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star/httpreverse/rp/reverseproxy.go

853 lines
24 KiB
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.
// HTTP reverse proxy handler
package rp
import (
"context"
"errors"
"fmt"
"io"
"log"
"mime"
"net"
"net/http"
"net/http/httptrace"
"net/textproto"
"net/url"
"strings"
"sync"
"time"
"golang.org/x/net/http/httpguts"
)
func lower(b byte) byte {
if 'A' <= b && b <= 'Z' {
return b + ('a' - 'A')
}
return b
}
func EqualFold(s, t string) bool {
if len(s) != len(t) {
return false
}
for i := 0; i < len(s); i++ {
if lower(s[i]) != lower(t[i]) {
return false
}
}
return true
}
func IsPrint(s string) bool {
for i := 0; i < len(s); i++ {
if s[i] < ' ' || s[i] > '~' {
return false
}
}
return true
}
// A ProxyRequest contains a request to be rewritten by a ReverseProxy.
type ProxyRequest struct {
// In is the request received by the proxy.
// The Rewrite function must not modify In.
In *http.Request
// Out is the request which will be sent by the proxy.
// The Rewrite function may modify or replace this request.
// Hop-by-hop headers are removed from this request
// before Rewrite is called.
Out *http.Request
}
// SetURL routes the outbound request to the scheme, host, and base path
// provided in target. If the target's path is "/base" and the incoming
// request was for "/dir", the target request will be for "/base/dir".
//
// SetURL rewrites the outbound Host header to match the target's host.
// To preserve the inbound request's Host header (the default behavior
// of NewSingleHostReverseProxy):
//
// rewriteFunc := func(r *httputil.ProxyRequest) {
// r.SetURL(url)
// r.Out.Host = r.In.Host
// }
func (r *ProxyRequest) SetURL(target *url.URL) {
rewriteRequestURL(r.Out, target)
r.Out.Host = ""
}
// SetXForwarded sets the X-Forwarded-For, X-Forwarded-Host, and
// X-Forwarded-Proto headers of the outbound request.
//
// - The X-Forwarded-For header is set to the client IP address.
// - The X-Forwarded-Host header is set to the host name requested
// by the client.
// - The X-Forwarded-Proto header is set to "http" or "https", depending
// on whether the inbound request was made on a TLS-enabled connection.
//
// If the outbound request contains an existing X-Forwarded-For header,
// SetXForwarded appends the client IP address to it. To append to the
// inbound request's X-Forwarded-For header (the default behavior of
// ReverseProxy when using a Director function), copy the header
// from the inbound request before calling SetXForwarded:
//
// rewriteFunc := func(r *httputil.ProxyRequest) {
// r.Out.Header["X-Forwarded-For"] = r.In.Header["X-Forwarded-For"]
// r.SetXForwarded()
// }
func (r *ProxyRequest) SetXForwarded() {
clientIP, _, err := net.SplitHostPort(r.In.RemoteAddr)
if err == nil {
prior := r.Out.Header["X-Forwarded-For"]
if len(prior) > 0 {
clientIP = strings.Join(prior, ", ") + ", " + clientIP
}
r.Out.Header.Set("X-Forwarded-For", clientIP)
} else {
r.Out.Header.Del("X-Forwarded-For")
}
r.Out.Header.Set("X-Forwarded-Host", r.In.Host)
if r.In.TLS == nil {
r.Out.Header.Set("X-Forwarded-Proto", "http")
} else {
r.Out.Header.Set("X-Forwarded-Proto", "https")
}
}
// ReverseProxy is an HTTP Handler that takes an incoming request and
// sends it to another server, proxying the response back to the
// client.
//
// 1xx responses are forwarded to the client if the underlying
// transport supports ClientTrace.Got1xxResponse.
type ReverseProxy struct {
// Rewrite must be a function which modifies
// the request into a new request to be sent
// using Transport. Its response is then copied
// back to the original client unmodified.
// Rewrite must not access the provided ProxyRequest
// or its contents after returning.
//
// The Forwarded, X-Forwarded, X-Forwarded-Host,
// and X-Forwarded-Proto headers are removed from the
// outbound request before Rewrite is called. See also
// the ProxyRequest.SetXForwarded method.
//
// Unparsable query parameters are removed from the
// outbound request before Rewrite is called.
