Serge Bazanski | cc25bdf | 2018-10-25 14:02:58 +0200 | [diff] [blame] | 1 | // Package telnet provides simple interface for interacting with Telnet |
| 2 | // connection. |
| 3 | package telnet |
| 4 | |
| 5 | import ( |
| 6 | "bufio" |
| 7 | "bytes" |
| 8 | "fmt" |
| 9 | "net" |
| 10 | "time" |
| 11 | "unicode" |
| 12 | ) |
| 13 | |
| 14 | const ( |
| 15 | CR = byte('\r') |
| 16 | LF = byte('\n') |
| 17 | ) |
| 18 | |
| 19 | const ( |
| 20 | cmdSE = 240 |
| 21 | cmdNOP = 241 |
| 22 | cmdData = 242 |
| 23 | |
| 24 | cmdBreak = 243 |
| 25 | cmdGA = 249 |
| 26 | cmdSB = 250 |
| 27 | |
| 28 | cmdWill = 251 |
| 29 | cmdWont = 252 |
| 30 | cmdDo = 253 |
| 31 | cmdDont = 254 |
| 32 | |
| 33 | cmdIAC = 255 |
| 34 | ) |
| 35 | |
| 36 | const ( |
| 37 | optEcho = 1 |
| 38 | optSuppressGoAhead = 3 |
| 39 | // optTerminalType = 24 |
| 40 | optNAWS = 31 |
| 41 | ) |
| 42 | |
| 43 | // Conn implements net.Conn interface for Telnet protocol plus some set of |
| 44 | // Telnet specific methods. |
| 45 | type Conn struct { |
| 46 | net.Conn |
| 47 | r *bufio.Reader |
| 48 | |
| 49 | unixWriteMode bool |
| 50 | |
| 51 | cliSuppressGoAhead bool |
| 52 | cliEcho bool |
| 53 | } |
| 54 | |
| 55 | func NewConn(conn net.Conn) (*Conn, error) { |
| 56 | c := Conn{ |
| 57 | Conn: conn, |
| 58 | r: bufio.NewReaderSize(conn, 256), |
| 59 | } |
| 60 | return &c, nil |
| 61 | } |
| 62 | |
| 63 | func Dial(network, addr string) (*Conn, error) { |
| 64 | conn, err := net.Dial(network, addr) |
| 65 | if err != nil { |
| 66 | return nil, err |
| 67 | } |
| 68 | return NewConn(conn) |
| 69 | } |
| 70 | |
| 71 | func DialTimeout(network, addr string, timeout time.Duration) (*Conn, error) { |
| 72 | conn, err := net.DialTimeout(network, addr, timeout) |
| 73 | if err != nil { |
| 74 | return nil, err |
| 75 | } |
| 76 | return NewConn(conn) |
| 77 | } |
| 78 | |
| 79 | // SetUnixWriteMode sets flag that applies only to the Write method. |
| 80 | // If set, Write converts any '\n' (LF) to '\r\n' (CR LF). |
| 81 | func (c *Conn) SetUnixWriteMode(uwm bool) { |
| 82 | c.unixWriteMode = uwm |
| 83 | } |
| 84 | |
| 85 | func (c *Conn) do(option byte) error { |
| 86 | //log.Println("do:", option) |
| 87 | _, err := c.Conn.Write([]byte{cmdIAC, cmdDo, option}) |
| 88 | return err |
| 89 | } |
| 90 | |
| 91 | func (c *Conn) dont(option byte) error { |
| 92 | //log.Println("dont:", option) |
| 93 | _, err := c.Conn.Write([]byte{cmdIAC, cmdDont, option}) |
| 94 | return err |
| 95 | } |
| 96 | |
| 97 | func (c *Conn) will(option byte) error { |
| 98 | //log.Println("will:", option) |
| 99 | _, err := c.Conn.Write([]byte{cmdIAC, cmdWill, option}) |
| 100 | return err |
| 101 | } |
| 102 | |
| 103 | func (c *Conn) wont(option byte) error { |
| 104 | //log.Println("wont:", option) |
| 105 | _, err := c.Conn.Write([]byte{cmdIAC, cmdWont, option}) |
| 106 | return err |
| 107 | } |
| 108 | |
| 109 | func (c *Conn) sub(opt byte, data ...byte) error { |
| 110 | if _, err := c.Conn.Write([]byte{cmdIAC, cmdSB, opt}); err != nil { |
| 111 | return err |
