mirror of
https://github.com/labstack/echo.git
synced 2024-12-24 20:14:31 +02:00
420 lines
13 KiB
Go
420 lines
13 KiB
Go
package middleware
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import (
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"context"
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"fmt"
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"io"
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"math/rand"
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"net"
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"net/http"
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"net/http/httputil"
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"net/url"
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"regexp"
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"strings"
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"sync"
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"time"
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"github.com/labstack/echo/v4"
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)
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// TODO: Handle TLS proxy
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type (
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// ProxyConfig defines the config for Proxy middleware.
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ProxyConfig struct {
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// Skipper defines a function to skip middleware.
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Skipper Skipper
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// Balancer defines a load balancing technique.
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// Required.
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Balancer ProxyBalancer
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// RetryCount defines the number of times a failed proxied request should be retried
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// using the next available ProxyTarget. Defaults to 0, meaning requests are never retried.
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RetryCount int
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// RetryFilter defines a function used to determine if a failed request to a
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// ProxyTarget should be retried. The RetryFilter will only be called when the number
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// of previous retries is less than RetryCount. If the function returns true, the
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// request will be retried. The provided error indicates the reason for the request
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// failure. When the ProxyTarget is unavailable, the error will be an instance of
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// echo.HTTPError with a Code of http.StatusBadGateway. In all other cases, the error
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// will indicate an internal error in the Proxy middleware. When a RetryFilter is not
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// specified, all requests that fail with http.StatusBadGateway will be retried. A custom
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// RetryFilter can be provided to only retry specific requests. Note that RetryFilter is
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// only called when the request to the target fails, or an internal error in the Proxy
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// middleware has occurred. Successful requests that return a non-200 response code cannot
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// be retried.
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RetryFilter func(c echo.Context, e error) bool
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// ErrorHandler defines a function which can be used to return custom errors from
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// the Proxy middleware. ErrorHandler is only invoked when there has been
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// either an internal error in the Proxy middleware or the ProxyTarget is
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// unavailable. Due to the way requests are proxied, ErrorHandler is not invoked
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// when a ProxyTarget returns a non-200 response. In these cases, the response
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// is already written so errors cannot be modified. ErrorHandler is only
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// invoked after all retry attempts have been exhausted.
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ErrorHandler func(c echo.Context, err error) error
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// Rewrite defines URL path rewrite rules. The values captured in asterisk can be
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// retrieved by index e.g. $1, $2 and so on.
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// Examples:
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// "/old": "/new",
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// "/api/*": "/$1",
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// "/js/*": "/public/javascripts/$1",
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// "/users/*/orders/*": "/user/$1/order/$2",
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Rewrite map[string]string
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// RegexRewrite defines rewrite rules using regexp.Rexexp with captures
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// Every capture group in the values can be retrieved by index e.g. $1, $2 and so on.
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// Example:
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// "^/old/[0.9]+/": "/new",
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// "^/api/.+?/(.*)": "/v2/$1",
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RegexRewrite map[*regexp.Regexp]string
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// Context key to store selected ProxyTarget into context.
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// Optional. Default value "target".
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ContextKey string
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// To customize the transport to remote.
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// Examples: If custom TLS certificates are required.
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Transport http.RoundTripper
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// ModifyResponse defines function to modify response from ProxyTarget.
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ModifyResponse func(*http.Response) error
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}
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// ProxyTarget defines the upstream target.
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ProxyTarget struct {
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Name string
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URL *url.URL
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Meta echo.Map
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}
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// ProxyBalancer defines an interface to implement a load balancing technique.
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ProxyBalancer interface {
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AddTarget(*ProxyTarget) bool
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RemoveTarget(string) bool
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Next(echo.Context) *ProxyTarget
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}
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// TargetProvider defines an interface that gives the opportunity for balancer
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// to return custom errors when selecting target.
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TargetProvider interface {
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NextTarget(echo.Context) (*ProxyTarget, error)
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}
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commonBalancer struct {
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targets []*ProxyTarget
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mutex sync.Mutex
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}
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// RandomBalancer implements a random load balancing technique.
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randomBalancer struct {
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commonBalancer
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random *rand.Rand
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}
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// RoundRobinBalancer implements a round-robin load balancing technique.
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roundRobinBalancer struct {
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commonBalancer
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// tracking the index on `targets` slice for the next `*ProxyTarget` to be used
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i int
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}
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)
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var (
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// DefaultProxyConfig is the default Proxy middleware config.
