Merge pull request #1533 from OttoAllmendinger/add-buffer-writer

Add BufferWriter and BufferReader class

src/block.js

@@ -26,43 +26,24 @@ class Block {
   }
   static fromBuffer(buffer) {
     if (buffer.length < 80) throw new Error('Buffer too small (< 80 bytes)');
-    let offset = 0;
+    const bufferReader = new bufferutils_1.BufferReader(buffer);
-    const readSlice = n => {
-      offset += n;
-      return buffer.slice(offset - n, offset);
-    };
-    const readUInt32 = () => {
-      const i = buffer.readUInt32LE(offset);
-      offset += 4;
-      return i;
-    };
-    const readInt32 = () => {
-      const i = buffer.readInt32LE(offset);
-      offset += 4;
-      return i;
-    };
     const block = new Block();
-    block.version = readInt32();
+    block.version = bufferReader.readInt32();
-    block.prevHash = readSlice(32);
+    block.prevHash = bufferReader.readSlice(32);
-    block.merkleRoot = readSlice(32);
+    block.merkleRoot = bufferReader.readSlice(32);
-    block.timestamp = readUInt32();
+    block.timestamp = bufferReader.readUInt32();
-    block.bits = readUInt32();
+    block.bits = bufferReader.readUInt32();
-    block.nonce = readUInt32();
+    block.nonce = bufferReader.readUInt32();
     if (buffer.length === 80) return block;
-    const readVarInt = () => {
-      const vi = varuint.decode(buffer, offset);
-      offset += varuint.decode.bytes;
-      return vi;
-    };
     const readTransaction = () => {
       const tx = transaction_1.Transaction.fromBuffer(
-        buffer.slice(offset),
+        bufferReader.buffer.slice(bufferReader.offset),
         true,
       );
-      offset += tx.byteLength();
+      bufferReader.offset += tx.byteLength();
       return tx;
     };
-    const nTransactions = readVarInt();
+    const nTransactions = bufferReader.readVarInt();
     block.transactions = [];
     for (let i = 0; i < nTransactions; ++i) {
       const tx = readTransaction();
@@ -154,32 +135,20 @@ class Block {
   // TODO: buffer, offset compatibility
   toBuffer(headersOnly) {
     const buffer = Buffer.allocUnsafe(this.byteLength(headersOnly));
-    let offset = 0;
+    const bufferWriter = new bufferutils_1.BufferWriter(buffer);
-    const writeSlice = slice => {
+    bufferWriter.writeInt32(this.version);
-      slice.copy(buffer, offset);
+    bufferWriter.writeSlice(this.prevHash);
-      offset += slice.length;
+    bufferWriter.writeSlice(this.merkleRoot);
-    };
+    bufferWriter.writeUInt32(this.timestamp);
-    const writeInt32 = i => {
+    bufferWriter.writeUInt32(this.bits);
-      buffer.writeInt32LE(i, offset);
+    bufferWriter.writeUInt32(this.nonce);
-      offset += 4;
-    };
-    const writeUInt32 = i => {
-      buffer.writeUInt32LE(i, offset);
-      offset += 4;
-    };
-    writeInt32(this.version);
-    writeSlice(this.prevHash);
-    writeSlice(this.merkleRoot);
-    writeUInt32(this.timestamp);
-    writeUInt32(this.bits);
-    writeUInt32(this.nonce);
     if (headersOnly || !this.transactions) return buffer;
-    varuint.encode(this.transactions.length, buffer, offset);
+    varuint.encode(this.transactions.length, buffer, bufferWriter.offset);
-    offset += varuint.encode.bytes;
+    bufferWriter.offset += varuint.encode.bytes;
     this.transactions.forEach(tx => {
       const txSize = tx.byteLength(); // TODO: extract from toBuffer?
-      tx.toBuffer(buffer, offset);
+      tx.toBuffer(buffer, bufferWriter.offset);
-      offset += txSize;
+      bufferWriter.offset += txSize;
     });
     return buffer;
   }

src/bufferutils.js

@@ -1,5 +1,8 @@
 'use strict';
 Object.defineProperty(exports, '__esModule', { value: true });
+const types = require('./types');
+const typeforce = require('typeforce');
+const varuint = require('varuint-bitcoin');
 // https://github.com/feross/buffer/blob/master/index.js#L1127
 function verifuint(value, max) {
   if (typeof value !== 'number')
@@ -38,3 +41,97 @@ function reverseBuffer(buffer) {
   return buffer;
 }
 exports.reverseBuffer = reverseBuffer;
+/**
+ * Helper class for serialization of bitcoin data types into a pre-allocated buffer.
+ */
+class BufferWriter {
+  constructor(buffer, offset = 0) {
+    this.buffer = buffer;
+    this.offset = offset;
+    typeforce(types.tuple(types.Buffer, types.UInt32), [buffer, offset]);
+  }
+  writeUInt8(i) {
+    this.offset = this.buffer.writeUInt8(i, this.offset);
+  }
+  writeInt32(i) {
+    this.offset = this.buffer.writeInt32LE(i, this.offset);
+  }
+  writeUInt32(i) {
+    this.offset = this.buffer.writeUInt32LE(i, this.offset);
+  }
+  writeUInt64(i) {
+    this.offset = writeUInt64LE(this.buffer, i, this.offset);
+  }
+  writeVarInt(i) {
+    varuint.encode(i, this.buffer, this.offset);
+    this.offset += varuint.encode.bytes;
+  }
+  writeSlice(slice) {
+    if (this.buffer.length < this.offset + slice.length) {
+      throw new Error('Cannot write slice out of bounds');
+    }
+    this.offset += slice.copy(this.buffer, this.offset);
+  }
+  writeVarSlice(slice) {
+    this.writeVarInt(slice.length);
+    this.writeSlice(slice);
+  }
+  writeVector(vector) {
+    this.writeVarInt(vector.length);
+    vector.forEach(buf => this.writeVarSlice(buf));
+  }
+}
+exports.BufferWriter = BufferWriter;
+/**
+ * Helper class for reading of bitcoin data types from a buffer.
+ */
+class BufferReader {
+  constructor(buffer, offset = 0) {
+    this.buffer = buffer;
+    this.offset = offset;
+    typeforce(types.tuple(types.Buffer, types.UInt32), [buffer, offset]);
+  }
+  readUInt8() {
+    const result = this.buffer.readUInt8(this.offset);
+    this.offset++;
+    return result;
+  }
+  readInt32() {
+    const result = this.buffer.readInt32LE(this.offset);
+    this.offset += 4;
+    return result;
+  }
+  readUInt32() {
+    const result = this.buffer.readUInt32LE(this.offset);
+    this.offset += 4;
+    return result;
+  }
+  readUInt64() {
+    const result = readUInt64LE(this.buffer, this.offset);
+    this.offset += 8;
+    return result;
+  }
+  readVarInt() {
+    const vi = varuint.decode(this.buffer, this.offset);
+    this.offset += varuint.decode.bytes;
+    return vi;
+  }
+  readSlice(n) {
+    if (this.buffer.length < this.offset + n) {
+      throw new Error('Cannot read slice out of bounds');
+    }
+    const result = this.buffer.slice(this.offset, this.offset + n);
+    this.offset += n;
+    return result;
+  }
+  readVarSlice() {
+    return this.readSlice(this.readVarInt());
+  }
+  readVector() {
+    const count = this.readVarInt();
+    const vector = [];
+    for (let i = 0; i < count; i++) vector.push(this.readVarSlice());
+    return vector;
+  }
+}
+exports.BufferReader = BufferReader;

