vendor/github.com/bradfitz/gomemcache/memcache/memcache.go - gddo - Git at Google

 /*
 Copyright 2011 Google Inc.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */

 // Package memcache provides a client for the memcached cache server.
 package memcache

 import (
 	"bufio"
 	"bytes"
 	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"net"

 	"strconv"
 	"strings"
 	"sync"
 	"time"
 )

 // Similar to:
 // http://code.google.com/appengine/docs/go/memcache/reference.html

 var (
 	// ErrCacheMiss means that a Get failed because the item wasn't present.
 	ErrCacheMiss = errors.New("memcache: cache miss")

 	// ErrCASConflict means that a CompareAndSwap call failed due to the
 	// cached value being modified between the Get and the CompareAndSwap.
 	// If the cached value was simply evicted rather than replaced,
 	// ErrNotStored will be returned instead.
 	ErrCASConflict = errors.New("memcache: compare-and-swap conflict")

 	// ErrNotStored means that a conditional write operation (i.e. Add or
 	// CompareAndSwap) failed because the condition was not satisfied.
 	ErrNotStored = errors.New("memcache: item not stored")

 	// ErrServer means that a server error occurred.
 	ErrServerError = errors.New("memcache: server error")

 	// ErrNoStats means that no statistics were available.
 	ErrNoStats = errors.New("memcache: no statistics available")

 	// ErrMalformedKey is returned when an invalid key is used.
 	// Keys must be at maximum 250 bytes long, ASCII, and not
 	// contain whitespace or control characters.
 	ErrMalformedKey = errors.New("malformed: key is too long or contains invalid characters")

 	// ErrNoServers is returned when no servers are configured or available.
 	ErrNoServers = errors.New("memcache: no servers configured or available")
 )

 // DefaultTimeout is the default socket read/write timeout.
 const DefaultTimeout = 100 * time.Millisecond

 const (
 	buffered            = 8 // arbitrary buffered channel size, for readability
 	maxIdleConnsPerAddr = 2 // TODO(bradfitz): make this configurable?
 )

 // resumableError returns true if err is only a protocol-level cache error.
 // This is used to determine whether or not a server connection should
 // be re-used or not. If an error occurs, by default we don't reuse the
 // connection, unless it was just a cache error.
 func resumableError(err error) bool {
 	switch err {
 	case ErrCacheMiss, ErrCASConflict, ErrNotStored, ErrMalformedKey:
 		return true
 	}
 	return false
 }

 func legalKey(key string) bool {
 	if len(key) > 250 {
 		return false
 	}
 	for i := 0; i < len(key); i++ {
 		if key[i] <= ' ' || key[i] > 0x7e {
 			return false
 		}
 	}
 	return true
 }

 var (
 	crlf            = []byte("\r\n")
 	space           = []byte(" ")
 	resultOK        = []byte("OK\r\n")
 	resultStored    = []byte("STORED\r\n")
 	resultNotStored = []byte("NOT_STORED\r\n")
 	resultExists    = []byte("EXISTS\r\n")
 	resultNotFound  = []byte("NOT_FOUND\r\n")
 	resultDeleted   = []byte("DELETED\r\n")
 	resultEnd       = []byte("END\r\n")
 	resultOk        = []byte("OK\r\n")
 	resultTouched   = []byte("TOUCHED\r\n")

 	resultClientErrorPrefix = []byte("CLIENT_ERROR ")
 )

 // New returns a memcache client using the provided server(s)
 // with equal weight. If a server is listed multiple times,
 // it gets a proportional amount of weight.
 func New(server ...string) *Client {
 	ss := new(ServerList)
 	ss.SetServers(server...)
 	return NewFromSelector(ss)
 }

 // NewFromSelector returns a new Client using the provided ServerSelector.
 func NewFromSelector(ss ServerSelector) *Client {
 	return &Client{selector: ss}
 }

 // Client is a memcache client.
 // It is safe for unlocked use by multiple concurrent goroutines.
 type Client struct {
 	// Timeout specifies the socket read/write timeout.
 	// If zero, DefaultTimeout is used.
 	Timeout time.Duration

 	selector ServerSelector

 	lk       sync.Mutex
 	freeconn map[string][]*conn
 }

 // Item is an item to be got or stored in a memcached server.
 type Item struct {
 	// Key is the Item's key (250 bytes maximum).
 	Key string

 	// Value is the Item's value.
 	Value []byte

 	// Flags are server-opaque flags whose semantics are entirely
 	// up to the app.
 	Flags uint32

 	// Expiration is the cache expiration time, in seconds: either a relative
 	// time from now (up to 1 month), or an absolute Unix epoch time.
 	// Zero means the Item has no expiration time.
 	Expiration int32

 	// Compare and swap ID.
 	casid uint64
 }

 // conn is a connection to a server.
 type conn struct {
 	nc   net.Conn
 	rw   *bufio.ReadWriter
 	addr net.Addr
 	c    *Client
 }

 // release returns this connection back to the client's free pool
 func (cn *conn) release() {
 	cn.c.putFreeConn(cn.addr, cn)
 }

 func (cn *conn) extendDeadline() {
 	cn.nc.SetDeadline(time.Now().Add(cn.c.netTimeout()))
 }