// The Rewrite function may copy the inbound URL's
// RawQuery to the outbound URL to preserve the original
// parameter string. Note that this can lead to security
// issues if the proxy's interpretation of query parameters
// does not match that of the downstream server.
//
// At most one of Rewrite or Director may be set.
Rewrite func(*ProxyRequest)
// Director is a function which modifies
// the request into a new request to be sent
// using Transport. Its response is then copied
// back to the original client unmodified.
// Director must not access the provided Request
// after returning.
//
// By default, the X-Forwarded-For header is set to the
// value of the client IP address. If an X-Forwarded-For
// header already exists, the client IP is appended to the
// existing values. As a special case, if the header
// exists in the Request.Header map but has a nil value
// (such as when set by the Director func), the X-Forwarded-For
// header is not modified.
//
// To prevent IP spoofing, be sure to delete any pre-existing
// X-Forwarded-For header coming from the client or
// an untrusted proxy.
//
// Hop-by-hop headers are removed from the request after
// Director returns, which can remove headers added by
// Director. Use a Rewrite function instead to ensure
// modifications to the request are preserved.
//
// Unparsable query parameters are removed from the outbound
// request if Request.Form is set after Director returns.
//
// At most one of Rewrite or Director may be set.
Director func(*http.Request)
// The transport used to perform proxy requests.
// If nil, http.DefaultTransport is used.
Transport http.RoundTripper
// FlushInterval specifies the flush interval
// to flush to the client while copying the
// response body.
// If zero, no periodic flushing is done.
// A negative value means to flush immediately
// after each write to the client.
// The FlushInterval is ignored when ReverseProxy
// recognizes a response as a streaming response, or
// if its ContentLength is -1; for such responses, writes
// are flushed to the client immediately.
FlushInterval time.Duration
// ErrorLog specifies an optional logger for errors
// that occur when attempting to proxy the request.
// If nil, logging is done via the log package's standard logger.
ErrorLog *log.Logger
// BufferPool optionally specifies a buffer pool to
// get byte slices for use by io.CopyBuffer when
// copying HTTP response bodies.
BufferPool BufferPool
// ModifyResponse is an optional function that modifies the
// Response from the backend. It is called if the backend
// returns a response at all, with any HTTP status code.
// If the backend is unreachable, the optional ErrorHandler is
// called without any call to ModifyResponse.
//
// If ModifyResponse returns an error, ErrorHandler is called
// with its error value. If ErrorHandler is nil, its default
// implementation is used.
ModifyResponse func(*http.Response) error
// ErrorHandler is an optional function that handles errors
// reaching the backend or errors from ModifyResponse.
//
// If nil, the default is to log the provided error and return
// a 502 Status Bad Gateway response.
ErrorHandler func(http.ResponseWriter, *http.Request, error)
}
// A BufferPool is an interface for getting and returning temporary
// byte slices for use by io.CopyBuffer.
type BufferPool interface {
Get() []byte
Put([]byte)
}
func singleJoiningSlash(a, b string) string {
aslash := strings.HasSuffix(a, "/")
bslash := strings.HasPrefix(b, "/")
switch {
case aslash && bslash:
return a + b[1:]
case !aslash && !bslash:
return a + "/" + b
}
return a + b
}
func joinURLPath(a, b *url.URL) (path, rawpath string) {
if a.RawPath == "" && b.RawPath == "" {
return singleJoiningSlash(a.Path, b.Path), ""
}
// Same as singleJoiningSlash, but uses EscapedPath to determine
// whether a slash should be added
apath := a.EscapedPath()
bpath := b.EscapedPath()
aslash := strings.HasSuffix(apath, "/")
bslash := strings.HasPrefix(bpath, "/")
switch {
case aslash && bslash:
return a.Path + b.Path[1:], apath + bpath[1:]
case !aslash && !bslash:
return a.Path + "/" + b.Path, apath + "/" + bpath
}
return a.Path + b.Path, apath + bpath
}
// NewSingleHostReverseProxy returns a new ReverseProxy that routes
// URLs to the scheme, host, and base path provided in target. If the
// target's path is "/base" and the incoming request was for "/dir",
// the target request will be for /base/dir.
//
// NewSingleHostReverseProxy does not rewrite the Host header.
