github.com/la5nta/wl2k-go@v0.11.8/fbb/proposal.go

// Copyright 2015 Martin Hebnes Pedersen (LA5NTA). All rights reserved.
// Use of this source code is governed by the MIT-license that can be
// found in the LICENSE file.

package fbb

import (
	"bytes"
	"compress/gzip"
	"errors"
	"fmt"
	"io"
	"strconv"
	"strings"

	"github.com/la5nta/wl2k-go/lzhuf"
)

type PropCode byte

const (
	BasicProposal PropCode = 'B' // Basic ASCII proposal (or compressed binary in v0/1)
	AsciiProposal          = 'A' // Compressed v0/1 ASCII proposal
	Wl2kProposal           = 'C' // Compressed v2 proposal (winlink extension)
	GzipProposal           = 'D' // Gzip compressed v2 proposal
)

type ProposalAnswer byte

const (
	Accept ProposalAnswer = '+'
	Reject                = '-'
	Defer                 = '='

	// Offset not supported yet
)

// Proposal is the type representing a inbound or outbound proposal.
type Proposal struct {
	code           PropCode
	msgType        string
	mid            string
	answer         ProposalAnswer
	title          string
	offset         int
	sent           bool
	size           int
	compressedData []byte
	compressedSize int
}

// Constructor for a new Proposal given a Winlink Message.
//
// Reads the Winlink Message given and constructs a new proposal
// based on what's read and prepares for outbound delivery, returning
// a Proposal with the given data.
//
func NewProposal(MID, title string, code PropCode, data []byte) *Proposal {
	prop := &Proposal{
		mid:     MID,
		code:    code,
		msgType: "EM",
		title:   title,
		size:    len(data),
	}

	if prop.title == `` {
		prop.title = `No title`
	}

	var (
		z   io.WriteCloser
		buf bytes.Buffer
	)
	switch prop.code {
	case GzipProposal:
		z, _ = gzip.NewWriterLevel(&buf, gzip.BestCompression)
	default:
		z = lzhuf.NewB2Writer(&buf)
	}

	z.Write(data)
	if err := z.Close(); err != nil {
		panic(err)
	}

	prop.compressedData = buf.Bytes()
	prop.compressedSize = len(prop.compressedData)

	return prop
}

// Method for checking if the Proposal is completely
// downloaded/loaded and ready to be read/sent.
//
// Typically used to check if the whole message was
// successfully downloaded from the CMS.
//
func (p *Proposal) DataIsComplete() bool {
	return len(p.compressedData) == p.compressedSize
}

// Returns the uniqe Message ID
func (p *Proposal) MID() string {
	return p.mid
}

// Returns the title of this proposal
func (p *Proposal) Title() string {
	return p.title
}

func (p *Proposal) Message() (*Message, error) {
	buf := bytes.NewBuffer(p.Data())
	m := new(Message)
	err := m.ReadFrom(buf)
	return m, err
}

// Data returns the decompressed raw message
func (p *Proposal) Data() []byte {
	var r io.ReadCloser
	var err error

	switch p.code {
	case GzipProposal:
		r, err = gzip.NewReader(bytes.NewBuffer(p.compressedData))
	default:
		r, err = lzhuf.NewB2Reader(bytes.NewBuffer(p.compressedData))
	}

	if err != nil {
		panic(err) //TODO: Should return error
	}

	var buf bytes.Buffer
	if _, err := io.Copy(&buf, r); err != nil {
		panic(err) //TODO
	}

	return buf.Bytes()
}

func parseProposal(line string, prop *Proposal) (err error) {
	if len(line) < 1 {
		return
	} else if line[0] != 'F' {
		return
	}

	prop.code = PropCode(line[1])

	switch prop.code {
	case BasicProposal, AsciiProposal: // TODO: implement
	case Wl2kProposal, GzipProposal:
		err = parseB2Proposal(line, prop)
	default:
		err = fmt.Errorf("Unsupported proposal code '%c'", prop.code)
	}
	return
}

func parseB2Proposal(line string, prop *Proposal) (err error) {
	if len(line) < 4 {
		return errors.New("Unexpected end of proposal line")
	}

	if !(line[1] == Wl2kProposal || line[1] == GzipProposal) {
		return errors.New("Not a type C or D proposal")
	}

	// FC EM TJKYEIMMHSRB 527 123 0
	parts := strings.Split(line[3:], " ")
	if len(parts) < 5 {
		return errors.New(`Malformed proposal: ` + line[2:])
	}

	for i, part := range parts {
		switch i {
		case 0:
			if len(part) < 1 || len(part) > 2 {
				return errors.New(`Malformed proposal 0`)
			} else if part != "EM" && part != "CM" {
				return fmt.Errorf(`Expected message type CM or EM, but found %s`, part)
			}
			prop.msgType = part
		case 1:
			prop.mid = part
		case 2:
			prop.size, _ = strconv.Atoi(part)
		case 3:
			prop.compressedSize, _ = strconv.Atoi(part)
		case 4:
		default:
			return errors.New(fmt.Sprintf(`Too many parts in proposal: %+v`, parts))
		}
	}
	return
}

// precedence returns the priority level of the message. Lower precedence value is more important
// and should be handled sooner.
//
// See https://www.winlink.org/content/how_use_message_precedence_precedence.
func (p *Proposal) precedence() int {
	const (
		Flash = iota
		Immediate
		Priority
		Routine
	)
	switch {
	case strings.Contains(p.title, "//WL2K Z/"):
		return Flash
	case strings.Contains(p.title, "//WL2K O/"):
		return Immediate
	case strings.Contains(p.title, "//WL2K P/"):
		return Priority
	default:
		return Routine
	}
}