 // condRelease releases this connection if the error pointed to by err
 // is nil (not an error) or is only a protocol level error (e.g. a
 // cache miss).  The purpose is to not recycle TCP connections that
 // are bad.
 func (cn *conn) condRelease(err *error) {
 	if *err == nil || resumableError(*err) {
 		cn.release()
 	} else {
 		cn.nc.Close()
 	}
 }

 func (c *Client) putFreeConn(addr net.Addr, cn *conn) {
 	c.lk.Lock()
 	defer c.lk.Unlock()
 	if c.freeconn == nil {
 		c.freeconn = make(map[string][]*conn)
 	}
 	freelist := c.freeconn[addr.String()]
 	if len(freelist) >= maxIdleConnsPerAddr {
 		cn.nc.Close()
 		return
 	}
 	c.freeconn[addr.String()] = append(freelist, cn)
 }

 func (c *Client) getFreeConn(addr net.Addr) (cn *conn, ok bool) {
 	c.lk.Lock()
 	defer c.lk.Unlock()
 	if c.freeconn == nil {
 		return nil, false
 	}
 	freelist, ok := c.freeconn[addr.String()]
 	if !ok || len(freelist) == 0 {
 		return nil, false
 	}
 	cn = freelist[len(freelist)-1]
 	c.freeconn[addr.String()] = freelist[:len(freelist)-1]
 	return cn, true
 }

 func (c *Client) netTimeout() time.Duration {
 	if c.Timeout != 0 {
 		return c.Timeout
 	}
 	return DefaultTimeout
 }

 // ConnectTimeoutError is the error type used when it takes
 // too long to connect to the desired host. This level of
 // detail can generally be ignored.
 type ConnectTimeoutError struct {
 	Addr net.Addr
 }

 func (cte *ConnectTimeoutError) Error() string {
 	return "memcache: connect timeout to " + cte.Addr.String()
 }

 func (c *Client) dial(addr net.Addr) (net.Conn, error) {
 	type connError struct {
 		cn  net.Conn
 		err error
 	}

 	nc, err := net.DialTimeout(addr.Network(), addr.String(), c.netTimeout())
 	if err == nil {
 		return nc, nil
 	}

 	if ne, ok := err.(net.Error); ok && ne.Timeout() {
 		return nil, &ConnectTimeoutError{addr}
 	}

 	return nil, err
 }

 func (c *Client) getConn(addr net.Addr) (*conn, error) {
 	cn, ok := c.getFreeConn(addr)
 	if ok {
 		cn.extendDeadline()
 		return cn, nil
 	}
 	nc, err := c.dial(addr)
 	if err != nil {
 		return nil, err
 	}
 	cn = &conn{
 		nc:   nc,
 		addr: addr,
 		rw:   bufio.NewReadWriter(bufio.NewReader(nc), bufio.NewWriter(nc)),
 		c:    c,
 	}
 	cn.extendDeadline()
 	return cn, nil
 }

 func (c *Client) onItem(item *Item, fn func(*Client, *bufio.ReadWriter, *Item) error) error {
 	addr, err := c.selector.PickServer(item.Key)
 	if err != nil {
 		return err
 	}
 	cn, err := c.getConn(addr)
 	if err != nil {
 		return err
 	}
 	defer cn.condRelease(&err)
 	if err = fn(c, cn.rw, item); err != nil {
 		return err
 	}
 	return nil
 }

 func (c *Client) FlushAll() error {
 	return c.selector.Each(c.flushAllFromAddr)
 }

 // Get gets the item for the given key. ErrCacheMiss is returned for a
 // memcache cache miss. The key must be at most 250 bytes in length.
 func (c *Client) Get(key string) (item *Item, err error) {
 	err = c.withKeyAddr(key, func(addr net.Addr) error {
 		return c.getFromAddr(addr, []string{key}, func(it *Item) { item = it })
 	})
 	if err == nil && item == nil {
 		err = ErrCacheMiss
 	}
 	return
 }

 // Touch updates the expiry for the given key. The seconds parameter is either
 // a Unix timestamp or, if seconds is less than 1 month, the number of seconds
 // into the future at which time the item will expire. ErrCacheMiss is returned if the
 // key is not in the cache. The key must be at most 250 bytes in length.
 func (c *Client) Touch(key string, seconds int32) (err error) {
 	return c.withKeyAddr(key, func(addr net.Addr) error {
 		return c.touchFromAddr(addr, []string{key}, seconds)
 	})
 }

 func (c *Client) withKeyAddr(key string, fn func(net.Addr) error) (err error) {
 	if !legalKey(key) {
 		return ErrMalformedKey
 	}
 	addr, err := c.selector.PickServer(key)
 	if err != nil {
 		return err
 	}
 	return fn(addr)
 }

 func (c *Client) withAddrRw(addr net.Addr, fn func(*bufio.ReadWriter) error) (err error) {
 	cn, err := c.getConn(addr)
 	if err != nil {
 		return err
 	}
 	defer cn.condRelease(&err)
 	return fn(cn.rw)
 }

 func (c *Client) withKeyRw(key string, fn func(*bufio.ReadWriter) error) error {
 	return c.withKeyAddr(key, func(addr net.Addr) error {
 		return c.withAddrRw(addr, fn)
 	})
 }

 func (c *Client) getFromAddr(addr net.Addr, keys []string, cb func(*Item)) error {
 	return c.withAddrRw(addr, func(rw *bufio.ReadWriter) error {
 		if _, err := fmt.Fprintf(rw, "gets %s\r\n", strings.Join(keys, " ")); err != nil {
 			return err
 		}
 		if err := rw.Flush(); err != nil {
 			return err
 		}
 		if err := parseGetResponse(rw.Reader, cb); err != nil {
 			return err
 		}
 		return nil
 	})
 }