//
// To customize the ReverseProxy behavior beyond what
// NewSingleHostReverseProxy provides, use ReverseProxy directly
// with a Rewrite function. The ProxyRequest SetURL method
// may be used to route the outbound request. (Note that SetURL,
// unlike NewSingleHostReverseProxy, rewrites the Host header
// of the outbound request by default.)
//
// proxy := &ReverseProxy{
// Rewrite: func(r *ProxyRequest) {
// r.SetURL(target)
// r.Out.Host = r.In.Host // if desired
// }
// }
func NewSingleHostReverseProxy(target *url.URL) *ReverseProxy {
director := func(req *http.Request) {
rewriteRequestURL(req, target)
}
return &ReverseProxy{Director: director}
}
func rewriteRequestURL(req *http.Request, target *url.URL) {
targetQuery := target.RawQuery
req.URL.Scheme = target.Scheme
req.URL.Host = target.Host
req.URL.Path, req.URL.RawPath = joinURLPath(target, req.URL)
if targetQuery == "" || req.URL.RawQuery == "" {
req.URL.RawQuery = targetQuery + req.URL.RawQuery
} else {
req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
}
}
func copyHeader(dst, src http.Header) {
for k, vv := range src {
for _, v := range vv {
dst.Add(k, v)
}
}
}
// Hop-by-hop headers. These are removed when sent to the backend.
// As of RFC 7230, hop-by-hop headers are required to appear in the
// Connection header field. These are the headers defined by the
// obsoleted RFC 2616 (section 13.5.1) and are used for backward
// compatibility.
var hopHeaders = []string{
"Connection",
"Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
"Keep-Alive",
"Proxy-Authenticate",
"Proxy-Authorization",
"Te", // canonicalized version of "TE"
"Trailer", // not Trailers per URL above; https://www.rfc-editor.org/errata_search.php?eid=4522
"Transfer-Encoding",
"Upgrade",
}
func (p *ReverseProxy) defaultErrorHandler(rw http.ResponseWriter, req *http.Request, err error) {
p.logf("http: proxy error: %v", err)
rw.WriteHeader(http.StatusBadGateway)
}
func (p *ReverseProxy) getErrorHandler() func(http.ResponseWriter, *http.Request, error) {
if p.ErrorHandler != nil {
return p.ErrorHandler
}
return p.defaultErrorHandler
}
// modifyResponse conditionally runs the optional ModifyResponse hook
// and reports whether the request should proceed.
func (p *ReverseProxy) modifyResponse(rw http.ResponseWriter, res *http.Response, req *http.Request) bool {
if p.ModifyResponse == nil {
return true
}
if err := p.ModifyResponse(res); err != nil {
res.Body.Close()
p.getErrorHandler()(rw, req, err)
return false
}
return true
}
func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
transport := p.Transport
if transport == nil {
transport = http.DefaultTransport
}
ctx := req.Context()
if ctx.Done() != nil {
// CloseNotifier predates context.Context, and has been
// entirely superseded by it. If the request contains
// a Context that carries a cancellation signal, don't
// bother spinning up a goroutine to watch the CloseNotify
// channel (if any).
//
// If the request Context has a nil Done channel (which
// means it is either context.Background, or a custom
// Context implementation with no cancellation signal),
// then consult the CloseNotifier if available.
} else if cn, ok := rw.(http.CloseNotifier); ok {
var cancel context.CancelFunc
ctx, cancel = context.WithCancel(ctx)
defer cancel()
notifyChan := cn.CloseNotify()
go func() {
select {
case <-notifyChan:
cancel()
case <-ctx.Done():
}
}()
}
outreq := req.Clone(ctx)
if req.ContentLength == 0 {
outreq.Body = nil // Issue 16036: nil Body for http.Transport retries
}
if outreq.Body != nil {
// Reading from the request body after returning from a handler is not
// allowed, and the RoundTrip goroutine that reads the Body can outlive
// this handler. This can lead to a crash if the handler panics (see
// Issue 46866). Although calling Close doesn't guarantee there isn't
// any Read in flight after the handle returns, in practice it's safe to
// read after closing it.
