Enables mssql support (#383)

* Enables mssql support

Port of dlobs work in gogs.
Enables options in index.js
Enables MSSQL as a database option in go.
Sets ID to 0 on initial migration. Required for
MSSQL insert statements.

Signed-off-by: Beau Trepp <beautrepp@gmail.com>

* Vendors in denisenkom/go-mssqldb

Includes golang.org/x/crypto/md4
as this is required by go-msssqldb

Signed-off-by: Beau Trepp <beautrepp@gmail.com>

vendor/github.com/denisenkom/go-mssqldb/buf.go

@@ -0,0 +1,222 @@
+package mssql
+
+import (
+	"encoding/binary"
+	"io"
+	"errors"
+)
+
+type header struct {
+	PacketType uint8
+	Status     uint8
+	Size       uint16
+	Spid       uint16
+	PacketNo   uint8
+	Pad        uint8
+}
+
+type tdsBuffer struct {
+	buf         []byte
+	pos         uint16
+	transport   io.ReadWriteCloser
+	size        uint16
+	final       bool
+	packet_type uint8
+	afterFirst  func()
+}
+
+func newTdsBuffer(bufsize int, transport io.ReadWriteCloser) *tdsBuffer {
+	buf := make([]byte, bufsize)
+	w := new(tdsBuffer)
+	w.buf = buf
+	w.pos = 8
+	w.transport = transport
+	w.size = 0
+	return w
+}
+
+func (w *tdsBuffer) flush() (err error) {
+	// writing packet size
+	binary.BigEndian.PutUint16(w.buf[2:], w.pos)
+
+	// writing packet into underlying transport
+	if _, err = w.transport.Write(w.buf[:w.pos]); err != nil {
+		return err
+	}
+
+	// execute afterFirst hook if it is set
+	if w.afterFirst != nil {
+		w.afterFirst()
+		w.afterFirst = nil
+	}
+
+	w.pos = 8
+	// packet number
+	w.buf[6] += 1
+	return nil
+}
+
+func (w *tdsBuffer) Write(p []byte) (total int, err error) {
+	total = 0
+	for {
+		copied := copy(w.buf[w.pos:], p)
+		w.pos += uint16(copied)
+		total += copied
+		if copied == len(p) {
+			break
+		}
+		if err = w.flush(); err != nil {
+			return
+		}
+		p = p[copied:]
+	}
+	return
+}
+
+func (w *tdsBuffer) WriteByte(b byte) error {
+	if int(w.pos) == len(w.buf) {
+		if err := w.flush(); err != nil {
+			return err
+		}
+	}
+	w.buf[w.pos] = b
+	w.pos += 1
+	return nil
+}
+
+func (w *tdsBuffer) BeginPacket(packet_type byte) {
+	w.buf[0] = packet_type
+	w.buf[1] = 0 // packet is incomplete
+	w.buf[4] = 0 // spid
+	w.buf[5] = 0
+	w.buf[6] = 1 // packet id
+	w.buf[7] = 0 // window
+	w.pos = 8
+}
+
+func (w *tdsBuffer) FinishPacket() error {
+	w.buf[1] = 1 // this is last packet
+	return w.flush()
+}
+
+func (r *tdsBuffer) readNextPacket() error {
+	header := header{}
+	var err error
+	err = binary.Read(r.transport, binary.BigEndian, &header)
+	if err != nil {
+		return err
+	}
+	offset := uint16(binary.Size(header))
+	if int(header.Size) > len(r.buf) {
+		return errors.New("Invalid packet size, it is longer than buffer size")
+	}
+	if int(offset) > int(header.Size) {
+		return errors.New("Invalid packet size, it is shorter than header size")
+	}
+	_, err = io.ReadFull(r.transport, r.buf[offset:header.Size])
+	if err != nil {
+		return err
+	}
+	r.pos = offset
+	r.size = header.Size
+	r.final = header.Status != 0
+	r.packet_type = header.PacketType
+	return nil
+}
+
+func (r *tdsBuffer) BeginRead() (uint8, error) {
+	err := r.readNextPacket()
+	if err != nil {
+		return 0, err
+	}
+	return r.packet_type, nil
+}
+
+func (r *tdsBuffer) ReadByte() (res byte, err error) {
+	if r.pos == r.size {
+		if r.final {
+			return 0, io.EOF
+		}
+		err = r.readNextPacket()
+		if err != nil {
+			return 0, err
+		}
+	}
+	res = r.buf[r.pos]
+	r.pos++
+	return res, nil
+}
+
+func (r *tdsBuffer) byte() byte {
+	b, err := r.ReadByte()
+	if err != nil {
+		badStreamPanic(err)
+	}
+	return b
+}
+
+func (r *tdsBuffer) ReadFull(buf []byte) {
+	_, err := io.ReadFull(r, buf[:])
+	if err != nil {
+		badStreamPanic(err)
+	}
+}
+
+func (r *tdsBuffer) uint64() uint64 {
+	var buf [8]byte
+	r.ReadFull(buf[:])
+	return binary.LittleEndian.Uint64(buf[:])
+}
+
+func (r *tdsBuffer) int32() int32 {
+	return int32(r.uint32())
+}
+
+func (r *tdsBuffer) uint32() uint32 {
+	var buf [4]byte
+	r.ReadFull(buf[:])
+	return binary.LittleEndian.Uint32(buf[:])
+}
+
+func (r *tdsBuffer) uint16() uint16 {
+	var buf [2]byte
+	r.ReadFull(buf[:])
+	return binary.LittleEndian.Uint16(buf[:])
+}
+
+func (r *tdsBuffer) BVarChar() string {
+	l := int(r.byte())
+	return r.readUcs2(l)
+}
+
+func (r *tdsBuffer) UsVarChar() string {
+	l := int(r.uint16())
+	return r.readUcs2(l)
+}
+
+func (r *tdsBuffer) readUcs2(numchars int) string {
+	b := make([]byte, numchars*2)
+	r.ReadFull(b)
+	res, err := ucs22str(b)
+	if err != nil {
+		badStreamPanic(err)
+	}
+	return res
+}
+
+func (r *tdsBuffer) Read(buf []byte) (copied int, err error) {
+	copied = 0
+	err = nil
+	if r.pos == r.size {
+		if r.final {
+			return 0, io.EOF
+		}
+		err = r.readNextPacket()
+		if err != nil {
+			return
+		}
+	}
+	copied = copy(buf, r.buf[r.pos:r.size])
+	r.pos += uint16(copied)
+	return
+}