package nhttp

import (
	"bufio"
	"context"
	"errors"
	"fmt"
	"io"
	"math"
	"net"
	_http "net/http"
	"net/url"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"golang.org/x/net/http/httpguts"
)

type connReader struct {
	conn *conn

	mu      sync.Mutex // guards following
	hasByte bool
	byteBuf [1]byte
	cond    *sync.Cond
	inRead  bool
	aborted bool  // set true before conn.rwc deadline is set to past
	remain  int64 // bytes remaining
}

// aLongTimeAgo is a non-zero time, far in the past, used for
// immediate cancellation of network operations.
var aLongTimeAgo = time.Unix(1, 0)

func (cr *connReader) lock() {
	cr.mu.Lock()
	if cr.cond == nil {
		cr.cond = sync.NewCond(&cr.mu)
	}
}

func (cr *connReader) unlock() { cr.mu.Unlock() }

func (cr *connReader) abortPendingRead() {
	cr.lock()
	defer cr.unlock()
	if !cr.inRead {
		return
	}
	cr.aborted = true
	cr.conn.rwc.SetReadDeadline(aLongTimeAgo)
	for cr.inRead {
		cr.cond.Wait()
	}
	cr.conn.rwc.SetReadDeadline(time.Time{})
}

func (cr *connReader) startBackgroundRead() {
	cr.lock()
	defer cr.unlock()
	if cr.inRead {
		panic("invalid concurrent Body.Read call")
	}
	if cr.hasByte {
		return
	}
	cr.inRead = true
	cr.conn.rwc.SetReadDeadline(time.Time{})
	go cr.backgroundRead()
}

func (cr *connReader) backgroundRead() {
	n, err := cr.conn.rwc.Read(cr.byteBuf[:])
	cr.lock()
	if n == 1 {
		cr.hasByte = true
		// We were past the end of the previous request's body already
		// (since we wouldn't be in a background read otherwise), so
		// this is a pipelined HTTP request. Prior to Go 1.11 we used to
		// send on the CloseNotify channel and cancel the context here,
		// but the behavior was documented as only "may", and we only
		// did that because that's how CloseNotify accidentally behaved
		// in very early Go releases prior to context support. Once we
		// added context support, people used a Handler's
		// Request.Context() and passed it along. Having that context
		// cancel on pipelined HTTP requests caused problems.
		// Fortunately, almost nothing uses HTTP/1.x pipelining.
		// Unfortunately, apt-get does, or sometimes does.
		// New Go 1.11 behavior: don't fire CloseNotify or cancel
		// contexts on pipelined requests. Shouldn't affect people, but
		// fixes cases like Issue 23921. This does mean that a client
		// closing their TCP connection after sending a pipelined
		// request won't cancel the context, but we'll catch that on any
		// write failure (in checkConnErrorWriter.Write).
		// If the server never writes, yes, there are still contrived
		// server & client behaviors where this fails to ever cancel the
		// context, but that's kinda why HTTP/1.x pipelining died
		// anyway.
	}
	if ne, ok := err.(net.Error); ok && cr.aborted && ne.Timeout() {
		// Ignore this error. It's the expected error from
		// another goroutine calling abortPendingRead.
	} else if err != nil {
		cr.handleReadError(err)
	}
	cr.aborted = false
	cr.inRead = false
	cr.unlock()
	cr.cond.Broadcast()
}

func (cr *connReader) handleReadError(_ error) {
	cr.conn.cancelCtx()
	cr.closeNotify()
}

