Don Newton | 379ae25 | 2019-04-01 12:17:06 -0400 | [diff] [blame^] | 1 | // Copyright (C) MongoDB, Inc. 2017-present. |
| 2 | // |
| 3 | // Licensed under the Apache License, Version 2.0 (the "License"); you may |
| 4 | // not use this file except in compliance with the License. You may obtain |
| 5 | // a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 |
| 6 | |
| 7 | package bsonrw |
| 8 | |
| 9 | import ( |
| 10 | "errors" |
| 11 | "fmt" |
| 12 | "io" |
| 13 | "math" |
| 14 | "strconv" |
| 15 | "sync" |
| 16 | |
| 17 | "github.com/mongodb/mongo-go-driver/bson/bsontype" |
| 18 | "github.com/mongodb/mongo-go-driver/bson/primitive" |
| 19 | "github.com/mongodb/mongo-go-driver/x/bsonx/bsoncore" |
| 20 | ) |
| 21 | |
| 22 | var _ ValueWriter = (*valueWriter)(nil) |
| 23 | |
| 24 | var vwPool = sync.Pool{ |
| 25 | New: func() interface{} { |
| 26 | return new(valueWriter) |
| 27 | }, |
| 28 | } |
| 29 | |
| 30 | // BSONValueWriterPool is a pool for BSON ValueWriters. |
| 31 | type BSONValueWriterPool struct { |
| 32 | pool sync.Pool |
| 33 | } |
| 34 | |
| 35 | // NewBSONValueWriterPool creates a new pool for ValueWriter instances that write to BSON. |
| 36 | func NewBSONValueWriterPool() *BSONValueWriterPool { |
| 37 | return &BSONValueWriterPool{ |
| 38 | pool: sync.Pool{ |
| 39 | New: func() interface{} { |
| 40 | return new(valueWriter) |
| 41 | }, |
| 42 | }, |
| 43 | } |
| 44 | } |
| 45 | |
| 46 | // Get retrieves a BSON ValueWriter from the pool and resets it to use w as the destination. |
| 47 | func (bvwp *BSONValueWriterPool) Get(w io.Writer) ValueWriter { |
| 48 | vw := bvwp.pool.Get().(*valueWriter) |
| 49 | if writer, ok := w.(*SliceWriter); ok { |
| 50 | vw.reset(*writer) |
| 51 | vw.w = writer |
| 52 | return vw |
| 53 | } |
| 54 | vw.buf = vw.buf[:0] |
| 55 | vw.w = w |
| 56 | return vw |
| 57 | } |
| 58 | |
| 59 | // Put inserts a ValueWriter into the pool. If the ValueWriter is not a BSON ValueWriter, nothing |
| 60 | // happens and ok will be false. |
| 61 | func (bvwp *BSONValueWriterPool) Put(vw ValueWriter) (ok bool) { |
| 62 | bvw, ok := vw.(*valueWriter) |
| 63 | if !ok { |
| 64 | return false |
| 65 | } |
| 66 | |
| 67 | if _, ok := bvw.w.(*SliceWriter); ok { |
| 68 | bvw.buf = nil |
| 69 | } |
| 70 | bvw.w = nil |
| 71 | |
| 72 | bvwp.pool.Put(bvw) |
| 73 | return true |
| 74 | } |
| 75 | |
| 76 | // This is here so that during testing we can change it and not require |
| 77 | // allocating a 4GB slice. |
| 78 | var maxSize = math.MaxInt32 |
| 79 | |
| 80 | var errNilWriter = errors.New("cannot create a ValueWriter from a nil io.Writer") |
| 81 | |
| 82 | type errMaxDocumentSizeExceeded struct { |
| 83 | size int64 |
| 84 | } |
| 85 | |
| 86 | func (mdse errMaxDocumentSizeExceeded) Error() string { |
| 87 | return fmt.Sprintf("document size (%d) is larger than the max int32", mdse.size) |
| 88 | } |
| 89 | |
| 90 | type vwMode int |
| 91 | |
| 92 | const ( |
| 93 | _ vwMode = iota |
| 94 | vwTopLevel |
| 95 | vwDocument |
| 96 | vwArray |
| 97 | vwValue |
| 98 | vwElement |
| 99 | vwCodeWithScope |
| 100 | ) |
| 101 | |
| 102 | func (vm vwMode) String() string { |
