Merge branch 'development' of https://github.com/0xProject/0x-monorepo into feature/website/instant-configurator

7 files changed, 644 insertions, 0 deletions

diff --git a/packages/utils/src/abi_encoder/calldata/blocks/blob.ts b/packages/utils/src/abi_encoder/calldata/blocks/blob.ts
new file mode 100644
index 000000000..219ea6c61
--- /dev/null
+++ b/packages/utils/src/abi_encoder/calldata/blocks/blob.ts
@@ -0,0 +1,20 @@
+import { CalldataBlock } from '../calldata_block';
+
+export class BlobCalldataBlock extends CalldataBlock {
+    private readonly _blob: Buffer;
+
+    constructor(name: string, signature: string, parentName: string, blob: Buffer) {
+        const headerSizeInBytes = 0;
+        const bodySizeInBytes = blob.byteLength;
+        super(name, signature, parentName, headerSizeInBytes, bodySizeInBytes);
+        this._blob = blob;
+    }
+
+    public toBuffer(): Buffer {
+        return this._blob;
+    }
+
+    public getRawData(): Buffer {
+        return this._blob;
+    }
+}
diff --git a/packages/utils/src/abi_encoder/calldata/blocks/pointer.ts b/packages/utils/src/abi_encoder/calldata/blocks/pointer.ts
new file mode 100644
index 000000000..72d6a3173
--- /dev/null
+++ b/packages/utils/src/abi_encoder/calldata/blocks/pointer.ts
@@ -0,0 +1,61 @@
+import * as ethUtil from 'ethereumjs-util';
+import * as _ from 'lodash';
+
+import { constants } from '../../utils/constants';
+
+import { CalldataBlock } from '../calldata_block';
+
+export class PointerCalldataBlock extends CalldataBlock {
+    public static readonly RAW_DATA_START = new Buffer('<');
+    public static readonly RAW_DATA_END = new Buffer('>');
+    private static readonly _DEPENDENT_PAYLOAD_SIZE_IN_BYTES = 32;
+    private static readonly _EMPTY_HEADER_SIZE = 0;
+    private readonly _parent: CalldataBlock;
+    private readonly _dependency: CalldataBlock;
+    private _aliasFor: CalldataBlock | undefined;
+
+    constructor(name: string, signature: string, parentName: string, dependency: CalldataBlock, parent: CalldataBlock) {
+        const headerSizeInBytes = PointerCalldataBlock._EMPTY_HEADER_SIZE;
+        const bodySizeInBytes = PointerCalldataBlock._DEPENDENT_PAYLOAD_SIZE_IN_BYTES;
+        super(name, signature, parentName, headerSizeInBytes, bodySizeInBytes);
+        this._parent = parent;
+        this._dependency = dependency;
+        this._aliasFor = undefined;
+    }
+
+    public toBuffer(): Buffer {
+        const destinationOffset = !_.isUndefined(this._aliasFor)
+            ? this._aliasFor.getOffsetInBytes()
+            : this._dependency.getOffsetInBytes();
+        const parentOffset = this._parent.getOffsetInBytes();
+        const parentHeaderSize = this._parent.getHeaderSizeInBytes();
+        const pointer: number = destinationOffset - (parentOffset + parentHeaderSize);
+        const pointerHex = `0x${pointer.toString(constants.HEX_BASE)}`;
+        const pointerBuf = ethUtil.toBuffer(pointerHex);
+        const pointerBufPadded = ethUtil.setLengthLeft(pointerBuf, constants.EVM_WORD_WIDTH_IN_BYTES);
+        return pointerBufPadded;
+    }
+
+    public getDependency(): CalldataBlock {
+        return this._dependency;
+    }
+
+    public setAlias(block: CalldataBlock): void {
+        this._aliasFor = block;
+        this._setName(`${this.getName()} (alias for ${block.getName()})`);
+    }
+
+    public getAlias(): CalldataBlock | undefined {
+        return this._aliasFor;
+    }
+
+    public getRawData(): Buffer {
+        const dependencyRawData = this._dependency.getRawData();
+        const rawDataComponents: Buffer[] = [];
+        rawDataComponents.push(PointerCalldataBlock.RAW_DATA_START);
