gitee.com/liu-zhao234568/cntest@v1.0.0/accounts/usbwallet/ledger.go (about)

     1  // Copyright 2017 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  // This file contains the implementation for interacting with the Ledger hardware
    18  // wallets. The wire protocol spec can be found in the Ledger Blue GitHub repo:
    19  // https://raw.githubusercontent.com/LedgerHQ/blue-app-eth/master/doc/ethapp.asc
    20  
    21  package usbwallet
    22  
    23  import (
    24  	"encoding/binary"
    25  	"encoding/hex"
    26  	"errors"
    27  	"fmt"
    28  	"io"
    29  	"math/big"
    30  
    31  	"gitee.com/liu-zhao234568/cntest/accounts"
    32  	"gitee.com/liu-zhao234568/cntest/common"
    33  	"gitee.com/liu-zhao234568/cntest/common/hexutil"
    34  	"gitee.com/liu-zhao234568/cntest/core/types"
    35  	"gitee.com/liu-zhao234568/cntest/crypto"
    36  	"gitee.com/liu-zhao234568/cntest/log"
    37  	"gitee.com/liu-zhao234568/cntest/rlp"
    38  )
    39  
    40  // ledgerOpcode is an enumeration encoding the supported Ledger opcodes.
    41  type ledgerOpcode byte
    42  
    43  // ledgerParam1 is an enumeration encoding the supported Ledger parameters for
    44  // specific opcodes. The same parameter values may be reused between opcodes.
    45  type ledgerParam1 byte
    46  
    47  // ledgerParam2 is an enumeration encoding the supported Ledger parameters for
    48  // specific opcodes. The same parameter values may be reused between opcodes.
    49  type ledgerParam2 byte
    50  
    51  const (
    52  	ledgerOpRetrieveAddress  ledgerOpcode = 0x02 // Returns the public key and Ethereum address for a given BIP 32 path
    53  	ledgerOpSignTransaction  ledgerOpcode = 0x04 // Signs an Ethereum transaction after having the user validate the parameters
    54  	ledgerOpGetConfiguration ledgerOpcode = 0x06 // Returns specific wallet application configuration
    55  	ledgerOpSignTypedMessage ledgerOpcode = 0x0c // Signs an Ethereum message following the EIP 712 specification
    56  
    57  	ledgerP1DirectlyFetchAddress    ledgerParam1 = 0x00 // Return address directly from the wallet
    58  	ledgerP1InitTypedMessageData    ledgerParam1 = 0x00 // First chunk of Typed Message data
    59  	ledgerP1InitTransactionData     ledgerParam1 = 0x00 // First transaction data block for signing
    60  	ledgerP1ContTransactionData     ledgerParam1 = 0x80 // Subsequent transaction data block for signing
    61  	ledgerP2DiscardAddressChainCode ledgerParam2 = 0x00 // Do not return the chain code along with the address
    62  )
    63  
    64  // errLedgerReplyInvalidHeader is the error message returned by a Ledger data exchange
    65  // if the device replies with a mismatching header. This usually means the device
    66  // is in browser mode.
    67  var errLedgerReplyInvalidHeader = errors.New("ledger: invalid reply header")
    68  
    69  // errLedgerInvalidVersionReply is the error message returned by a Ledger version retrieval
    70  // when a response does arrive, but it does not contain the expected data.
    71  var errLedgerInvalidVersionReply = errors.New("ledger: invalid version reply")
    72  
    73  // ledgerDriver implements the communication with a Ledger hardware wallet.
    74  type ledgerDriver struct {
    75  	device  io.ReadWriter // USB device connection to communicate through
    76  	version [3]byte       // Current version of the Ledger firmware (zero if app is offline)
    77  	browser bool          // Flag whether the Ledger is in browser mode (reply channel mismatch)
    78  	failure error         // Any failure that would make the device unusable
    79  	log     log.Logger    // Contextual logger to tag the ledger with its id
    80  }
    81  
    82  // newLedgerDriver creates a new instance of a Ledger USB protocol driver.
    83  func newLedgerDriver(logger log.Logger) driver {
    84  	return &ledgerDriver{
    85  		log: logger,
    86  	}
    87  }
    88  
    89  // Status implements usbwallet.driver, returning various states the Ledger can
    90  // currently be in.