| 103 | var str string |
| 104 | |
| 105 | switch vm { |
| 106 | case vwTopLevel: |
| 107 | str = "TopLevel" |
| 108 | case vwDocument: |
| 109 | str = "DocumentMode" |
| 110 | case vwArray: |
| 111 | str = "ArrayMode" |
| 112 | case vwValue: |
| 113 | str = "ValueMode" |
| 114 | case vwElement: |
| 115 | str = "ElementMode" |
| 116 | case vwCodeWithScope: |
| 117 | str = "CodeWithScopeMode" |
| 118 | default: |
| 119 | str = "UnknownMode" |
| 120 | } |
| 121 | |
| 122 | return str |
| 123 | } |
| 124 | |
| 125 | type vwState struct { |
| 126 | mode mode |
| 127 | key string |
| 128 | arrkey int |
| 129 | start int32 |
| 130 | } |
| 131 | |
| 132 | type valueWriter struct { |
| 133 | w io.Writer |
| 134 | buf []byte |
| 135 | |
| 136 | stack []vwState |
| 137 | frame int64 |
| 138 | } |
| 139 | |
| 140 | func (vw *valueWriter) advanceFrame() { |
| 141 | if vw.frame+1 >= int64(len(vw.stack)) { // We need to grow the stack |
| 142 | length := len(vw.stack) |
| 143 | if length+1 >= cap(vw.stack) { |
| 144 | // double it |
| 145 | buf := make([]vwState, 2*cap(vw.stack)+1) |
| 146 | copy(buf, vw.stack) |
| 147 | vw.stack = buf |
| 148 | } |
| 149 | vw.stack = vw.stack[:length+1] |
| 150 | } |
| 151 | vw.frame++ |
| 152 | } |
| 153 | |
| 154 | func (vw *valueWriter) push(m mode) { |
| 155 | vw.advanceFrame() |
| 156 | |
| 157 | // Clean the stack |
| 158 | vw.stack[vw.frame].mode = m |
| 159 | vw.stack[vw.frame].key = "" |
| 160 | vw.stack[vw.frame].arrkey = 0 |
| 161 | vw.stack[vw.frame].start = 0 |
| 162 | |
| 163 | vw.stack[vw.frame].mode = m |
| 164 | switch m { |
| 165 | case mDocument, mArray, mCodeWithScope: |
| 166 | vw.reserveLength() |
| 167 | } |
| 168 | } |
| 169 | |
| 170 | func (vw *valueWriter) reserveLength() { |
| 171 | vw.stack[vw.frame].start = int32(len(vw.buf)) |
| 172 | vw.buf = append(vw.buf, 0x00, 0x00, 0x00, 0x00) |
| 173 | } |
| 174 | |
| 175 | func (vw *valueWriter) pop() { |
| 176 | switch vw.stack[vw.frame].mode { |
| 177 | case mElement, mValue: |
| 178 | vw.frame-- |
| 179 | case mDocument, mArray, mCodeWithScope: |
| 180 | vw.frame -= 2 // we pop twice to jump over the mElement: mDocument -> mElement -> mDocument/mTopLevel/etc... |
| 181 | } |
| 182 | } |
| 183 | |
| 184 | // NewBSONValueWriter creates a ValueWriter that writes BSON to w. |
| 185 | // |
| 186 | // This ValueWriter will only write entire documents to the io.Writer and it |
| 187 | // will buffer the document as it is built. |
| 188 | func NewBSONValueWriter(w io.Writer) (ValueWriter, error) { |
| 189 | if w == nil { |
| 190 | return nil, errNilWriter |
| 191 | } |
| 192 | return newValueWriter(w), nil |
| 193 | } |
| 194 | |
| 195 | func newValueWriter(w io.Writer) *valueWriter { |
| 196 | vw := new(valueWriter) |
| 197 | stack := make([]vwState, 1, 5) |
| 198 | stack[0] = vwState{mode: mTopLevel} |
| 199 | vw.w = w |
| 200 | vw.stack = stack |
| 201 | |
| 202 | return vw |
| 203 | } |
| 204 | |
| 205 | func newValueWriterFromSlice(buf []byte) *valueWriter { |
| 206 | vw := new(valueWriter) |
| 207 | stack := make([]vwState, 1, 5) |
| 208 | stack[0] = vwState{mode: mTopLevel} |
| 209 | vw.stack = stack |
