1 files changed, 59 insertions, 0 deletions
diff --git a/packages/utils/src/abi_encoder/evm_data_types/string.ts b/packages/utils/src/abi_encoder/evm_data_types/string.ts
new file mode 100644
index 000000000..91a72ad3f
--- /dev/null
+++ b/packages/utils/src/abi_encoder/evm_data_types/string.ts
@@ -0,0 +1,59 @@
+import { DataItem, SolidityTypes } from 'ethereum-types';
+import * as ethUtil from 'ethereumjs-util';
+import * as _ from 'lodash';
+
+import { DataTypeFactory } from '../abstract_data_types/interfaces';
+import { AbstractBlobDataType } from '../abstract_data_types/types/blob';
+import { RawCalldata } from '../calldata/raw_calldata';
+import { constants } from '../utils/constants';
+
+export class StringDataType extends AbstractBlobDataType {
+    private static readonly _SIZE_KNOWN_AT_COMPILE_TIME: boolean = false;
+
+    public static matchType(type: string): boolean {
+        return type === SolidityTypes.String;
+    }
+
+    public constructor(dataItem: DataItem, dataTypeFactory: DataTypeFactory) {
+        super(dataItem, dataTypeFactory, StringDataType._SIZE_KNOWN_AT_COMPILE_TIME);
+        if (!StringDataType.matchType(dataItem.type)) {
+            throw new Error(`Tried to instantiate String with bad input: ${dataItem}`);
+        }
+    }
+
+    // Disable prefer-function-over-method for inherited abstract methods.
+    /* tslint:disable prefer-function-over-method */
+    public encodeValue(value: string): Buffer {
+        // Encoded value is of the form: <length><value>, with each field padded to be word-aligned.
+        // 1/3 Construct the length
+        const wordsToStoreValuePadded = Math.ceil(value.length / constants.EVM_WORD_WIDTH_IN_BYTES);
+        const bytesToStoreValuePadded = wordsToStoreValuePadded * constants.EVM_WORD_WIDTH_IN_BYTES;
+        const lengthBuf = ethUtil.toBuffer(value.length);
+        const lengthBufPadded = ethUtil.setLengthLeft(lengthBuf, constants.EVM_WORD_WIDTH_IN_BYTES);
+        // 2/3 Construct the value
+        const valueBuf = new Buffer(value);
+        const valueBufPadded = ethUtil.setLengthRight(valueBuf, bytesToStoreValuePadded);
+        // 3/3 Combine length and value
+        const encodedValue = Buffer.concat([lengthBufPadded, valueBufPadded]);
+        return encodedValue;
+    }
+
+    public decodeValue(calldata: RawCalldata): string {
+        // Encoded value is of the form: <length><value>, with each field padded to be word-aligned.
+        // 1/2 Decode length
+        const lengthBufPadded = calldata.popWord();
+        const lengthHexPadded = ethUtil.bufferToHex(lengthBufPadded);
+        const length = parseInt(lengthHexPadded, constants.HEX_BASE);
+        // 2/2 Decode value
+        const wordsToStoreValuePadded = Math.ceil(length / constants.EVM_WORD_WIDTH_IN_BYTES);
+        const valueBufPadded = calldata.popWords(wordsToStoreValuePadded);
+        const valueBuf = valueBufPadded.slice(0, length);
+        const value = valueBuf.toString('ascii');
+        return value;
+    }
+
+    public getSignature(): string {
+        return SolidityTypes.String;
+    }
+    /* tslint:enable prefer-function-over-method */
+}