src/transaction.js

@@ -1,6 +1,5 @@
 'use strict';
 Object.defineProperty(exports, '__esModule', { value: true });
-const bufferutils = require('./bufferutils');
 const bufferutils_1 = require('./bufferutils');
 const bcrypto = require('./crypto');
 const bscript = require('./script');
@@ -47,80 +46,48 @@ class Transaction {
     this.outs = [];
   }
   static fromBuffer(buffer, _NO_STRICT) {
-    let offset = 0;
+    const bufferReader = new bufferutils_1.BufferReader(buffer);
-    function readSlice(n) {
-      offset += n;
-      return buffer.slice(offset - n, offset);
-    }
-    function readUInt32() {
-      const i = buffer.readUInt32LE(offset);
-      offset += 4;
-      return i;
-    }
-    function readInt32() {
-      const i = buffer.readInt32LE(offset);
-      offset += 4;
-      return i;
-    }
-    function readUInt64() {
-      const i = bufferutils.readUInt64LE(buffer, offset);
-      offset += 8;
-      return i;
-    }
-    function readVarInt() {
-      const vi = varuint.decode(buffer, offset);
-      offset += varuint.decode.bytes;
-      return vi;
-    }
-    function readVarSlice() {
-      return readSlice(readVarInt());
-    }
-    function readVector() {
-      const count = readVarInt();
-      const vector = [];
-      for (let i = 0; i < count; i++) vector.push(readVarSlice());
-      return vector;
-    }
     const tx = new Transaction();
-    tx.version = readInt32();
+    tx.version = bufferReader.readInt32();
-    const marker = buffer.readUInt8(offset);
+    const marker = bufferReader.readUInt8();
-    const flag = buffer.readUInt8(offset + 1);
+    const flag = bufferReader.readUInt8();
     let hasWitnesses = false;
     if (
       marker === Transaction.ADVANCED_TRANSACTION_MARKER &&
       flag === Transaction.ADVANCED_TRANSACTION_FLAG
     ) {
-      offset += 2;
       hasWitnesses = true;
+    } else {
+      bufferReader.offset -= 2;
     }
-    const vinLen = readVarInt();
+    const vinLen = bufferReader.readVarInt();
     for (let i = 0; i < vinLen; ++i) {
       tx.ins.push({
-        hash: readSlice(32),
+        hash: bufferReader.readSlice(32),
-        index: readUInt32(),
+        index: bufferReader.readUInt32(),
-        script: readVarSlice(),
+        script: bufferReader.readVarSlice(),
-        sequence: readUInt32(),
+        sequence: bufferReader.readUInt32(),
         witness: EMPTY_WITNESS,
       });
     }
-    const voutLen = readVarInt();
+    const voutLen = bufferReader.readVarInt();
     for (let i = 0; i < voutLen; ++i) {
       tx.outs.push({
-        value: readUInt64(),
+        value: bufferReader.readUInt64(),
-        script: readVarSlice(),
+        script: bufferReader.readVarSlice(),
       });
     }
     if (hasWitnesses) {
       for (let i = 0; i < vinLen; ++i) {
-        tx.ins[i].witness = readVector();
+        tx.ins[i].witness = bufferReader.readVector();
       }
       // was this pointless?
       if (!tx.hasWitnesses())
         throw new Error('Transaction has superfluous witness data');
     }
-    tx.locktime = readUInt32();
+    tx.locktime = bufferReader.readUInt32();
     if (_NO_STRICT) return tx;
-    if (offset !== buffer.length)
+    if (bufferReader.offset !== buffer.length)
       throw new Error('Transaction has unexpected data');
     return tx;
   }
@@ -296,33 +263,16 @@ class Transaction {
       arguments,
     );
     let tbuffer = Buffer.from([]);
-    let toffset = 0;
+    let bufferWriter;
-    function writeSlice(slice) {
-      toffset += slice.copy(tbuffer, toffset);
-    }
-    function writeUInt32(i) {
-      toffset = tbuffer.writeUInt32LE(i, toffset);
-    }
-    function writeUInt64(i) {
-      toffset = bufferutils.writeUInt64LE(tbuffer, i, toffset);
-    }
-    function writeVarInt(i) {
-      varuint.encode(i, tbuffer, toffset);
-      toffset += varuint.encode.bytes;
-    }
-    function writeVarSlice(slice) {
-      writeVarInt(slice.length);
-      writeSlice(slice);
-    }
     let hashOutputs = ZERO;
     let hashPrevouts = ZERO;
     let hashSequence = ZERO;
     if (!(hashType & Transaction.SIGHASH_ANYONECANPAY)) {
       tbuffer = Buffer.allocUnsafe(36 * this.ins.length);
-      toffset = 0;
+      bufferWriter = new bufferutils_1.BufferWriter(tbuffer, 0);
       this.ins.forEach(txIn => {
-        writeSlice(txIn.hash);
+        bufferWriter.writeSlice(txIn.hash);
-        writeUInt32(txIn.index);
+        bufferWriter.writeUInt32(txIn.index);
       });
       hashPrevouts = bcrypto.hash256(tbuffer);
     }
@@ -332,9 +282,9 @@ class Transaction {
       (hashType & 0x1f) !== Transaction.SIGHASH_NONE
     ) {
       tbuffer = Buffer.allocUnsafe(4 * this.ins.length);
-      toffset = 0;
+      bufferWriter = new bufferutils_1.BufferWriter(tbuffer, 0);
       this.ins.forEach(txIn => {
-        writeUInt32(txIn.sequence);
+        bufferWriter.writeUInt32(txIn.sequence);
       });
       hashSequence = bcrypto.hash256(tbuffer);
     }
