		return &Row{err: err}
+	}
+	return &Row{rows: rows}
+}
+
+// Begin starts a transaction.  The isolation level is dependent on
+// the driver.
+func (db *DB) Begin() (*Tx, os.Error) {
+	// TODO(bradfitz): add another method for beginning a transaction
+	// at a specific isolation level.
+	panic(todo())
+}
+
+// DriverDatabase returns the database's underlying driver.
+func (db *DB) Driver() driver.Driver {
+	return db.driver
+}
+
+// Tx is an in-progress database transaction.
+type Tx struct {
+
+}
+
+// Commit commits the transaction.
+func (tx *Tx) Commit() os.Error {
+	panic(todo())
+}
+
+// Rollback aborts the transaction.
+func (tx *Tx) Rollback() os.Error {
+	panic(todo())
+}
+
+// Prepare creates a prepared statement.
+func (tx *Tx) Prepare(query string) (*Stmt, os.Error) {
+	panic(todo())
+}
+
+// Exec executes a query that doesn't return rows.
+// For example: an INSERT and UPDATE.
+func (tx *Tx) Exec(query string, args ...interface{}) {
+	panic(todo())
+}
+
+// Query executes a query that returns rows, typically a SELECT.
+func (tx *Tx) Query(query string, args ...interface{}) (*Rows, os.Error) {
+	panic(todo())
+}
+
+// QueryRow executes a query that is expected to return at most one row.
+// QueryRow always return a non-nil value. Errors are deferred until
+// Row's Scan method is called.
+func (tx *Tx) QueryRow(query string, args ...interface{}) *Row {
+	panic(todo())
+}
+
+// connStmt is a prepared statement on a particular connection.
+type connStmt struct {
+	ci driver.Conn
+	si driver.Stmt
+}
+
+// Stmt is a prepared statement. Stmt is safe for concurrent use by multiple goroutines.
+type Stmt struct {
+	// Immutable:
+	db    *DB    // where we came from
+	query string // that created the Sttm
+
+	mu     sync.Mutex
+	closed bool
+	css    []connStmt // can use any that have idle connections
+}
+
+func todo() string {
+	_, file, line, _ := runtime.Caller(1)
+	return fmt.Sprintf("%s:%d: TODO: implement", file, line)
+}
+
+// Exec executes a prepared statement with the given arguments and
+// returns a Result summarizing the effect of the statement.
+func (s *Stmt) Exec(args ...interface{}) (Result, os.Error) {
+	ci, si, err := s.connStmt()
+	if err != nil {
+		return nil, err
+	}
+	defer s.db.putConn(ci)
+
+	if want := si.NumInput(); len(args) != want {
+		return nil, fmt.Errorf("db: expected %d arguments, got %d", want, len(args))
+	}
+
+	// Convert args to subset types.
+	if cc, ok := si.(driver.ColumnConverter); ok {
+		for n, arg := range args {
+			args[n], err = cc.ColumnConverter(n).ConvertValue(arg)
+			if err != nil {
+				return nil, fmt.Errorf("db: converting Exec argument #%d's type: %v", n, err)
+			}
+			if !driver.IsParameterSubsetType(args[n]) {
+				return nil, fmt.Errorf("db: driver ColumnConverter error converted %T to unsupported type %T",
+					arg, args[n])
+			}
+		}
+	} else {
+		for n, arg := range args {
+			args[n], err = driver.DefaultParameterConverter.ConvertValue(arg)
+			if err != nil {
+				return nil, fmt.Errorf("db: converting Exec argument #%d's type: %v", n, err)
+			}
+		}
+	}
+
+	resi, err := si.Exec(args)
+	if err != nil {
+		return nil, err
+	}
+	return result{resi}, nil
+}
+
+func (s *Stmt) connStmt(args ...interface{}) (driver.Conn, driver.Stmt, os.Error) {
+	s.mu.Lock()
+	if s.closed {
+		return nil, nil, os.NewError("db: statement is closed")
+	}
+	var cs connStmt
+	match := false
+	for _, v := range s.css {
+		// TODO(bradfitz): lazily clean up entries in this
+		// list with dead conns while enumerating
+		if _, match = s.db.connIfFree(cs.ci); match {
+			cs = v
+			break
+		}
+	}
+	s.mu.Unlock()
+
+	// Make a new conn if all are busy.
