telebit/packer/packer.go

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package packer
import (
"bytes"
"fmt"
"net"
"strconv"
"strings"
)
const (
_ = iota // skip the iota value of 0
packerV1 byte = 255 - iota
packerV2
)
//Packer -- contains both header and data
type Packer struct {
Header
Data packerData
}
// NewPacker creates a new Packer struct using the information from the provided header as
// its own header. (Because the header is stored directly and not as a pointer/reference
// it should be safe to override items like the service without affecting the template header.)
func NewPacker(header *Header) *Packer {
p := new(Packer)
if header != nil {
p.Header = *header
}
return p
}
func splitHeader(header []byte, names []string) (map[string]string, error) {
parts := strings.Split(string(header), ",")
if p, n := len(parts), len(names); p > n {
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//return nil, fmt.Errorf("Header contains %d extra fields", p-n)
} else if p < n {
return nil, fmt.Errorf("Header missing fields %q", names[p:])
}
result := make(map[string]string, len(names))
for ind, key := range names {
result[key] = parts[ind]
}
return result, nil
}
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// ReadMessage checks the protocol and switches accordingly
func ReadMessage(b []byte) (*Packer, error) {
// Detect protocol in use
if b[0] == packerV1 {
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return ReadV1Message(b)
}
return nil, fmt.Errorf("Version %d not supported", 255-b[0])
}
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// ReadV1Message parses a v1-formatted message
func ReadV1Message(b []byte) (*Packer, error) {
// Separate the header and body using the header length in the second byte.
p := NewPacker(nil)
header := b[2 : b[1]+2]
data := b[b[1]+2:]
// Handle the different parts of the header.
parts, err := splitHeader(header, []string{"address family", "address", "port", "data length", "service"})
if err != nil {
return nil, err
}
if familyText := parts["address family"]; familyText == addressFamilyText[FamilyIPv4] {
p.Header.family = FamilyIPv4
} else if familyText == addressFamilyText[FamilyIPv6] {
p.Header.family = FamilyIPv6
} else {
return nil, fmt.Errorf("Address family %q not supported", familyText)
}
p.Header.address = net.ParseIP(parts["address"])
if p.Header.address == nil {
return nil, fmt.Errorf("Invalid network address %q", parts["address"])
} else if p.Header.family == FamilyIPv4 && p.Header.address.To4() == nil {
return nil, fmt.Errorf("Address %q is not in address family %s", parts["address"], p.Header.Family())
}
//handle port
if port, err := strconv.Atoi(parts["port"]); err != nil {
return nil, fmt.Errorf("Error converting port %q: %v", parts["port"], err)
} else if port <= 0 || port > 65535 {
return nil, fmt.Errorf("Port %d out of range", port)
} else {
p.Header.port = port
}
//handle data length
if dataLen, err := strconv.Atoi(parts["data length"]); err != nil {
return nil, fmt.Errorf("Error converting data length %q: %v", parts["data length"], err)
} else if dataLen != len(data) {
return nil, fmt.Errorf("Data length %d doesn't match received length %d", dataLen, len(data))
}
//handle Service
p.Header.service = parts["service"]
//handle payload
p.Data.AppendBytes(data)
return p, nil
}
//PackV1 -- Outputs version 1 of packer
func (p *Packer) PackV1() bytes.Buffer {
header := strings.Join([]string{
p.Header.Family(),
p.Header.Address(),
strconv.Itoa(p.Header.Port()),
strconv.Itoa(p.Data.DataLen()),
p.Header.Service(),
}, ",")
var buf bytes.Buffer
buf.WriteByte(packerV1)
buf.WriteByte(byte(len(header)))
buf.WriteString(header)
buf.Write(p.Data.Data())
return buf
}