@@ -346,10 +296,10 @@ class Transaction {
         return sum + 8 + varSliceSize(output.script);
       }, 0);
       tbuffer = Buffer.allocUnsafe(txOutsSize);
-      toffset = 0;
+      bufferWriter = new bufferutils_1.BufferWriter(tbuffer, 0);
       this.outs.forEach(out => {
-        writeUInt64(out.value);
+        bufferWriter.writeUInt64(out.value);
-        writeVarSlice(out.script);
+        bufferWriter.writeVarSlice(out.script);
       });
       hashOutputs = bcrypto.hash256(tbuffer);
     } else if (
@@ -358,25 +308,25 @@ class Transaction {
     ) {
       const output = this.outs[inIndex];
       tbuffer = Buffer.allocUnsafe(8 + varSliceSize(output.script));
-      toffset = 0;
+      bufferWriter = new bufferutils_1.BufferWriter(tbuffer, 0);
-      writeUInt64(output.value);
+      bufferWriter.writeUInt64(output.value);
-      writeVarSlice(output.script);
+      bufferWriter.writeVarSlice(output.script);
       hashOutputs = bcrypto.hash256(tbuffer);
     }
     tbuffer = Buffer.allocUnsafe(156 + varSliceSize(prevOutScript));
-    toffset = 0;
+    bufferWriter = new bufferutils_1.BufferWriter(tbuffer, 0);
     const input = this.ins[inIndex];
-    writeUInt32(this.version);
+    bufferWriter.writeUInt32(this.version);
-    writeSlice(hashPrevouts);
+    bufferWriter.writeSlice(hashPrevouts);
-    writeSlice(hashSequence);
+    bufferWriter.writeSlice(hashSequence);
-    writeSlice(input.hash);
+    bufferWriter.writeSlice(input.hash);
-    writeUInt32(input.index);
+    bufferWriter.writeUInt32(input.index);
-    writeVarSlice(prevOutScript);
+    bufferWriter.writeVarSlice(prevOutScript);
-    writeUInt64(value);
+    bufferWriter.writeUInt64(value);
-    writeUInt32(input.sequence);
+    bufferWriter.writeUInt32(input.sequence);
-    writeSlice(hashOutputs);
+    bufferWriter.writeSlice(hashOutputs);
-    writeUInt32(this.locktime);
+    bufferWriter.writeUInt32(this.locktime);
-    writeUInt32(hashType);
+    bufferWriter.writeUInt32(hashType);
     return bcrypto.hash256(tbuffer);
   }
   getHash(forWitness) {
@@ -404,64 +354,41 @@ class Transaction {
   }
   __toBuffer(buffer, initialOffset, _ALLOW_WITNESS = false) {
     if (!buffer) buffer = Buffer.allocUnsafe(this.byteLength(_ALLOW_WITNESS));
-    let offset = initialOffset || 0;
+    const bufferWriter = new bufferutils_1.BufferWriter(
-    function writeSlice(slice) {
+      buffer,
-      offset += slice.copy(buffer, offset);
+      initialOffset || 0,
-    }
+    );
-    function writeUInt8(i) {
+    bufferWriter.writeInt32(this.version);
-      offset = buffer.writeUInt8(i, offset);
-    }
-    function writeUInt32(i) {
-      offset = buffer.writeUInt32LE(i, offset);
-    }
-    function writeInt32(i) {
-      offset = buffer.writeInt32LE(i, offset);
-    }
-    function writeUInt64(i) {
-      offset = bufferutils.writeUInt64LE(buffer, i, offset);
-    }
-    function writeVarInt(i) {
-      varuint.encode(i, buffer, offset);
-      offset += varuint.encode.bytes;
-    }
-    function writeVarSlice(slice) {
-      writeVarInt(slice.length);
-      writeSlice(slice);
-    }
-    function writeVector(vector) {
-      writeVarInt(vector.length);
-      vector.forEach(writeVarSlice);
-    }
-    writeInt32(this.version);
     const hasWitnesses = _ALLOW_WITNESS && this.hasWitnesses();
     if (hasWitnesses) {
-      writeUInt8(Transaction.ADVANCED_TRANSACTION_MARKER);
+      bufferWriter.writeUInt8(Transaction.ADVANCED_TRANSACTION_MARKER);
-      writeUInt8(Transaction.ADVANCED_TRANSACTION_FLAG);
+      bufferWriter.writeUInt8(Transaction.ADVANCED_TRANSACTION_FLAG);
     }
-    writeVarInt(this.ins.length);
+    bufferWriter.writeVarInt(this.ins.length);
     this.ins.forEach(txIn => {
-      writeSlice(txIn.hash);
+      bufferWriter.writeSlice(txIn.hash);
-      writeUInt32(txIn.index);
+      bufferWriter.writeUInt32(txIn.index);
-      writeVarSlice(txIn.script);
+      bufferWriter.writeVarSlice(txIn.script);
-      writeUInt32(txIn.sequence);
+      bufferWriter.writeUInt32(txIn.sequence);
     });
-    writeVarInt(this.outs.length);
+    bufferWriter.writeVarInt(this.outs.length);
     this.outs.forEach(txOut => {
       if (isOutput(txOut)) {
-        writeUInt64(txOut.value);
+        bufferWriter.writeUInt64(txOut.value);
       } else {
-        writeSlice(txOut.valueBuffer);
+        bufferWriter.writeSlice(txOut.valueBuffer);
       }
-      writeVarSlice(txOut.script);
+      bufferWriter.writeVarSlice(txOut.script);
     });
     if (hasWitnesses) {
       this.ins.forEach(input => {
-        writeVector(input.witness);
+        bufferWriter.writeVector(input.witness);
       });
     }
-    writeUInt32(this.locktime);
+    bufferWriter.writeUInt32(this.locktime);
     // avoid slicing unless necessary
-    if (initialOffset !== undefined) return buffer.slice(initialOffset, offset);
+    if (initialOffset !== undefined)
+      return buffer.slice(initialOffset, bufferWriter.offset);
     return buffer;
   }
 }

