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metamask-extension/ui/pages/confirm-approve/confirm-approve.util.js

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import { TRANSACTION_TYPES } from '../../../shared/constants/transaction';
import { decimalToHex } from '../../helpers/utils/conversions.util';
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import {
calcTokenValue,
getTokenAddressParam,
} from '../../helpers/utils/token-util';
import { getTokenData } from '../../helpers/utils/transactions.util';
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export function getCustomTxParamsData(
data,
{ customPermissionAmount, decimals },
) {
const tokenData = getTokenData(data);
if (!tokenData) {
throw new Error('Invalid data');
} else if (tokenData.name !== TRANSACTION_TYPES.TOKEN_METHOD_APPROVE) {
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throw new Error(
`Invalid data; should be 'approve' method, but instead is '${tokenData.name}'`,
);
}
let spender = getTokenAddressParam(tokenData);
if (spender.startsWith('0x')) {
spender = spender.substring(2);
}
const [signature, tokenValue] = data.split(spender);
if (!signature || !tokenValue) {
throw new Error('Invalid data');
} else if (tokenValue.length !== 64) {
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throw new Error(
'Invalid token value; should be exactly 64 hex digits long (u256)',
);
}
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let customPermissionValue = decimalToHex(
calcTokenValue(customPermissionAmount, decimals),
);
if (customPermissionValue.length > 64) {
throw new Error('Custom value is larger than u256');
}
customPermissionValue = customPermissionValue.padStart(
tokenValue.length,
'0',
);
const customTxParamsData = `${signature}${spender}${customPermissionValue}`;
return customTxParamsData;
}