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DefaultProxyConfig = ProxyConfig{
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Skipper: DefaultSkipper,
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ContextKey: "target",
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}
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)
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func proxyRaw(t *ProxyTarget, c echo.Context) http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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in, _, err := c.Response().Hijack()
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if err != nil {
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c.Set("_error", fmt.Errorf("proxy raw, hijack error=%w, url=%s", err, t.URL))
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return
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}
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defer in.Close()
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out, err := net.Dial("tcp", t.URL.Host)
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if err != nil {
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c.Set("_error", echo.NewHTTPError(http.StatusBadGateway, fmt.Sprintf("proxy raw, dial error=%v, url=%s", err, t.URL)))
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return
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}
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defer out.Close()
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// Write header
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err = r.Write(out)
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if err != nil {
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c.Set("_error", echo.NewHTTPError(http.StatusBadGateway, fmt.Sprintf("proxy raw, request header copy error=%v, url=%s", err, t.URL)))
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return
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}
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errCh := make(chan error, 2)
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cp := func(dst io.Writer, src io.Reader) {
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_, err = io.Copy(dst, src)
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errCh <- err
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}
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go cp(out, in)
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go cp(in, out)
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err = <-errCh
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if err != nil && err != io.EOF {
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c.Set("_error", fmt.Errorf("proxy raw, copy body error=%w, url=%s", err, t.URL))
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}
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})
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}
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// NewRandomBalancer returns a random proxy balancer.
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func NewRandomBalancer(targets []*ProxyTarget) ProxyBalancer {
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b := randomBalancer{}
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b.targets = targets
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b.random = rand.New(rand.NewSource(int64(time.Now().Nanosecond())))
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return &b
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}
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// NewRoundRobinBalancer returns a round-robin proxy balancer.
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func NewRoundRobinBalancer(targets []*ProxyTarget) ProxyBalancer {
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b := roundRobinBalancer{}
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b.targets = targets
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return &b
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}
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// AddTarget adds an upstream target to the list and returns `true`.
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//
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// However, if a target with the same name already exists then the operation is aborted returning `false`.
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func (b *commonBalancer) AddTarget(target *ProxyTarget) bool {
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b.mutex.Lock()
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defer b.mutex.Unlock()
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for _, t := range b.targets {
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if t.Name == target.Name {
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return false
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}
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}
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b.targets = append(b.targets, target)
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return true
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}
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// RemoveTarget removes an upstream target from the list by name.
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//
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// Returns `true` on success, `false` if no target with the name is found.
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func (b *commonBalancer) RemoveTarget(name string) bool {
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b.mutex.Lock()
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defer b.mutex.Unlock()
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for i, t := range b.targets {
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if t.Name == name {
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b.targets = append(b.targets[:i], b.targets[i+1:]...)
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return true
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}
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}
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return false
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}
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// Next randomly returns an upstream target.
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//
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// Note: `nil` is returned in case upstream target list is empty.
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func (b *randomBalancer) Next(c echo.Context) *ProxyTarget {
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b.mutex.Lock()
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defer b.mutex.Unlock()
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if len(b.targets) == 0 {
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return nil
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} else if len(b.targets) == 1 {
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return b.targets[0]
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}
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return b.targets[b.random.Intn(len(b.targets))]
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}
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// Next returns an upstream target using round-robin technique. In the case
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// where a previously failed request is being retried, the round-robin
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// balancer will attempt to use the next target relative to the original
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// request. If the list of targets held by the balancer is modified while a
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// failed request is being retried, it is possible that the balancer will
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// return the original failed target.
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//
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// Note: `nil` is returned in case upstream target list is empty.
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func (b *roundRobinBalancer) Next(c echo.Context) *ProxyTarget {
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b.mutex.Lock()
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defer b.mutex.Unlock()
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if len(b.targets) == 0 {
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return nil
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} else if len(b.targets) == 1 {
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return b.targets[0]
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}
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var i int
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const lastIdxKey = "_round_robin_last_index"
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// This request is a retry, start from the index of the previous
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// target to ensure we don't attempt to retry the request with
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// the same failed target
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if c.Get(lastIdxKey) != nil {
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i = c.Get(lastIdxKey).(int)
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i++
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if i >= len(b.targets) {
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i = 0
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}
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} else {
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// This is a first time request, use the global index
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if b.i >= len(b.targets) {
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b.i = 0
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}
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i = b.i
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b.i++
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}
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c.Set(lastIdxKey, i)
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return b.targets[i]
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}
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// Proxy returns a Proxy middleware.
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//
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// Proxy middleware forwards the request to upstream server using a configured load balancing technique.
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func Proxy(balancer ProxyBalancer) echo.MiddlewareFunc {
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c := DefaultProxyConfig
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c.Balancer = balancer
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return ProxyWithConfig(c)
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}
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// ProxyWithConfig returns a Proxy middleware with config.