test/bufferutils.spec.ts

@@ -1,10 +1,16 @@
 import * as assert from 'assert';
 import { describe, it } from 'mocha';
 import * as bufferutils from '../src/bufferutils';
+import { BufferReader, BufferWriter } from '../src/bufferutils';
 
 import * as fixtures from './fixtures/bufferutils.json';
+const varuint = require('varuint-bitcoin');
 
 describe('bufferutils', () => {
+  function concatToBuffer(values: number[][]): Buffer {
+    return Buffer.concat(values.map(data => Buffer.from(data)));
+  }
+
   describe('readUInt64LE', () => {
     fixtures.valid.forEach(f => {
       it('decodes ' + f.hex, () => {
@@ -46,4 +52,444 @@ describe('bufferutils', () => {
       });
     });
   });
+
+  describe('BufferWriter', () => {
+    function testBuffer(
+      bufferWriter: BufferWriter,
+      expectedBuffer: Buffer,
+      expectedOffset: number = expectedBuffer.length,
+    ): void {
+      assert.strictEqual(bufferWriter.offset, expectedOffset);
+      assert.deepStrictEqual(
+        bufferWriter.buffer.slice(0, expectedOffset),
+        expectedBuffer.slice(0, expectedOffset),
+      );
+    }
+
+    it('writeUint8', () => {
+      const values = [0, 1, 254, 255];
+      const expectedBuffer = Buffer.from([0, 1, 0xfe, 0xff]);
+      const bufferWriter = new BufferWriter(
+        Buffer.allocUnsafe(expectedBuffer.length),
+      );
+      values.forEach((v: number) => {
+        const expectedOffset = bufferWriter.offset + 1;
+        bufferWriter.writeUInt8(v);
+        testBuffer(bufferWriter, expectedBuffer, expectedOffset);
+      });
+      testBuffer(bufferWriter, expectedBuffer);
+    });
+
+    it('writeInt32', () => {
+      const values = [
+        0,
+        1,
+        Math.pow(2, 31) - 2,
+        Math.pow(2, 31) - 1,
+        -1,
+        -Math.pow(2, 31),
+      ];
+      const expectedBuffer = concatToBuffer([
+        [0, 0, 0, 0],
+        [1, 0, 0, 0],
+        [0xfe, 0xff, 0xff, 0x7f],
+        [0xff, 0xff, 0xff, 0x7f],
+        [0xff, 0xff, 0xff, 0xff],
+        [0x00, 0x00, 0x00, 0x80],
+      ]);
+      const bufferWriter = new BufferWriter(
+        Buffer.allocUnsafe(expectedBuffer.length),
+      );
+      values.forEach((value: number) => {
+        const expectedOffset = bufferWriter.offset + 4;
+        bufferWriter.writeInt32(value);
+        testBuffer(bufferWriter, expectedBuffer, expectedOffset);
+      });
+      testBuffer(bufferWriter, expectedBuffer);
+    });
+
+    it('writeUInt32', () => {
+      const maxUInt32 = Math.pow(2, 32) - 1;
+      const values = [0, 1, Math.pow(2, 16), maxUInt32];
+      const expectedBuffer = concatToBuffer([
+        [0, 0, 0, 0],
+        [1, 0, 0, 0],
+        [0, 0, 1, 0],
+        [0xff, 0xff, 0xff, 0xff],
+      ]);
+      const bufferWriter = new BufferWriter(
+        Buffer.allocUnsafe(expectedBuffer.length),
+      );
+      values.forEach((value: number) => {
+        const expectedOffset = bufferWriter.offset + 4;
+        bufferWriter.writeUInt32(value);
+        testBuffer(bufferWriter, expectedBuffer, expectedOffset);
+      });
+      testBuffer(bufferWriter, expectedBuffer);
+    });
+
+    it('writeUInt64', () => {
+      const values = [
+        0,
+        1,
+        Math.pow(2, 32),
+        Number.MAX_SAFE_INTEGER /* 2^53 - 1 */,
+      ];
+      const expectedBuffer = concatToBuffer([
+        [0, 0, 0, 0, 0, 0, 0, 0],
+        [1, 0, 0, 0, 0, 0, 0, 0],
+        [0, 0, 0, 0, 1, 0, 0, 0],
+        [0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1f, 0x00],
+      ]);
+      const bufferWriter = new BufferWriter(
+        Buffer.allocUnsafe(expectedBuffer.length),
+      );
+      values.forEach((value: number) => {
+        const expectedOffset = bufferWriter.offset + 8;
+        bufferWriter.writeUInt64(value);
+        testBuffer(bufferWriter, expectedBuffer, expectedOffset);
+      });
+      testBuffer(bufferWriter, expectedBuffer);
+    });
+
+    it('writeVarInt', () => {
+      const values = [
+        0,
+        1,
+        252,
+        253,
+        254,
+        255,
+        256,
+        Math.pow(2, 16) - 2,
+        Math.pow(2, 16) - 1,
+        Math.pow(2, 16),
+        Math.pow(2, 32) - 2,
+        Math.pow(2, 32) - 1,
+        Math.pow(2, 32),
+        Number.MAX_SAFE_INTEGER,
+      ];
+      const expectedBuffer = concatToBuffer([
+        [0x00],
+        [0x01],
+        [0xfc],
+        [0xfd, 0xfd, 0x00],
+        [0xfd, 0xfe, 0x00],
+        [0xfd, 0xff, 0x00],
+        [0xfd, 0x00, 0x01],
+        [0xfd, 0xfe, 0xff],
+        [0xfd, 0xff, 0xff],
+        [0xfe, 0x00, 0x00, 0x01, 0x00],
+        [0xfe, 0xfe, 0xff, 0xff, 0xff],
+        [0xfe, 0xff, 0xff, 0xff, 0xff],
+        [0xff, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00],
+        [0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1f, 0x00],
+      ]);
+      const bufferWriter = new BufferWriter(
+        Buffer.allocUnsafe(expectedBuffer.length),
+      );
+      values.forEach((value: number) => {
+        const expectedOffset =
+          bufferWriter.offset + varuint.encodingLength(value);
+        bufferWriter.writeVarInt(value);
+        testBuffer(bufferWriter, expectedBuffer, expectedOffset);
+      });
+      testBuffer(bufferWriter, expectedBuffer);
+    });
+
+    it('writeSlice', () => {
+      const values = [[], [1], [1, 2, 3, 4], [254, 255]];
+      const expectedBuffer = concatToBuffer(values);
+      const bufferWriter = new BufferWriter(
+        Buffer.allocUnsafe(expectedBuffer.length),
+      );
+      values.forEach((v: number[]) => {
+        const expectedOffset = bufferWriter.offset + v.length;
+        bufferWriter.writeSlice(Buffer.from(v));
+        testBuffer(bufferWriter, expectedBuffer, expectedOffset);
+      });
+      testBuffer(bufferWriter, expectedBuffer);
+      assert.throws(() => {
+        bufferWriter.writeSlice(Buffer.from([0, 0]));
+      }, /^Error: Cannot write slice out of bounds$/);
+    });
+
+    it('writeVarSlice', () => {
+      const values = [
+        Buffer.alloc(1, 1),
+        Buffer.alloc(252, 2),
+        Buffer.alloc(253, 3),
+      ];
+      const expectedBuffer = Buffer.concat([
+        Buffer.from([0x01, 0x01]),
+        Buffer.from([0xfc]),
+        Buffer.alloc(252, 0x02),
+        Buffer.from([0xfd, 0xfd, 0x00]),
+        Buffer.alloc(253, 0x03),
+      ]);
+      const bufferWriter = new BufferWriter(
+        Buffer.allocUnsafe(expectedBuffer.length),
+      );
+      values.forEach((value: Buffer) => {
+        const expectedOffset =
+          bufferWriter.offset +
+          varuint.encodingLength(value.length) +
+          value.length;
+        bufferWriter.writeVarSlice(value);
+        testBuffer(bufferWriter, expectedBuffer, expectedOffset);
+      });
+      testBuffer(bufferWriter, expectedBuffer);
+    });
+
+    it('writeVector', () => {
+      const values = [
+        [Buffer.alloc(1, 4), Buffer.alloc(253, 5)],
+        Array(253).fill(Buffer.alloc(1, 6)),
+      ];
+      const expectedBuffer = Buffer.concat([
+        Buffer.from([0x02]),
+        Buffer.from([0x01, 0x04]),
+        Buffer.from([0xfd, 0xfd, 0x00]),
+        Buffer.alloc(253, 5),
+
+        Buffer.from([0xfd, 0xfd, 0x00]),
+        Buffer.concat(
+          Array(253)
+            .fill(0)
+            .map(() => Buffer.from([0x01, 0x06])),