+        rawDataComponents.push(dependencyRawData);
+        rawDataComponents.push(PointerCalldataBlock.RAW_DATA_END);
+        const rawData = Buffer.concat(rawDataComponents);
+        return rawData;
+    }
+}
diff --git a/packages/utils/src/abi_encoder/calldata/blocks/set.ts b/packages/utils/src/abi_encoder/calldata/blocks/set.ts
new file mode 100644
index 000000000..d1abc4986
--- /dev/null
+++ b/packages/utils/src/abi_encoder/calldata/blocks/set.ts
@@ -0,0 +1,47 @@
+import * as _ from 'lodash';
+
+import { CalldataBlock } from '../calldata_block';
+
+export class SetCalldataBlock extends CalldataBlock {
+    private _header: Buffer | undefined;
+    private _members: CalldataBlock[];
+
+    constructor(name: string, signature: string, parentName: string) {
+        super(name, signature, parentName, 0, 0);
+        this._members = [];
+        this._header = undefined;
+    }
+
+    public getRawData(): Buffer {
+        const rawDataComponents: Buffer[] = [];
+        if (!_.isUndefined(this._header)) {
+            rawDataComponents.push(this._header);
+        }
+        _.each(this._members, (member: CalldataBlock) => {
+            const memberBuffer = member.getRawData();
+            rawDataComponents.push(memberBuffer);
+        });
+        const rawData = Buffer.concat(rawDataComponents);
+        return rawData;
+    }
+
+    public setMembers(members: CalldataBlock[]): void {
+        this._members = members;
+    }
+
+    public setHeader(header: Buffer): void {
+        this._setHeaderSize(header.byteLength);
+        this._header = header;
+    }
+
+    public toBuffer(): Buffer {
+        if (!_.isUndefined(this._header)) {
+            return this._header;
+        }
+        return new Buffer('');
+    }
+
+    public getMembers(): CalldataBlock[] {
+        return this._members;
+    }
+}
diff --git a/packages/utils/src/abi_encoder/calldata/calldata.ts b/packages/utils/src/abi_encoder/calldata/calldata.ts
new file mode 100644
index 000000000..5f3eee94a
--- /dev/null
+++ b/packages/utils/src/abi_encoder/calldata/calldata.ts
@@ -0,0 +1,243 @@
+import * as ethUtil from 'ethereumjs-util';
+import * as _ from 'lodash';
+
+import { constants } from '../utils/constants';
+import { EncodingRules } from '../utils/rules';
+
+import { PointerCalldataBlock } from './blocks/pointer';
+import { SetCalldataBlock } from './blocks/set';
+import { CalldataBlock } from './calldata_block';
+import { CalldataIterator, ReverseCalldataIterator } from './iterator';
+
+export class Calldata {
+    private readonly _rules: EncodingRules;
+    private _selector: string;
+    private _root: CalldataBlock | undefined;
+
+    public constructor(rules: EncodingRules) {
+        this._rules = rules;
+        this._selector = '';
+        this._root = undefined;
+    }
+    /**
+     * Sets the root calldata block. This block usually corresponds to a Method.
+     */
+    public setRoot(block: CalldataBlock): void {
+        this._root = block;
+    }
+    /**
+     * Sets the selector to be prepended onto the calldata.
+     * If the root block was created by a Method then a selector will likely be set.
+     */
+    public setSelector(selector: string): void {
+        if (!_.startsWith(selector, '0x')) {
+            throw new Error(`Expected selector to be hex. Missing prefix '0x'`);
+        } else if (selector.length !== constants.HEX_SELECTOR_LENGTH_IN_CHARS) {
+            throw new Error(`Invalid selector '${selector}'`);
+        }
+        this._selector = selector;
+    }
+    /**
+     * Iterates through the calldata blocks, starting from the root block, to construct calldata as a hex string.
