AutistMask/src/shared/approvalAmount.js

// The scale an ERC-20 amount in a dApp's calldata is displayed with, and what
// to display when there is no such scale.
//
// The approval screen decodes `transfer` and `approve` calldata into a
// quantity the user confirms against. That quantity is a base-unit integer,
// and turning it into a number a person can read needs the token's decimals.
// Assuming a scale is how a drain gets confirmed: a `transfer` of 5000000000
// units of a 6-decimal token is 5,000 tokens, but formatted with the ERC-20
// default of 18 it reads `0.0000`, and a user who reads zero signs.
//
// So a scale is either found or the amount is not formatted. Decimals are
// looked for in the bundled token list, then in the tokens the user tracks,
// then in what the block explorer reported for the contract; where none of
// them answers, unknownDecimalsAmount() renders the base-unit integer with the
// unknown scale stated, and no formatUnits() call is reached at all.
//
// The Uniswap decoder's Amount and Min. received lines land on this same
// screen and use these same two functions, so there is one way of resolving a
// scale and one way of saying there is none.
//
// This is the display counterpart to transferAmount.js, which takes the same
// stance on the wallet's own send path: an amount whose scale is unknown or
// disputed is refused rather than guessed at.

// Solidity's decimals() is a uint8, and every source here is ultimately
// reporting that call's result. toDecimals() is that check, stopping at the 80
// places formatUnits() accepts, and shared with the send path rather than
// copied: the bundled list stores numbers, the explorer's copy arrives as a
// string, and a token the user added by hand carries whatever lookupTokenInfo()
// got back, so the accepted types are enumerated rather than coerced.
const { toDecimals } = require("./transferAmount");
const { TOKEN_BY_ADDRESS } = require("./tokenList");
const { isSpoofedSymbol } = require("./symbolSpoof");

// Every decimals the explorer reported for this contract, across all the
// addresses whose balances have been fetched. They describe one contract, so
// they should agree; a set that does not agree is a scale in dispute, and this
// screen has no way to tell which member is the true one.
function explorerDecimals(lower, wallets) {
    let found = null;
    for (const wallet of wallets || []) {
        for (const addr of wallet.addresses || []) {
            for (const tb of addr.tokenBalances || []) {
                if ((tb.address || "").toLowerCase() !== lower) continue;
                const d = toDecimals(tb.decimals);
                if (d === null) continue;
                if (found !== null && found !== d) return null;
                found = d;
            }
        }
    }
    return found;
}

// The decimals to render a token amount with, or null when nothing knows.
// `sources` is { trackedTokens, wallets }, both shaped as they are on `state`.
function resolveTokenDecimals(tokenAddress, sources) {
    const lower = (tokenAddress || "").toLowerCase();
    if (!lower) return null;

    const bundled = TOKEN_BY_ADDRESS.get(lower);
    if (bundled) {
        const d = toDecimals(bundled.decimals);
        if (d !== null) return d;
    }

    const tracked = ((sources && sources.trackedTokens) || []).find(
        (t) => (t.address || "").toLowerCase() === lower,
    );
    if (tracked) {
        const d = toDecimals(tracked.decimals);
        if (d !== null) return d;
    }

    return explorerDecimals(lower, sources && sources.wallets);
}

// Every symbol the explorer reported for this contract, across the addresses
// whose balances have been fetched. The counterpart to explorerDecimals(): one
// contract, so the reports should agree, and a set that does not agree is a
// name this screen has no way to choose between.
function explorerSymbol(lower, wallets) {
    let found = null;
    for (const wallet of wallets || []) {
        for (const addr of wallet.addresses || []) {
            for (const tb of addr.tokenBalances || []) {
                if ((tb.address || "").toLowerCase() !== lower) continue;
                if (!tb.symbol) continue;
                if (found !== null && found !== tb.symbol) return null;
                found = tb.symbol;
            }
        }
    }
    return found;
}

// The symbol to label a token with, or null when no source the wallet trusts
// names one — in which case the screen keeps saying `Unknown token` rather than
// guessing. The bundled list, then the tokens the user tracks, then what the
// explorer reported: the same sources and the same precedence
// resolveTokenDecimals() uses, so a token's name and its scale are drawn from
// the same place and the two can no longer disagree about which sources they
// trust. `sources` is { trackedTokens, wallets }, shaped as on `state`.
//
// A tracked or explorer-reported symbol is attacker-influenced text, so it is
// held to the spoof rule (symbolSpoof.js): a candidate that wears a bundled or
// native ticker from a contract not entitled to it is refused and the next
// source tried, so resolving a symbol never becomes a new way to claim a known
// ticker. The bundled list is the wallet's own data and is trusted as it is.
function resolveTokenSymbol(tokenAddress, sources) {
    const lower = (tokenAddress || "").toLowerCase();
    if (!lower) return null;

    const bundled = TOKEN_BY_ADDRESS.get(lower);
    if (bundled && bundled.symbol) return bundled.symbol;

    const tracked = ((sources && sources.trackedTokens) || []).find(
        (t) => (t.address || "").toLowerCase() === lower,
    );
    const candidates = [];
    if (tracked && tracked.symbol) candidates.push(tracked.symbol);
    const reported = explorerSymbol(lower, sources && sources.wallets);
    if (reported) candidates.push(reported);

    for (const symbol of candidates) {
        if (!isSpoofedSymbol(symbol, tokenAddress)) return symbol;
    }
    return null;
}

// What the amount line reads when the scale is unknown. The base units are
// exact and the caveat is part of the same string, so the number on the screen
// cannot be mistaken for a token quantity, and it can never read as zero for a
// transfer that is not zero.
function unknownDecimalsAmount(rawAmount) {
    return String(rawAmount) + " base units (decimals unknown)";
}

module.exports = {
    resolveTokenDecimals,
    resolveTokenSymbol,
    unknownDecimalsAmount,
};