| 210 | vw.buf = buf |
| 211 | |
| 212 | return vw |
| 213 | } |
| 214 | |
| 215 | func (vw *valueWriter) reset(buf []byte) { |
| 216 | if vw.stack == nil { |
| 217 | vw.stack = make([]vwState, 1, 5) |
| 218 | } |
| 219 | vw.stack = vw.stack[:1] |
| 220 | vw.stack[0] = vwState{mode: mTopLevel} |
| 221 | vw.buf = buf |
| 222 | vw.frame = 0 |
| 223 | vw.w = nil |
| 224 | } |
| 225 | |
| 226 | func (vw *valueWriter) invalidTransitionError(destination mode, name string, modes []mode) error { |
| 227 | te := TransitionError{ |
| 228 | name: name, |
| 229 | current: vw.stack[vw.frame].mode, |
| 230 | destination: destination, |
| 231 | modes: modes, |
| 232 | action: "write", |
| 233 | } |
| 234 | if vw.frame != 0 { |
| 235 | te.parent = vw.stack[vw.frame-1].mode |
| 236 | } |
| 237 | return te |
| 238 | } |
| 239 | |
| 240 | func (vw *valueWriter) writeElementHeader(t bsontype.Type, destination mode, callerName string, addmodes ...mode) error { |
| 241 | switch vw.stack[vw.frame].mode { |
| 242 | case mElement: |
| 243 | vw.buf = bsoncore.AppendHeader(vw.buf, t, vw.stack[vw.frame].key) |
| 244 | case mValue: |
| 245 | // TODO: Do this with a cache of the first 1000 or so array keys. |
| 246 | vw.buf = bsoncore.AppendHeader(vw.buf, t, strconv.Itoa(vw.stack[vw.frame].arrkey)) |
| 247 | default: |
| 248 | modes := []mode{mElement, mValue} |
| 249 | if addmodes != nil { |
| 250 | modes = append(modes, addmodes...) |
| 251 | } |
| 252 | return vw.invalidTransitionError(destination, callerName, modes) |
| 253 | } |
| 254 | |
| 255 | return nil |
| 256 | } |
| 257 | |
| 258 | func (vw *valueWriter) WriteValueBytes(t bsontype.Type, b []byte) error { |
| 259 | if err := vw.writeElementHeader(t, mode(0), "WriteValueBytes"); err != nil { |
| 260 | return err |
| 261 | } |
| 262 | vw.buf = append(vw.buf, b...) |
| 263 | vw.pop() |
| 264 | return nil |
| 265 | } |
| 266 | |
| 267 | func (vw *valueWriter) WriteArray() (ArrayWriter, error) { |
| 268 | if err := vw.writeElementHeader(bsontype.Array, mArray, "WriteArray"); err != nil { |
| 269 | return nil, err |
| 270 | } |
| 271 | |
| 272 | vw.push(mArray) |
| 273 | |
| 274 | return vw, nil |
| 275 | } |
| 276 | |
| 277 | func (vw *valueWriter) WriteBinary(b []byte) error { |
| 278 | return vw.WriteBinaryWithSubtype(b, 0x00) |
| 279 | } |
| 280 | |
| 281 | func (vw *valueWriter) WriteBinaryWithSubtype(b []byte, btype byte) error { |
| 282 | if err := vw.writeElementHeader(bsontype.Binary, mode(0), "WriteBinaryWithSubtype"); err != nil { |
| 283 | return err |
| 284 | } |
| 285 | |
| 286 | vw.buf = bsoncore.AppendBinary(vw.buf, btype, b) |
| 287 | vw.pop() |
| 288 | return nil |
| 289 | } |
| 290 | |
| 291 | func (vw *valueWriter) WriteBoolean(b bool) error { |
| 292 | if err := vw.writeElementHeader(bsontype.Boolean, mode(0), "WriteBoolean"); err != nil { |
| 293 | return err |
| 294 | } |
| 295 | |
| 296 | vw.buf = bsoncore.AppendBoolean(vw.buf, b) |
| 297 | vw.pop() |
| 298 | return nil |
| 299 | } |
| 300 | |
| 301 | func (vw *valueWriter) WriteCodeWithScope(code string) (DocumentWriter, error) { |
| 302 | if err := vw.writeElementHeader(bsontype.CodeWithScope, mCodeWithScope, "WriteCodeWithScope"); err != nil { |
