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

Send's Review accepted any amount parseFloat() read as above zero, so 1e-3, 1abc and amounts with too many decimal places reached ConfirmTx, which then refused them or failed to estimate the fee.

isValidAmount() in src/shared/txValidation.js is now the one amount check, used by Send's Review and Max and by validateTransfer() for ConfirmTx: plain digits with at most one decimal point, above zero, nothing but zeros past the token's places. Zeros past those places are accepted, since the transfer encodes the amount exactly. Send now reads the token's decimal places before the ENS lookup, because the check needs them.

Judgement call: ConfirmTx now also refuses zero, as Send already did.

Model: opus-5-5

src/popup/views/send.js

@@ -24,6 +24,7 @@ const {
 } = require("../../shared/amountDisplay");
 const {
     feeReserveWei,
+    isValidAmount,
     maxEthAmount,
     maxTokenAmount,
 } = require("../../shared/txValidation");
@@ -255,13 +256,18 @@ async function fillMaxAmount() {
     const token = state.selectedToken || $("send-token").value;
 
     if (token !== "ETH") {
-        const bal = tokenBalanceAndDecimals(addr, token).tokenBalance;
+        const { tokenBalance: bal, tokenDecimals } = tokenBalanceAndDecimals(
+            addr,
+            token,
+        );
         if (bal == null) {
             showFlash("This token's balance is unknown.");
             return;
         }
         const amount = maxTokenAmount(bal);
-        if (!(parseFloat(amount) > 0)) {
+        // The balance is stored at the token's own decimal places and cut to
+        // 18 above, so the only balance this refuses is zero.
+        if (!isValidAmount(amount, tokenDecimals)) {
             showFlash("This token's balance is zero.");
             return;
         }
@@ -367,7 +373,28 @@ function init(_ctx) {
             );
             return;
         }
-        if (!amount || isNaN(parseFloat(amount)) || parseFloat(amount) <= 0) {
+
+        const token = state.selectedToken || $("send-token").value;
+        const addr = currentAddress();
+
+        let tokenSymbol = null;
+        let tokenBalance = null;
+        let tokenDecimals = null;
+        if (token !== "ETH") {
+            tokenSymbol = resolveSymbol(
+                token,
+                addr.tokenBalances,
+                state.trackedTokens,
+            );
+            ({ tokenBalance, tokenDecimals } = tokenBalanceAndDecimals(
+                addr,
+                token,
+            ));
+        }
+
+        // The confirmation screen's own amount check, so it is never shown
+        // an amount it would refuse.
+        if (!isValidAmount(amount, tokenDecimals)) {
             showFlash("Please enter a valid amount.");
             return;
         }
@@ -391,24 +418,6 @@ function init(_ctx) {
             }
         }
 
-        const token = state.selectedToken || $("send-token").value;
-        const addr = currentAddress();
-
-        let tokenSymbol = null;
-        let tokenBalance = null;
-        let tokenDecimals = null;
-        if (token !== "ETH") {
-            tokenSymbol = resolveSymbol(
-                token,
-                addr.tokenBalances,
-                state.trackedTokens,
-            );
-            ({ tokenBalance, tokenDecimals } = tokenBalanceAndDecimals(
-                addr,
-                token,
-            ));
-        }
-
         ctx.showConfirmTx({
             from: addr.address,
             to: resolvedTo,