defer outreq.Body.Close()
}
if outreq.Header == nil {
outreq.Header = make(http.Header) // Issue 33142: historical behavior was to always allocate
}
if (p.Director != nil) == (p.Rewrite != nil) {
p.getErrorHandler()(rw, req, errors.New("ReverseProxy must have exactly one of Director or Rewrite set"))
return
}
if p.Director != nil {
p.Director(outreq)
if outreq.Form != nil {
outreq.URL.RawQuery = cleanQueryParams(outreq.URL.RawQuery)
}
}
outreq.Close = false
reqUpType := upgradeType(outreq.Header)
if !IsPrint(reqUpType) {
p.getErrorHandler()(rw, req, fmt.Errorf("client tried to switch to invalid protocol %q", reqUpType))
return
}
removeHopByHopHeaders(outreq.Header)
// Issue 21096: tell backend applications that care about trailer support
// that we support trailers. (We do, but we don't go out of our way to
// advertise that unless the incoming client request thought it was worth
// mentioning.) Note that we look at req.Header, not outreq.Header, since
// the latter has passed through removeHopByHopHeaders.
if httpguts.HeaderValuesContainsToken(req.Header["Te"], "trailers") {
outreq.Header.Set("Te", "trailers")
}
// After stripping all the hop-by-hop connection headers above, add back any
// necessary for protocol upgrades, such as for websockets.
if reqUpType != "" {
outreq.Header.Set("Connection", "Upgrade")
outreq.Header.Set("Upgrade", reqUpType)
}
if p.Rewrite != nil {
// Strip client-provided forwarding headers.
// The Rewrite func may use SetXForwarded to set new values
// for these or copy the previous values from the inbound request.
outreq.Header.Del("Forwarded")
outreq.Header.Del("X-Forwarded-For")
outreq.Header.Del("X-Forwarded-Host")
outreq.Header.Del("X-Forwarded-Proto")
// Remove unparsable query parameters from the outbound request.
outreq.URL.RawQuery = cleanQueryParams(outreq.URL.RawQuery)
pr := &ProxyRequest{
In: req,
Out: outreq,
}
p.Rewrite(pr)
outreq = pr.Out
}
if _, ok := outreq.Header["User-Agent"]; !ok {
// If the outbound request doesn't have a User-Agent header set,
// don't send the default Go HTTP client User-Agent.
outreq.Header.Set("User-Agent", "")
}
trace := &httptrace.ClientTrace{
Got1xxResponse: func(code int, header textproto.MIMEHeader) error {
h := rw.Header()
copyHeader(h, http.Header(header))
rw.WriteHeader(code)
// Clear headers, it's not automatically done by ResponseWriter.WriteHeader() for 1xx responses
for k := range h {
delete(h, k)
}
return nil
},
}
outreq = outreq.WithContext(httptrace.WithClientTrace(outreq.Context(), trace))
res, err := transport.RoundTrip(outreq)
if err != nil {
p.getErrorHandler()(rw, outreq, err)
return
}
// Deal with 101 Switching Protocols responses: (WebSocket, h2c, etc)
if res.StatusCode == http.StatusSwitchingProtocols {
if !p.modifyResponse(rw, res, outreq) {
return
}
p.handleUpgradeResponse(rw, outreq, res)
return
}
removeHopByHopHeaders(res.Header)
if !p.modifyResponse(rw, res, outreq) {
return
}
copyHeader(rw.Header(), res.Header)
// The "Trailer" header isn't included in the Transport's response,
// at least for *http.Transport. Build it up from Trailer.
announcedTrailers := len(res.Trailer)
if announcedTrailers > 0 {
trailerKeys := make([]string, 0, len(res.Trailer))
for k := range res.Trailer {
trailerKeys = append(trailerKeys, k)
}
rw.Header().Add("Trailer", strings.Join(trailerKeys, ", "))
}
rw.WriteHeader(res.StatusCode)
err = p.copyResponse(rw, res.Body, p.flushInterval(res))
if err != nil {
defer res.Body.Close()
// Since we're streaming the response, if we run into an error all we can do
// is abort the request. Issue 23643: ReverseProxy should use ErrAbortHandler
// on read error while copying body.
if !shouldPanicOnCopyError(req) {
p.logf("suppressing panic for copyResponse error in test; copy error: %v", err)
return
}
panic(http.ErrAbortHandler)
}
res.Body.Close() // close now, instead of defer, to populate res.Trailer
if len(res.Trailer) > 0 {
// Force chunking if we saw a response trailer.
