msgalert.go

// Copyright (c) 2013-2015 The btcsuite developers
// Copyright (c) 2015 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package wire

import (
	"bytes"
	"fmt"
	"io"
)

// MsgAlert contains a payload and a signature:
//
//        ===============================================
//        |   Field         |   Data Type   |   Size    |
//        ===============================================
//        |   payload       |   []uchar     |   ?       |
//        -----------------------------------------------
//        |   signature     |   []uchar     |   ?       |
//        -----------------------------------------------
//
// Here payload is an Alert serialized into a byte array to ensure that
// versions using incompatible alert formats can still relay
// alerts among one another.
//
// An Alert is the payload deserialized as follows:
//
//        ===============================================
//        |   Field         |   Data Type   |   Size    |
//        ===============================================
//        |   Version       |   int32       |   4       |
//        -----------------------------------------------
//        |   RelayUntil    |   int64       |   8       |
//        -----------------------------------------------
//        |   Expiration    |   int64       |   8       |
//        -----------------------------------------------
//        |   ID            |   int32       |   4       |
//        -----------------------------------------------
//        |   Cancel        |   int32       |   4       |
//        -----------------------------------------------
//        |   SetCancel     |   set<int32>  |   ?       |
//        -----------------------------------------------
//        |   MinVer        |   int32       |   4       |
//        -----------------------------------------------
//        |   MaxVer        |   int32       |   4       |
//        -----------------------------------------------
//        |   SetSubVer     |   set<string> |   ?       |
//        -----------------------------------------------
//        |   Priority      |   int32       |   4       |
//        -----------------------------------------------
//        |   Comment       |   string      |   ?       |
//        -----------------------------------------------
//        |   StatusBar     |   string      |   ?       |
//        -----------------------------------------------
//        |   Reserved      |   string      |   ?       |
//        -----------------------------------------------
//        |   Total  (Fixed)                |   45      |
//        -----------------------------------------------
//
// NOTE:
//      * string is a VarString i.e VarInt length followed by the string itself
//      * set<string> is a VarInt followed by as many number of strings
//      * set<int32> is a VarInt followed by as many number of ints
//      * fixedAlertSize = 40 + 5*min(VarInt)  = 40 + 5*1 = 45
//
// Now we can define bounds on Alert size, SetCancel and SetSubVer

// Fixed size of the alert payload
const fixedAlertSize = 45

// maxSignatureSize is the max size of an ECDSA signature.
// NOTE: Since this size is fixed and < 255, the size of VarInt required = 1.
const maxSignatureSize = 72

// maxAlertSize is the maximum size an alert.
//
// MessagePayload = VarInt(Alert) + Alert + VarInt(Signature) + Signature
// MaxMessagePayload = maxAlertSize + max(VarInt) + maxSignatureSize + 1
const maxAlertSize = MaxMessagePayload - maxSignatureSize - MaxVarIntPayload - 1

// maxCountSetCancel is the maximum number of cancel IDs that could possibly
// fit into a maximum size alert.
//
// maxAlertSize = fixedAlertSize + max(SetCancel) + max(SetSubVer) + 3*(string)
// for caculating maximum number of cancel IDs, set all other var  sizes to 0
// maxAlertSize = fixedAlertSize + (MaxVarIntPayload-1) + x*sizeOf(int32)
// x = (maxAlertSize - fixedAlertSize - MaxVarIntPayload + 1) / 4
const maxCountSetCancel = (maxAlertSize - fixedAlertSize - MaxVarIntPayload + 1) / 4

// maxCountSetSubVer is the maximum number of subversions that could possibly
// fit into a maximum size alert.
//
// maxAlertSize = fixedAlertSize + max(SetCancel) + max(SetSubVer) + 3*(string)
// for caculating maximum number of subversions, set all other var sizes to 0
// maxAlertSize = fixedAlertSize + (MaxVarIntPayload-1) + x*sizeOf(string)
// x = (maxAlertSize - fixedAlertSize - MaxVarIntPayload + 1) / sizeOf(string)
// subversion would typically be something like "/Dcrd:0.7.2/" (15 bytes)
// so assuming < 255 bytes, sizeOf(string) = sizeOf(uint8) + 255 = 256
const maxCountSetSubVer = (maxAlertSize - fixedAlertSize - MaxVarIntPayload + 1) / 256

// Alert contains the data deserialized from the MsgAlert payload.
type Alert struct {
	// Alert format version
	Version int32