 // flushAllFromAddr send the flush_all command to the given addr
 func (c *Client) flushAllFromAddr(addr net.Addr) error {
 	return c.withAddrRw(addr, func(rw *bufio.ReadWriter) error {
 		if _, err := fmt.Fprintf(rw, "flush_all\r\n"); err != nil {
 			return err
 		}
 		if err := rw.Flush(); err != nil {
 			return err
 		}
 		line, err := rw.ReadSlice('\n')
 		if err != nil {
 			return err
 		}
 		switch {
 		case bytes.Equal(line, resultOk):
 			break
 		default:
 			return fmt.Errorf("memcache: unexpected response line from flush_all: %q", string(line))
 		}
 		return nil
 	})
 }

 func (c *Client) touchFromAddr(addr net.Addr, keys []string, expiration int32) error {
 	return c.withAddrRw(addr, func(rw *bufio.ReadWriter) error {
 		for _, key := range keys {
 			if _, err := fmt.Fprintf(rw, "touch %s %d\r\n", key, expiration); err != nil {
 				return err
 			}
 			if err := rw.Flush(); err != nil {
 				return err
 			}
 			line, err := rw.ReadSlice('\n')
 			if err != nil {
 				return err
 			}
 			switch {
 			case bytes.Equal(line, resultTouched):
 				break
 			case bytes.Equal(line, resultNotFound):
 				return ErrCacheMiss
 			default:
 				return fmt.Errorf("memcache: unexpected response line from touch: %q", string(line))
 			}
 		}
 		return nil
 	})
 }

 // GetMulti is a batch version of Get. The returned map from keys to
 // items may have fewer elements than the input slice, due to memcache
 // cache misses. Each key must be at most 250 bytes in length.
 // If no error is returned, the returned map will also be non-nil.
 func (c *Client) GetMulti(keys []string) (map[string]*Item, error) {
 	var lk sync.Mutex
 	m := make(map[string]*Item)
 	addItemToMap := func(it *Item) {
 		lk.Lock()
 		defer lk.Unlock()
 		m[it.Key] = it
 	}

 	keyMap := make(map[net.Addr][]string)
 	for _, key := range keys {
 		if !legalKey(key) {
 			return nil, ErrMalformedKey
 		}
 		addr, err := c.selector.PickServer(key)
 		if err != nil {
 			return nil, err
 		}
 		keyMap[addr] = append(keyMap[addr], key)
 	}

 	ch := make(chan error, buffered)
 	for addr, keys := range keyMap {
 		go func(addr net.Addr, keys []string) {
 			ch <- c.getFromAddr(addr, keys, addItemToMap)
 		}(addr, keys)
 	}

 	var err error
 	for _ = range keyMap {
 		if ge := <-ch; ge != nil {
 			err = ge
 		}
 	}
 	return m, err
 }

 // parseGetResponse reads a GET response from r and calls cb for each
 // read and allocated Item
 func parseGetResponse(r *bufio.Reader, cb func(*Item)) error {
 	for {
 		line, err := r.ReadSlice('\n')
 		if err != nil {
 			return err
 		}
 		if bytes.Equal(line, resultEnd) {
 			return nil
 		}
 		it := new(Item)
 		size, err := scanGetResponseLine(line, it)
 		if err != nil {
 			return err
 		}
 		it.Value, err = ioutil.ReadAll(io.LimitReader(r, int64(size)+2))
 		if err != nil {
 			return err
 		}
 		if !bytes.HasSuffix(it.Value, crlf) {
 			return fmt.Errorf("memcache: corrupt get result read")
 		}
 		it.Value = it.Value[:size]
 		cb(it)
 	}
 }

 // scanGetResponseLine populates it and returns the declared size of the item.
 // It does not read the bytes of the item.
 func scanGetResponseLine(line []byte, it *Item) (size int, err error) {
 	pattern := "VALUE %s %d %d %d\r\n"
 	dest := []interface{}{&it.Key, &it.Flags, &size, &it.casid}
 	if bytes.Count(line, space) == 3 {
 		pattern = "VALUE %s %d %d\r\n"
 		dest = dest[:3]
 	}
 	n, err := fmt.Sscanf(string(line), pattern, dest...)
 	if err != nil || n != len(dest) {
 		return -1, fmt.Errorf("memcache: unexpected line in get response: %q", line)
 	}
 	return size, nil
 }

 // Set writes the given item, unconditionally.
 func (c *Client) Set(item *Item) error {
 	return c.onItem(item, (*Client).set)
 }

 func (c *Client) set(rw *bufio.ReadWriter, item *Item) error {
 	return c.populateOne(rw, "set", item)
 }

 // Add writes the given item, if no value already exists for its
 // key. ErrNotStored is returned if that condition is not met.
 func (c *Client) Add(item *Item) error {
 	return c.onItem(item, (*Client).add)
 }

 func (c *Client) add(rw *bufio.ReadWriter, item *Item) error {
 	return c.populateOne(rw, "add", item)
 }