// This prevents net/http from calculating the length for short
// bodies and adding a Content-Length.
if fl, ok := rw.(http.Flusher); ok {
fl.Flush()
}
}
if len(res.Trailer) == announcedTrailers {
copyHeader(rw.Header(), res.Trailer)
return
}
for k, vv := range res.Trailer {
k = http.TrailerPrefix + k
for _, v := range vv {
rw.Header().Add(k, v)
}
}
}
var inOurTests bool // whether we're in our own tests
// shouldPanicOnCopyError reports whether the reverse proxy should
// panic with http.ErrAbortHandler. This is the right thing to do by
// default, but Go 1.10 and earlier did not, so existing unit tests
// weren't expecting panics. Only panic in our own tests, or when
// running under the HTTP server.
func shouldPanicOnCopyError(req *http.Request) bool {
if inOurTests {
// Our tests know to handle this panic.
return true
}
if req.Context().Value(http.ServerContextKey) != nil {
// We seem to be running under an HTTP server, so
// it'll recover the panic.
return true
}
// Otherwise act like Go 1.10 and earlier to not break
// existing tests.
return false
}
// removeHopByHopHeaders removes hop-by-hop headers.
func removeHopByHopHeaders(h http.Header) {
// RFC 7230, section 6.1: Remove headers listed in the "Connection" header.
for _, f := range h["Connection"] {
for _, sf := range strings.Split(f, ",") {
if sf = textproto.TrimString(sf); sf != "" {
h.Del(sf)
}
}
}
// RFC 2616, section 13.5.1: Remove a set of known hop-by-hop headers.
// This behavior is superseded by the RFC 7230 Connection header, but
// preserve it for backwards compatibility.
for _, f := range hopHeaders {
h.Del(f)
}
}
// flushInterval returns the p.FlushInterval value, conditionally
// overriding its value for a specific request/response.
func (p *ReverseProxy) flushInterval(res *http.Response) time.Duration {
resCT := res.Header.Get("Content-Type")
// For Server-Sent Events responses, flush immediately.
// The MIME type is defined in https://www.w3.org/TR/eventsource/#text-event-stream
if baseCT, _, _ := mime.ParseMediaType(resCT); baseCT == "text/event-stream" {
return -1 // negative means immediately
}
// We might have the case of streaming for which Content-Length might be unset.
if res.ContentLength == -1 {
return -1
}
return p.FlushInterval
}
func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader, flushInterval time.Duration) error {
if flushInterval != 0 {
if wf, ok := dst.(writeFlusher); ok {
mlw := &maxLatencyWriter{
dst: wf,
latency: flushInterval,
}
defer mlw.stop()
// set up initial timer so headers get flushed even if body writes are delayed
mlw.flushPending = true
mlw.t = time.AfterFunc(flushInterval, mlw.delayedFlush)
dst = mlw
}
}
var buf []byte
if p.BufferPool != nil {
buf = p.BufferPool.Get()
defer p.BufferPool.Put(buf)
}
_, err := p.copyBuffer(dst, src, buf)
return err
}
// copyBuffer returns any write errors or non-EOF read errors, and the amount
// of bytes written.
func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
if len(buf) == 0 {
buf = make([]byte, 32*1024)
}
var written int64
for {
nr, rerr := src.Read(buf)
if rerr != nil && rerr != io.EOF && rerr != context.Canceled {
p.logf("httputil: ReverseProxy read error during body copy: %v", rerr)
}
if nr > 0 {
nw, werr := dst.Write(buf[:nr])
if nw > 0 {
written += int64(nw)
}
if werr != nil {
return written, werr
}
if nr != nw {
return written, io.ErrShortWrite
}
}
if rerr != nil {
if rerr == io.EOF {
rerr = nil
}
return written, rerr
}
}
}
func (p *ReverseProxy) logf(format string, args ...any) {
if p.ErrorLog != nil {
p.ErrorLog.Printf(format, args...)
} else {
log.Printf(format, args...)