+        ),
+      ]);
+
+      const bufferWriter = new BufferWriter(
+        Buffer.allocUnsafe(expectedBuffer.length),
+      );
+      values.forEach((value: Buffer[]) => {
+        const expectedOffset =
+          bufferWriter.offset +
+          varuint.encodingLength(value.length) +
+          value.reduce(
+            (sum: number, v) =>
+              sum + varuint.encodingLength(v.length) + v.length,
+            0,
+          );
+        bufferWriter.writeVector(value);
+        testBuffer(bufferWriter, expectedBuffer, expectedOffset);
+      });
+      testBuffer(bufferWriter, expectedBuffer);
+    });
+  });
+
+  describe('BufferReader', () => {
+    function testValue(
+      bufferReader: BufferReader,
+      value: Buffer | number,
+      expectedValue: Buffer | number,
+      expectedOffset: number = Buffer.isBuffer(expectedValue)
+        ? expectedValue.length
+        : 0,
+    ): void {
+      assert.strictEqual(bufferReader.offset, expectedOffset);
+      if (Buffer.isBuffer(expectedValue)) {
+        assert.deepStrictEqual(
+          (value as Buffer).slice(0, expectedOffset),
+          expectedValue.slice(0, expectedOffset),
+        );
+      } else {
+        assert.strictEqual(value as number, expectedValue);
+      }
+    }
+
+    it('readUint8', () => {
+      const values = [0, 1, 0xfe, 0xff];
+      const buffer = Buffer.from([0, 1, 0xfe, 0xff]);
+      const bufferReader = new BufferReader(buffer);
+      values.forEach((v: number) => {
+        const expectedOffset = bufferReader.offset + 1;
+        const val = bufferReader.readUInt8();
+        testValue(bufferReader, val, v, expectedOffset);
+      });
+    });
+
+    it('readInt32', () => {
+      const values = [
+        0,
+        1,
+        Math.pow(2, 31) - 2,
+        Math.pow(2, 31) - 1,
+        -1,
+        -Math.pow(2, 31),
+      ];
+      const buffer = concatToBuffer([
+        [0, 0, 0, 0],
+        [1, 0, 0, 0],
+        [0xfe, 0xff, 0xff, 0x7f],
+        [0xff, 0xff, 0xff, 0x7f],
+        [0xff, 0xff, 0xff, 0xff],
+        [0x00, 0x00, 0x00, 0x80],
+      ]);
+      const bufferReader = new BufferReader(buffer);
+      values.forEach((value: number) => {
+        const expectedOffset = bufferReader.offset + 4;
+        const val = bufferReader.readInt32();
+        testValue(bufferReader, val, value, expectedOffset);
+      });
+    });
+
+    it('readUInt32', () => {
+      const maxUInt32 = Math.pow(2, 32) - 1;
+      const values = [0, 1, Math.pow(2, 16), maxUInt32];
+      const buffer = concatToBuffer([
+        [0, 0, 0, 0],
+        [1, 0, 0, 0],
+        [0, 0, 1, 0],
+        [0xff, 0xff, 0xff, 0xff],
+      ]);
+      const bufferReader = new BufferReader(buffer);
+      values.forEach((value: number) => {
+        const expectedOffset = bufferReader.offset + 4;
+        const val = bufferReader.readUInt32();
+        testValue(bufferReader, val, value, expectedOffset);
+      });
+    });
+
+    it('readUInt64', () => {
+      const values = [
+        0,
+        1,
+        Math.pow(2, 32),
+        Number.MAX_SAFE_INTEGER /* 2^53 - 1 */,
+      ];
+      const buffer = concatToBuffer([
+        [0, 0, 0, 0, 0, 0, 0, 0],
+        [1, 0, 0, 0, 0, 0, 0, 0],
+        [0, 0, 0, 0, 1, 0, 0, 0],
+        [0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1f, 0x00],
+      ]);
+      const bufferReader = new BufferReader(buffer);
+      values.forEach((value: number) => {
+        const expectedOffset = bufferReader.offset + 8;
+        const val = bufferReader.readUInt64();
+        testValue(bufferReader, val, value, expectedOffset);
+      });
+    });
+
+    it('readVarInt', () => {
+      const values = [
+        0,
+        1,
+        252,
+        253,
+        254,
+        255,
+        256,
+        Math.pow(2, 16) - 2,
+        Math.pow(2, 16) - 1,
+        Math.pow(2, 16),
+        Math.pow(2, 32) - 2,
+        Math.pow(2, 32) - 1,
+        Math.pow(2, 32),
+        Number.MAX_SAFE_INTEGER,
+      ];
+      const buffer = concatToBuffer([
+        [0x00],
+        [0x01],
+        [0xfc],
+        [0xfd, 0xfd, 0x00],
+        [0xfd, 0xfe, 0x00],
+        [0xfd, 0xff, 0x00],
+        [0xfd, 0x00, 0x01],
+        [0xfd, 0xfe, 0xff],
+        [0xfd, 0xff, 0xff],
+        [0xfe, 0x00, 0x00, 0x01, 0x00],
+        [0xfe, 0xfe, 0xff, 0xff, 0xff],
+        [0xfe, 0xff, 0xff, 0xff, 0xff],
+        [0xff, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00],
+        [0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1f, 0x00],
+      ]);
+      const bufferReader = new BufferReader(buffer);
+      values.forEach((value: number) => {
+        const expectedOffset =
+          bufferReader.offset + varuint.encodingLength(value);
+        const val = bufferReader.readVarInt();
+        testValue(bufferReader, val, value, expectedOffset);
+      });
+    });
+
+    it('readSlice', () => {
+      const values = [[1], [1, 2, 3, 4], [254, 255]];
+      const buffer = concatToBuffer(values);
+      const bufferReader = new BufferReader(buffer);
+      values.forEach((v: number[]) => {
+        const expectedOffset = bufferReader.offset + v.length;
+        const val = bufferReader.readSlice(v.length);
+        testValue(bufferReader, val, Buffer.from(v), expectedOffset);
+      });
+      assert.throws(() => {
+        bufferReader.readSlice(2);
+      }, /^Error: Cannot read slice out of bounds$/);
+    });
+
+    it('readVarSlice', () => {
+      const values = [
+        Buffer.alloc(1, 1),
+        Buffer.alloc(252, 2),
+        Buffer.alloc(253, 3),
+      ];
+      const buffer = Buffer.concat([
+        Buffer.from([0x01, 0x01]),
+        Buffer.from([0xfc]),
+        Buffer.alloc(252, 0x02),
+        Buffer.from([0xfd, 0xfd, 0x00]),
+        Buffer.alloc(253, 0x03),
+      ]);
+      const bufferReader = new BufferReader(buffer);
+      values.forEach((value: Buffer) => {
+        const expectedOffset =
+          bufferReader.offset +
+          varuint.encodingLength(value.length) +
+          value.length;
+        const val = bufferReader.readVarSlice();
+        testValue(bufferReader, val, value, expectedOffset);
+      });
+    });
+
+    it('readVector', () => {
+      const values = [
+        [Buffer.alloc(1, 4), Buffer.alloc(253, 5)],
+        Array(253).fill(Buffer.alloc(1, 6)),
+      ];
+      const buffer = Buffer.concat([
+        Buffer.from([0x02]),
+        Buffer.from([0x01, 0x04]),
+        Buffer.from([0xfd, 0xfd, 0x00]),
+        Buffer.alloc(253, 5),
+
+        Buffer.from([0xfd, 0xfd, 0x00]),
+        Buffer.concat(
+          Array(253)
+            .fill(0)
+            .map(() => Buffer.from([0x01, 0x06])),
+        ),
+      ]);
+
+      const bufferReader = new BufferReader(buffer);
+      values.forEach((value: Buffer[]) => {
+        const expectedOffset =
+          bufferReader.offset +
+          varuint.encodingLength(value.length) +
+          value.reduce(
+            (sum: number, v) =>
+              sum + varuint.encodingLength(v.length) + v.length,
+            0,
+          );
+        const val = bufferReader.readVector();
+        testValue(
+          bufferReader,
+          Buffer.concat(val),
+          Buffer.concat(value),
+          expectedOffset,
+        );
+      });
+    });
+  });
 });