 // Replace writes the given item, but only if the server *does*
 // already hold data for this key
 func (c *Client) Replace(item *Item) error {
 	return c.onItem(item, (*Client).replace)
 }

 func (c *Client) replace(rw *bufio.ReadWriter, item *Item) error {
 	return c.populateOne(rw, "replace", item)
 }

 // CompareAndSwap writes the given item that was previously returned
 // by Get, if the value was neither modified or evicted between the
 // Get and the CompareAndSwap calls. The item's Key should not change
 // between calls but all other item fields may differ. ErrCASConflict
 // is returned if the value was modified in between the
 // calls. ErrNotStored is returned if the value was evicted in between
 // the calls.
 func (c *Client) CompareAndSwap(item *Item) error {
 	return c.onItem(item, (*Client).cas)
 }

 func (c *Client) cas(rw *bufio.ReadWriter, item *Item) error {
 	return c.populateOne(rw, "cas", item)
 }

 func (c *Client) populateOne(rw *bufio.ReadWriter, verb string, item *Item) error {
 	if !legalKey(item.Key) {
 		return ErrMalformedKey
 	}
 	var err error
 	if verb == "cas" {
 		_, err = fmt.Fprintf(rw, "%s %s %d %d %d %d\r\n",
 			verb, item.Key, item.Flags, item.Expiration, len(item.Value), item.casid)
 	} else {
 		_, err = fmt.Fprintf(rw, "%s %s %d %d %d\r\n",
 			verb, item.Key, item.Flags, item.Expiration, len(item.Value))
 	}
 	if err != nil {
 		return err
 	}
 	if _, err = rw.Write(item.Value); err != nil {
 		return err
 	}
 	if _, err := rw.Write(crlf); err != nil {
 		return err
 	}
 	if err := rw.Flush(); err != nil {
 		return err
 	}
 	line, err := rw.ReadSlice('\n')
 	if err != nil {
 		return err
 	}
 	switch {
 	case bytes.Equal(line, resultStored):
 		return nil
 	case bytes.Equal(line, resultNotStored):
 		return ErrNotStored
 	case bytes.Equal(line, resultExists):
 		return ErrCASConflict
 	case bytes.Equal(line, resultNotFound):
 		return ErrCacheMiss
 	}
 	return fmt.Errorf("memcache: unexpected response line from %q: %q", verb, string(line))
 }

 func writeReadLine(rw *bufio.ReadWriter, format string, args ...interface{}) ([]byte, error) {
 	_, err := fmt.Fprintf(rw, format, args...)
 	if err != nil {
 		return nil, err
 	}
 	if err := rw.Flush(); err != nil {
 		return nil, err
 	}
 	line, err := rw.ReadSlice('\n')
 	return line, err
 }

 func writeExpectf(rw *bufio.ReadWriter, expect []byte, format string, args ...interface{}) error {
 	line, err := writeReadLine(rw, format, args...)
 	if err != nil {
 		return err
 	}
 	switch {
 	case bytes.Equal(line, resultOK):
 		return nil
 	case bytes.Equal(line, expect):
 		return nil
 	case bytes.Equal(line, resultNotStored):
 		return ErrNotStored
 	case bytes.Equal(line, resultExists):
 		return ErrCASConflict
 	case bytes.Equal(line, resultNotFound):
 		return ErrCacheMiss
 	}
 	return fmt.Errorf("memcache: unexpected response line: %q", string(line))
 }

 // Delete deletes the item with the provided key. The error ErrCacheMiss is
 // returned if the item didn't already exist in the cache.
 func (c *Client) Delete(key string) error {
 	return c.withKeyRw(key, func(rw *bufio.ReadWriter) error {
 		return writeExpectf(rw, resultDeleted, "delete %s\r\n", key)
 	})
 }

 // DeleteAll deletes all items in the cache.
 func (c *Client) DeleteAll() error {
 	return c.withKeyRw("", func(rw *bufio.ReadWriter) error {
 		return writeExpectf(rw, resultDeleted, "flush_all\r\n")
 	})
 }

 // Increment atomically increments key by delta. The return value is
 // the new value after being incremented or an error. If the value
 // didn't exist in memcached the error is ErrCacheMiss. The value in
 // memcached must be an decimal number, or an error will be returned.
 // On 64-bit overflow, the new value wraps around.
 func (c *Client) Increment(key string, delta uint64) (newValue uint64, err error) {
 	return c.incrDecr("incr", key, delta)
 }

 // Decrement atomically decrements key by delta. The return value is
 // the new value after being decremented or an error. If the value
 // didn't exist in memcached the error is ErrCacheMiss. The value in
 // memcached must be an decimal number, or an error will be returned.
 // On underflow, the new value is capped at zero and does not wrap
 // around.
 func (c *Client) Decrement(key string, delta uint64) (newValue uint64, err error) {
 	return c.incrDecr("decr", key, delta)
 }

 func (c *Client) incrDecr(verb, key string, delta uint64) (uint64, error) {
 	var val uint64
 	err := c.withKeyRw(key, func(rw *bufio.ReadWriter) error {
 		line, err := writeReadLine(rw, "%s %s %d\r\n", verb, key, delta)
 		if err != nil {
 			return err
 		}
 		switch {
 		case bytes.Equal(line, resultNotFound):
 			return ErrCacheMiss
 		case bytes.HasPrefix(line, resultClientErrorPrefix):
 			errMsg := line[len(resultClientErrorPrefix) : len(line)-2]
 			return errors.New("memcache: client error: " + string(errMsg))
 		}
 		val, err = strconv.ParseUint(string(line[:len(line)-2]), 10, 64)
 		if err != nil {
 			return err
 		}
 		return nil
 	})
 	return val, err
 }
	/*
	Copyright 2011 Google Inc.