+	// TODO(bradfitz): or wait for one? make configurable later?
+	if !match {
+		ci, err := s.db.conn()
+		if err != nil {
+			return nil, nil, err
+		}
+		si, err := ci.Prepare(s.query)
+		if err != nil {
+			return nil, nil, err
+		}
+		s.mu.Lock()
+		cs = connStmt{ci, si}
+		s.css = append(s.css, cs)
+		s.mu.Unlock()
+	}
+
+	return cs.ci, cs.si, nil
+}
+
+// Query executes a prepared query statement with the given arguments
+// and returns the query results as a *Rows.
+func (s *Stmt) Query(args ...interface{}) (*Rows, os.Error) {
+	ci, si, err := s.connStmt(args...)
+	if err != nil {
+		return nil, err
+	}
+	if len(args) != si.NumInput() {
+		return nil, fmt.Errorf("db: statement expects %d inputs; got %d", si.NumInput(), len(args))
+	}
+	rowsi, err := si.Query(args)
+	if err != nil {
+		s.db.putConn(ci)
+		return nil, err
+	}
+	// Note: ownership of ci passes to the *Rows
+	rows := &Rows{
+		db:    s.db,
+		ci:    ci,
+		rowsi: rowsi,
+	}
+	return rows, nil
+}
+
+// QueryRow executes a prepared query statement with the given arguments.
+// If an error occurs during the execution of the statement, that error will
+// be returned by a call to Scan on the returned *Row, which is always non-nil.
+// If the query selects no rows, the *Row's Scan will return ErrNoRows.
+// Otherwise, the *Row's Scan scans the first selected row and discards
+// the rest.
+//
+// Example usage:
+//
+//  var name string
+//  err := nameByUseridStmt.QueryRow(id).Scan(&s)
+func (s *Stmt) QueryRow(args ...interface{}) *Row {
+	rows, err := s.Query(args...)
+	if err != nil {
+		return &Row{err: err}
+	}
+	return &Row{rows: rows}
+}
+
+// Close closes the statement.
+func (s *Stmt) Close() os.Error {
+	s.mu.Lock()
+	defer s.mu.Unlock() // TODO(bradfitz): move this unlock after 'closed = true'?
+	if s.closed {
+		return nil
+	}
+	s.closed = true
+	for _, v := range s.css {
+		if ci, match := s.db.connIfFree(v.ci); match {
+			v.si.Close()
+			s.db.putConn(ci)
+		} else {
+			// TODO(bradfitz): care that we can't close
+			// this statement because the statement's
+			// connection is in use?
+		}
+	}
+	return nil
+}
+
+// Rows is the result of a query. Its cursor starts before the first row
+// of the result set. Use Next to advance through the rows:
+//
+//     rows, err := db.Query("SELECT ...")
+//     ...
+//     for rows.Next() {
+//         var id int
+//         var name string
+//         err = rows.Scan(&id, &name)
+//         ...
+//     }
+//     err = rows.Error() // get any Error encountered during iteration
+//     ...
+type Rows struct {
+	db    *DB
+	ci    driver.Conn // owned; must be returned when Rows is closed
+	rowsi driver.Rows
+
+	closed   bool
+	lastcols []interface{}
+	lasterr  os.Error
+}
+
+// Next prepares the next result row for reading with the Scan method.
+// It returns true on success, false if there is no next result row.
+// Every call to Scan, even the first one, must be preceded by a call
+// to Next.
