fix: Send refuses every amount the confirmation screen would refuse (closes #532)

Send accepted any amount parseFloat() read as above zero, so "1e-3",
"1abc" and an amount with a nonzero digit past the token's decimal places
reached ConfirmTx, which then refused them. isValidAmount() in
src/shared/txValidation.js is now the one check: Review and Max on Send
call it with the token's decimal places, and validateTransfer() calls it
for ConfirmTx, which now also refuses a zero amount and a token amount
with a nonzero digit past the token's places. Zeros past those places
are accepted, since the amount encoded for the transfer is the same.

Model: opus-5-5

README.md

@@ -1687,9 +1687,12 @@ view would leave a wallet one click from deletion.
     - "Review" (valid inputs, ENS resolved) → **ConfirmTx**
     - "Review" with an unresolvable ENS name or an invalid amount → flash
       message, no screen change. An amount is valid when it is a number above
-      zero written as digits with at most one decimal point, with no more
-      decimal places than the token has and never more than 18 (ETH's own),
-      which is also the check ConfirmTx makes before anything can be sent
+      zero, written as digits with at most one decimal point, with nothing but
+      zeros after the token's last decimal place. ETH has 18 places, and a token
+      with more, or with an unknown number, is held to 18. Zeros past those
+      places leave the amount unchanged, so `1.0000000` of a 6-place token
+      passes and is sent as exactly 1. ConfirmTx makes the same check before
+      anything can be sent
     - "Back" → previous screen (Home, AddressDetail, or AddressToken)
 
 #### ConfirmTx (`confirm-tx`)

src/shared/txValidation.js

@@ -89,13 +89,16 @@ function toFixedPoint(value) {
 }
 
 // Whether `amount` can be sent: a number above zero, written as digits with
-// at most one decimal point ("0.5", "12", ".5"), with no more decimal places
-// than `tokenDecimals`, a token's own, and never more than the 18 the
-// arithmetic here works in, which are ETH's. ETH, and a token whose decimal
-// places are unknown, pass null and are held to the 18 (the confirmation
-// screen refuses to send such a token anyway). Refuses "1e-3", "1abc", "0"
-// and "-1". The Send screen checks it before the confirmation screen opens,
-// and validateTransfer() checks it again there.
+// at most one decimal point ("0.5", "12", ".5"), with nothing but zeros after
+// the token's last decimal place, `tokenDecimals`, and nothing but zeros after
+// the 18th, the places the arithmetic here works in, which are ETH's. ETH, and
+// a token whose decimal places are unknown, pass null and are held to the 18
+// (the confirmation screen refuses to send such a token anyway). Zeros past
+// those places are accepted because parseUnits() drops them here and again
+// when the transfer is encoded, so "1.0000000" of a 6-place token is exactly
+// 1 everywhere. Refuses "1e-3", "1abc", "0" and "-1". The Send screen checks
+// it before the confirmation screen opens, and validateTransfer() checks it
+// again there.
 function isValidAmount(amount, tokenDecimals = null) {
     if (typeof amount !== "string") return false;
     const places = Math.min(tokenDecimals ?? SCALE_DECIMALS, SCALE_DECIMALS);

tests/sendAmountRule.test.js

@@ -194,6 +194,9 @@ describe.each([
     ["0.5", "TOK"],
     // Exactly the 6 decimal places the token has.
     ["0.000001", "TOK"],
+    // Only zeros past the token's 6 places, and past ETH's 18.
+    ["1.0000000", "TOK"],
+    ["0.5000000000000000000", "ETH"],
 ])("%s %s", (amount, symbol) => {
     const token = TOKEN_BY_SYMBOL[symbol];
 

tests/transferAmount.test.js

@@ -116,6 +116,12 @@ describe("transferAmountUnits", () => {
         expect(() => transferAmountUnits("0.0000001", 6, 6n)).toThrow();
     });
 
+    test("encodes zeros past the token's scale as the amount typed", () => {
+        // The Send screen accepts "1.0000000" for a 6-place token, so the
+        // transfer must move exactly 1 of it.
+        expect(transferAmountUnits("1.0000000", 6, 6n)).toBe(1000000n);
+    });
+
     test("every refusal is a full sentence", () => {
         const messages = [];
         for (const args of [

tests/txValidation.test.js

@@ -54,13 +54,20 @@ describe("isValidAmount", () => {
         expect(isValidAmount(undefined)).toBe(false);
     });
 
-    test("refuses more decimal places than the token has", () => {
+    test("refuses a digit other than 0 past the token's places", () => {
         expect(isValidAmount("0.000001", 6)).toBe(true);
         expect(isValidAmount("0.0000001", 6)).toBe(false);
         expect(isValidAmount("5", 0)).toBe(true);
         expect(isValidAmount("0.5", 0)).toBe(false);
     });
 
+    test("accepts zeros past the token's places, which leave the amount unchanged", () => {
+        expect(isValidAmount("1.0000000", 6)).toBe(true);
+        expect(isValidAmount("5.0", 0)).toBe(true);
+        expect(isValidAmount("1.0000000000000000000")).toBe(true);
+        expect(isValidAmount("0.0000000", 6)).toBe(false);
+    });
+
     test("holds ETH, a token of unknown places, and any token to 18 places", () => {
         const nineteen = "0.0000000000000000001";
         expect(isValidAmount(nineteen)).toBe(false);