	Licensed under the Apache License, Version 2.0 (the "License");
	you may not use this file except in compliance with the License.
	You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	*/

	// Package memcache provides a client for the memcached cache server.
	package memcache

	import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"net"

	"strconv"
	"strings"
	"sync"
	"time"
	)

	// Similar to:
	// http://code.google.com/appengine/docs/go/memcache/reference.html

	var (
	// ErrCacheMiss means that a Get failed because the item wasn't present.
	ErrCacheMiss = errors.New("memcache: cache miss")

	// ErrCASConflict means that a CompareAndSwap call failed due to the
	// cached value being modified between the Get and the CompareAndSwap.
	// If the cached value was simply evicted rather than replaced,
	// ErrNotStored will be returned instead.
	ErrCASConflict = errors.New("memcache: compare-and-swap conflict")

	// ErrNotStored means that a conditional write operation (i.e. Add or
	// CompareAndSwap) failed because the condition was not satisfied.
	ErrNotStored = errors.New("memcache: item not stored")

	// ErrServer means that a server error occurred.
	ErrServerError = errors.New("memcache: server error")

	// ErrNoStats means that no statistics were available.
	ErrNoStats = errors.New("memcache: no statistics available")

	// ErrMalformedKey is returned when an invalid key is used.
	// Keys must be at maximum 250 bytes long, ASCII, and not
	// contain whitespace or control characters.
	ErrMalformedKey = errors.New("malformed: key is too long or contains invalid characters")

	// ErrNoServers is returned when no servers are configured or available.
	ErrNoServers = errors.New("memcache: no servers configured or available")
	)

	// DefaultTimeout is the default socket read/write timeout.
	const DefaultTimeout = 100 * time.Millisecond

	const (
	buffered = 8 // arbitrary buffered channel size, for readability
	maxIdleConnsPerAddr = 2 // TODO(bradfitz): make this configurable?
	)

	// resumableError returns true if err is only a protocol-level cache error.
	// This is used to determine whether or not a server connection should
	// be re-used or not. If an error occurs, by default we don't reuse the
	// connection, unless it was just a cache error.
	func resumableError(err error) bool {
	switch err {
	case ErrCacheMiss, ErrCASConflict, ErrNotStored, ErrMalformedKey:
	return true
	}
	return false
	}

	func legalKey(key string) bool {
	if len(key) > 250 {
	return false
	}
	for i := 0; i < len(key); i++ {
	if key[i] <= ' ' \|\| key[i] > 0x7e {
	return false
	}
	}
	return true
	}

	var (
	crlf = []byte("\r\n")
	space = []byte(" ")
	resultOK = []byte("OK\r\n")
	resultStored = []byte("STORED\r\n")
	resultNotStored = []byte("NOT_STORED\r\n")
	resultExists = []byte("EXISTS\r\n")
	resultNotFound = []byte("NOT_FOUND\r\n")
	resultDeleted = []byte("DELETED\r\n")
	resultEnd = []byte("END\r\n")
	resultOk = []byte("OK\r\n")
	resultTouched = []byte("TOUCHED\r\n")

	resultClientErrorPrefix = []byte("CLIENT_ERROR ")
	)

	// New returns a memcache client using the provided server(s)
	// with equal weight. If a server is listed multiple times,
	// it gets a proportional amount of weight.
	func New(server ...string) *Client {
	ss := new(ServerList)
	ss.SetServers(server...)
	return NewFromSelector(ss)
	}

	// NewFromSelector returns a new Client using the provided ServerSelector.
	func NewFromSelector(ss ServerSelector) *Client {
	return &Client{selector: ss}
	}

	// Client is a memcache client.
	// It is safe for unlocked use by multiple concurrent goroutines.
	type Client struct {
	// Timeout specifies the socket read/write timeout.
	// If zero, DefaultTimeout is used.
	Timeout time.Duration

	selector ServerSelector

	lk sync.Mutex
	freeconn map[string][]*conn
	}

	// Item is an item to be got or stored in a memcached server.
	type Item struct {
	// Key is the Item's key (250 bytes maximum).
	Key string

	// Value is the Item's value.
	Value []byte

	// Flags are server-opaque flags whose semantics are entirely
	// up to the app.
	Flags uint32

	// Expiration is the cache expiration time, in seconds: either a relative
	// time from now (up to 1 month), or an absolute Unix epoch time.
	// Zero means the Item has no expiration time.
	Expiration int32

	// Compare and swap ID.
	casid uint64
	}

	// conn is a connection to a server.
	type conn struct {
	nc net.Conn
	rw *bufio.ReadWriter
	addr net.Addr
	c *Client
	}

