AutistMask/tests/transferAmount.test.js

// The scale an ERC-20 transfer from the wallet's own Send screen is encoded
// with (issue #305). The screen renders from the block explorer's cached
// decimals; the transfer used to be encoded from decimals() read off the
// contract at signing time, with nothing comparing the two, so a token whose
// on-chain scale differed signed an amount that was never displayed.

const { formatUnits, parseUnits } = require("ethers");
const {
    displayedDecimals,
    transferAmountUnits,
    MAX_DECIMALS,
    UNKNOWN_DISPLAYED_DECIMALS_MESSAGE,
    UNREADABLE_CONTRACT_DECIMALS_MESSAGE,
} = require("../src/shared/transferAmount");

describe("displayedDecimals", () => {
    test("accepts what the explorer and the contract each answer with", () => {
        // A string is what fetchTokenBalances() parses out of Blockscout, a
        // number is what it stores, and a bigint is what ethers hands back
        // from a uint8 return.
        expect(displayedDecimals("6")).toBe(6);
        expect(displayedDecimals(6)).toBe(6);
        expect(displayedDecimals(6n)).toBe(6);
        expect(displayedDecimals(0)).toBe(0);
        expect(displayedDecimals(MAX_DECIMALS)).toBe(MAX_DECIMALS);
    });

    // decimals() is a uint8, but formatUnits() and parseUnits() stop at 80
    // places, so a larger scale cannot be shown or encoded
    // (https://git.eeqj.de/sneak/AutistMask/issues/350).
    test("accepts exactly the scales the formatter accepts", () => {
        expect(() => formatUnits(1n, MAX_DECIMALS)).not.toThrow();
        expect(() => parseUnits("1", MAX_DECIMALS)).not.toThrow();
        expect(() => formatUnits(1n, MAX_DECIMALS + 1)).toThrow();
        expect(() => parseUnits("1", MAX_DECIMALS + 1)).toThrow();
    });

    test("refuses anything that is not a uint8 the formatter accepts", () => {
        for (const bad of [
            null,
            undefined,
            "",
            "eighteen",
            NaN,
            6.5,
            -1,
            MAX_DECIMALS + 1,
            true,
            {},
            [],
        ]) {
            expect(() => displayedDecimals(bad)).toThrow(
                UNKNOWN_DISPLAYED_DECIMALS_MESSAGE,
            );
        }
    });
});

describe("transferAmountUnits", () => {
    test("encodes with the displayed scale when the contract agrees", () => {
        expect(transferAmountUnits("0.25", 6, 6n)).toBe(parseUnits("0.25", 6));
        expect(transferAmountUnits("0.25", "6", 6n)).toBe(
            parseUnits("0.25", 6),
        );
        expect(transferAmountUnits("1.5", 18, 18n)).toBe(parseUnits("1.5", 18));
    });

    // The reproduction on the issue: 0.25 of a token displayed at 6 decimals,
    // signed against a contract answering 18, moves 10^12 times the amount
    // that was approved.
    test("refuses the reproduction rather than signing either amount", () => {
        expect(() => transferAmountUnits("0.25", 6, 18n)).toThrow(
            /contract reports 18 decimal places, but the amount was displayed using 6/,
        );
    });

    test("refuses a disagreement in the other direction too", () => {
        expect(() => transferAmountUnits("0.25", 18, 6n)).toThrow(
            /contract reports 6 decimal places, but the amount was displayed using 18/,
        );
    });

    test("never returns the amount at either scale on a disagreement", () => {
        // The point of the refusal: both candidate encodings exist, and the
        // wallet must produce neither.
        let thrown = null;
        try {
            transferAmountUnits("0.25", 6, 18n);
        } catch (e) {
            thrown = e;
        }
        expect(thrown).toBeInstanceOf(Error);
        expect(thrown.message).toMatch(/was not sent/);
    });

    test("refuses when the screen's scale is unknown", () => {
        expect(() => transferAmountUnits("0.25", null, 6n)).toThrow(
            UNKNOWN_DISPLAYED_DECIMALS_MESSAGE,
        );
        expect(() => transferAmountUnits("0.25", undefined, 6n)).toThrow(
            UNKNOWN_DISPLAYED_DECIMALS_MESSAGE,
        );
    });

    test("refuses when the contract's answer is not a uint8", () => {
        for (const bad of [null, undefined, "", "eighteen", 6.5, -1, 256]) {
            expect(() => transferAmountUnits("0.25", 6, bad)).toThrow(
                UNREADABLE_CONTRACT_DECIMALS_MESSAGE,
            );
        }
    });

    test("rejects an amount finer than the token's scale", () => {
        // parseUnits' own refusal, reached only once the scales agree: a
        // fractional base unit cannot be sent and must not be truncated.
        expect(() => transferAmountUnits("0.0000001", 6, 6n)).toThrow();
    });

    test("every refusal is a full sentence", () => {
        const messages = [];
        for (const args of [
            ["0.25", 6, 18n],
            ["0.25", null, 6n],
            ["0.25", 6, "eighteen"],
        ]) {
            try {
                transferAmountUnits(...args);
            } catch (e) {
                messages.push(e.message);
            }
        }
        expect(messages).toHaveLength(3);
        for (const m of messages) {
            expect(m).toMatch(/^[A-Z]/);
            expect(m).toMatch(/\.$/);
        }
    });
});