// may be called from multiple goroutines.
func (cr *connReader) closeNotify() {
	res := cr.conn.curReq.Load()
	if res != nil && atomic.CompareAndSwapInt32(&res.didCloseNotify, 0, 1) {
		res.closeNotifyCh <- true
	}
}

func (cr *connReader) Read(p []byte) (n int, err error) {
	cr.lock()

	if cr.hitReadLimit() {
		cr.unlock()
		return 0, io.EOF
	}
	if len(p) == 0 {
		cr.unlock()
		return 0, nil
	}
	if int64(len(p)) > cr.remain {
		p = p[:cr.remain]
	}
	if cr.hasByte {
		p[0] = cr.byteBuf[0]
		cr.hasByte = false
		cr.unlock()
		return 1, nil
	}
	cr.inRead = true
	cr.unlock()
	n, err = cr.conn.rwc.Read(p)

	cr.lock()
	cr.inRead = false
	if err != nil {
		cr.handleReadError(err)
	}
	cr.remain -= int64(n)
	cr.unlock()

	cr.cond.Broadcast()
	return n, err
}

func (cr *connReader) setReadLimit(remain int64) { cr.remain = remain }
func (cr *connReader) setInfiniteReadLimit()     { cr.remain = math.MaxInt64 }
func (cr *connReader) hitReadLimit() bool        { return cr.remain <= 0 }

// chunkWriter writes to a response's conn buffer, and is the writer
// wrapped by the response.w buffered writer.
//
// chunkWriter also is responsible for finalizing the Header, including
// conditionally setting the Content-Type and setting a Content-Length
// in cases where the handler's final output is smaller than the buffer
// size. It also conditionally adds chunk headers, when in chunking mode.
//
// See the comment above (*response).Write for the entire write flow.
type chunkWriter struct {
	res *response

	// header is either nil or a deep clone of res.handlerHeader
	// at the time of res.writeHeader, if res.writeHeader is
	// called and extra buffering is being done to calculate
	// Content-Type and/or Content-Length.
	header _http.Header

	// wroteHeader tells whether the header's been written to "the
	// wire" (or rather: w.conn.buf). this is unlike
	// (*response).wroteHeader, which tells only whether it was
	// logically written.
	wroteHeader bool

	// set by the writeHeader method:
	chunking bool // using chunked transfer encoding for reply body
}

// TimeFormat is the time format to use when generating times in HTTP
// headers. It is like time.RFC1123 but hard-codes GMT as the time
// zone. The time being formatted must be in UTC for Format to
// generate the correct format.
//
// For parsing this time format, see ParseTime.
const TimeFormat = "Mon, 02 Jan 2006 15:04:05 GMT"

// A response represents the server side of an HTTP response.
type response struct {
	conn             *conn
	req              *_http.Request // request for this response
	reqBody          io.ReadCloser
	cancelCtx        context.CancelFunc // when ServeHTTP exits
	wroteHeader      bool               // a non-1xx header has been (logically) written
	wroteContinue    bool               // 100 Continue response was written
	wants10KeepAlive bool               // HTTP/1.0 w/ Connection "keep-alive"
	wantsClose       bool               // HTTP request has Connection "close"

	// canWriteContinue is a boolean value accessed as an atomic int32
	// that says whether or not a 100 Continue header can be written
	// to the connection.
	// writeContinueMu must be held while writing the header.
	// These two fields together synchronize the body reader
	// (the expectContinueReader, which wants to write 100 Continue)
	// against the main writer.
	canWriteContinue atomicBool
	writeContinueMu  sync.Mutex

	w  *bufio.Writer // buffers output in chunks to chunkWriter
	cw chunkWriter

	// handlerHeader is the Header that Handlers get access to,
	// which may be retained and mutated even after WriteHeader.
	// handlerHeader is copied into cw.header at WriteHeader
	// time, and privately mutated thereafter.
	handlerHeader _http.Header
	calledHeader  bool // handler accessed handlerHeader via Header

	written       int64 // number of bytes written in body
	contentLength int64 // explicitly-declared Content-Length; or -1
	status        int   // status code passed to WriteHeader

	// close connection after this reply.  set on request and
	// updated after response from handler if there's a
	// "Connection: keep-alive" response header and a
	// Content-Length.
	closeAfterReply bool

	// requestBodyLimitHit is set by requestTooLarge when
	// maxBytesReader hits its max size. It is checked in
	// WriteHeader, to make sure we don't consume the
	// remaining request body to try to advance to the next HTTP
	// request. Instead, when this is set, we stop reading
	// subsequent requests on this connection and stop reading
	// input from it.
	requestBodyLimitHit bool