	// release returns this connection back to the client's free pool
	func (cn *conn) release() {
	cn.c.putFreeConn(cn.addr, cn)
	}

	func (cn *conn) extendDeadline() {
	cn.nc.SetDeadline(time.Now().Add(cn.c.netTimeout()))
	}

	// condRelease releases this connection if the error pointed to by err
	// is nil (not an error) or is only a protocol level error (e.g. a
	// cache miss). The purpose is to not recycle TCP connections that
	// are bad.
	func (cn conn) condRelease(err error) {
	if err == nil \|\| resumableError(err) {
	cn.release()
	} else {
	cn.nc.Close()
	}
	}

	func (c Client) putFreeConn(addr net.Addr, cn conn) {
	c.lk.Lock()
	defer c.lk.Unlock()
	if c.freeconn == nil {
	c.freeconn = make(map[string][]*conn)
	}
	freelist := c.freeconn[addr.String()]
	if len(freelist) >= maxIdleConnsPerAddr {
	cn.nc.Close()
	return
	}
	c.freeconn[addr.String()] = append(freelist, cn)
	}

	func (c Client) getFreeConn(addr net.Addr) (cn conn, ok bool) {
	c.lk.Lock()
	defer c.lk.Unlock()
	if c.freeconn == nil {
	return nil, false
	}
	freelist, ok := c.freeconn[addr.String()]
	if !ok \|\| len(freelist) == 0 {
	return nil, false
	}
	cn = freelist[len(freelist)-1]
	c.freeconn[addr.String()] = freelist[:len(freelist)-1]
	return cn, true
	}

	func (c *Client) netTimeout() time.Duration {
	if c.Timeout != 0 {
	return c.Timeout
	}
	return DefaultTimeout
	}

	// ConnectTimeoutError is the error type used when it takes
	// too long to connect to the desired host. This level of
	// detail can generally be ignored.
	type ConnectTimeoutError struct {
	Addr net.Addr
	}

	func (cte *ConnectTimeoutError) Error() string {
	return "memcache: connect timeout to " + cte.Addr.String()
	}

	func (c *Client) dial(addr net.Addr) (net.Conn, error) {
	type connError struct {
	cn net.Conn
	err error
	}

	nc, err := net.DialTimeout(addr.Network(), addr.String(), c.netTimeout())
	if err == nil {
	return nc, nil
	}

	if ne, ok := err.(net.Error); ok && ne.Timeout() {
	return nil, &ConnectTimeoutError{addr}
	}

	return nil, err
	}

	func (c Client) getConn(addr net.Addr) (conn, error) {
	cn, ok := c.getFreeConn(addr)
	if ok {
	cn.extendDeadline()
	return cn, nil
	}
	nc, err := c.dial(addr)
	if err != nil {
	return nil, err
	}
	cn = &conn{
	nc: nc,
	addr: addr,
	rw: bufio.NewReadWriter(bufio.NewReader(nc), bufio.NewWriter(nc)),
	c: c,
	}
	cn.extendDeadline()
	return cn, nil
	}

	func (c Client) onItem(item Item, fn func(Client, bufio.ReadWriter, *Item) error) error {
	addr, err := c.selector.PickServer(item.Key)
	if err != nil {
	return err
	}
	cn, err := c.getConn(addr)
	if err != nil {
	return err
	}
	defer cn.condRelease(&err)
	if err = fn(c, cn.rw, item); err != nil {
	return err
	}
	return nil
	}

	func (c *Client) FlushAll() error {
	return c.selector.Each(c.flushAllFromAddr)
	}

	// Get gets the item for the given key. ErrCacheMiss is returned for a
	// memcache cache miss. The key must be at most 250 bytes in length.
	func (c Client) Get(key string) (item Item, err error) {
	err = c.withKeyAddr(key, func(addr net.Addr) error {
	return c.getFromAddr(addr, []string{key}, func(it *Item) { item = it })
	})
	if err == nil && item == nil {
	err = ErrCacheMiss
	}
	return
	}

	// Touch updates the expiry for the given key. The seconds parameter is either
	// a Unix timestamp or, if seconds is less than 1 month, the number of seconds
	// into the future at which time the item will expire. ErrCacheMiss is returned if the
	// key is not in the cache. The key must be at most 250 bytes in length.
	func (c *Client) Touch(key string, seconds int32) (err error) {
	return c.withKeyAddr(key, func(addr net.Addr) error {
	return c.touchFromAddr(addr, []string{key}, seconds)
	})
	}

	func (c *Client) withKeyAddr(key string, fn func(net.Addr) error) (err error) {
	if !legalKey(key) {
	return ErrMalformedKey
	}
	addr, err := c.selector.PickServer(key)
	if err != nil {
	return err
	}
	return fn(addr)
	}

	func (c Client) withAddrRw(addr net.Addr, fn func(bufio.ReadWriter) error) (err error) {
	cn, err := c.getConn(addr)
	if err != nil {
	return err
	}
	defer cn.condRelease(&err)
	return fn(cn.rw)
	}

	func (c Client) withKeyRw(key string, fn func(bufio.ReadWriter) error) error {
	return c.withKeyAddr(key, func(addr net.Addr) error {
	return c.withAddrRw(addr, fn)
	})
	}

	func (c Client) getFromAddr(addr net.Addr, keys []string, cb func(Item)) error {
	return c.withAddrRw(addr, func(rw *bufio.ReadWriter) error {
	if _, err := fmt.Fprintf(rw, "gets %s\r\n", strings.Join(keys, " ")); err != nil {
	return err
	}
	if err := rw.Flush(); err != nil {
	return err
	}
	if err := parseGetResponse(rw.Reader, cb); err != nil {
	return err
	}
	return nil
	})
	}