| 303 | return nil, err |
| 304 | } |
| 305 | |
| 306 | // CodeWithScope is a different than other types because we need an extra |
| 307 | // frame on the stack. In the EndDocument code, we write the document |
| 308 | // length, pop, write the code with scope length, and pop. To simplify the |
| 309 | // pop code, we push a spacer frame that we'll always jump over. |
| 310 | vw.push(mCodeWithScope) |
| 311 | vw.buf = bsoncore.AppendString(vw.buf, code) |
| 312 | vw.push(mSpacer) |
| 313 | vw.push(mDocument) |
| 314 | |
| 315 | return vw, nil |
| 316 | } |
| 317 | |
| 318 | func (vw *valueWriter) WriteDBPointer(ns string, oid primitive.ObjectID) error { |
| 319 | if err := vw.writeElementHeader(bsontype.DBPointer, mode(0), "WriteDBPointer"); err != nil { |
| 320 | return err |
| 321 | } |
| 322 | |
| 323 | vw.buf = bsoncore.AppendDBPointer(vw.buf, ns, oid) |
| 324 | vw.pop() |
| 325 | return nil |
| 326 | } |
| 327 | |
| 328 | func (vw *valueWriter) WriteDateTime(dt int64) error { |
| 329 | if err := vw.writeElementHeader(bsontype.DateTime, mode(0), "WriteDateTime"); err != nil { |
| 330 | return err |
| 331 | } |
| 332 | |
| 333 | vw.buf = bsoncore.AppendDateTime(vw.buf, dt) |
| 334 | vw.pop() |
| 335 | return nil |
| 336 | } |
| 337 | |
| 338 | func (vw *valueWriter) WriteDecimal128(d128 primitive.Decimal128) error { |
| 339 | if err := vw.writeElementHeader(bsontype.Decimal128, mode(0), "WriteDecimal128"); err != nil { |
| 340 | return err |
| 341 | } |
| 342 | |
| 343 | vw.buf = bsoncore.AppendDecimal128(vw.buf, d128) |
| 344 | vw.pop() |
| 345 | return nil |
| 346 | } |
| 347 | |
| 348 | func (vw *valueWriter) WriteDouble(f float64) error { |
| 349 | if err := vw.writeElementHeader(bsontype.Double, mode(0), "WriteDouble"); err != nil { |
| 350 | return err |
| 351 | } |
| 352 | |
| 353 | vw.buf = bsoncore.AppendDouble(vw.buf, f) |
| 354 | vw.pop() |
| 355 | return nil |
| 356 | } |
| 357 | |
| 358 | func (vw *valueWriter) WriteInt32(i32 int32) error { |
| 359 | if err := vw.writeElementHeader(bsontype.Int32, mode(0), "WriteInt32"); err != nil { |
| 360 | return err |
| 361 | } |
| 362 | |
| 363 | vw.buf = bsoncore.AppendInt32(vw.buf, i32) |
| 364 | vw.pop() |
| 365 | return nil |
| 366 | } |
| 367 | |
| 368 | func (vw *valueWriter) WriteInt64(i64 int64) error { |
| 369 | if err := vw.writeElementHeader(bsontype.Int64, mode(0), "WriteInt64"); err != nil { |
| 370 | return err |
| 371 | } |
| 372 | |
| 373 | vw.buf = bsoncore.AppendInt64(vw.buf, i64) |
| 374 | vw.pop() |
| 375 | return nil |
| 376 | } |
| 377 | |
| 378 | func (vw *valueWriter) WriteJavascript(code string) error { |
| 379 | if err := vw.writeElementHeader(bsontype.JavaScript, mode(0), "WriteJavascript"); err != nil { |
| 380 | return err |
| 381 | } |
| 382 | |
| 383 | vw.buf = bsoncore.AppendJavaScript(vw.buf, code) |
| 384 | vw.pop() |
| 385 | return nil |
| 386 | } |
| 387 | |
| 388 | func (vw *valueWriter) WriteMaxKey() error { |
| 389 | if err := vw.writeElementHeader(bsontype.MaxKey, mode(0), "WriteMaxKey"); err != nil { |
| 390 | return err |
| 391 | } |
| 392 | |
