path: root/pkg/libgopher/libgopher.go

package libgopher

import (
	"bufio"
	"errors"
	"io"
	"log"
	"net"
	"net/url"
	"strings"
)

// Item Types
const (
	FILE        = ItemType('0') // Item is a file
	DIRECTORY   = ItemType('1') // Item is a directory
	PHONEBOOK   = ItemType('2') // Item is a CSO phone-book server
	ERROR       = ItemType('3') // Error
	BINHEX      = ItemType('4') // Item is a BinHexed Macintosh file.
	DOSARCHIVE  = ItemType('5') // Item is DOS binary archive of some sort. (*)
	UUENCODED   = ItemType('6') // Item is a UNIX uuencoded file.
	INDEXSEARCH = ItemType('7') // Item is an Index-Search server.
	TELNET      = ItemType('8') // Item points to a text-based telnet session.
	BINARY      = ItemType('9') // Item is a binary file! (*)

	// (*) Client must read until the TCP connection is closed.

	REDUNDANT = ItemType('+') // Item is a redundant server
	TN3270    = ItemType('T') // Item points to a text-based tn3270 session.
	GIF       = ItemType('g') // Item is a GIF format graphics file.
	IMAGE     = ItemType('I') // Item is some kind of image file.

	// non-standard
	INFO  = ItemType('i') // Item is an informational message
	HTML  = ItemType('h') // Item is a HTML document
	AUDIO = ItemType('s') // Item is an Audio file
	PNG   = ItemType('p') // Item is a PNG Image
	DOC   = ItemType('d') // Item is a Document
)

const (
	// END represents the terminator used in directory responses
	END = byte('.')

	// TAB is the delimiter used to separate item response parts
	TAB = byte('\t')

	// CRLF is the delimiter used per line of response item
	CRLF = "\r\n"

	// DEFAULT is the default item type
	DEFAULT = BINARY
)

// ItemType represents the type of an item
type ItemType byte

// Return a human friendly represation of an ItemType
func (it ItemType) String() string {
	switch it {
	case FILE:
		return "TXT"
	case DIRECTORY:
		return "DIR"
	case PHONEBOOK:
		return "PHO"
	case ERROR:
		return "ERR"
	case BINHEX:
		return "HEX"
	case DOSARCHIVE:
		return "ARC"
	case UUENCODED:
		return "UUE"
	case INDEXSEARCH:
		return "QRY"
	case TELNET:
		return "TEL"
	case BINARY:
		return "BIN"
	case REDUNDANT:
		return "DUP"
	case TN3270:
		return "TN3"
	case GIF:
		return "GIF"
	case IMAGE:
		return "IMG"
	case INFO:
		return "NFO"
	case HTML:
		return "HTM"
	case AUDIO:
		return "SND"
	case PNG:
		return "PNG"
	case DOC:
		return "DOC"
	default:
		return "???"
	}
}

// Item describes an entry in a directory listing.
type Item struct {
	Type        ItemType `json:"type"`
	Description string   `json:"description"`
	Selector    string   `json:"selector"`
	Host        string   `json:"host"`
	Port        string   `json:"port"`

	// non-standard extensions (ignored by standard clients)
	Extras []string `json:"extras"`
}

// ParseItem parses a line of text into an item
func ParseItem(line string) (item *Item, err error) {
	parts := strings.Split(strings.Trim(line, "\r\n"), "\t")

	if len(parts[0]) < 1 {
		return nil, errors.New("no item type: " + string(line))
	}

	item = &Item{
		Type:        ItemType(parts[0][0]),
		Description: string(parts[0][1:]),
		Extras:      make([]string, 0),
	}

	// Selector
	if len(parts) > 1 {
		item.Selector = string(parts[1])
	} else {
		item.Selector = ""
	}

	// Host
	if len(parts) > 2 {
		item.Host = string(parts[2])
	} else {
		item.Host = "null.host"
	}

	// Port
	if len(parts) > 3 {
		item.Port = string(parts[3])
	} else {
		item.Port = "0"
	}

	// Extras
	if len(parts) >= 4 {
		for _, v := range parts[4:] {
			item.Extras = append(item.Extras, string(v))
		}
	}

	return
}

func (i *Item) isDirectoryLike() bool {
	switch i.Type {
	case DIRECTORY:
		return true
	case INDEXSEARCH:
		return true
	default:
		return false
	}
}

// Directory representes a Gopher Menu of Items
type Directory struct {
	Items []*Item `json:"items"`
}

// Response represents a Gopher resource that
// Items contains a non-empty array of Item(s)
// for directory types, otherwise the Body
// contains the fetched resource (file, image, etc).
type Response struct {
	Type ItemType
	Dir  Directory
	Body io.Reader
}

// Get fetches a Gopher resource by URL
func Get(uri string) (*Response, error) {
	u, err := url.Parse(uri)
	if err != nil {
		return nil, err
	}

	if u.Scheme != "gopher" {
		return nil, errors.New("invalid scheme for uri")
	}

	host := u.Hostname()
	port := u.Port()

	if port == "" {
		port = "70"
	}

	var (
		Type     ItemType
		Selector string
	)

	path := strings.TrimPrefix(u.Path, "/")
	if len(path) > 2 {
		Type = ItemType(path[0])
		Selector = path[1:]
		if u.RawQuery != "" {
			Selector += "\t" + u.RawQuery
		}
	} else if len(path) == 1 {
		Type = ItemType(path[0])
		Selector = ""
	} else {
		Type = ItemType(DIRECTORY)
		Selector = ""
	}

	i := Item{Type: Type, Selector: Selector, Host: host, Port: port}
	res := Response{Type: i.Type}

	if i.isDirectoryLike() {
		d, err := i.FetchDirectory()
		if err != nil {
			return nil, err
		}

		res.Dir = d
	} else {
		reader, err := i.FetchFile()
		if err != nil {
			return nil, err
		}

		res.Body = reader
	}

	return &res, nil
}

// FetchFile fetches data, not directory information.
// Calling this on a DIRECTORY Item type
// or unsupported type will return an error.
func (i *Item) FetchFile() (io.Reader, error) {
	if i.Type == DIRECTORY {
		return nil, errors.New("cannot fetch a directory as a file")
	}

	conn, err := net.Dial("tcp", net.JoinHostPort(i.Host, i.Port))
	if err != nil {
		return nil, err
	}

	_, err = conn.Write([]byte(i.Selector + CRLF))
	if err != nil {
		conn.Close()
		return nil, err
	}

	return conn, nil
}

// FetchDirectory fetches directory information, not data.
// Calling this on an Item whose type is not DIRECTORY will return an error.
func (i *Item) FetchDirectory() (Directory, error) {
	if !i.isDirectoryLike() {
		return Directory{}, errors.New("cannot fetch a file as a directory")
	}

	conn, err := net.Dial("tcp", net.JoinHostPort(i.Host, i.Port))
	if err != nil {
		return Directory{}, err
	}

	_, err = conn.Write([]byte(i.Selector + CRLF))
	if err != nil {
		return Directory{}, err
	}

	reader := bufio.NewReader(conn)
	scanner := bufio.NewScanner(reader)
	scanner.Split(bufio.ScanLines)

	var items []*Item

	for scanner.Scan() {
		line := strings.Trim(scanner.Text(), "\r\n")

		if len(line) == 0 {
			continue
		}

		if len(line) == 1 && line[0] == END {
			break
		}

		item, err := ParseItem(line)
		if err != nil {
			log.Printf("Error parsing %q: %q", line, err)
			continue
		}
		items = append(items, item)
	}

	return Directory{items}, nil
}