ts_src/block.ts

@@ -1,4 +1,4 @@
-import { reverseBuffer } from './bufferutils';
+import { BufferReader, BufferWriter, reverseBuffer } from './bufferutils';
 import * as bcrypto from './crypto';
 import { Transaction } from './transaction';
 import * as types from './types';
@@ -18,47 +18,28 @@ export class Block {
   static fromBuffer(buffer: Buffer): Block {
     if (buffer.length < 80) throw new Error('Buffer too small (< 80 bytes)');
 
-    let offset: number = 0;
+    const bufferReader = new BufferReader(buffer);
-    const readSlice = (n: number): Buffer => {
-      offset += n;
-      return buffer.slice(offset - n, offset);
-    };
-
-    const readUInt32 = (): number => {
-      const i = buffer.readUInt32LE(offset);
-      offset += 4;
-      return i;
-    };
-
-    const readInt32 = (): number => {
-      const i = buffer.readInt32LE(offset);
-      offset += 4;
-      return i;
-    };
 
     const block = new Block();
-    block.version = readInt32();
+    block.version = bufferReader.readInt32();
-    block.prevHash = readSlice(32);
+    block.prevHash = bufferReader.readSlice(32);
-    block.merkleRoot = readSlice(32);
+    block.merkleRoot = bufferReader.readSlice(32);
-    block.timestamp = readUInt32();
+    block.timestamp = bufferReader.readUInt32();
-    block.bits = readUInt32();
+    block.bits = bufferReader.readUInt32();
-    block.nonce = readUInt32();
+    block.nonce = bufferReader.readUInt32();
 
     if (buffer.length === 80) return block;
 
-    const readVarInt = (): number => {
-      const vi = varuint.decode(buffer, offset);
-      offset += varuint.decode.bytes;
-      return vi;
-    };
-
     const readTransaction = (): any => {
-      const tx = Transaction.fromBuffer(buffer.slice(offset), true);
+      const tx = Transaction.fromBuffer(
-      offset += tx.byteLength();
+        bufferReader.buffer.slice(bufferReader.offset),
+        true,
+      );
+      bufferReader.offset += tx.byteLength();
       return tx;
     };
 
-    const nTransactions = readVarInt();
+    const nTransactions = bufferReader.readVarInt();
     block.transactions = [];
 
     for (let i = 0; i < nTransactions; ++i) {
@@ -183,37 +164,24 @@ export class Block {
   toBuffer(headersOnly?: boolean): Buffer {
     const buffer: Buffer = Buffer.allocUnsafe(this.byteLength(headersOnly));
 
-    let offset: number = 0;
+    const bufferWriter = new BufferWriter(buffer);
-    const writeSlice = (slice: Buffer): void => {
-      slice.copy(buffer, offset);
-      offset += slice.length;
-    };
 
-    const writeInt32 = (i: number): void => {
+    bufferWriter.writeInt32(this.version);
-      buffer.writeInt32LE(i, offset);
+    bufferWriter.writeSlice(this.prevHash!);
-      offset += 4;
+    bufferWriter.writeSlice(this.merkleRoot!);
-    };
+    bufferWriter.writeUInt32(this.timestamp);
-    const writeUInt32 = (i: number): void => {
+    bufferWriter.writeUInt32(this.bits);
-      buffer.writeUInt32LE(i, offset);
+    bufferWriter.writeUInt32(this.nonce);
-      offset += 4;
-    };
-
-    writeInt32(this.version);
-    writeSlice(this.prevHash!);
-    writeSlice(this.merkleRoot!);
-    writeUInt32(this.timestamp);
-    writeUInt32(this.bits);
-    writeUInt32(this.nonce);
 
     if (headersOnly || !this.transactions) return buffer;
 
-    varuint.encode(this.transactions.length, buffer, offset);
+    varuint.encode(this.transactions.length, buffer, bufferWriter.offset);
-    offset += varuint.encode.bytes;
+    bufferWriter.offset += varuint.encode.bytes;
 
     this.transactions.forEach(tx => {
       const txSize = tx.byteLength(); // TODO: extract from toBuffer?
-      tx.toBuffer(buffer, offset);
+      tx.toBuffer(buffer, bufferWriter.offset);
-      offset += txSize;
+      bufferWriter.offset += txSize;
     });
 
     return buffer;

ts_src/bufferutils.ts

@@ -1,3 +1,8 @@
+import * as types from './types';
+
+const typeforce = require('typeforce');
+const varuint = require('varuint-bitcoin');
+
 // https://github.com/feross/buffer/blob/master/index.js#L1127
 function verifuint(value: number, max: number): void {
   if (typeof value !== 'number')
@@ -42,3 +47,109 @@ export function reverseBuffer(buffer: Buffer): Buffer {
   }
   return buffer;
 }
+
+/**
+ * Helper class for serialization of bitcoin data types into a pre-allocated buffer.
+ */
+export class BufferWriter {
+  constructor(public buffer: Buffer, public offset: number = 0) {
+    typeforce(types.tuple(types.Buffer, types.UInt32), [buffer, offset]);
+  }
+
+  writeUInt8(i: number): void {
+    this.offset = this.buffer.writeUInt8(i, this.offset);
+  }
+
+  writeInt32(i: number): void {
+    this.offset = this.buffer.writeInt32LE(i, this.offset);
+  }
+
+  writeUInt32(i: number): void {
+    this.offset = this.buffer.writeUInt32LE(i, this.offset);
+  }
+
+  writeUInt64(i: number): void {
+    this.offset = writeUInt64LE(this.buffer, i, this.offset);
+  }
+
+  writeVarInt(i: number): void {
+    varuint.encode(i, this.buffer, this.offset);
+    this.offset += varuint.encode.bytes;
+  }
+
+  writeSlice(slice: Buffer): void {
+    if (this.buffer.length < this.offset + slice.length) {
+      throw new Error('Cannot write slice out of bounds');
+    }
+    this.offset += slice.copy(this.buffer, this.offset);
+  }
+
+  writeVarSlice(slice: Buffer): void {
+    this.writeVarInt(slice.length);
+    this.writeSlice(slice);
+  }
+
+  writeVector(vector: Buffer[]): void {
+    this.writeVarInt(vector.length);
+    vector.forEach((buf: Buffer) => this.writeVarSlice(buf));
+  }
+}
+
+/**
+ * Helper class for reading of bitcoin data types from a buffer.
+ */
+export class BufferReader {
+  constructor(public buffer: Buffer, public offset: number = 0) {
+    typeforce(types.tuple(types.Buffer, types.UInt32), [buffer, offset]);
+  }
+
+  readUInt8(): number {
+    const result = this.buffer.readUInt8(this.offset);
+    this.offset++;
+    return result;
+  }
+
+  readInt32(): number {
+    const result = this.buffer.readInt32LE(this.offset);
+    this.offset += 4;
+    return result;
+  }
+
+  readUInt32(): number {
+    const result = this.buffer.readUInt32LE(this.offset);
+    this.offset += 4;
+    return result;
+  }
+
+  readUInt64(): number {
+    const result = readUInt64LE(this.buffer, this.offset);
+    this.offset += 8;
+    return result;
+  }
+
+  readVarInt(): number {
+    const vi = varuint.decode(this.buffer, this.offset);
+    this.offset += varuint.decode.bytes;
+    return vi;
+  }
+
+  readSlice(n: number): Buffer {
+    if (this.buffer.length < this.offset + n) {
+      throw new Error('Cannot read slice out of bounds');
+    }
+    const result = this.buffer.slice(this.offset, this.offset + n);
+    this.offset += n;
+    return result;
+  }
+
+  readVarSlice(): Buffer {
+    return this.readSlice(this.readVarInt());
+  }
+
+  readVector(): Buffer[] {
+    const count = this.readVarInt();
+    const vector: Buffer[] = [];
+    for (let i = 0; i < count; i++) vector.push(this.readVarSlice());
+    return vector;
+  }
+}

