/*
Copyright 2016 The Kubernetes Authors.

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 filters

import (
	"bufio"
	"context"
	"encoding/json"
	"fmt"
	"net"
	"net/http"
	"runtime"
	"sync"
	"time"

	apierrors "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apiserver/pkg/endpoints/metrics"
	apirequest "k8s.io/apiserver/pkg/endpoints/request"
)

var errConnKilled = fmt.Errorf("killing connection/stream because serving request timed out and response had been started")

// WithTimeoutForNonLongRunningRequests times out non-long-running requests after the time given by timeout.
func WithTimeoutForNonLongRunningRequests(handler http.Handler, longRunning apirequest.LongRunningRequestCheck, timeout time.Duration) http.Handler {
	if longRunning == nil {
		return handler
	}
	timeoutFunc := func(req *http.Request) (*http.Request, <-chan time.Time, func(), *apierrors.StatusError) {
		// TODO unify this with apiserver.MaxInFlightLimit
		ctx := req.Context()

		requestInfo, ok := apirequest.RequestInfoFrom(ctx)
		if !ok {
			// if this happens, the handler chain isn't setup correctly because there is no request info
			return req, time.After(timeout), func() {}, apierrors.NewInternalError(fmt.Errorf("no request info found for request during timeout"))
		}

		if longRunning(req, requestInfo) {
			return req, nil, nil, nil
		}

		ctx, cancel := context.WithCancel(ctx)
		req = req.WithContext(ctx)

		postTimeoutFn := func() {
			cancel()
			metrics.Record(req, requestInfo, metrics.APIServerComponent, "", http.StatusGatewayTimeout, 0, 0)
		}
		return req, time.After(timeout), postTimeoutFn, apierrors.NewTimeoutError(fmt.Sprintf("request did not complete within %s", timeout), 0)
	}
	return WithTimeout(handler, timeoutFunc)
}

type timeoutFunc = func(*http.Request) (req *http.Request, timeout <-chan time.Time, postTimeoutFunc func(), err *apierrors.StatusError)

// WithTimeout returns an http.Handler that runs h with a timeout
// determined by timeoutFunc. The new http.Handler calls h.ServeHTTP to handle
// each request, but if a call runs for longer than its time limit, the
// handler responds with a 504 Gateway Timeout error and the message
// provided. (If msg is empty, a suitable default message will be sent.) After
// the handler times out, writes by h to its http.ResponseWriter will return
// http.ErrHandlerTimeout. If timeoutFunc returns a nil timeout channel, no
// timeout will be enforced. recordFn is a function that will be invoked whenever
// a timeout happens.
func WithTimeout(h http.Handler, timeoutFunc timeoutFunc) http.Handler {
	return &timeoutHandler{h, timeoutFunc}
}

type timeoutHandler struct {
	handler http.Handler
	timeout timeoutFunc
}

func (t *timeoutHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	r, after, postTimeoutFn, err := t.timeout(r)
	if after == nil {
		t.handler.ServeHTTP(w, r)
		return
	}

	// resultCh is used as both errCh and stopCh
	resultCh := make(chan interface{})
	tw := newTimeoutWriter(w)
	go func() {
		defer func() {
			err := recover()
			if err != nil {
				// Same as stdlib http server code. Manually allocate stack
				// trace buffer size to prevent excessively large logs
				const size = 64 << 10
				buf := make([]byte, size)
				buf = buf[:runtime.Stack(buf, false)]
				err = fmt.Sprintf("%v\n%s", err, buf)
			}
			resultCh <- err
		}()
		t.handler.ServeHTTP(tw, r)
	}()
	select {
	case err := <-resultCh:
		// panic if error occurs; stop otherwise
		if err != nil {
			panic(err)
		}
		return
	case <-after:
		postTimeoutFn()
		tw.timeout(err)
	}
}

type timeoutWriter interface {
	http.ResponseWriter
	timeout(*apierrors.StatusError)
}

func newTimeoutWriter(w http.ResponseWriter) timeoutWriter {
	base := &baseTimeoutWriter{w: w}