| 112 | } |
| 113 | if _, err := c.Conn.Write(data); err != nil { |
| 114 | return err |
| 115 | } |
| 116 | _, err := c.Conn.Write([]byte{cmdIAC, cmdSE}) |
| 117 | return err |
| 118 | } |
| 119 | |
| 120 | func (c *Conn) deny(cmd, opt byte) (err error) { |
| 121 | switch cmd { |
| 122 | case cmdDo: |
| 123 | err = c.wont(opt) |
| 124 | case cmdDont: |
| 125 | // nop |
| 126 | case cmdWill, cmdWont: |
| 127 | err = c.dont(opt) |
| 128 | } |
| 129 | return |
| 130 | } |
| 131 | |
| 132 | func (c *Conn) skipSubneg() error { |
| 133 | for { |
| 134 | if b, err := c.r.ReadByte(); err != nil { |
| 135 | return err |
| 136 | } else if b == cmdIAC { |
| 137 | if b, err = c.r.ReadByte(); err != nil { |
| 138 | return err |
| 139 | } else if b == cmdSE { |
| 140 | return nil |
| 141 | } |
| 142 | } |
| 143 | } |
| 144 | } |
| 145 | |
| 146 | func (c *Conn) cmd(cmd byte) error { |
| 147 | switch cmd { |
| 148 | case cmdGA: |
| 149 | return nil |
| 150 | case cmdDo, cmdDont, cmdWill, cmdWont: |
| 151 | // Process cmd after this switch. |
| 152 | case cmdSB: |
| 153 | return c.skipSubneg() |
| 154 | default: |
| 155 | return fmt.Errorf("unknown command: %d", cmd) |
| 156 | } |
| 157 | // Read an option |
| 158 | o, err := c.r.ReadByte() |
| 159 | if err != nil { |
| 160 | return err |
| 161 | } |
| 162 | //log.Println("received cmd:", cmd, o) |
| 163 | switch o { |
| 164 | case optEcho: |
| 165 | // Accept any echo configuration. |
| 166 | switch cmd { |
| 167 | case cmdDo: |
| 168 | if !c.cliEcho { |
| 169 | c.cliEcho = true |
| 170 | err = c.will(o) |
| 171 | } |
| 172 | case cmdDont: |
| 173 | if c.cliEcho { |
| 174 | c.cliEcho = false |
| 175 | err = c.wont(o) |
| 176 | } |
| 177 | case cmdWill: |
| 178 | if !c.cliEcho { |
| 179 | c.cliEcho = true |
| 180 | err = c.do(o) |
| 181 | } |
| 182 | case cmdWont: |
| 183 | if c.cliEcho { |
| 184 | c.cliEcho = false |
| 185 | err = c.dont(o) |
| 186 | } |
| 187 | } |
| 188 | case optSuppressGoAhead: |
| 189 | // We don't use GA so can allways accept every configuration |
| 190 | switch cmd { |
| 191 | case cmdDo: |
| 192 | if !c.cliSuppressGoAhead { |
| 193 | c.cliSuppressGoAhead = true |
| 194 | err = c.will(o) |
| 195 | } |
| 196 | case cmdDont: |
| 197 | if c.cliSuppressGoAhead { |
| 198 | c.cliSuppressGoAhead = false |
| 199 | err = c.wont(o) |
| 200 | } |
| 201 | case cmdWill: |
| 202 | if !c.cliSuppressGoAhead { |
| 203 | c.cliSuppressGoAhead = true |
| 204 | err = c.do(o) |
| 205 | } |
| 206 | case cmdWont: |
| 207 | if c.cliSuppressGoAhead { |
| 208 | c.cliSuppressGoAhead = false |
| 209 | err = c.dont(o) |
| 210 | } |
| 211 | } |
| 212 | case optNAWS: |
| 213 | if cmd != cmdDo { |
| 214 | err = c.deny(cmd, o) |
| 215 | break |
| 216 | } |
| 217 | if err = c.will(o); err != nil { |
| 218 | break |
| 219 | } |
| 220 | // Reply with max window size: 65535x65535 |
| 221 | err = c.sub(o, 255, 255, 255, 255) |
| 222 | default: |
| 223 | // Deny any other option |
| 224 | err = c.deny(cmd, o) |
| 225 | } |
| 226 | return err |
| 227 | } |
| 228 | |