ts_src/transaction.ts

@@ -1,5 +1,4 @@
-import * as bufferutils from './bufferutils';
+import { BufferReader, BufferWriter, reverseBuffer } from './bufferutils';
-import { reverseBuffer } from './bufferutils';
 import * as bcrypto from './crypto';
 import * as bscript from './script';
 import { OPS as opcodes } from './script';
@@ -68,85 +67,46 @@ export class Transaction {
   static readonly ADVANCED_TRANSACTION_FLAG = 0x01;
 
   static fromBuffer(buffer: Buffer, _NO_STRICT?: boolean): Transaction {
-    let offset: number = 0;
+    const bufferReader = new BufferReader(buffer);
-
-    function readSlice(n: number): Buffer {
-      offset += n;
-      return buffer.slice(offset - n, offset);
-    }
-
-    function readUInt32(): number {
-      const i = buffer.readUInt32LE(offset);
-      offset += 4;
-      return i;
-    }
-
-    function readInt32(): number {
-      const i = buffer.readInt32LE(offset);
-      offset += 4;
-      return i;
-    }
-
-    function readUInt64(): number {
-      const i = bufferutils.readUInt64LE(buffer, offset);
-      offset += 8;
-      return i;
-    }
-
-    function readVarInt(): number {
-      const vi = varuint.decode(buffer, offset);
-      offset += varuint.decode.bytes;
-      return vi;
-    }
-
-    function readVarSlice(): Buffer {
-      return readSlice(readVarInt());
-    }
-
-    function readVector(): Buffer[] {
-      const count = readVarInt();
-      const vector: Buffer[] = [];
-      for (let i = 0; i < count; i++) vector.push(readVarSlice());
-      return vector;
-    }
 
     const tx = new Transaction();
-    tx.version = readInt32();
+    tx.version = bufferReader.readInt32();
 
-    const marker = buffer.readUInt8(offset);
+    const marker = bufferReader.readUInt8();
-    const flag = buffer.readUInt8(offset + 1);
+    const flag = bufferReader.readUInt8();
 
     let hasWitnesses = false;
     if (
       marker === Transaction.ADVANCED_TRANSACTION_MARKER &&
       flag === Transaction.ADVANCED_TRANSACTION_FLAG
     ) {
-      offset += 2;
       hasWitnesses = true;
+    } else {
+      bufferReader.offset -= 2;
     }
 
-    const vinLen = readVarInt();
+    const vinLen = bufferReader.readVarInt();
     for (let i = 0; i < vinLen; ++i) {
       tx.ins.push({
-        hash: readSlice(32),
+        hash: bufferReader.readSlice(32),
-        index: readUInt32(),
+        index: bufferReader.readUInt32(),
-        script: readVarSlice(),
+        script: bufferReader.readVarSlice(),
-        sequence: readUInt32(),
+        sequence: bufferReader.readUInt32(),
         witness: EMPTY_WITNESS,
       });
     }
 
-    const voutLen = readVarInt();
+    const voutLen = bufferReader.readVarInt();
     for (let i = 0; i < voutLen; ++i) {
       tx.outs.push({
-        value: readUInt64(),
+        value: bufferReader.readUInt64(),
-        script: readVarSlice(),
+        script: bufferReader.readVarSlice(),
       });
     }
 
     if (hasWitnesses) {
       for (let i = 0; i < vinLen; ++i) {
-        tx.ins[i].witness = readVector();
+        tx.ins[i].witness = bufferReader.readVector();
       }
 
       // was this pointless?
@@ -154,10 +114,10 @@ export class Transaction {
         throw new Error('Transaction has superfluous witness data');
     }
 
-    tx.locktime = readUInt32();
+    tx.locktime = bufferReader.readUInt32();
 
     if (_NO_STRICT) return tx;
-    if (offset !== buffer.length)
+    if (bufferReader.offset !== buffer.length)
       throw new Error('Transaction has unexpected data');
 
     return tx;
@@ -388,29 +348,7 @@ export class Transaction {
     );
 
     let tbuffer: Buffer = Buffer.from([]);
-    let toffset: number = 0;
+    let bufferWriter: BufferWriter;
-
-    function writeSlice(slice: Buffer): void {
-      toffset += slice.copy(tbuffer, toffset);
-    }
-
-    function writeUInt32(i: number): void {
-      toffset = tbuffer.writeUInt32LE(i, toffset);
-    }
-
-    function writeUInt64(i: number): void {
-      toffset = bufferutils.writeUInt64LE(tbuffer, i, toffset);
-    }
-
-    function writeVarInt(i: number): void {
-      varuint.encode(i, tbuffer, toffset);
-      toffset += varuint.encode.bytes;
-    }
-
-    function writeVarSlice(slice: Buffer): void {
-      writeVarInt(slice.length);
-      writeSlice(slice);
-    }
 
     let hashOutputs = ZERO;
     let hashPrevouts = ZERO;
@@ -418,11 +356,11 @@ export class Transaction {
 
     if (!(hashType & Transaction.SIGHASH_ANYONECANPAY)) {
       tbuffer = Buffer.allocUnsafe(36 * this.ins.length);
-      toffset = 0;
+      bufferWriter = new BufferWriter(tbuffer, 0);
 
       this.ins.forEach(txIn => {
-        writeSlice(txIn.hash);
+        bufferWriter.writeSlice(txIn.hash);
-        writeUInt32(txIn.index);
+        bufferWriter.writeUInt32(txIn.index);
       });
 
       hashPrevouts = bcrypto.hash256(tbuffer);
@@ -434,10 +372,10 @@ export class Transaction {
       (hashType & 0x1f) !== Transaction.SIGHASH_NONE
     ) {
       tbuffer = Buffer.allocUnsafe(4 * this.ins.length);
-      toffset = 0;
+      bufferWriter = new BufferWriter(tbuffer, 0);
 
       this.ins.forEach(txIn => {
-        writeUInt32(txIn.sequence);
+        bufferWriter.writeUInt32(txIn.sequence);
       });
 
       hashSequence = bcrypto.hash256(tbuffer);
@@ -452,11 +390,11 @@ export class Transaction {
       }, 0);
 
       tbuffer = Buffer.allocUnsafe(txOutsSize);
-      toffset = 0;
+      bufferWriter = new BufferWriter(tbuffer, 0);
 