+func (rs *Rows) Next() bool {
+	if rs.closed {
+		return false
+	}
+	if rs.lasterr != nil {
+		return false
+	}
+	if rs.lastcols == nil {
+		rs.lastcols = make([]interface{}, len(rs.rowsi.Columns()))
+	}
+	rs.lasterr = rs.rowsi.Next(rs.lastcols)
+	return rs.lasterr == nil
+}
+
+// Error returns the error, if any, that was encountered during iteration.
+func (rs *Rows) Error() os.Error {
+	if rs.lasterr == os.EOF {
+		return nil
+	}
+	return rs.lasterr
+}
+
+// Scan copies the columns in the current row into the values pointed
+// at by dest. If dest contains pointers to []byte, the slices should
+// not be modified and should only be considered valid until the next
+// call to Next or Scan.
+func (rs *Rows) Scan(dest ...interface{}) os.Error {
+	if rs.closed {
+		return os.NewError("db: Rows closed")
+	}
+	if rs.lasterr != nil {
+		return rs.lasterr
+	}
+	if rs.lastcols == nil {
+		return os.NewError("db: Scan called without calling Next")
+	}
+	if len(dest) != len(rs.lastcols) {
+		return fmt.Errorf("db: expected %d destination arguments in Scan, not %d", len(rs.lastcols), len(dest))
+	}
+	for i, sv := range rs.lastcols {
+		err := convertAssign(dest[i], sv)
+		if err != nil {
+			return fmt.Errorf("db: Scan error on column index %d: %v", i, err)
+		}
+	}
+	return nil
+}
+
+// Close closes the Rows, preventing further enumeration. If the
+// end is encountered, the Rows are closed automatically. Close
+// is idempotent.
+func (rs *Rows) Close() os.Error {
+	if rs.closed {
+		return nil
+	}
+	rs.closed = true
+	err := rs.rowsi.Close()
+	rs.db.putConn(rs.ci)
+	return err
+}
+
+// Row is the result of calling QueryRow to select a single row.
+type Row struct {
+	// One of these two will be non-nil:
+	err  os.Error // deferred error for easy chaining
+	rows *Rows
+}
+
+// Scan copies the columns from the matched row into the values
+// pointed at by dest.  If more than one row matches the query,
+// Scan uses the first row and discards the rest.  If no row matches
+// the query, Scan returns ErrNoRows.
+//
+// If dest contains pointers to []byte, the slices should not be
+// modified and should only be considered valid until the next call to
+// Next or Scan.
+func (r *Row) Scan(dest ...interface{}) os.Error {
+	if r.err != nil {
+		return r.err
+	}
+	defer r.rows.Close()
+	if !r.rows.Next() {
+		return ErrNoRows
+	}
+	return r.rows.Scan(dest...)
+}
+
+// A Result summarizes an executed SQL command.
+type Result interface {
+	LastInsertId() (int64, os.Error)
+	RowsAffected() (int64, os.Error)
+}
+
+type result struct {
+	driver.Result
+}

src/pkg/exp/sql/sql_test.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sql
+
+import (
+	"strings"
+	"testing"
+)
+
+func newTestDB(t *testing.T, name string) *DB {
+	db, err := Open("test", "foo")
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	if _, err := db.Exec("WIPE"); err != nil {
+		t.Fatalf("exec wipe: %v", err)
+	}
+	if name == "people" {
+		exec(t, db, "CREATE|people|name=string,age=int32,dead=bool")
+		exec(t, db, "INSERT|people|name=Alice,age=?", 1)
+		exec(t, db, "INSERT|people|name=Bob,age=?", 2)
+		exec(t, db, "INSERT|people|name=Chris,age=?", 3)
+
+	}
+	return db
+}
+
+func exec(t *testing.T, db *DB, query string, args ...interface{}) {
+	_, err := db.Exec(query, args...)