+     * If the `optimize` flag is set then this calldata will be condensed, to save gas.
+     * If the `annotate` flag is set then this will return human-readable calldata.
+     * If the `annotate` flag is *not* set then this will return EVM-compatible calldata.
+     */
+    public toString(): string {
+        // Sanity check: root block must be set
+        if (_.isUndefined(this._root)) {
+            throw new Error('expected root');
+        }
+        // Optimize, if flag set
+        if (this._rules.optimize) {
+            this._optimize();
+        }
+        // Set offsets
+        const iterator = new CalldataIterator(this._root);
+        let offset = 0;
+        for (const block of iterator) {
+            block.setOffset(offset);
+            offset += block.getSizeInBytes();
+        }
+        // Generate hex string
+        const hexString = this._rules.annotate ? this._toHumanReadableCallData() : this._toEvmCompatibeCallDataHex();
+        return hexString;
+    }
+    /**
+     * There are three types of calldata blocks: Blob, Set and Pointer.
+     * Scenarios arise where distinct pointers resolve to identical values.
+     * We optimize by keeping only one such instance of the identical value, and redirecting all pointers here.
+     * We keep the last such duplicate value because pointers can only be positive (they cannot point backwards).
+     *
+     * Example #1:
+     *  function f(string[], string[])
+     *  f(["foo", "bar", "blitz"], ["foo", "bar", "blitz"])
+     *  The array ["foo", "bar", "blitz"] will only be included in the calldata once.
+     *
+     * Example #2:
+     *  function f(string[], string)
+     *  f(["foo", "bar", "blitz"], "foo")
+     *  The string "foo" will only be included in the calldata once.
+     *
+     * Example #3:
+     *  function f((string, uint, bytes), string, uint, bytes)
+     *  f(("foo", 5, "0x05"), "foo", 5, "0x05")
+     *  The string "foo" and bytes "0x05" will only be included in the calldata once.
+     *  The duplicate `uint 5` values cannot be optimized out because they are static values (no pointer points to them).
+     *
+     * @TODO #1:
+     *   This optimization strategy handles blocks that are exact duplicates of one another.
+     *   But what if some block is a combination of two other blocks? Or a subset of another block?
+     *   This optimization problem is not much different from the current implemetation.
+     *   Instead of tracking "observed" hashes, at each node we would simply do pattern-matching on the calldata.
+     *   This strategy would be applied after assigning offsets to the tree, rather than before (as in this strategy).
+     *   Note that one consequence of this strategy is pointers may resolve to offsets that are not word-aligned.
+     *   This shouldn't be a problem but further investigation should be done.
+     *
+     * @TODO #2:
+     *   To be done as a follow-up to @TODO #1.
+     *   Since we optimize from the bottom-up, we could be affecting the outcome of a later potential optimization.
+     *   For example, what if by removing one duplicate value we miss out on optimizing another block higher in the tree.
+     *   To handle this case, at each node we can store a candidate optimization in a priority queue (sorted by calldata size).
+     *   At the end of traversing the tree, the candidate at the front of the queue will be the most optimal output.
+     *
+     */
+    private _optimize(): void {
+        // Step 1/1 Create a reverse iterator (starts from the end of the calldata to the beginning)
+        if (_.isUndefined(this._root)) {
+            throw new Error('expected root');
+        }
+        const iterator = new ReverseCalldataIterator(this._root);
+        // Step 2/2 Iterate over each block, keeping track of which blocks have been seen and pruning redundant blocks.
+        const blocksByHash: { [key: string]: CalldataBlock } = {};
+        for (const block of iterator) {
+            // If a block is a pointer and its value has already been observed, then update
+            // the pointer to resolve to the existing value.