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// See: `Proxy()`
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func ProxyWithConfig(config ProxyConfig) echo.MiddlewareFunc {
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if config.Balancer == nil {
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panic("echo: proxy middleware requires balancer")
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}
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// Defaults
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if config.Skipper == nil {
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config.Skipper = DefaultProxyConfig.Skipper
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}
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if config.RetryFilter == nil {
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config.RetryFilter = func(c echo.Context, e error) bool {
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if httpErr, ok := e.(*echo.HTTPError); ok {
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return httpErr.Code == http.StatusBadGateway
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}
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return false
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}
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}
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if config.ErrorHandler == nil {
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config.ErrorHandler = func(c echo.Context, err error) error {
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return err
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}
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}
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if config.Rewrite != nil {
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if config.RegexRewrite == nil {
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config.RegexRewrite = make(map[*regexp.Regexp]string)
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}
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for k, v := range rewriteRulesRegex(config.Rewrite) {
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config.RegexRewrite[k] = v
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}
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}
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provider, isTargetProvider := config.Balancer.(TargetProvider)
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return func(next echo.HandlerFunc) echo.HandlerFunc {
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return func(c echo.Context) error {
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if config.Skipper(c) {
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return next(c)
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}
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req := c.Request()
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res := c.Response()
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if err := rewriteURL(config.RegexRewrite, req); err != nil {
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return config.ErrorHandler(c, err)
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}
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// Fix header
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// Basically it's not good practice to unconditionally pass incoming x-real-ip header to upstream.
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// However, for backward compatibility, legacy behavior is preserved unless you configure Echo#IPExtractor.
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if req.Header.Get(echo.HeaderXRealIP) == "" || c.Echo().IPExtractor != nil {
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req.Header.Set(echo.HeaderXRealIP, c.RealIP())
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}
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if req.Header.Get(echo.HeaderXForwardedProto) == "" {
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req.Header.Set(echo.HeaderXForwardedProto, c.Scheme())
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}
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if c.IsWebSocket() && req.Header.Get(echo.HeaderXForwardedFor) == "" { // For HTTP, it is automatically set by Go HTTP reverse proxy.
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req.Header.Set(echo.HeaderXForwardedFor, c.RealIP())
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}
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retries := config.RetryCount
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for {
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var tgt *ProxyTarget
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var err error
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if isTargetProvider {
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tgt, err = provider.NextTarget(c)
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if err != nil {
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return config.ErrorHandler(c, err)
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}
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} else {
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tgt = config.Balancer.Next(c)
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}
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c.Set(config.ContextKey, tgt)
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//If retrying a failed request, clear any previous errors from
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//context here so that balancers have the option to check for
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//errors that occurred using previous target
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if retries < config.RetryCount {
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c.Set("_error", nil)
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}
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// Proxy
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switch {
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case c.IsWebSocket():
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proxyRaw(tgt, c).ServeHTTP(res, req)
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case req.Header.Get(echo.HeaderAccept) == "text/event-stream":
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default:
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proxyHTTP(tgt, c, config).ServeHTTP(res, req)
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}
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err, hasError := c.Get("_error").(error)
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if !hasError {
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return nil
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}
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retry := retries > 0 && config.RetryFilter(c, err)
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if !retry {
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return config.ErrorHandler(c, err)
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}
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retries--
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}
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}
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}
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}
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// StatusCodeContextCanceled is a custom HTTP status code for situations
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// where a client unexpectedly closed the connection to the server.
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// As there is no standard error code for "client closed connection", but
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// various well-known HTTP clients and server implement this HTTP code we use
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// 499 too instead of the more problematic 5xx, which does not allow to detect this situation
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const StatusCodeContextCanceled = 499
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func proxyHTTP(tgt *ProxyTarget, c echo.Context, config ProxyConfig) http.Handler {
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proxy := httputil.NewSingleHostReverseProxy(tgt.URL)
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proxy.ErrorHandler = func(resp http.ResponseWriter, req *http.Request, err error) {
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desc := tgt.URL.String()
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if tgt.Name != "" {
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desc = fmt.Sprintf("%s(%s)", tgt.Name, tgt.URL.String())
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}
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// If the client canceled the request (usually by closing the connection), we can report a
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// client error (4xx) instead of a server error (5xx) to correctly identify the situation.
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// The Go standard library (at of late 2020) wraps the exported, standard
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// context.Canceled error with unexported garbage value requiring a substring check, see
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// https://github.com/golang/go/blob/6965b01ea248cabb70c3749fd218b36089a21efb/src/net/net.go#L416-L430
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if err == context.Canceled || strings.Contains(err.Error(), "operation was canceled") {
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httpError := echo.NewHTTPError(StatusCodeContextCanceled, fmt.Sprintf("client closed connection: %v", err))
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httpError.Internal = err
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c.Set("_error", httpError)
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} else {
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httpError := echo.NewHTTPError(http.StatusBadGateway, fmt.Sprintf("remote %s unreachable, could not forward: %v", desc, err))
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httpError.Internal = err
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c.Set("_error", httpError)
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}
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}
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proxy.Transport = config.Transport
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proxy.ModifyResponse = config.ModifyResponse
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return proxy
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}
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