	// Timestamp beyond which nodes should stop relaying this alert
	RelayUntil int64

	// Timestamp beyond which this alert is no longer in effect and
	// should be ignored
	Expiration int64

	// A unique ID number for this alert
	ID int32

	// All alerts with an ID less than or equal to this number should
	// cancelled, deleted and not accepted in the future
	Cancel int32

	// All alert IDs contained in this set should be cancelled as above
	SetCancel []int32

	// This alert only applies to versions greater than or equal to this
	// version. Other versions should still relay it.
	MinVer int32

	// This alert only applies to versions less than or equal to this version.
	// Other versions should still relay it.
	MaxVer int32

	// If this set contains any elements, then only nodes that have their
	// subVer contained in this set are affected by the alert. Other versions
	// should still relay it.
	SetSubVer []string

	// Relative priority compared to other alerts
	Priority int32

	// A comment on the alert that is not displayed
	Comment string

	// The alert message that is displayed to the user
	StatusBar string

	// Reserved
	Reserved string
}

// Serialize encodes the alert to w using the alert protocol encoding format.
func (alert *Alert) Serialize(w io.Writer, pver uint32) error {
	err := writeElements(w, alert.Version, alert.RelayUntil,
		alert.Expiration, alert.ID, alert.Cancel)
	if err != nil {
		return err
	}

	count := len(alert.SetCancel)
	if count > maxCountSetCancel {
		str := fmt.Sprintf("too many cancel alert IDs for alert "+
			"[count %v, max %v]", count, maxCountSetCancel)
		return messageError("Alert.Serialize", str)
	}
	err = writeVarInt(w, pver, uint64(count))
	if err != nil {
		return err
	}
	for i := 0; i < int(count); i++ {
		err = writeElement(w, alert.SetCancel[i])
		if err != nil {
			return err
		}
	}

	err = writeElements(w, alert.MinVer, alert.MaxVer)
	if err != nil {
		return err
	}

	count = len(alert.SetSubVer)
	if count > maxCountSetSubVer {
		str := fmt.Sprintf("too many sub versions for alert "+
			"[count %v, max %v]", count, maxCountSetSubVer)
		return messageError("Alert.Serialize", str)
	}
	err = writeVarInt(w, pver, uint64(count))
	if err != nil {
		return err
	}
	for i := 0; i < int(count); i++ {
		err = WriteVarString(w, pver, alert.SetSubVer[i])
		if err != nil {
			return err
		}
	}

	err = writeElement(w, alert.Priority)
	if err != nil {
		return err
	}
	err = WriteVarString(w, pver, alert.Comment)
	if err != nil {
		return err
	}
	err = WriteVarString(w, pver, alert.StatusBar)
	if err != nil {
		return err
	}
	err = WriteVarString(w, pver, alert.Reserved)
	if err != nil {
		return err
	}
	return nil
}

// Deserialize decodes from r into the receiver using the alert protocol
// encoding format.
func (alert *Alert) Deserialize(r io.Reader, pver uint32) error {
	err := readElements(r, &alert.Version, &alert.RelayUntil,
		&alert.Expiration, &alert.ID, &alert.Cancel)
	if err != nil {
		return err
	}

	// SetCancel: first read a VarInt that contains
	// count - the number of Cancel IDs, then
	// iterate count times and read them
	count, err := readVarInt(r, pver)
	if err != nil {
		return err
	}
	if count > maxCountSetCancel {
		str := fmt.Sprintf("too many cancel alert IDs for alert "+
			"[count %v, max %v]", count, maxCountSetCancel)
		return messageError("Alert.Deserialize", str)
	}
	alert.SetCancel = make([]int32, count)
	for i := 0; i < int(count); i++ {
		err := readElement(r, &alert.SetCancel[i])
		if err != nil {
			return err
		}
	}

	err = readElements(r, &alert.MinVer, &alert.MaxVer)
	if err != nil {
		return err
	}

	// SetSubVer: similar to SetCancel
	// but read count number of sub-version strings
	count, err = readVarInt(r, pver)
	if err != nil {
		return err
	}
	if count > maxCountSetSubVer {
		str := fmt.Sprintf("too many sub versions for alert "+
			"[count %v, max %v]", count, maxCountSetSubVer)
		return messageError("Alert.Deserialize", str)
	}
	alert.SetSubVer = make([]string, count)
	for i := 0; i < int(count); i++ {
		alert.SetSubVer[i], err = ReadVarString(r, pver)
		if err != nil {
			return err
		}
	}

	err = readElement(r, &alert.Priority)
	if err != nil {
		return err
	}
	alert.Comment, err = ReadVarString(r, pver)
	if err != nil {
		return err
	}
	alert.StatusBar, err = ReadVarString(r, pver)
	if err != nil {
		return err
	}
	alert.Reserved, err = ReadVarString(r, pver)
	if err != nil {
		return err
	}
	return nil
}