       this.outs.forEach(out => {
-        writeUInt64(out.value);
+        bufferWriter.writeUInt64(out.value);
-        writeVarSlice(out.script);
+        bufferWriter.writeVarSlice(out.script);
       });
 
       hashOutputs = bcrypto.hash256(tbuffer);
@@ -467,28 +405,28 @@ export class Transaction {
       const output = this.outs[inIndex];
 
       tbuffer = Buffer.allocUnsafe(8 + varSliceSize(output.script));
-      toffset = 0;
+      bufferWriter = new BufferWriter(tbuffer, 0);
-      writeUInt64(output.value);
+      bufferWriter.writeUInt64(output.value);
-      writeVarSlice(output.script);
+      bufferWriter.writeVarSlice(output.script);
 
       hashOutputs = bcrypto.hash256(tbuffer);
     }
 
     tbuffer = Buffer.allocUnsafe(156 + varSliceSize(prevOutScript));
-    toffset = 0;
+    bufferWriter = new BufferWriter(tbuffer, 0);
 
     const input = this.ins[inIndex];
-    writeUInt32(this.version);
+    bufferWriter.writeUInt32(this.version);
-    writeSlice(hashPrevouts);
+    bufferWriter.writeSlice(hashPrevouts);
-    writeSlice(hashSequence);
+    bufferWriter.writeSlice(hashSequence);
-    writeSlice(input.hash);
+    bufferWriter.writeSlice(input.hash);
-    writeUInt32(input.index);
+    bufferWriter.writeUInt32(input.index);
-    writeVarSlice(prevOutScript);
+    bufferWriter.writeVarSlice(prevOutScript);
-    writeUInt64(value);
+    bufferWriter.writeUInt64(value);
-    writeUInt32(input.sequence);
+    bufferWriter.writeUInt32(input.sequence);
-    writeSlice(hashOutputs);
+    bufferWriter.writeSlice(hashOutputs);
-    writeUInt32(this.locktime);
+    bufferWriter.writeUInt32(this.locktime);
-    writeUInt32(hashType);
+    bufferWriter.writeUInt32(hashType);
     return bcrypto.hash256(tbuffer);
   }
 
@@ -531,82 +469,48 @@ export class Transaction {
     if (!buffer)
       buffer = Buffer.allocUnsafe(this.byteLength(_ALLOW_WITNESS)) as Buffer;
 
-    let offset = initialOffset || 0;
+    const bufferWriter = new BufferWriter(buffer, initialOffset || 0);
 
-    function writeSlice(slice: Buffer): void {
+    bufferWriter.writeInt32(this.version);
-      offset += slice.copy(buffer!, offset);
-    }
-
-    function writeUInt8(i: number): void {
-      offset = buffer!.writeUInt8(i, offset);
-    }
-
-    function writeUInt32(i: number): void {
-      offset = buffer!.writeUInt32LE(i, offset);
-    }
-
-    function writeInt32(i: number): void {
-      offset = buffer!.writeInt32LE(i, offset);
-    }
-
-    function writeUInt64(i: number): void {
-      offset = bufferutils.writeUInt64LE(buffer!, i, offset);
-    }
-
-    function writeVarInt(i: number): void {
-      varuint.encode(i, buffer, offset);
-      offset += varuint.encode.bytes;
-    }
-
-    function writeVarSlice(slice: Buffer): void {
-      writeVarInt(slice.length);
-      writeSlice(slice);
-    }
-
-    function writeVector(vector: Buffer[]): void {
-      writeVarInt(vector.length);
-      vector.forEach(writeVarSlice);
-    }
-
-    writeInt32(this.version);
 
     const hasWitnesses = _ALLOW_WITNESS && this.hasWitnesses();
 
     if (hasWitnesses) {
-      writeUInt8(Transaction.ADVANCED_TRANSACTION_MARKER);
+      bufferWriter.writeUInt8(Transaction.ADVANCED_TRANSACTION_MARKER);
-      writeUInt8(Transaction.ADVANCED_TRANSACTION_FLAG);
+      bufferWriter.writeUInt8(Transaction.ADVANCED_TRANSACTION_FLAG);
     }
 
-    writeVarInt(this.ins.length);
+    bufferWriter.writeVarInt(this.ins.length);
 
     this.ins.forEach(txIn => {
-      writeSlice(txIn.hash);
+      bufferWriter.writeSlice(txIn.hash);
-      writeUInt32(txIn.index);
+      bufferWriter.writeUInt32(txIn.index);
-      writeVarSlice(txIn.script);
+      bufferWriter.writeVarSlice(txIn.script);
-      writeUInt32(txIn.sequence);
+      bufferWriter.writeUInt32(txIn.sequence);
     });
 
-    writeVarInt(this.outs.length);
+    bufferWriter.writeVarInt(this.outs.length);
     this.outs.forEach(txOut => {
       if (isOutput(txOut)) {
-        writeUInt64(txOut.value);
+        bufferWriter.writeUInt64(txOut.value);
       } else {
-        writeSlice((txOut as any).valueBuffer);
+        bufferWriter.writeSlice((txOut as any).valueBuffer);
       }
 
-      writeVarSlice(txOut.script);
+      bufferWriter.writeVarSlice(txOut.script);
     });
 
     if (hasWitnesses) {
       this.ins.forEach(input => {
-        writeVector(input.witness);
+        bufferWriter.writeVector(input.witness);
       });
     }
 
-    writeUInt32(this.locktime);
+    bufferWriter.writeUInt32(this.locktime);
 
     // avoid slicing unless necessary
-    if (initialOffset !== undefined) return buffer.slice(initialOffset, offset);
+    if (initialOffset !== undefined)
+      return buffer.slice(initialOffset, bufferWriter.offset);
     return buffer;
   }
 }

types/bufferutils.d.ts

@@ -1,3 +1,35 @@
 export declare function readUInt64LE(buffer: Buffer, offset: number): number;
 export declare function writeUInt64LE(buffer: Buffer, value: number, offset: number): number;
 export declare function reverseBuffer(buffer: Buffer): Buffer;
+/**
+ * Helper class for serialization of bitcoin data types into a pre-allocated buffer.
+ */
+export declare class BufferWriter {
+    buffer: Buffer;
+    offset: number;
+    constructor(buffer: Buffer, offset?: number);
+    writeUInt8(i: number): void;
+    writeInt32(i: number): void;
+    writeUInt32(i: number): void;
+    writeUInt64(i: number): void;
+    writeVarInt(i: number): void;
+    writeSlice(slice: Buffer): void;
+    writeVarSlice(slice: Buffer): void;
+    writeVector(vector: Buffer[]): void;
+}
+/**
+ * Helper class for reading of bitcoin data types from a buffer.
+ */
+export declare class BufferReader {
+    buffer: Buffer;
+    offset: number;
+    constructor(buffer: Buffer, offset?: number);
+    readUInt8(): number;
+    readInt32(): number;
+    readUInt32(): number;
+    readUInt64(): number;
+    readVarInt(): number;
+    readSlice(n: number): Buffer;
+    readVarSlice(): Buffer;
+    readVector(): Buffer[];
+}