| 229 | func (c *Conn) tryReadByte() (b byte, retry bool, err error) { |
| 230 | b, err = c.r.ReadByte() |
| 231 | if err != nil || b != cmdIAC { |
| 232 | return |
| 233 | } |
| 234 | b, err = c.r.ReadByte() |
| 235 | if err != nil { |
| 236 | return |
| 237 | } |
| 238 | if b != cmdIAC { |
| 239 | err = c.cmd(b) |
| 240 | if err != nil { |
| 241 | return |
| 242 | } |
| 243 | retry = true |
| 244 | } |
| 245 | return |
| 246 | } |
| 247 | |
| 248 | // SetEcho tries to enable/disable echo on server side. Typically telnet |
| 249 | // servers doesn't support this. |
| 250 | func (c *Conn) SetEcho(echo bool) error { |
| 251 | if echo { |
| 252 | return c.do(optEcho) |
| 253 | } |
| 254 | return c.dont(optEcho) |
| 255 | } |
| 256 | |
| 257 | // ReadByte works like bufio.ReadByte |
| 258 | func (c *Conn) ReadByte() (b byte, err error) { |
| 259 | retry := true |
| 260 | for retry && err == nil { |
| 261 | b, retry, err = c.tryReadByte() |
| 262 | } |
| 263 | return |
| 264 | } |
| 265 | |
| 266 | // ReadRune works like bufio.ReadRune |
| 267 | func (c *Conn) ReadRune() (r rune, size int, err error) { |
| 268 | loop: |
| 269 | r, size, err = c.r.ReadRune() |
| 270 | if err != nil { |
| 271 | return |
| 272 | } |
| 273 | if r != unicode.ReplacementChar || size != 1 { |
| 274 | // Properly readed rune |
| 275 | return |
| 276 | } |
| 277 | // Bad rune |
| 278 | err = c.r.UnreadRune() |
| 279 | if err != nil { |
| 280 | return |
| 281 | } |
| 282 | // Read telnet command or escaped IAC |
| 283 | _, retry, err := c.tryReadByte() |
| 284 | if err != nil { |
| 285 | return |
| 286 | } |
| 287 | if retry { |
| 288 | // This bad rune was a begining of telnet command. Try read next rune. |
| 289 | goto loop |
| 290 | } |
| 291 | // Return escaped IAC as unicode.ReplacementChar |
| 292 | return |
| 293 | } |
| 294 | |
| 295 | // Read is for implement an io.Reader interface |
| 296 | func (c *Conn) Read(buf []byte) (int, error) { |
| 297 | var n int |
| 298 | for n < len(buf) { |
| 299 | b, retry, err := c.tryReadByte() |
| 300 | if err != nil { |
| 301 | return n, err |
| 302 | } |
| 303 | if !retry { |
| 304 | buf[n] = b |
| 305 | n++ |
| 306 | } |
| 307 | if n > 0 && c.r.Buffered() == 0 { |
| 308 | // Don't block if can't return more data. |
| 309 | return n, err |
| 310 | } |
| 311 | } |
| 312 | return n, nil |
| 313 | } |
| 314 | |
| 315 | // ReadBytes works like bufio.ReadBytes |
| 316 | func (c *Conn) ReadBytes(delim byte) ([]byte, error) { |
| 317 | var line []byte |
| 318 | for { |
| 319 | b, err := c.ReadByte() |
| 320 | if err != nil { |
| 321 | return nil, err |
| 322 | } |
| 323 | line = append(line, b) |
| 324 | if b == delim { |
| 325 | break |
| 326 | } |
| 327 | } |
| 328 | return line, nil |
| 329 | } |
| 330 | |
| 331 | // SkipBytes works like ReadBytes but skips all read data. |
| 332 | func (c *Conn) SkipBytes(delim byte) error { |
| 333 | for { |
| 334 | b, err := c.ReadByte() |
| 335 | if err != nil { |
| 336 | return err |
| 337 | } |
| 338 | if b == delim { |
| 339 | break |