    91  func (w *ledgerDriver) Status() (string, error) {
    92  	if w.failure != nil {
    93  		return fmt.Sprintf("Failed: %v", w.failure), w.failure
    94  	}
    95  	if w.browser {
    96  		return "Ethereum app in browser mode", w.failure
    97  	}
    98  	if w.offline() {
    99  		return "Ethereum app offline", w.failure
   100  	}
   101  	return fmt.Sprintf("Ethereum app v%d.%d.%d online", w.version[0], w.version[1], w.version[2]), w.failure
   102  }
   103  
   104  // offline returns whether the wallet and the Ethereum app is offline or not.
   105  //
   106  // The method assumes that the state lock is held!
   107  func (w *ledgerDriver) offline() bool {
   108  	return w.version == [3]byte{0, 0, 0}
   109  }
   110  
   111  // Open implements usbwallet.driver, attempting to initialize the connection to the
   112  // Ledger hardware wallet. The Ledger does not require a user passphrase, so that
   113  // parameter is silently discarded.
   114  func (w *ledgerDriver) Open(device io.ReadWriter, passphrase string) error {
   115  	w.device, w.failure = device, nil
   116  
   117  	_, err := w.ledgerDerive(accounts.DefaultBaseDerivationPath)
   118  	if err != nil {
   119  		// Ethereum app is not running or in browser mode, nothing more to do, return
   120  		if err == errLedgerReplyInvalidHeader {
   121  			w.browser = true
   122  		}
   123  		return nil
   124  	}
   125  	// Try to resolve the Ethereum app's version, will fail prior to v1.0.2
   126  	if w.version, err = w.ledgerVersion(); err != nil {
   127  		w.version = [3]byte{1, 0, 0} // Assume worst case, can't verify if v1.0.0 or v1.0.1
   128  	}
   129  	return nil
   130  }
   131  
   132  // Close implements usbwallet.driver, cleaning up and metadata maintained within
   133  // the Ledger driver.
   134  func (w *ledgerDriver) Close() error {
   135  	w.browser, w.version = false, [3]byte{}
   136  	return nil
   137  }
   138  
   139  // Heartbeat implements usbwallet.driver, performing a sanity check against the
   140  // Ledger to see if it's still online.
   141  func (w *ledgerDriver) Heartbeat() error {
   142  	if _, err := w.ledgerVersion(); err != nil && err != errLedgerInvalidVersionReply {
   143  		w.failure = err
   144  		return err
   145  	}
   146  	return nil
   147  }
   148  
   149  // Derive implements usbwallet.driver, sending a derivation request to the Ledger
   150  // and returning the Ethereum address located on that derivation path.
   151  func (w *ledgerDriver) Derive(path accounts.DerivationPath) (common.Address, error) {
   152  	return w.ledgerDerive(path)
   153  }
   154  
   155  // SignTx implements usbwallet.driver, sending the transaction to the Ledger and
   156  // waiting for the user to confirm or deny the transaction.
   157  //
   158  // Note, if the version of the Ethereum application running on the Ledger wallet is
   159  // too old to sign EIP-155 transactions, but such is requested nonetheless, an error
   160  // will be returned opposed to silently signing in Homestead mode.
   161  func (w *ledgerDriver) SignTx(path accounts.DerivationPath, tx *types.Transaction, chainID *big.Int) (common.Address, *types.Transaction, error) {
   162  	// If the Ethereum app doesn't run, abort
   163  	if w.offline() {
   164  		return common.Address{}, nil, accounts.ErrWalletClosed
   165  	}
   166  	// Ensure the wallet is capable of signing the given transaction
   167  	if chainID != nil && w.version[0] <= 1 && w.version[1] <= 0 && w.version[2] <= 2 {
   168  		//lint:ignore ST1005 brand name displayed on the console
   169  		return common.Address{}, nil, fmt.Errorf("Ledger v%d.%d.%d doesn't support signing this transaction, please update to v1.0.3 at least", w.version[0], w.version[1], w.version[2])
   170  	}
   171  	// All infos gathered and metadata checks out, request signing
   172  	return w.ledgerSign(path, tx, chainID)
   173  }
   174  
   175  // SignTypedMessage implements usbwallet.driver, sending the message to the Ledger and
   176  // waiting for the user to sign or deny the transaction.