| 393 | vw.pop() |
| 394 | return nil |
| 395 | } |
| 396 | |
| 397 | func (vw *valueWriter) WriteMinKey() error { |
| 398 | if err := vw.writeElementHeader(bsontype.MinKey, mode(0), "WriteMinKey"); err != nil { |
| 399 | return err |
| 400 | } |
| 401 | |
| 402 | vw.pop() |
| 403 | return nil |
| 404 | } |
| 405 | |
| 406 | func (vw *valueWriter) WriteNull() error { |
| 407 | if err := vw.writeElementHeader(bsontype.Null, mode(0), "WriteNull"); err != nil { |
| 408 | return err |
| 409 | } |
| 410 | |
| 411 | vw.pop() |
| 412 | return nil |
| 413 | } |
| 414 | |
| 415 | func (vw *valueWriter) WriteObjectID(oid primitive.ObjectID) error { |
| 416 | if err := vw.writeElementHeader(bsontype.ObjectID, mode(0), "WriteObjectID"); err != nil { |
| 417 | return err |
| 418 | } |
| 419 | |
| 420 | vw.buf = bsoncore.AppendObjectID(vw.buf, oid) |
| 421 | vw.pop() |
| 422 | return nil |
| 423 | } |
| 424 | |
| 425 | func (vw *valueWriter) WriteRegex(pattern string, options string) error { |
| 426 | if err := vw.writeElementHeader(bsontype.Regex, mode(0), "WriteRegex"); err != nil { |
| 427 | return err |
| 428 | } |
| 429 | |
| 430 | vw.buf = bsoncore.AppendRegex(vw.buf, pattern, sortStringAlphebeticAscending(options)) |
| 431 | vw.pop() |
| 432 | return nil |
| 433 | } |
| 434 | |
| 435 | func (vw *valueWriter) WriteString(s string) error { |
| 436 | if err := vw.writeElementHeader(bsontype.String, mode(0), "WriteString"); err != nil { |
| 437 | return err |
| 438 | } |
| 439 | |
| 440 | vw.buf = bsoncore.AppendString(vw.buf, s) |
| 441 | vw.pop() |
| 442 | return nil |
| 443 | } |
| 444 | |
| 445 | func (vw *valueWriter) WriteDocument() (DocumentWriter, error) { |
| 446 | if vw.stack[vw.frame].mode == mTopLevel { |
| 447 | vw.reserveLength() |
| 448 | return vw, nil |
| 449 | } |
| 450 | if err := vw.writeElementHeader(bsontype.EmbeddedDocument, mDocument, "WriteDocument", mTopLevel); err != nil { |
| 451 | return nil, err |
| 452 | } |
| 453 | |
| 454 | vw.push(mDocument) |
| 455 | return vw, nil |
| 456 | } |
| 457 | |
| 458 | func (vw *valueWriter) WriteSymbol(symbol string) error { |
| 459 | if err := vw.writeElementHeader(bsontype.Symbol, mode(0), "WriteSymbol"); err != nil { |
| 460 | return err |
| 461 | } |
| 462 | |
| 463 | vw.buf = bsoncore.AppendSymbol(vw.buf, symbol) |
| 464 | vw.pop() |
| 465 | return nil |
| 466 | } |
| 467 | |
| 468 | func (vw *valueWriter) WriteTimestamp(t uint32, i uint32) error { |
| 469 | if err := vw.writeElementHeader(bsontype.Timestamp, mode(0), "WriteTimestamp"); err != nil { |
| 470 | return err |
| 471 | } |
| 472 | |
| 473 | vw.buf = bsoncore.AppendTimestamp(vw.buf, t, i) |
| 474 | vw.pop() |
| 475 | return nil |
| 476 | } |
| 477 | |
| 478 | func (vw *valueWriter) WriteUndefined() error { |
| 479 | if err := vw.writeElementHeader(bsontype.Undefined, mode(0), "WriteUndefined"); err != nil { |
| 480 | return err |
| 481 | } |
| 482 | |
| 483 | vw.pop() |
| 484 | return nil |
| 485 | } |
| 486 | |
| 487 | func (vw *valueWriter) WriteDocumentElement(key string) (ValueWriter, error) { |
| 488 | switch vw.stack[vw.frame].mode { |
| 489 | case mTopLevel, mDocument: |