	// flushAllFromAddr send the flush_all command to the given addr
	func (c *Client) flushAllFromAddr(addr net.Addr) error {
	return c.withAddrRw(addr, func(rw *bufio.ReadWriter) error {
	if _, err := fmt.Fprintf(rw, "flush_all\r\n"); err != nil {
	return err
	}
	if err := rw.Flush(); err != nil {
	return err
	}
	line, err := rw.ReadSlice('\n')
	if err != nil {
	return err
	}
	switch {
	case bytes.Equal(line, resultOk):
	break
	default:
	return fmt.Errorf("memcache: unexpected response line from flush_all: %q", string(line))
	}
	return nil
	})
	}

	func (c *Client) touchFromAddr(addr net.Addr, keys []string, expiration int32) error {
	return c.withAddrRw(addr, func(rw *bufio.ReadWriter) error {
	for _, key := range keys {
	if _, err := fmt.Fprintf(rw, "touch %s %d\r\n", key, expiration); err != nil {
	return err
	}
	if err := rw.Flush(); err != nil {
	return err
	}
	line, err := rw.ReadSlice('\n')
	if err != nil {
	return err
	}
	switch {
	case bytes.Equal(line, resultTouched):
	break
	case bytes.Equal(line, resultNotFound):
	return ErrCacheMiss
	default:
	return fmt.Errorf("memcache: unexpected response line from touch: %q", string(line))
	}
	}
	return nil
	})
	}

	// GetMulti is a batch version of Get. The returned map from keys to
	// items may have fewer elements than the input slice, due to memcache
	// cache misses. Each key must be at most 250 bytes in length.
	// If no error is returned, the returned map will also be non-nil.
	func (c Client) GetMulti(keys []string) (map[string]Item, error) {
	var lk sync.Mutex
	m := make(map[string]*Item)
	addItemToMap := func(it *Item) {
	lk.Lock()
	defer lk.Unlock()
	m[it.Key] = it
	}

	keyMap := make(map[net.Addr][]string)
	for _, key := range keys {
	if !legalKey(key) {
	return nil, ErrMalformedKey
	}
	addr, err := c.selector.PickServer(key)
	if err != nil {
	return nil, err
	}
	keyMap[addr] = append(keyMap[addr], key)
	}

	ch := make(chan error, buffered)
	for addr, keys := range keyMap {
	go func(addr net.Addr, keys []string) {
	ch <- c.getFromAddr(addr, keys, addItemToMap)
	}(addr, keys)
	}

	var err error
	for _ = range keyMap {
	if ge := <-ch; ge != nil {
	err = ge
	}
	}
	return m, err
	}

	// parseGetResponse reads a GET response from r and calls cb for each
	// read and allocated Item
	func parseGetResponse(r bufio.Reader, cb func(Item)) error {
	for {
	line, err := r.ReadSlice('\n')
	if err != nil {
	return err
	}
	if bytes.Equal(line, resultEnd) {
	return nil
	}
	it := new(Item)
	size, err := scanGetResponseLine(line, it)
	if err != nil {
	return err
	}
	it.Value, err = ioutil.ReadAll(io.LimitReader(r, int64(size)+2))
	if err != nil {
	return err
	}
	if !bytes.HasSuffix(it.Value, crlf) {
	return fmt.Errorf("memcache: corrupt get result read")
	}
	it.Value = it.Value[:size]
	cb(it)
	}
	}

	// scanGetResponseLine populates it and returns the declared size of the item.
	// It does not read the bytes of the item.
	func scanGetResponseLine(line []byte, it *Item) (size int, err error) {
	pattern := "VALUE %s %d %d %d\r\n"
	dest := []interface{}{&it.Key, &it.Flags, &size, &it.casid}
	if bytes.Count(line, space) == 3 {
	pattern = "VALUE %s %d %d\r\n"
	dest = dest[:3]
	}
	n, err := fmt.Sscanf(string(line), pattern, dest...)
	if err != nil \|\| n != len(dest) {
	return -1, fmt.Errorf("memcache: unexpected line in get response: %q", line)
	}
	return size, nil
	}

	// Set writes the given item, unconditionally.
	func (c Client) Set(item Item) error {
	return c.onItem(item, (*Client).set)
	}

	func (c Client) set(rw bufio.ReadWriter, item *Item) error {
	return c.populateOne(rw, "set", item)
	}

	// Add writes the given item, if no value already exists for its
	// key. ErrNotStored is returned if that condition is not met.
	func (c Client) Add(item Item) error {
	return c.onItem(item, (*Client).add)
	}

	func (c Client) add(rw bufio.ReadWriter, item *Item) error {
	return c.populateOne(rw, "add", item)
	}

	// Replace writes the given item, but only if the server does
	// already hold data for this key
	func (c Client) Replace(item Item) error {
	return c.onItem(item, (*Client).replace)
	}

	func (c Client) replace(rw bufio.ReadWriter, item *Item) error {
	return c.populateOne(rw, "replace", item)
	}