   177  //
   178  // Note: this was introduced in the ledger 1.5.0 firmware
   179  func (w *ledgerDriver) SignTypedMessage(path accounts.DerivationPath, domainHash []byte, messageHash []byte) ([]byte, error) {
   180  	// If the Ethereum app doesn't run, abort
   181  	if w.offline() {
   182  		return nil, accounts.ErrWalletClosed
   183  	}
   184  	// Ensure the wallet is capable of signing the given transaction
   185  	if w.version[0] < 1 && w.version[1] < 5 {
   186  		//lint:ignore ST1005 brand name displayed on the console
   187  		return nil, fmt.Errorf("Ledger version >= 1.5.0 required for EIP-712 signing (found version v%d.%d.%d)", w.version[0], w.version[1], w.version[2])
   188  	}
   189  	// All infos gathered and metadata checks out, request signing
   190  	return w.ledgerSignTypedMessage(path, domainHash, messageHash)
   191  }
   192  
   193  // ledgerVersion retrieves the current version of the Ethereum wallet app running
   194  // on the Ledger wallet.
   195  //
   196  // The version retrieval protocol is defined as follows:
   197  //
   198  //   CLA | INS | P1 | P2 | Lc | Le
   199  //   ----+-----+----+----+----+---
   200  //    E0 | 06  | 00 | 00 | 00 | 04
   201  //
   202  // With no input data, and the output data being:
   203  //
   204  //   Description                                        | Length
   205  //   ---------------------------------------------------+--------
   206  //   Flags 01: arbitrary data signature enabled by user | 1 byte
   207  //   Application major version                          | 1 byte
   208  //   Application minor version                          | 1 byte
   209  //   Application patch version                          | 1 byte
   210  func (w *ledgerDriver) ledgerVersion() ([3]byte, error) {
   211  	// Send the request and wait for the response
   212  	reply, err := w.ledgerExchange(ledgerOpGetConfiguration, 0, 0, nil)
   213  	if err != nil {
   214  		return [3]byte{}, err
   215  	}
   216  	if len(reply) != 4 {
   217  		return [3]byte{}, errLedgerInvalidVersionReply
   218  	}
   219  	// Cache the version for future reference
   220  	var version [3]byte
   221  	copy(version[:], reply[1:])
   222  	return version, nil
   223  }
   224  
   225  // ledgerDerive retrieves the currently active Ethereum address from a Ledger
   226  // wallet at the specified derivation path.
   227  //
   228  // The address derivation protocol is defined as follows:
   229  //
   230  //   CLA | INS | P1 | P2 | Lc  | Le
   231  //   ----+-----+----+----+-----+---
   232  //    E0 | 02  | 00 return address
   233  //               01 display address and confirm before returning
   234  //                  | 00: do not return the chain code
   235  //                  | 01: return the chain code
   236  //                       | var | 00
   237  //
   238  // Where the input data is:
   239  //
   240  //   Description                                      | Length
   241  //   -------------------------------------------------+--------
   242  //   Number of BIP 32 derivations to perform (max 10) | 1 byte
   243  //   First derivation index (big endian)              | 4 bytes
   244  //   ...                                              | 4 bytes
   245  //   Last derivation index (big endian)               | 4 bytes
   246  //
   247  // And the output data is:
   248  //
   249  //   Description             | Length
   250  //   ------------------------+-------------------
   251  //   Public Key length       | 1 byte
   252  //   Uncompressed Public Key | arbitrary
   253  //   Ethereum address length | 1 byte
   254  //   Ethereum address        | 40 bytes hex ascii
   255  //   Chain code if requested | 32 bytes
   256  func (w *ledgerDriver) ledgerDerive(derivationPath []uint32) (common.Address, error) {
   257  	// Flatten the derivation path into the Ledger request
   258  	path := make([]byte, 1+4*len(derivationPath))
   259  	path[0] = byte(len(derivationPath))
   260  	for i, component := range derivationPath {
   261  		binary.BigEndian.PutUint32(path[1+4*i:], component)
   262  	}
   263  	// Send the request and wait for the response
   264  	reply, err := w.ledgerExchange(ledgerOpRetrieveAddress, ledgerP1DirectlyFetchAddress, ledgerP2DiscardAddressChainCode, path)
   265  	if err != nil {
   266  		return common.Address{}, err
   267  	}
   268  	// Discard the public key, we don't need that for now
   269  	if len(reply) < 1 || len(reply) < 1+int(reply[0]) {
   270  		return common.Address{}, errors.New("reply lacks public key entry")
   271  	}
   272  	reply = reply[1+int(reply[0]):]
   273  
   274  	// Extract the Ethereum hex address string
   275  	if len(reply) < 1 || len(reply) < 1+int(reply[0]) {
   276  		return common.Address{}, errors.New("reply lacks address entry")
   277  	}
   278  	hexstr := reply[1 : 1+int(reply[0])]
   279  
   280  	// Decode the hex sting into an Ethereum address and return
   281  	var address common.Address
   282  	if _, err = hex.Decode(address[:], hexstr); err != nil {
   283  		return common.Address{}, err
   284  	}
   285  	return address, nil
   286  }
   287  
   288  // ledgerSign sends the transaction to the Ledger wallet, and waits for the user
   289  // to confirm or deny the transaction.
