Comments and inline documentation for dynamic bytes

1 files changed, 33 insertions, 22 deletions

diff --git a/packages/utils/src/abi_encoder/evm_data_types/dynamic_bytes.ts b/packages/utils/src/abi_encoder/evm_data_types/dynamic_bytes.ts
index 626e266c9..ce6ace627 100644
--- a/packages/utils/src/abi_encoder/evm_data_types/dynamic_bytes.ts
+++ b/packages/utils/src/abi_encoder/evm_data_types/dynamic_bytes.ts
@@ -17,42 +17,53 @@ export class DynamicBytes extends PayloadDataType {
     public constructor(dataItem: DataItem, dataTypeFactory: DataTypeFactory) {
         super(dataItem, dataTypeFactory, DynamicBytes._SIZE_KNOWN_AT_COMPILE_TIME);
         if (!DynamicBytes.matchType(dataItem.type)) {
-            throw new Error(`Tried to instantiate DynamicBytes with bad input: ${dataItem}`);
+            throw new Error(`Tried to instantiate Dynamic Bytes with bad input: ${dataItem}`);
         }
     }
 
     public encodeValue(value: string | Buffer): Buffer {
-        if (typeof value === 'string' && !value.startsWith('0x')) {
-            throw new Error(`Tried to encode non-hex value. Value must inlcude '0x' prefix. Got '${value}'`);
-        }
+        // Encoded value is of the form: <length><value>, with each field padded to be word-aligned.
+        // 1/3 Construct the length
         const valueBuf = ethUtil.toBuffer(value);
-        if (value.length % 2 !== 0) {
-            throw new Error(`Tried to assign ${value}, which is contains a half-byte. Use full bytes only.`);
-        }
-
-        const wordsForValue = Math.ceil(valueBuf.byteLength / Constants.EVM_WORD_WIDTH_IN_BYTES);
-        const paddedDynamicBytesForValue = wordsForValue * Constants.EVM_WORD_WIDTH_IN_BYTES;
-        const paddedValueBuf = ethUtil.setLengthRight(valueBuf, paddedDynamicBytesForValue);
-        const paddedLengthBuf = ethUtil.setLengthLeft(
-            ethUtil.toBuffer(valueBuf.byteLength),
-            Constants.EVM_WORD_WIDTH_IN_BYTES,
-        );
-        const encodedValueBuf = Buffer.concat([paddedLengthBuf, paddedValueBuf]);
-        return encodedValueBuf;
+        const wordsToStoreValuePadded = Math.ceil(valueBuf.byteLength / Constants.EVM_WORD_WIDTH_IN_BYTES);
+        const bytesToStoreValuePadded = wordsToStoreValuePadded * Constants.EVM_WORD_WIDTH_IN_BYTES;
+        const lengthBuf = ethUtil.toBuffer(valueBuf.byteLength);
+        const lengthBufPadded = ethUtil.setLengthLeft(lengthBuf, Constants.EVM_WORD_WIDTH_IN_BYTES);
+        // 2/3 Construct the value
+        this._sanityCheckValue(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 lengthBuf = calldata.popWord();
         const lengthHex = ethUtil.bufferToHex(lengthBuf);
         const length = parseInt(lengthHex, Constants.HEX_BASE);
-        const wordsForValue = Math.ceil(length / Constants.EVM_WORD_WIDTH_IN_BYTES);
-        const paddedValueBuf = calldata.popWords(wordsForValue);
-        const valueBuf = paddedValueBuf.slice(0, length);
-        const decodedValue = ethUtil.bufferToHex(valueBuf);
-        return decodedValue;
+        // 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 = ethUtil.bufferToHex(valueBuf);
+        this._sanityCheckValue(value);
+        return value;
     }
 
     public getSignature(): string {
         return 'bytes';
     }
+
+    private _sanityCheckValue(value: string | Buffer): void {
+        if (typeof value !== 'string') {
+            return;
+        }
+        if (!value.startsWith('0x')) {
+            throw new Error(`Tried to encode non-hex value. Value must inlcude '0x' prefix.`);
+        } else if (value.length % 2 !== 0) {
+            throw new Error(`Tried to assign ${value}, which is contains a half-byte. Use full bytes only.`);
+        }
+    }
 }