	// trailers are the headers to be sent after the handler
	// finishes writing the body. This field is initialized from
	// the Trailer response header when the response header is
	// written.
	trailers []string

	handlerDone atomicBool // set true when the handler exits

	// Buffers for Date, Content-Length, and status code
	dateBuf   [len(TimeFormat)]byte
	clenBuf   [10]byte
	statusBuf [3]byte

	// closeNotifyCh is the channel returned by CloseNotify.
	// TODO(bradfitz): this is currently (for Go 1.8) always
	// non-nil. Make this lazily-created again as it used to be?
	closeNotifyCh  chan bool
	didCloseNotify int32 // atomic (only 0->1 winner should send)
}

// http1ServerSupportsRequest reports whether Go's HTTP/1.x server
// supports the given request.
func http1ServerSupportsRequest(req *_http.Request) bool {
	if req.ProtoMajor == 1 {
		return true
	}
	// Accept "PRI * HTTP/2.0" upgrade requests, so Handlers can
	// wire up their own HTTP/2 upgrades.
	if req.ProtoMajor == 2 && req.ProtoMinor == 0 &&
		req.Method == "PRI" && req.RequestURI == "*" {
		return true
	}
	// Reject HTTP/0.x, and all other HTTP/2+ requests (which
	// aren't encoded in ASCII anyway).
	return false
}

var errTooLarge = errors.New("nhttp: request too large")

// Read next request from connection.
func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
	var (
		wholeReqDeadline time.Time // or zero if none
		hdrDeadline      time.Time // or zero if none
	)

	c.r.setReadLimit(c.server.initialReadLimitSize())
	if c.lastMethod == "POST" {
		// RFC 7230 section 3 tolerance for old buggy clients.
		peek, _ := c.bufr.Peek(4) // ReadRequest will get err below
		c.bufr.Discard(numLeadingCRorLF(peek))
	}
	req, err := readRequest(c.bufr)
	if err != nil {
		if c.r.hitReadLimit() {
			return nil, errTooLarge
		}
		return nil, err
	}

	if !http1ServerSupportsRequest(req) {
		return nil, errors.New("unsupported protocol version")
	}

	c.lastMethod = req.Method
	c.r.setInfiniteReadLimit()

	hosts, haveHost := req.Header["Host"]
	if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) && req.Method != "CONNECT" {
		return nil, errors.New("missing required Host header")
	}
	if len(hosts) == 1 && !httpguts.ValidHostHeader(hosts[0]) {
		return nil, errors.New("malformed Host header")
	}
	for k, vv := range req.Header {
		if !httpguts.ValidHeaderFieldName(k) {
			return nil, errors.New("invalid header name")
		}
		for _, v := range vv {
			if !httpguts.ValidHeaderFieldValue(v) {
				return nil, errors.New("invalid header value")
			}
		}
	}
	delete(req.Header, "Host")

	ctx, cancelCtx := context.WithCancel(ctx)
	req = req.WithContext(ctx)
	req.RemoteAddr = c.remoteAddr
	req.TLS = c.tlsState
	if body, ok := req.Body.(*body); ok {
		body.doEarlyClose = true
	}

	// Adjust the read deadline if necessary.
	if !hdrDeadline.Equal(wholeReqDeadline) {
		c.rwc.SetReadDeadline(wholeReqDeadline)
	}

	w = &response{
		conn:          c,
		cancelCtx:     cancelCtx,
		req:           req,
		reqBody:       req.Body,
		handlerHeader: make(_http.Header),
		contentLength: -1,
		closeNotifyCh: make(chan bool, 1),

		// We populate these ahead of time so we're not
		// reading from req.Header after their Handler starts
		// and maybe mutates it (Issue 14940)
		wants10KeepAlive: wantsHttp10KeepAlive(req),
		wantsClose:       wantsClose(req),
	}

	w.cw.res = w
	w.w = newBufioWriterSize(&w.cw, 2048)
	return w, nil
}

func wantsHttp10KeepAlive(r *_http.Request) bool {
	if r.ProtoMajor != 1 || r.ProtoMinor != 0 {
		return false
	}
	return hasToken(r.Header.Get("Connection"), "keep-alive")
}

func wantsClose(r *_http.Request) bool {
	if r.Close {
		return true
	}
	return hasToken(r.Header.Get("Connection"), "close")
}

func readRequest(b *bufio.Reader) (req *_http.Request, err error) {
	tp := newTextprotoReader(b)
	req = new(_http.Request)