   290  //
   291  // The transaction signing protocol is defined as follows:
   292  //
   293  //   CLA | INS | P1 | P2 | Lc  | Le
   294  //   ----+-----+----+----+-----+---
   295  //    E0 | 04  | 00: first transaction data block
   296  //               80: subsequent transaction data block
   297  //                  | 00 | variable | variable
   298  //
   299  // Where the input for the first transaction block (first 255 bytes) is:
   300  //
   301  //   Description                                      | Length
   302  //   -------------------------------------------------+----------
   303  //   Number of BIP 32 derivations to perform (max 10) | 1 byte
   304  //   First derivation index (big endian)              | 4 bytes
   305  //   ...                                              | 4 bytes
   306  //   Last derivation index (big endian)               | 4 bytes
   307  //   RLP transaction chunk                            | arbitrary
   308  //
   309  // And the input for subsequent transaction blocks (first 255 bytes) are:
   310  //
   311  //   Description           | Length
   312  //   ----------------------+----------
   313  //   RLP transaction chunk | arbitrary
   314  //
   315  // And the output data is:
   316  //
   317  //   Description | Length
   318  //   ------------+---------
   319  //   signature V | 1 byte
   320  //   signature R | 32 bytes
   321  //   signature S | 32 bytes
   322  func (w *ledgerDriver) ledgerSign(derivationPath []uint32, tx *types.Transaction, chainID *big.Int) (common.Address, *types.Transaction, error) {
   323  	// Flatten the derivation path into the Ledger request
   324  	path := make([]byte, 1+4*len(derivationPath))
   325  	path[0] = byte(len(derivationPath))
   326  	for i, component := range derivationPath {
   327  		binary.BigEndian.PutUint32(path[1+4*i:], component)
   328  	}
   329  	// Create the transaction RLP based on whether legacy or EIP155 signing was requested
   330  	var (
   331  		txrlp []byte
   332  		err   error
   333  	)
   334  	if chainID == nil {
   335  		if txrlp, err = rlp.EncodeToBytes([]interface{}{tx.Nonce(), tx.GasPrice(), tx.Gas(), tx.To(), tx.Value(), tx.Data()}); err != nil {
   336  			return common.Address{}, nil, err
   337  		}
   338  	} else {
   339  		if txrlp, err = rlp.EncodeToBytes([]interface{}{tx.Nonce(), tx.GasPrice(), tx.Gas(), tx.To(), tx.Value(), tx.Data(), chainID, big.NewInt(0), big.NewInt(0)}); err != nil {
   340  			return common.Address{}, nil, err
   341  		}
   342  	}
   343  	payload := append(path, txrlp...)