+	if err != nil {
+		t.Fatalf("Exec of %q: %v", query, err)
+	}
+}
+
+func TestQuery(t *testing.T) {
+	db := newTestDB(t, "people")
+	var name string
+	var age int
+
+	err := db.QueryRow("SELECT|people|age,name|age=?", 3).Scan(&age)
+	if err == nil || !strings.Contains(err.String(), "expected 2 destination arguments") {
+		t.Errorf("expected error from wrong number of arguments; actually got: %v", err)
+	}
+
+	err = db.QueryRow("SELECT|people|age,name|age=?", 2).Scan(&age, &name)
+	if err != nil {
+		t.Fatalf("age QueryRow+Scan: %v", err)
+	}
+	if name != "Bob" {
+		t.Errorf("expected name Bob, got %q", name)
+	}
+	if age != 2 {
+		t.Errorf("expected age 2, got %d", age)
+	}
+
+	err = db.QueryRow("SELECT|people|age,name|name=?", "Alice").Scan(&age, &name)
+	if err != nil {
+		t.Fatalf("name QueryRow+Scan: %v", err)
+	}
+	if name != "Alice" {
+		t.Errorf("expected name Alice, got %q", name)
+	}
+	if age != 1 {
+		t.Errorf("expected age 1, got %d", age)
+	}
+}
+
+func TestStatementQueryRow(t *testing.T) {
+	db := newTestDB(t, "people")
+	stmt, err := db.Prepare("SELECT|people|age|name=?")
+	if err != nil {
+		t.Fatalf("Prepare: %v", err)
+	}
+	var age int
+	for n, tt := range []struct {
+		name string
+		want int
+	}{
+		{"Alice", 1},
+		{"Bob", 2},
+		{"Chris", 3},
+	} {
+		if err := stmt.QueryRow(tt.name).Scan(&age); err != nil {
+			t.Errorf("%d: on %q, QueryRow/Scan: %v", n, tt.name, err)
+		} else if age != tt.want {
+			t.Errorf("%d: age=%d, want %d", age, tt.want)
+		}
+	}
+
+}
+
+// just a test of fakedb itself
+func TestBogusPreboundParameters(t *testing.T) {
+	db := newTestDB(t, "foo")
+	exec(t, db, "CREATE|t1|name=string,age=int32,dead=bool")
+	_, err := db.Prepare("INSERT|t1|name=?,age=bogusconversion")
+	if err == nil {
+		t.Fatalf("expected error")
+	}
+	if err.String() != `fakedb: invalid conversion to int32 from "bogusconversion"` {
+		t.Errorf("unexpected error: %v", err)
+	}
+}
+
+func TestDb(t *testing.T) {
+	db := newTestDB(t, "foo")
+	exec(t, db, "CREATE|t1|name=string,age=int32,dead=bool")
+	stmt, err := db.Prepare("INSERT|t1|name=?,age=?")
+	if err != nil {
+		t.Errorf("Stmt, err = %v, %v", stmt, err)
+	}
+
+	type execTest struct {
+		args    []interface{}
+		wantErr string
+	}
+	execTests := []execTest{
+		// Okay:
+		{[]interface{}{"Brad", 31}, ""},
+		{[]interface{}{"Brad", int64(31)}, ""},
+		{[]interface{}{"Bob", "32"}, ""},
+		{[]interface{}{7, 9}, ""},
+
+		// Invalid conversions:
+		{[]interface{}{"Brad", int64(0xFFFFFFFF)}, "db: converting Exec argument #1's type: sql/driver: value 4294967295 overflows int32"},
+		{[]interface{}{"Brad", "strconv fail"}, "db: converting Exec argument #1's type: sql/driver: value \"strconv fail\" can't be converted to int32"},
+
+		// Wrong number of args:
+		{[]interface{}{}, "db: expected 2 arguments, got 0"},
+		{[]interface{}{1, 2, 3}, "db: expected 2 arguments, got 3"},
+	}
+	for n, et := range execTests {
+		_, err := stmt.Exec(et.args...)
+		errStr := ""
+		if err != nil {
+			errStr = err.String()
+		}
+		if errStr != et.wantErr {
+			t.Errorf("stmt.Execute #%d: for %v, got error %q, want error %q",
+				n, et.args, errStr, et.wantErr)
+		}
+	}
+}