+            if (block instanceof PointerCalldataBlock) {
+                const dependencyBlockHashBuf = block.getDependency().computeHash();
+                const dependencyBlockHash = ethUtil.bufferToHex(dependencyBlockHashBuf);
+                if (dependencyBlockHash in blocksByHash) {
+                    const blockWithSameHash = blocksByHash[dependencyBlockHash];
+                    if (blockWithSameHash !== block.getDependency()) {
+                        block.setAlias(blockWithSameHash);
+                    }
+                }
+                continue;
+            }
+            // This block has not been seen. Record its hash.
+            const blockHashBuf = block.computeHash();
+            const blockHash = ethUtil.bufferToHex(blockHashBuf);
+            if (!(blockHash in blocksByHash)) {
+                blocksByHash[blockHash] = block;
+            }
+        }
+    }
+    private _toEvmCompatibeCallDataHex(): string {
+        // Sanity check: must have a root block.
+        if (_.isUndefined(this._root)) {
+            throw new Error('expected root');
+        }
+        // Construct an array of buffers (one buffer for each block).
+        const selectorBuffer = ethUtil.toBuffer(this._selector);
+        const valueBufs: Buffer[] = [selectorBuffer];
+        const iterator = new CalldataIterator(this._root);
+        for (const block of iterator) {
+            valueBufs.push(block.toBuffer());
+        }
+        // Create hex from buffer array.
+        const combinedBuffers = Buffer.concat(valueBufs);
+        const hexValue = ethUtil.bufferToHex(combinedBuffers);
+        return hexValue;
+    }
+    /**
+     * Returns human-readable calldata.
+     *
+     * Example:
+     *   simpleFunction(string[], string[])
+     *   strings = ["Hello", "World"]
+     *   simpleFunction(strings, strings)
+     *
+     * Output:
+     *   0xbb4f12e3
+     *                                                                                      ### simpleFunction
+     *   0x0       0000000000000000000000000000000000000000000000000000000000000040              ptr<array1> (alias for array2)
+     *   0x20      0000000000000000000000000000000000000000000000000000000000000040              ptr<array2>
+     *
+     *   0x40      0000000000000000000000000000000000000000000000000000000000000002          ### array2
+     *   0x60      0000000000000000000000000000000000000000000000000000000000000040              ptr<array2[0]>
+     *   0x80      0000000000000000000000000000000000000000000000000000000000000080              ptr<array2[1]>
+     *   0xa0      0000000000000000000000000000000000000000000000000000000000000005              array2[0]
+     *   0xc0      48656c6c6f000000000000000000000000000000000000000000000000000000
+     *   0xe0      0000000000000000000000000000000000000000000000000000000000000005              array2[1]
+     *   0x100     576f726c64000000000000000000000000000000000000000000000000000000
+     */
+    private _toHumanReadableCallData(): string {
+        // Sanity check: must have a root block.
+        if (_.isUndefined(this._root)) {
+            throw new Error('expected root');
+        }
+        // Constants for constructing annotated string
+        const offsetPadding = 10;
+        const valuePadding = 74;
+        const namePadding = 80;
+        const evmWordStartIndex = 0;
+        const emptySize = 0;
+        // Construct annotated calldata
+        let hexValue = `${this._selector}`;
+        let offset = 0;
+        const functionName: string = this._root.getName();
+        const iterator = new CalldataIterator(this._root);
+        for (const block of iterator) {
+            // Process each block 1 word at a time
+            const size = block.getSizeInBytes();
+            const name = block.getName();
+            const parentName = block.getParentName();
+            const prettyName = name.replace(`${parentName}.`, '').replace(`${functionName}.`, '');
+            // Resulting line will be <offsetStr><valueStr><nameStr>
+            let offsetStr = '';
+            let valueStr = '';
+            let nameStr = '';
+            let lineStr = '';
+            if (size === emptySize) {
+                // This is a Set block with no header.