}
}
type writeFlusher interface {
io.Writer
http.Flusher
}
type maxLatencyWriter struct {
dst writeFlusher
latency time.Duration // non-zero; negative means to flush immediately
mu sync.Mutex // protects t, flushPending, and dst.Flush
t *time.Timer
flushPending bool
}
func (m *maxLatencyWriter) Write(p []byte) (n int, err error) {
m.mu.Lock()
defer m.mu.Unlock()
n, err = m.dst.Write(p)
if m.latency < 0 {
m.dst.Flush()
return
}
if m.flushPending {
return
}
if m.t == nil {
m.t = time.AfterFunc(m.latency, m.delayedFlush)
} else {
m.t.Reset(m.latency)
}
m.flushPending = true
return
}
func (m *maxLatencyWriter) delayedFlush() {
m.mu.Lock()
defer m.mu.Unlock()
if !m.flushPending { // if stop was called but AfterFunc already started this goroutine
return
}
m.dst.Flush()
m.flushPending = false
}
func (m *maxLatencyWriter) stop() {
m.mu.Lock()
defer m.mu.Unlock()
m.flushPending = false
if m.t != nil {
m.t.Stop()
}
}
func upgradeType(h http.Header) string {
if !httpguts.HeaderValuesContainsToken(h["Connection"], "Upgrade") {
return ""
}
return h.Get("Upgrade")
}
func (p *ReverseProxy) handleUpgradeResponse(rw http.ResponseWriter, req *http.Request, res *http.Response) {
reqUpType := upgradeType(req.Header)
resUpType := upgradeType(res.Header)
if !IsPrint(resUpType) { // We know reqUpType is ASCII, it's checked by the caller.
p.getErrorHandler()(rw, req, fmt.Errorf("backend tried to switch to invalid protocol %q", resUpType))
}
if !EqualFold(reqUpType, resUpType) {
p.getErrorHandler()(rw, req, fmt.Errorf("backend tried to switch protocol %q when %q was requested", resUpType, reqUpType))
return
}
hj, ok := rw.(http.Hijacker)
if !ok {
p.getErrorHandler()(rw, req, fmt.Errorf("can't switch protocols using non-Hijacker ResponseWriter type %T", rw))
return
}
backConn, ok := res.Body.(io.ReadWriteCloser)
if !ok {
p.getErrorHandler()(rw, req, fmt.Errorf("internal error: 101 switching protocols response with non-writable body"))
return
}
backConnCloseCh := make(chan bool)
go func() {
// Ensure that the cancellation of a request closes the backend.
// See issue https://golang.org/issue/35559.
select {
case <-req.Context().Done():
case <-backConnCloseCh:
}
backConn.Close()
}()
defer close(backConnCloseCh)
conn, brw, err := hj.Hijack()
if err != nil {
p.getErrorHandler()(rw, req, fmt.Errorf("Hijack failed on protocol switch: %v", err))
return
}
defer conn.Close()
copyHeader(rw.Header(), res.Header)
res.Header = rw.Header()
res.Body = nil // so res.Write only writes the headers; we have res.Body in backConn above
if err := res.Write(brw); err != nil {
p.getErrorHandler()(rw, req, fmt.Errorf("response write: %v", err))
return
}
if err := brw.Flush(); err != nil {
p.getErrorHandler()(rw, req, fmt.Errorf("response flush: %v", err))
return
}
errc := make(chan error, 1)
spc := switchProtocolCopier{user: conn, backend: backConn}
go spc.copyToBackend(errc)
go spc.copyFromBackend(errc)
<-errc
}
// switchProtocolCopier exists so goroutines proxying data back and
// forth have nice names in stacks.
type switchProtocolCopier struct {
user, backend io.ReadWriter
}
func (c switchProtocolCopier) copyFromBackend(errc chan<- error) {
_, err := io.Copy(c.user, c.backend)
errc <- err
}
func (c switchProtocolCopier) copyToBackend(errc chan<- error) {
_, err := io.Copy(c.backend, c.user)
errc <- err
}
func cleanQueryParams(s string) string {
reencode := func(s string) string {
v, _ := url.ParseQuery(s)
return v.Encode()
}
for i := 0; i < len(s); {
switch s[i] {
case ';':
return reencode(s)
case '%':
if i+2 >= len(s) || !ishex(s[i+1]) || !ishex(s[i+2]) {
return reencode(s)
}
i += 3
default:
i++
}
}
return s
}
func ishex(c byte) bool {
switch {
case '0' <= c && c <= '9':
return true
case 'a' <= c && c <= 'f':
return true
case 'A' <= c && c <= 'F':
return true
}
return false
}