| 340 | } |
| 341 | } |
| 342 | return nil |
| 343 | } |
| 344 | |
| 345 | // ReadString works like bufio.ReadString |
| 346 | func (c *Conn) ReadString(delim byte) (string, error) { |
| 347 | bytes, err := c.ReadBytes(delim) |
| 348 | return string(bytes), err |
| 349 | } |
| 350 | |
| 351 | func (c *Conn) readUntil(read bool, delims ...string) ([]byte, int, error) { |
| 352 | if len(delims) == 0 { |
| 353 | return nil, 0, nil |
| 354 | } |
| 355 | p := make([]string, len(delims)) |
| 356 | for i, s := range delims { |
| 357 | if len(s) == 0 { |
| 358 | return nil, 0, nil |
| 359 | } |
| 360 | p[i] = s |
| 361 | } |
| 362 | var line []byte |
| 363 | for { |
| 364 | b, err := c.ReadByte() |
| 365 | if err != nil { |
| 366 | return nil, 0, err |
| 367 | } |
| 368 | if read { |
| 369 | line = append(line, b) |
| 370 | } |
| 371 | for i, s := range p { |
| 372 | if s[0] == b { |
| 373 | if len(s) == 1 { |
| 374 | return line, i, nil |
| 375 | } |
| 376 | p[i] = s[1:] |
| 377 | } else { |
| 378 | p[i] = delims[i] |
| 379 | } |
| 380 | } |
| 381 | } |
| 382 | panic(nil) |
| 383 | } |
| 384 | |
| 385 | // ReadUntilIndex reads from connection until one of delimiters occurs. Returns |
| 386 | // read data and an index of delimiter or error. |
| 387 | func (c *Conn) ReadUntilIndex(delims ...string) ([]byte, int, error) { |
| 388 | return c.readUntil(true, delims...) |
| 389 | } |
| 390 | |
| 391 | // ReadUntil works like ReadUntilIndex but don't return a delimiter index. |
| 392 | func (c *Conn) ReadUntil(delims ...string) ([]byte, error) { |
| 393 | d, _, err := c.readUntil(true, delims...) |
| 394 | return d, err |
| 395 | } |
| 396 | |
| 397 | // SkipUntilIndex works like ReadUntilIndex but skips all read data. |
| 398 | func (c *Conn) SkipUntilIndex(delims ...string) (int, error) { |
| 399 | _, i, err := c.readUntil(false, delims...) |
| 400 | return i, err |
| 401 | } |
| 402 | |
| 403 | // SkipUntil works like ReadUntil but skips all read data. |
| 404 | func (c *Conn) SkipUntil(delims ...string) error { |
| 405 | _, _, err := c.readUntil(false, delims...) |
| 406 | return err |
| 407 | } |
| 408 | |
| 409 | // Write is for implement an io.Writer interface |
| 410 | func (c *Conn) Write(buf []byte) (int, error) { |
| 411 | search := "\xff" |
| 412 | if c.unixWriteMode { |
| 413 | search = "\xff\n" |
| 414 | } |
| 415 | var ( |
| 416 | n int |
| 417 | err error |
| 418 | ) |
| 419 | for len(buf) > 0 { |
| 420 | var k int |
| 421 | i := bytes.IndexAny(buf, search) |
| 422 | if i == -1 { |
| 423 | k, err = c.Conn.Write(buf) |
| 424 | n += k |
| 425 | break |
| 426 | } |
| 427 | k, err = c.Conn.Write(buf[:i]) |
| 428 | n += k |
| 429 | if err != nil { |
| 430 | break |
| 431 | } |
| 432 | switch buf[i] { |
| 433 | case LF: |
| 434 | k, err = c.Conn.Write([]byte{CR, LF}) |
| 435 | case cmdIAC: |
| 436 | k, err = c.Conn.Write([]byte{cmdIAC, cmdIAC}) |
| 437 | } |
| 438 | n += k |
| 439 | if err != nil { |
| 440 | break |
| 441 | } |
| 442 | buf = buf[i+1:] |
| 443 | } |
| 444 | return n, err |
| 445 | } |