+                // For example, a tuple or an array with a defined length.
+                offsetStr = ' '.repeat(offsetPadding);
+                valueStr = ' '.repeat(valuePadding);
+                nameStr = `### ${prettyName.padEnd(namePadding)}`;
+                lineStr = `\n${offsetStr}${valueStr}${nameStr}`;
+            } else {
+                // This block has at least one word of value.
+                offsetStr = `0x${offset.toString(constants.HEX_BASE)}`.padEnd(offsetPadding);
+                valueStr = ethUtil
+                    .stripHexPrefix(
+                        ethUtil.bufferToHex(
+                            block.toBuffer().slice(evmWordStartIndex, constants.EVM_WORD_WIDTH_IN_BYTES),
+                        ),
+                    )
+                    .padEnd(valuePadding);
+                if (block instanceof SetCalldataBlock) {
+                    nameStr = `### ${prettyName.padEnd(namePadding)}`;
+                    lineStr = `\n${offsetStr}${valueStr}${nameStr}`;
+                } else {
+                    nameStr = `    ${prettyName.padEnd(namePadding)}`;
+                    lineStr = `${offsetStr}${valueStr}${nameStr}`;
+                }
+            }
+            // This block has a value that is more than 1 word.
+            for (let j = constants.EVM_WORD_WIDTH_IN_BYTES; j < size; j += constants.EVM_WORD_WIDTH_IN_BYTES) {
+                offsetStr = `0x${(offset + j).toString(constants.HEX_BASE)}`.padEnd(offsetPadding);
+                valueStr = ethUtil
+                    .stripHexPrefix(
+                        ethUtil.bufferToHex(block.toBuffer().slice(j, j + constants.EVM_WORD_WIDTH_IN_BYTES)),
+                    )
+                    .padEnd(valuePadding);
+                nameStr = ' '.repeat(namePadding);
+                lineStr = `${lineStr}\n${offsetStr}${valueStr}${nameStr}`;
+            }
+            // Append to hex value
+            hexValue = `${hexValue}\n${lineStr}`;
+            offset += size;
+        }
+        return hexValue;
+    }
+}
diff --git a/packages/utils/src/abi_encoder/calldata/calldata_block.ts b/packages/utils/src/abi_encoder/calldata/calldata_block.ts
new file mode 100644
index 000000000..35bd994e5
--- /dev/null
+++ b/packages/utils/src/abi_encoder/calldata/calldata_block.ts
@@ -0,0 +1,77 @@
+import * as ethUtil from 'ethereumjs-util';
+
+export abstract class CalldataBlock {
+    private readonly _signature: string;
+    private readonly _parentName: string;
+    private _name: string;
+    private _offsetInBytes: number;
+    private _headerSizeInBytes: number;
+    private _bodySizeInBytes: number;
+
+    constructor(
+        name: string,
+        signature: string,
+        parentName: string,
+        headerSizeInBytes: number,
+        bodySizeInBytes: number,
+    ) {
+        this._name = name;
+        this._signature = signature;
+        this._parentName = parentName;
+        this._offsetInBytes = 0;
+        this._headerSizeInBytes = headerSizeInBytes;
+        this._bodySizeInBytes = bodySizeInBytes;
+    }
+
+    protected _setHeaderSize(headerSizeInBytes: number): void {
+        this._headerSizeInBytes = headerSizeInBytes;
+    }
+
+    protected _setBodySize(bodySizeInBytes: number): void {
+        this._bodySizeInBytes = bodySizeInBytes;
+    }
+
