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proxy.go
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proxy.go
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package redis
import (
"bufio"
"context"
"errors"
"fmt"
"io"
"log"
"net"
"github.com/segmentio/objconv/resp"
)
// ReverseProxy is the implementation of a redis reverse proxy.
type ReverseProxy struct {
// Transport specifies the mechanism by which individual requests are made.
// If nil, DefaultTransport is used.
Transport RoundTripper
// The registry exposing the set of redis servers that the proxy routes
// requests to.
Registry ServerRegistry
// ErrorLog specifies an optional logger for errors accepting connections
// and unexpected behavior from handlers. If nil, logging goes to os.Stderr
// via the log package's standard logger.
ErrorLog *log.Logger
}
// ServeRedis satisfies the Handler interface.
func (proxy *ReverseProxy) ServeRedis(w ResponseWriter, r *Request) {
proxy.serveRequest(w, r)
}
func (proxy *ReverseProxy) serveRequest(w ResponseWriter, req *Request) {
keys := make([]string, 0, 10)
cmds := req.Cmds
for i := range cmds {
keys = cmds[i].getKeys(keys)
}
servers, err := proxy.lookupServers(req.Context)
if err != nil {
w.Write(errorf("ERR No upstream server were found to route the request to."))
proxy.log(err)
return
}
// TODO: looking up servers and rebuilding the hash ring for every request
// is not efficient, we should cache and reuse the state.
hashring := makeHashRing(servers...)
upstream := ""
for _, key := range keys {
addr := hashring.lookup(key)
if len(upstream) == 0 {
upstream = addr
} else if upstream != addr {
w.Write(errorf("EXECABORT The transaction contains keys that hash to different upstream servers."))
return
}
}
req.Addr = upstream
res, err := proxy.roundTrip(req)
switch err.(type) {
case nil:
case *resp.Error:
w.Write(err)
return
default:
w.Write(errorf("ERR Connecting to the upstream server failed."))
proxy.blacklistServer(upstream)
proxy.log(err)
return
}
if res.Args != nil {
err = proxy.writeArgs(w, res.Args)
} else {
err = proxy.writeTxArgs(w, res.TxArgs)
}
if err != nil {
// Get caught by the server, that way the connection is closed and not
// left in an unpredictable state.
panic(err)
}
}
func (proxy *ReverseProxy) writeTxArgs(w ResponseWriter, tx TxArgs) (err error) {
w.WriteStream(tx.Len())
var v []interface{} // TODO: figure out a way to avoid loading values in memory
for a := tx.Next(); a != nil; a = tx.Next() {
n := 0
v = append(v, nil)
for a.Next(&v[n]) {
v = append(v, nil)
n++
}
err = a.Close()
if _, ok := err.(*resp.Error); ok {
v = append(v, err)
n++
}
w.Write(v[:n])
}
if e := tx.Close(); e != nil && err == nil {
err = e
}
return
}
func (proxy *ReverseProxy) writeArgs(w ResponseWriter, a Args) (err error) {
var v interface{}
w.WriteStream(a.Len())
for a.Next(&v) {
w.Write(v)
v = nil
}
err = a.Close()
if e, ok := err.(*resp.Error); ok {
w.Write(e)
err = nil
}
if f, ok := w.(Flusher); ok {
err = f.Flush()
}
return
}
func (proxy *ReverseProxy) servePubSub(conn net.Conn, rw *bufio.ReadWriter, command string, channels ...string) {
defer conn.Close()
// TODO:
// - select the backend server to subscribe to by hashing the channel
// - refresh the list of servers periodically so we can rebalance when new servers are added
}
func (proxy *ReverseProxy) lookupServers(ctx context.Context) ([]ServerEndpoint, error) {
r := proxy.Registry
if r == nil {
return nil, errors.New("a redis proxy needs a non-nil registry to lookup the list of avaiable servers")
}
return r.LookupServers(ctx)
}
func (proxy *ReverseProxy) blacklistServer(upstream string) {
if b, ok := proxy.Registry.(ServerBlacklist); !ok {
b.BlacklistServer(ServerEndpoint{Addr: upstream})
}
}
func (proxy *ReverseProxy) roundTrip(req *Request) (*Response, error) {
t := proxy.Transport
if t == nil {
t = DefaultTransport
}
return t.RoundTrip(req)
}
func (proxy *ReverseProxy) log(err error) {
switch err {
case io.EOF, io.ErrUnexpectedEOF, io.ErrClosedPipe:
// Don't log these errors because they are very common and it doesn't
// bring any value to know that a client disconnected.
return
}
print := log.Print
if logger := proxy.ErrorLog; logger != nil {
print = logger.Print
}
print(err)
}
func (proxy *ReverseProxy) transport() RoundTripper {
if transport := proxy.Transport; transport != nil {
return transport
}
return DefaultTransport
}
func errorf(format string, args ...interface{}) error {
return resp.NewError(fmt.Sprintf(format, args...))
}