	// CompareAndSwap writes the given item that was previously returned
	// by Get, if the value was neither modified or evicted between the
	// Get and the CompareAndSwap calls. The item's Key should not change
	// between calls but all other item fields may differ. ErrCASConflict
	// is returned if the value was modified in between the
	// calls. ErrNotStored is returned if the value was evicted in between
	// the calls.
	func (c Client) CompareAndSwap(item Item) error {
	return c.onItem(item, (*Client).cas)
	}

	func (c Client) cas(rw bufio.ReadWriter, item *Item) error {
	return c.populateOne(rw, "cas", item)
	}

	func (c Client) populateOne(rw bufio.ReadWriter, verb string, item *Item) error {
	if !legalKey(item.Key) {
	return ErrMalformedKey
	}
	var err error
	if verb == "cas" {
	_, err = fmt.Fprintf(rw, "%s %s %d %d %d %d\r\n",
	verb, item.Key, item.Flags, item.Expiration, len(item.Value), item.casid)
	} else {
	_, err = fmt.Fprintf(rw, "%s %s %d %d %d\r\n",
	verb, item.Key, item.Flags, item.Expiration, len(item.Value))
	}
	if err != nil {
	return err
	}
	if _, err = rw.Write(item.Value); err != nil {
	return err
	}
	if _, err := rw.Write(crlf); err != nil {
	return err
	}
	if err := rw.Flush(); err != nil {
	return err
	}
	line, err := rw.ReadSlice('\n')
	if err != nil {
	return err
	}
	switch {
	case bytes.Equal(line, resultStored):
	return nil
	case bytes.Equal(line, resultNotStored):
	return ErrNotStored
	case bytes.Equal(line, resultExists):
	return ErrCASConflict
	case bytes.Equal(line, resultNotFound):
	return ErrCacheMiss
	}
	return fmt.Errorf("memcache: unexpected response line from %q: %q", verb, string(line))
	}

	func writeReadLine(rw *bufio.ReadWriter, format string, args ...interface{}) ([]byte, error) {
	_, err := fmt.Fprintf(rw, format, args...)
	if err != nil {
	return nil, err
	}
	if err := rw.Flush(); err != nil {
	return nil, err
	}
	line, err := rw.ReadSlice('\n')
	return line, err
	}

	func writeExpectf(rw *bufio.ReadWriter, expect []byte, format string, args ...interface{}) error {
	line, err := writeReadLine(rw, format, args...)
	if err != nil {
	return err
	}
	switch {
	case bytes.Equal(line, resultOK):
	return nil
	case bytes.Equal(line, expect):
	return nil
	case bytes.Equal(line, resultNotStored):
	return ErrNotStored
	case bytes.Equal(line, resultExists):
	return ErrCASConflict
	case bytes.Equal(line, resultNotFound):
	return ErrCacheMiss
	}
	return fmt.Errorf("memcache: unexpected response line: %q", string(line))
	}

	// Delete deletes the item with the provided key. The error ErrCacheMiss is
	// returned if the item didn't already exist in the cache.
	func (c *Client) Delete(key string) error {
	return c.withKeyRw(key, func(rw *bufio.ReadWriter) error {
	return writeExpectf(rw, resultDeleted, "delete %s\r\n", key)
	})
	}

	// DeleteAll deletes all items in the cache.
	func (c *Client) DeleteAll() error {
	return c.withKeyRw("", func(rw *bufio.ReadWriter) error {
	return writeExpectf(rw, resultDeleted, "flush_all\r\n")
	})
	}

	// Increment atomically increments key by delta. The return value is
	// the new value after being incremented or an error. If the value
	// didn't exist in memcached the error is ErrCacheMiss. The value in
	// memcached must be an decimal number, or an error will be returned.
	// On 64-bit overflow, the new value wraps around.
	func (c *Client) Increment(key string, delta uint64) (newValue uint64, err error) {
	return c.incrDecr("incr", key, delta)
	}

	// Decrement atomically decrements key by delta. The return value is
	// the new value after being decremented or an error. If the value
	// didn't exist in memcached the error is ErrCacheMiss. The value in
	// memcached must be an decimal number, or an error will be returned.
	// On underflow, the new value is capped at zero and does not wrap
	// around.
	func (c *Client) Decrement(key string, delta uint64) (newValue uint64, err error) {
	return c.incrDecr("decr", key, delta)
	}

	func (c *Client) incrDecr(verb, key string, delta uint64) (uint64, error) {
	var val uint64
	err := c.withKeyRw(key, func(rw *bufio.ReadWriter) error {
	line, err := writeReadLine(rw, "%s %s %d\r\n", verb, key, delta)
	if err != nil {
	return err
	}
	switch {
	case bytes.Equal(line, resultNotFound):
	return ErrCacheMiss
	case bytes.HasPrefix(line, resultClientErrorPrefix):
	errMsg := line[len(resultClientErrorPrefix) : len(line)-2]
	return errors.New("memcache: client error: " + string(errMsg))
	}
	val, err = strconv.ParseUint(string(line[:len(line)-2]), 10, 64)
	if err != nil {
	return err
	}
	return nil
	})
	return val, err
	}