   344  
   345  	// Send the request and wait for the response
   346  	var (
   347  		op    = ledgerP1InitTransactionData
   348  		reply []byte
   349  	)
   350  	for len(payload) > 0 {
   351  		// Calculate the size of the next data chunk
   352  		chunk := 255
   353  		if chunk > len(payload) {
   354  			chunk = len(payload)
   355  		}
   356  		// Send the chunk over, ensuring it's processed correctly
   357  		reply, err = w.ledgerExchange(ledgerOpSignTransaction, op, 0, payload[:chunk])
   358  		if err != nil {
   359  			return common.Address{}, nil, err
   360  		}
   361  		// Shift the payload and ensure subsequent chunks are marked as such
   362  		payload = payload[chunk:]
   363  		op = ledgerP1ContTransactionData
   364  	}
   365  	// Extract the Ethereum signature and do a sanity validation
   366  	if len(reply) != crypto.SignatureLength {
   367  		return common.Address{}, nil, errors.New("reply lacks signature")
   368  	}
   369  	signature := append(reply[1:], reply[0])
   370  
   371  	// Create the correct signer and signature transform based on the chain ID
   372  	var signer types.Signer
   373  	if chainID == nil {
   374  		signer = new(types.HomesteadSigner)
   375  	} else {
   376  		signer = types.NewEIP155Signer(chainID)
   377  		signature[64] -= byte(chainID.Uint64()*2 + 35)
   378  	}
   379  	signed, err := tx.WithSignature(signer, signature)
   380  	if err != nil {
   381  		return common.Address{}, nil, err
   382  	}
   383  	sender, err := types.Sender(signer, signed)
   384  	if err != nil {
   385  		return common.Address{}, nil, err
   386  	}
   387  	return sender, signed, nil
   388  }
   389  
   390  // ledgerSignTypedMessage sends the transaction to the Ledger wallet, and waits for the user
   391  // to confirm or deny the transaction.
   392  //
   393  // The signing protocol is defined as follows:
   394  //
   395  //   CLA | INS | P1 | P2                          | Lc  | Le
   396  //   ----+-----+----+-----------------------------+-----+---
   397  //    E0 | 0C  | 00 | implementation version : 00 | variable | variable
   398  //
   399  // Where the input is:
   400  //
   401  //   Description                                      | Length
   402  //   -------------------------------------------------+----------
   403  //   Number of BIP 32 derivations to perform (max 10) | 1 byte
   404  //   First derivation index (big endian)              | 4 bytes
   405  //   ...                                              | 4 bytes
   406  //   Last derivation index (big endian)               | 4 bytes
   407  //   domain hash                                      | 32 bytes
   408  //   message hash                                     | 32 bytes
   409  //
   410  //
   411  //
   412  // And the output data is:
   413  //
   414  //   Description | Length
   415  //   ------------+---------
   416  //   signature V | 1 byte
   417  //   signature R | 32 bytes
   418  //   signature S | 32 bytes
   419  func (w *ledgerDriver) ledgerSignTypedMessage(derivationPath []uint32, domainHash []byte, messageHash []byte) ([]byte, error) {
   420  	// Flatten the derivation path into the Ledger request
   421  	path := make([]byte, 1+4*len(derivationPath))
   422  	path[0] = byte(len(derivationPath))
   423  	for i, component := range derivationPath {
   424  		binary.BigEndian.PutUint32(path[1+4*i:], component)
   425  	}
   426  	// Create the 712 message
   427  	payload := append(path, domainHash...)
   428  	payload = append(payload, messageHash...)
   429  
   430  	// Send the request and wait for the response
   431  	var (
   432  		op    = ledgerP1InitTypedMessageData
   433  		reply []byte
   434  		err   error
   435  	)
   436  
   437  	// Send the message over, ensuring it's processed correctly
   438  	reply, err = w.ledgerExchange(ledgerOpSignTypedMessage, op, 0, payload)
   439  
   440  	if err != nil {
   441  		return nil, err
   442  	}
   443  
   444  	// Extract the Ethereum signature and do a sanity validation
   445  	if len(reply) != crypto.SignatureLength {
   446  		return nil, errors.New("reply lacks signature")
   447  	}
   448  	signature := append(reply[1:], reply[0])
   449  	return signature, nil
   450  }
   451  
   452  // ledgerExchange performs a data exchange with the Ledger wallet, sending it a
   453  // message and retrieving the response.