+    protected _setName(name: string): void {
+        this._name = name;
+    }
+
+    public getName(): string {
+        return this._name;
+    }
+
+    public getParentName(): string {
+        return this._parentName;
+    }
+
+    public getSignature(): string {
+        return this._signature;
+    }
+    public getHeaderSizeInBytes(): number {
+        return this._headerSizeInBytes;
+    }
+
+    public getBodySizeInBytes(): number {
+        return this._bodySizeInBytes;
+    }
+
+    public getSizeInBytes(): number {
+        return this.getHeaderSizeInBytes() + this.getBodySizeInBytes();
+    }
+
+    public getOffsetInBytes(): number {
+        return this._offsetInBytes;
+    }
+
+    public setOffset(offsetInBytes: number): void {
+        this._offsetInBytes = offsetInBytes;
+    }
+
+    public computeHash(): Buffer {
+        const rawData = this.getRawData();
+        const hash = ethUtil.sha3(rawData);
+        return hash;
+    }
+
+    public abstract toBuffer(): Buffer;
+    public abstract getRawData(): Buffer;
+}
diff --git a/packages/utils/src/abi_encoder/calldata/iterator.ts b/packages/utils/src/abi_encoder/calldata/iterator.ts
new file mode 100644
index 000000000..333b32b4f
--- /dev/null
+++ b/packages/utils/src/abi_encoder/calldata/iterator.ts
@@ -0,0 +1,114 @@
+/* tslint:disable max-classes-per-file */
+import * as _ from 'lodash';
+
+import { Queue } from '../utils/queue';
+
+import { BlobCalldataBlock } from './blocks/blob';
+import { PointerCalldataBlock } from './blocks/pointer';
+import { SetCalldataBlock } from './blocks/set';
+import { CalldataBlock } from './calldata_block';
+
+/**
+ * Iterator class for Calldata Blocks. Blocks follows the order
+ * they should be put into calldata that is passed to he EVM.
+ *
+ * Example #1:
+ * Let root = Set {
+ *                  Blob{} A,
+ *                  Pointer {
+ *                      Blob{} a
+ *                  } B,
+ *                  Blob{} C
+ *            }
+ * It will iterate as follows: [A, B, C, B.a]
+ *
+ * Example #2:
+ * Let root = Set {
+ *                  Blob{} A,
+ *                  Pointer {
+ *                      Blob{} a
+ *                      Pointer {
+ *                          Blob{} b
+ *                      }
+ *                  } B,
+ *                  Pointer {
+ *                      Blob{} c
+ *                  } C
+ *            }
+ * It will iterate as follows: [A, B, C, B.a, B.b, C.c]
+ */
+abstract class BaseIterator implements Iterable<CalldataBlock> {
+    protected readonly _root: CalldataBlock;
+    protected readonly _queue: Queue<CalldataBlock>;
+
+    private static _createQueue(block: CalldataBlock): Queue<CalldataBlock> {
+        const queue = new Queue<CalldataBlock>();
+        // Base case
+        if (!(block instanceof SetCalldataBlock)) {
+            queue.pushBack(block);
+            return queue;
+        }
+        // This is a set; add members
+        const set = block;
+        _.eachRight(set.getMembers(), (member: CalldataBlock) => {
+            queue.mergeFront(BaseIterator._createQueue(member));
+        });
+        // Add children
+        _.each(set.getMembers(), (member: CalldataBlock) => {
+            // Traverse child if it is a unique pointer.
+            // A pointer that is an alias for another pointer is ignored.
