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// 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.

// Package fcgi implements the FastCGI protocol.
// Currently only the responder role is supported.
// The protocol is defined at http://www.fastcgi.com/drupal/node/6?q=node/22
package fcgi

// This file defines the raw protocol and some utilities used by the child and
// the host.

import (
        "bufio"
        "bytes"
        "encoding/binary"
        "errors"
        "io"
        "sync"
)

// recType is a record type, as defined by
// http://www.fastcgi.com/devkit/doc/fcgi-spec.html#S8
type recType uint8

const (
        typeBeginRequest    recType = 1
        typeAbortRequest    recType = 2
        typeEndRequest      recType = 3
        typeParams          recType = 4
        typeStdin           recType = 5
        typeStdout          recType = 6
        typeStderr          recType = 7
        typeData            recType = 8
        typeGetValues       recType = 9
        typeGetValuesResult recType = 10
        typeUnknownType     recType = 11
)

// keep the connection between web-server and responder open after request
const flagKeepConn = 1

const (
        maxWrite = 65535 // maximum record body
        maxPad   = 255
)

const (
        roleResponder = iota + 1 // only Responders are implemented.
        roleAuthorizer
        roleFilter
)

const (
        statusRequestComplete = iota
        statusCantMultiplex
        statusOverloaded
        statusUnknownRole
)

const headerLen = 8

type header struct {
        Version       uint8
        Type          recType
        Id            uint16
        ContentLength uint16
        PaddingLength uint8
        Reserved      uint8
}

type beginRequest struct {
        role     uint16
        flags    uint8
        reserved [5]uint8
}

func (br *beginRequest) read(content []byte) error {
        if len(content) != 8 {
                return errors.New("fcgi: invalid begin request record")
        }
        br.role = binary.BigEndian.Uint16(content)
        br.flags = content[2]
        return nil
}

// for padding so we don't have to allocate all the time
// not synchronized because we don't care what the contents are
var pad [maxPad]byte

func (h *header) init(recType recType, reqId uint16, contentLength int) {
        h.Version = 1
        h.Type = recType
        h.Id = reqId
        h.ContentLength = uint16(contentLength)
        h.PaddingLength = uint8(-contentLength & 7)
}

// conn sends records over rwc
type conn struct {
        mutex sync.Mutex
        rwc   io.ReadWriteCloser

        // to avoid allocations
        buf bytes.Buffer
        h   header
}

func newConn(rwc io.ReadWriteCloser) *conn {
        return &conn{rwc: rwc}
}

func (c *conn) Close() error {
        c.mutex.Lock()
        defer c.mutex.Unlock()
        return c.rwc.Close()
}

type record struct {
        h   header
        buf [maxWrite + maxPad]byte
}

func (rec *record) read(r io.Reader) (err error) {
        if err = binary.Read(r, binary.BigEndian, &rec.h); err != nil {
                return err
        }
        if rec.h.Version != 1 {
                return errors.New("fcgi: invalid header version")
        }
        n := int(rec.h.ContentLength) + int(rec.h.PaddingLength)
        if _, err = io.ReadFull(r, rec.buf[:n]); err != nil {
                return err
        }
        return nil
}

func (r *record) content() []byte {
        return r.buf[:r.h.ContentLength]
}

// writeRecord writes and sends a single record.
func (c *conn) writeRecord(recType recType, reqId uint16, b []byte) error {
        c.mutex.Lock()
        defer c.mutex.Unlock()
        c.buf.Reset()
        c.h.init(recType, reqId, len(b))
        if err := binary.Write(&c.buf, binary.BigEndian, c.h); err != nil {
                return err
        }
        if _, err := c.buf.Write(b); err != nil {
                return err
        }
        if _, err := c.buf.Write(pad[:c.h.PaddingLength]); err != nil {
                return err
        }
        _, err := c.rwc.Write(c.buf.Bytes())
        return err
}

func (c *conn) writeBeginRequest(reqId uint16, role uint16, flags uint8) error {
        b := [8]byte{byte(role >> 8), byte(role), flags}
        return c.writeRecord(typeBeginRequest, reqId, b[:])
}

func (c *conn) writeEndRequest(reqId uint16, appStatus int, protocolStatus uint8) error {
        b := make([]byte, 8)
        binary.BigEndian.PutUint32(b, uint32(appStatus))
        b[4] = protocolStatus
        return c.writeRecord(typeEndRequest, reqId, b)
}

func (c *conn) writePairs(recType recType, reqId uint16, pairs map[string]string) error {
        w := newWriter(c, recType, reqId)
        b := make([]byte, 8)
        for k, v := range pairs {
                n := encodeSize(b, uint32(len(k)))
                n += encodeSize(b[n:], uint32(len(v)))
                if _, err := w.Write(b[:n]); err != nil {
                        return err
                }
                if _, err := w.WriteString(k); err != nil {
                        return err
                }
                if _, err := w.WriteString(v); err != nil {
                        return err
                }
        }
        w.Close()
        return nil
}

func readSize(s []byte) (uint32, int) {
        if len(s) == 0 {
                return 0, 0
        }
        size, n := uint32(s[0]), 1
        if size&(1<<7) != 0 {
                if len(s) < 4 {
                        return 0, 0
                }
                n = 4
                size = binary.BigEndian.Uint32(s)
                size &^= 1 << 31
        }
        return size, n
}

func readString(s []byte, size uint32) string {
        if size > uint32(len(s)) {
                return ""
        }
        return string(s[:size])
}

func encodeSize(b []byte, size uint32) int {
        if size > 127 {
                size |= 1 << 31
                binary.BigEndian.PutUint32(b, size)
                return 4
        }
        b[0] = byte(size)
        return 1
}

// bufWriter encapsulates bufio.Writer but also closes the underlying stream when
// Closed.
type bufWriter struct {
        closer io.Closer
        *bufio.Writer
}

func (w *bufWriter) Close() error {
        if err := w.Writer.Flush(); err != nil {
                w.closer.Close()
                return err
        }
        return w.closer.Close()
}

func newWriter(c *conn, recType recType, reqId uint16) *bufWriter {
        s := &streamWriter{c: c, recType: recType, reqId: reqId}
        w := bufio.NewWriterSize(s, maxWrite)
        return &bufWriter{s, w}
}

// streamWriter abstracts out the separation of a stream into discrete records.
// It only writes maxWrite bytes at a time.
type streamWriter struct {
        c       *conn
        recType recType
        reqId   uint16
}

func (w *streamWriter) Write(p []byte) (int, error) {
        nn := 0
        for len(p) > 0 {
                n := len(p)
                if n > maxWrite {
                        n = maxWrite
                }
                if err := w.c.writeRecord(w.recType, w.reqId, p[:n]); err != nil {
                        return nn, err
                }
                nn += n
                p = p[n:]
        }
        return nn, nil
}

func (w *streamWriter) Close() error {
        // send empty record to close the stream
        return w.c.writeRecord(w.recType, w.reqId, nil)
}