   454  //
   455  // The common transport header is defined as follows:
   456  //
   457  //  Description                           | Length
   458  //  --------------------------------------+----------
   459  //  Communication channel ID (big endian) | 2 bytes
   460  //  Command tag                           | 1 byte
   461  //  Packet sequence index (big endian)    | 2 bytes
   462  //  Payload                               | arbitrary
   463  //
   464  // The Communication channel ID allows commands multiplexing over the same
   465  // physical link. It is not used for the time being, and should be set to 0101
   466  // to avoid compatibility issues with implementations ignoring a leading 00 byte.
   467  //
   468  // The Command tag describes the message content. Use TAG_APDU (0x05) for standard
   469  // APDU payloads, or TAG_PING (0x02) for a simple link test.
   470  //
   471  // The Packet sequence index describes the current sequence for fragmented payloads.
   472  // The first fragment index is 0x00.
   473  //
   474  // APDU Command payloads are encoded as follows:
   475  //
   476  //  Description              | Length
   477  //  -----------------------------------
   478  //  APDU length (big endian) | 2 bytes
   479  //  APDU CLA                 | 1 byte
   480  //  APDU INS                 | 1 byte
   481  //  APDU P1                  | 1 byte
   482  //  APDU P2                  | 1 byte
   483  //  APDU length              | 1 byte
   484  //  Optional APDU data       | arbitrary
   485  func (w *ledgerDriver) ledgerExchange(opcode ledgerOpcode, p1 ledgerParam1, p2 ledgerParam2, data []byte) ([]byte, error) {
   486  	// Construct the message payload, possibly split into multiple chunks
   487  	apdu := make([]byte, 2, 7+len(data))
   488  
   489  	binary.BigEndian.PutUint16(apdu, uint16(5+len(data)))
   490  	apdu = append(apdu, []byte{0xe0, byte(opcode), byte(p1), byte(p2), byte(len(data))}...)
   491  	apdu = append(apdu, data...)
   492  
   493  	// Stream all the chunks to the device
   494  	header := []byte{0x01, 0x01, 0x05, 0x00, 0x00} // Channel ID and command tag appended
   495  	chunk := make([]byte, 64)
   496  	space := len(chunk) - len(header)
   497  
   498  	for i := 0; len(apdu) > 0; i++ {
   499  		// Construct the new message to stream
   500  		chunk = append(chunk[:0], header...)
   501  		binary.BigEndian.PutUint16(chunk[3:], uint16(i))
   502  
   503  		if len(apdu) > space {
   504  			chunk = append(chunk, apdu[:space]...)
   505  			apdu = apdu[space:]
   506  		} else {
   507  			chunk = append(chunk, apdu...)
   508  			apdu = nil
   509  		}
   510  		// Send over to the device
   511  		w.log.Trace("Data chunk sent to the Ledger", "chunk", hexutil.Bytes(chunk))
   512  		if _, err := w.device.Write(chunk); err != nil {
   513  			return nil, err
   514  		}
   515  	}
   516  	// Stream the reply back from the wallet in 64 byte chunks
   517  	var reply []byte
   518  	chunk = chunk[:64] // Yeah, we surely have enough space
   519  	for {
   520  		// Read the next chunk from the Ledger wallet
   521  		if _, err := io.ReadFull(w.device, chunk); err != nil {
   522  			return nil, err
   523  		}
   524  		w.log.Trace("Data chunk received from the Ledger", "chunk", hexutil.Bytes(chunk))
   525  
   526  		// Make sure the transport header matches
   527  		if chunk[0] != 0x01 || chunk[1] != 0x01 || chunk[2] != 0x05 {
   528  			return nil, errLedgerReplyInvalidHeader
   529  		}
   530  		// If it's the first chunk, retrieve the total message length
   531  		var payload []byte
   532  
   533  		if chunk[3] == 0x00 && chunk[4] == 0x00 {
   534  			reply = make([]byte, 0, int(binary.BigEndian.Uint16(chunk[5:7])))
   535  			payload = chunk[7:]
   536  		} else {
   537  			payload = chunk[5:]
   538  		}
   539  		// Append to the reply and stop when filled up
   540  		if left := cap(reply) - len(reply); left > len(payload) {
   541  			reply = append(reply, payload...)
   542  		} else {
   543  			reply = append(reply, payload[:left]...)
   544  			break
   545  		}
   546  	}
   547  	return reply[:len(reply)-2], nil
   548  }