+            if (member instanceof PointerCalldataBlock && _.isUndefined(member.getAlias())) {
+                const dependency = member.getDependency();
+                queue.mergeBack(BaseIterator._createQueue(dependency));
+            }
+        });
+        // Put set block at the front of the queue
+        queue.pushFront(set);
+        return queue;
+    }
+
+    public constructor(root: CalldataBlock) {
+        this._root = root;
+        this._queue = BaseIterator._createQueue(root);
+    }
+
+    public [Symbol.iterator](): { next: () => IteratorResult<CalldataBlock> } {
+        return {
+            next: () => {
+                const nextBlock = this.nextBlock();
+                if (!_.isUndefined(nextBlock)) {
+                    return {
+                        value: nextBlock,
+                        done: false,
+                    };
+                }
+                return {
+                    done: true,
+                    value: new BlobCalldataBlock('', '', '', new Buffer('')),
+                };
+            },
+        };
+    }
+
+    public abstract nextBlock(): CalldataBlock | undefined;
+}
+
+export class CalldataIterator extends BaseIterator {
+    public constructor(root: CalldataBlock) {
+        super(root);
+    }
+
+    public nextBlock(): CalldataBlock | undefined {
+        return this._queue.popFront();
+    }
+}
+
+export class ReverseCalldataIterator extends BaseIterator {
+    public constructor(root: CalldataBlock) {
+        super(root);
+    }
+
+    public nextBlock(): CalldataBlock | undefined {
+        return this._queue.popBack();
+    }
+}
diff --git a/packages/utils/src/abi_encoder/calldata/raw_calldata.ts b/packages/utils/src/abi_encoder/calldata/raw_calldata.ts
new file mode 100644
index 000000000..189841989
--- /dev/null
+++ b/packages/utils/src/abi_encoder/calldata/raw_calldata.ts
@@ -0,0 +1,82 @@
+import * as ethUtil from 'ethereumjs-util';
+import * as _ from 'lodash';
+
+import { constants } from '../utils/constants';
+import { Queue } from '../utils/queue';
+
+export class RawCalldata {
+    private static readonly _INITIAL_OFFSET = 0;
+    private readonly _value: Buffer;
+    private readonly _selector: string;
+    private readonly _scopes: Queue<number>;
+    private _offset: number;
+
+    public constructor(value: string | Buffer, hasSelector: boolean = true) {
+        // Sanity check
+        if (typeof value === 'string' && !_.startsWith(value, '0x')) {
+            throw new Error(`Expected raw calldata to start with '0x'`);
+        }
+        // Construct initial values
+        this._value = ethUtil.toBuffer(value);
+        this._selector = '0x';
+        this._scopes = new Queue<number>();
+        this._scopes.pushBack(RawCalldata._INITIAL_OFFSET);
+        this._offset = RawCalldata._INITIAL_OFFSET;
+        // If there's a selector then slice it
+        if (hasSelector) {
+            const selectorBuf = this._value.slice(constants.HEX_SELECTOR_LENGTH_IN_BYTES);
+            this._value = this._value.slice(constants.HEX_SELECTOR_LENGTH_IN_BYTES);
+            this._selector = ethUtil.bufferToHex(selectorBuf);
+        }
+    }
+
+    public popBytes(lengthInBytes: number): Buffer {
+        const value = this._value.slice(this._offset, this._offset + lengthInBytes);
+        this.setOffset(this._offset + lengthInBytes);
+        return value;
+    }
+
+    public popWord(): Buffer {
+        const wordInBytes = 32;
+        return this.popBytes(wordInBytes);
+    }
+
+    public popWords(length: number): Buffer {
+        const wordInBytes = 32;
+        return this.popBytes(length * wordInBytes);
+    }
+
+    public readBytes(from: number, to: number): Buffer {
+        const value = this._value.slice(from, to);
+        return value;
+    }
+
+    public setOffset(offsetInBytes: number): void {
+        this._offset = offsetInBytes;
+    }
+
+    public startScope(): void {
+        this._scopes.pushFront(this._offset);
+    }
+
+    public endScope(): void {
+        this._scopes.popFront();
+    }
+
+    public getOffset(): number {
+        return this._offset;
+    }
+
+    public toAbsoluteOffset(relativeOffset: number): number {
+        const scopeOffset = this._scopes.peekFront();
+        if (_.isUndefined(scopeOffset)) {
+            throw new Error(`Tried to access undefined scope.`);
+        }
+        const absoluteOffset = relativeOffset + scopeOffset;
+        return absoluteOffset;
+    }
+
+    public getSelector(): string {
+        return this._selector;
+    }
+}