// NewAlert returns an new Alert with values provided.
func NewAlert(version int32, relayUntil int64, expiration int64,
	id int32, cancel int32, setCancel []int32, minVer int32,
	maxVer int32, setSubVer []string, priority int32, comment string,
	statusBar string) *Alert {
	return &Alert{
		Version:    version,
		RelayUntil: relayUntil,
		Expiration: expiration,
		ID:         id,
		Cancel:     cancel,
		SetCancel:  setCancel,
		MinVer:     minVer,
		MaxVer:     maxVer,
		SetSubVer:  setSubVer,
		Priority:   priority,
		Comment:    comment,
		StatusBar:  statusBar,
		Reserved:   "",
	}
}

// NewAlertFromPayload returns an Alert with values deserialized from the
// serialized payload.
func NewAlertFromPayload(serializedPayload []byte, pver uint32) (*Alert, error) {
	var alert Alert
	r := bytes.NewReader(serializedPayload)
	err := alert.Deserialize(r, pver)
	if err != nil {
		return nil, err
	}
	return &alert, nil
}

// MsgAlert  implements the Message interface and defines a decred alert
// message.
//
// This is a signed message that provides notifications that the client should
// display if the signature matches the key.  bitcoind/bitcoin-qt only checks
// against a signature from the core developers.
type MsgAlert struct {
	// SerializedPayload is the alert payload serialized as a string so that the
	// version can change but the Alert can still be passed on by older
	// clients.
	SerializedPayload []byte

	// Signature is the ECDSA signature of the message.
	Signature []byte

	// Deserialized Payload
	Payload *Alert
}

// BtcDecode decodes r using the decred protocol encoding into the receiver.
// This is part of the Message interface implementation.
func (msg *MsgAlert) BtcDecode(r io.Reader, pver uint32) error {
	var err error

	msg.SerializedPayload, err = readVarBytes(r, pver, MaxMessagePayload,
		"alert serialized payload")
	if err != nil {
		return err
	}

	msg.Payload, err = NewAlertFromPayload(msg.SerializedPayload, pver)
	if err != nil {
		msg.Payload = nil
	}

	msg.Signature, err = readVarBytes(r, pver, MaxMessagePayload,
		"alert signature")
	if err != nil {
		return err
	}

	return nil
}

// BtcEncode encodes the receiver to w using the decred protocol encoding.
// This is part of the Message interface implementation.
func (msg *MsgAlert) BtcEncode(w io.Writer, pver uint32) error {
	var err error
	var serializedpayload []byte
	if msg.Payload != nil {
		// try to Serialize Payload if possible
		r := new(bytes.Buffer)
		err = msg.Payload.Serialize(r, pver)
		if err != nil {
			// Serialize failed - ignore & fallback
			// to SerializedPayload
			serializedpayload = msg.SerializedPayload
		} else {
			serializedpayload = r.Bytes()
		}
	} else {
		serializedpayload = msg.SerializedPayload
	}
	slen := uint64(len(serializedpayload))
	if slen == 0 {
		return messageError("MsgAlert.BtcEncode", "empty serialized payload")
	}
	err = writeVarBytes(w, pver, serializedpayload)
	if err != nil {
		return err
	}
	err = writeVarBytes(w, pver, msg.Signature)
	if err != nil {
		return err
	}
	return nil
}

// Command returns the protocol command string for the message.  This is part
// of the Message interface implementation.
func (msg *MsgAlert) Command() string {
	return CmdAlert
}

// MaxPayloadLength returns the maximum length the payload can be for the
// receiver.  This is part of the Message interface implementation.
func (msg *MsgAlert) MaxPayloadLength(pver uint32) uint32 {
	// Since this can vary depending on the message, make it the max
	// size allowed.
	return MaxMessagePayload
}

// NewMsgAlert returns a new decred alert message that conforms to the Message
// interface.  See MsgAlert for details.
func NewMsgAlert(serializedPayload []byte, signature []byte) *MsgAlert {
	return &MsgAlert{
		SerializedPayload: serializedPayload,
		Signature:         signature,
		Payload:           nil,
	}
}