	_, notifiable := w.(http.CloseNotifier)
	_, hijackable := w.(http.Hijacker)

	switch {
	case notifiable && hijackable:
		return &closeHijackTimeoutWriter{base}
	case notifiable:
		return &closeTimeoutWriter{base}
	case hijackable:
		return &hijackTimeoutWriter{base}
	default:
		return base
	}
}

type baseTimeoutWriter struct {
	w http.ResponseWriter

	mu sync.Mutex
	// if the timeout handler has timeout
	timedOut bool
	// if this timeout writer has wrote header
	wroteHeader bool
	// if this timeout writer has been hijacked
	hijacked bool
}

func (tw *baseTimeoutWriter) Header() http.Header {
	tw.mu.Lock()
	defer tw.mu.Unlock()

	if tw.timedOut {
		return http.Header{}
	}

	return tw.w.Header()
}

func (tw *baseTimeoutWriter) Write(p []byte) (int, error) {
	tw.mu.Lock()
	defer tw.mu.Unlock()

	if tw.timedOut {
		return 0, http.ErrHandlerTimeout
	}
	if tw.hijacked {
		return 0, http.ErrHijacked
	}

	tw.wroteHeader = true
	return tw.w.Write(p)
}

func (tw *baseTimeoutWriter) Flush() {
	tw.mu.Lock()
	defer tw.mu.Unlock()

	if tw.timedOut {
		return
	}

	if flusher, ok := tw.w.(http.Flusher); ok {
		flusher.Flush()
	}
}

func (tw *baseTimeoutWriter) WriteHeader(code int) {
	tw.mu.Lock()
	defer tw.mu.Unlock()

	if tw.timedOut || tw.wroteHeader || tw.hijacked {
		return
	}

	tw.wroteHeader = true
	tw.w.WriteHeader(code)
}

func (tw *baseTimeoutWriter) timeout(err *apierrors.StatusError) {
	tw.mu.Lock()
	defer tw.mu.Unlock()

	tw.timedOut = true

	// The timeout writer has not been used by the inner handler.
	// We can safely timeout the HTTP request by sending by a timeout
	// handler
	if !tw.wroteHeader && !tw.hijacked {
		tw.w.WriteHeader(http.StatusGatewayTimeout)
		enc := json.NewEncoder(tw.w)
		enc.Encode(&err.ErrStatus)
	} else {
		// The timeout writer has been used by the inner handler. There is
		// no way to timeout the HTTP request at the point. We have to shutdown
		// the connection for HTTP1 or reset stream for HTTP2.
		//
		// Note from: Brad Fitzpatrick
		// if the ServeHTTP goroutine panics, that will do the best possible thing for both
		// HTTP/1 and HTTP/2. In HTTP/1, assuming you're replying with at least HTTP/1.1 and
		// you've already flushed the headers so it's using HTTP chunking, it'll kill the TCP
		// connection immediately without a proper 0-byte EOF chunk, so the peer will recognize
		// the response as bogus. In HTTP/2 the server will just RST_STREAM the stream, leaving
		// the TCP connection open, but resetting the stream to the peer so it'll have an error,
		// like the HTTP/1 case.
		panic(errConnKilled)
	}
}

func (tw *baseTimeoutWriter) closeNotify() <-chan bool {
	tw.mu.Lock()
	defer tw.mu.Unlock()

	if tw.timedOut {
		done := make(chan bool)
		close(done)
		return done
	}

	return tw.w.(http.CloseNotifier).CloseNotify()
}

func (tw *baseTimeoutWriter) hijack() (net.Conn, *bufio.ReadWriter, error) {
	tw.mu.Lock()
	defer tw.mu.Unlock()

	if tw.timedOut {
		return nil, nil, http.ErrHandlerTimeout
	}
	conn, rw, err := tw.w.(http.Hijacker).Hijack()
	if err == nil {
		tw.hijacked = true
	}
	return conn, rw, err
}

type closeTimeoutWriter struct {
	*baseTimeoutWriter
}

func (tw *closeTimeoutWriter) CloseNotify() <-chan bool {
	return tw.closeNotify()
}

type hijackTimeoutWriter struct {
	*baseTimeoutWriter
}

func (tw *hijackTimeoutWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	return tw.hijack()
}

type closeHijackTimeoutWriter struct {
	*baseTimeoutWriter
}

func (tw *closeHijackTimeoutWriter) CloseNotify() <-chan bool {
	return tw.closeNotify()
}

func (tw *closeHijackTimeoutWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	return tw.hijack()
}