	// First line: GET /index.html HTTP/1.0
	var s string
	if s, err = tp.ReadLine(); err != nil {
		return nil, err
	}
	defer func() {
		putTextprotoReader(tp)
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
	}()

	var ok bool
	req.Method, req.RequestURI, req.Proto, ok = parseRequestLine(s)
	if !ok {
		return nil, errors.New("malformed HTTP request")
	}

	rawurl := req.RequestURI
	if req.ProtoMajor, req.ProtoMinor, ok = _http.ParseHTTPVersion(req.Proto); !ok {
		return nil, errors.New("malformed HTTP version")
	}

	// CONNECT requests are used two different ways, and neither uses a full URL:
	// The standard use is to tunnel HTTPS through an HTTP proxy.
	// It looks like "CONNECT www.google.com:443 HTTP/1.1", and the parameter is
	// just the authority section of a URL. This information should go in req.URL.Host.
	//
	// The net/rpc package also uses CONNECT, but there the parameter is a path
	// that starts with a slash. It can be parsed with the regular URL parser,
	// and the path will end up in req.URL.Path, where it needs to be in order for
	// RPC to work.
	justAuthority := req.Method == "CONNECT" && !strings.HasPrefix(rawurl, "/")
	if justAuthority {
		//goland:noinspection ALL
		rawurl = "http://" + rawurl
	}

	if req.URL, err = url.ParseRequestURI(rawurl); err != nil {
		return nil, err
	}

	if justAuthority {
		// Strip the bogus "nhttp://" back off.
		req.URL.Scheme = ""
	}

	// Subsequent lines: Key: value.
	mimeHeader, err := tp.ReadMIMEHeader()
	if err != nil {
		return nil, err
	}
	req.Header = _http.Header(mimeHeader)

	// RFC 7230, section 5.3: Must treat
	//	GET /index.html HTTP/1.1
	//	Host: www.google.com
	// and
	//	GET http://www.google.com/index.html HTTP/1.1
	//	Host: doesntmatter
	// the same. In the second case, any Host line is ignored.
	req.Host = req.URL.Host
	if req.Host == "" {
		req.Host = req.Header.Get("Host")
	}

	fixPragmaCacheControl(req.Header)

	req.Close = shouldClose(req.ProtoMajor, req.ProtoMinor, req.Header, false)

	err = readTransfer(req, b)
	if err != nil {
		return nil, err
	}

	return req, nil
}

// parseRequestLine parses "GET /foo HTTP/1.1" into its three parts.
func parseRequestLine(line string) (method, requestURI, proto string, ok bool) {
	method, rest, ok1 := strings.Cut(line, " ")
	requestURI, proto, ok2 := strings.Cut(rest, " ")
	if !ok1 || !ok2 {
		return "", "", "", false
	}
	return method, requestURI, proto, true
}

func expectsContinue(r *_http.Request) bool {
	return hasToken(r.Header.Get("Expect"), "100-continue")
}

// requestBodyRemains reports whether future calls to Read
// on rc might yield more data.
func requestBodyRemains(rc io.ReadCloser) bool {
	if rc == NoBody {
		return false
	}
	switch v := rc.(type) {
	case *expectContinueReader:
		return requestBodyRemains(v.readCloser)
	case *body:
		return v.bodyRemains()
	default:
		panic("unexpected type " + fmt.Sprintf("%T", rc))
	}
}

func registerOnHitEOF(rc io.ReadCloser, fn func()) {
	switch v := rc.(type) {
	case *expectContinueReader:
		registerOnHitEOF(v.readCloser, fn)
	case *body:
		v.registerOnHitEOF(fn)
	default:
		panic("unexpected type " + fmt.Sprintf("%T", rc))
	}
}