| 490 | default: |
| 491 | return nil, vw.invalidTransitionError(mElement, "WriteDocumentElement", []mode{mTopLevel, mDocument}) |
| 492 | } |
| 493 | |
| 494 | vw.push(mElement) |
| 495 | vw.stack[vw.frame].key = key |
| 496 | |
| 497 | return vw, nil |
| 498 | } |
| 499 | |
| 500 | func (vw *valueWriter) WriteDocumentEnd() error { |
| 501 | switch vw.stack[vw.frame].mode { |
| 502 | case mTopLevel, mDocument: |
| 503 | default: |
| 504 | return fmt.Errorf("incorrect mode to end document: %s", vw.stack[vw.frame].mode) |
| 505 | } |
| 506 | |
| 507 | vw.buf = append(vw.buf, 0x00) |
| 508 | |
| 509 | err := vw.writeLength() |
| 510 | if err != nil { |
| 511 | return err |
| 512 | } |
| 513 | |
| 514 | if vw.stack[vw.frame].mode == mTopLevel { |
| 515 | if vw.w != nil { |
| 516 | if sw, ok := vw.w.(*SliceWriter); ok { |
| 517 | *sw = vw.buf |
| 518 | } else { |
| 519 | _, err = vw.w.Write(vw.buf) |
| 520 | if err != nil { |
| 521 | return err |
| 522 | } |
| 523 | // reset buffer |
| 524 | vw.buf = vw.buf[:0] |
| 525 | } |
| 526 | } |
| 527 | } |
| 528 | |
| 529 | vw.pop() |
| 530 | |
| 531 | if vw.stack[vw.frame].mode == mCodeWithScope { |
| 532 | // We ignore the error here because of the gaurantee of writeLength. |
| 533 | // See the docs for writeLength for more info. |
| 534 | _ = vw.writeLength() |
| 535 | vw.pop() |
| 536 | } |
| 537 | return nil |
| 538 | } |
| 539 | |
| 540 | func (vw *valueWriter) WriteArrayElement() (ValueWriter, error) { |
| 541 | if vw.stack[vw.frame].mode != mArray { |
| 542 | return nil, vw.invalidTransitionError(mValue, "WriteArrayElement", []mode{mArray}) |
| 543 | } |
| 544 | |
| 545 | arrkey := vw.stack[vw.frame].arrkey |
| 546 | vw.stack[vw.frame].arrkey++ |
| 547 | |
| 548 | vw.push(mValue) |
| 549 | vw.stack[vw.frame].arrkey = arrkey |
| 550 | |
| 551 | return vw, nil |
| 552 | } |
| 553 | |
| 554 | func (vw *valueWriter) WriteArrayEnd() error { |
| 555 | if vw.stack[vw.frame].mode != mArray { |
| 556 | return fmt.Errorf("incorrect mode to end array: %s", vw.stack[vw.frame].mode) |
| 557 | } |
| 558 | |
| 559 | vw.buf = append(vw.buf, 0x00) |
| 560 | |
| 561 | err := vw.writeLength() |
| 562 | if err != nil { |
| 563 | return err |
| 564 | } |
| 565 | |
| 566 | vw.pop() |
| 567 | return nil |
| 568 | } |
| 569 | |
| 570 | // NOTE: We assume that if we call writeLength more than once the same function |
| 571 | // within the same function without altering the vw.buf that this method will |
| 572 | // not return an error. If this changes ensure that the following methods are |
| 573 | // updated: |
| 574 | // |
| 575 | // - WriteDocumentEnd |
| 576 | func (vw *valueWriter) writeLength() error { |
| 577 | length := len(vw.buf) |
| 578 | if length > maxSize { |
| 579 | return errMaxDocumentSizeExceeded{size: int64(len(vw.buf))} |
| 580 | } |
| 581 | length = length - int(vw.stack[vw.frame].start) |
| 582 | start := vw.stack[vw.frame].start |
| 583 | |
| 584 | vw.buf[start+0] = byte(length) |
| 585 | vw.buf[start+1] = byte(length >> 8) |
| 586 | vw.buf[start+2] = byte(length >> 16) |
| 587 | vw.buf[start+3] = byte(length >> 24) |
| 588 | return nil |
| 589 | } |