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echo/middleware/proxy.go

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package middleware
import (
"fmt"
"io"
"math/rand"
"net"
"net/http"
"net/url"
"regexp"
"sync"
"sync/atomic"
"time"
"github.com/labstack/echo/v4"
)
// TODO: Handle TLS proxy
type (
// ProxyConfig defines the config for Proxy middleware.
ProxyConfig struct {
// Skipper defines a function to skip middleware.
Skipper Skipper
// Balancer defines a load balancing technique.
// Required.
Balancer ProxyBalancer
// Rewrite defines URL path rewrite rules. The values captured in asterisk can be
// retrieved by index e.g. $1, $2 and so on.
// Examples:
// "/old": "/new",
// "/api/*": "/$1",
// "/js/*": "/public/javascripts/$1",
// "/users/*/orders/*": "/user/$1/order/$2",
Rewrite map[string]string
// Context key to store selected ProxyTarget into context.
// Optional. Default value "target".
ContextKey string
// To customize the transport to remote.
// Examples: If custom TLS certificates are required.
Transport http.RoundTripper
// ModifyResponse defines function to modify response from ProxyTarget.
ModifyResponse func(*http.Response) error
rewriteRegex map[*regexp.Regexp]string
}
// ProxyTarget defines the upstream target.
ProxyTarget struct {
Name string
URL *url.URL
Meta echo.Map
}
// ProxyBalancer defines an interface to implement a load balancing technique.
ProxyBalancer interface {
AddTarget(*ProxyTarget) bool
RemoveTarget(string) bool
Next(echo.Context) *ProxyTarget
}
commonBalancer struct {
targets []*ProxyTarget
mutex sync.RWMutex
}
// RandomBalancer implements a random load balancing technique.
randomBalancer struct {
*commonBalancer
random *rand.Rand
}
// RoundRobinBalancer implements a round-robin load balancing technique.
roundRobinBalancer struct {
*commonBalancer
i uint32
}
)
var (
// DefaultProxyConfig is the default Proxy middleware config.
DefaultProxyConfig = ProxyConfig{
Skipper: DefaultSkipper,
ContextKey: "target",
}
)
func proxyRaw(t *ProxyTarget, c echo.Context) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
in, _, err := c.Response().Hijack()
if err != nil {
c.Set("_error", fmt.Sprintf("proxy raw, hijack error=%v, url=%s", t.URL, err))
return
}
defer in.Close()
out, err := net.Dial("tcp", t.URL.Host)
if err != nil {
c.Set("_error", echo.NewHTTPError(http.StatusBadGateway, fmt.Sprintf("proxy raw, dial error=%v, url=%s", t.URL, err)))
return
}
defer out.Close()
// Write header
err = r.Write(out)
if err != nil {
c.Set("_error", echo.NewHTTPError(http.StatusBadGateway, fmt.Sprintf("proxy raw, request header copy error=%v, url=%s", t.URL, err)))
return
}
errCh := make(chan error, 2)
cp := func(dst io.Writer, src io.Reader) {
_, err = io.Copy(dst, src)
errCh <- err
}
go cp(out, in)
go cp(in, out)
err = <-errCh
if err != nil && err != io.EOF {
c.Set("_error", fmt.Errorf("proxy raw, copy body error=%v, url=%s", t.URL, err))
}
})
}
// NewRandomBalancer returns a random proxy balancer.
func NewRandomBalancer(targets []*ProxyTarget) ProxyBalancer {
b := &randomBalancer{commonBalancer: new(commonBalancer)}
b.targets = targets
return b
}
// NewRoundRobinBalancer returns a round-robin proxy balancer.
func NewRoundRobinBalancer(targets []*ProxyTarget) ProxyBalancer {
b := &roundRobinBalancer{commonBalancer: new(commonBalancer)}
b.targets = targets
return b
}
// AddTarget adds an upstream target to the list.
func (b *commonBalancer) AddTarget(target *ProxyTarget) bool {
for _, t := range b.targets {
if t.Name == target.Name {
return false
}
}
b.mutex.Lock()
defer b.mutex.Unlock()
b.targets = append(b.targets, target)
return true
}
// RemoveTarget removes an upstream target from the list.
func (b *commonBalancer) RemoveTarget(name string) bool {
b.mutex.Lock()
defer b.mutex.Unlock()
for i, t := range b.targets {
if t.Name == name {
b.targets = append(b.targets[:i], b.targets[i+1:]...)
return true
}
}
return false
}
// Next randomly returns an upstream target.
func (b *randomBalancer) Next(c echo.Context) *ProxyTarget {
if b.random == nil {
b.random = rand.New(rand.NewSource(int64(time.Now().Nanosecond())))
}
b.mutex.RLock()
defer b.mutex.RUnlock()
return b.targets[b.random.Intn(len(b.targets))]
}
// Next returns an upstream target using round-robin technique.
func (b *roundRobinBalancer) Next(c echo.Context) *ProxyTarget {
b.i = b.i % uint32(len(b.targets))
t := b.targets[b.i]
atomic.AddUint32(&b.i, 1)
return t
}
// Proxy returns a Proxy middleware.
//
// Proxy middleware forwards the request to upstream server using a configured load balancing technique.
func Proxy(balancer ProxyBalancer) echo.MiddlewareFunc {
c := DefaultProxyConfig
c.Balancer = balancer
return ProxyWithConfig(c)
}
// ProxyWithConfig returns a Proxy middleware with config.
// See: `Proxy()`
func ProxyWithConfig(config ProxyConfig) echo.MiddlewareFunc {
// Defaults
if config.Skipper == nil {
config.Skipper = DefaultProxyConfig.Skipper
}
if config.Balancer == nil {
panic("echo: proxy middleware requires balancer")
}
config.rewriteRegex = rewriteRulesRegex(config.Rewrite)
return func(next echo.HandlerFunc) echo.HandlerFunc {
return func(c echo.Context) (err error) {
if config.Skipper(c) {
return next(c)
}
req := c.Request()
res := c.Response()
tgt := config.Balancer.Next(c)
c.Set(config.ContextKey, tgt)
// Set rewrite path and raw path
rewritePath(config.rewriteRegex, req)
// Fix header
// Basically it's not good practice to unconditionally pass incoming x-real-ip header to upstream.
// However, for backward compatibility, legacy behavior is preserved unless you configure Echo#IPExtractor.
if req.Header.Get(echo.HeaderXRealIP) == "" || c.Echo().IPExtractor != nil {
req.Header.Set(echo.HeaderXRealIP, c.RealIP())
}
if req.Header.Get(echo.HeaderXForwardedProto) == "" {
req.Header.Set(echo.HeaderXForwardedProto, c.Scheme())
}
if c.IsWebSocket() && req.Header.Get(echo.HeaderXForwardedFor) == "" { // For HTTP, it is automatically set by Go HTTP reverse proxy.
req.Header.Set(echo.HeaderXForwardedFor, c.RealIP())
}
// Proxy
switch {
case c.IsWebSocket():
proxyRaw(tgt, c).ServeHTTP(res, req)
case req.Header.Get(echo.HeaderAccept) == "text/event-stream":
default:
proxyHTTP(tgt, c, config).ServeHTTP(res, req)
}
if e, ok := c.Get("_error").(error); ok {
err = e
}
return
}
}
}