fix: a V4 swap action not in the deployed shape is shown as not decoded (closes #358)

The four V4 swap actions are read only as the structs deployed on mainnet
and Sepolia. ethers read the newer v4-periphery structs, which add
minHopPriceX36, as the deployed ones, and the newer multi-hop exact-in
struct showed the offset of its hop-price array as the swap amount. A
decode now counts only when encoding it again gives back the same bytes.
A swap action that fails that marks its step "V4 Swap (could not be
decoded)", and a side its SETTLE or TAKE did not name reads "Unknown
(could not be decoded)". The wait and error screens no longer show the
ETH value as the amount of a swap whose amount was not read, unless the
swap is paid in native ETH.

Model: opus-5-5

src/popup/views/approval.js

@@ -298,6 +298,23 @@ function showTxApproval(details) {
                 sources,
             );
         }
+        // A swap the decoder read no amount for, such as one whose V4 swap
+        // action could not be read or a V4 exact-out swap. The wait and error
+        // screens say the amount could not be decoded, with no currency after
+        // it, rather than show the transaction's ETH value as the amount. A
+        // swap paid in native ETH keeps that value: it is the ETH the swap
+        // pays (for an exact-out swap, the most it pays), not a figure that
+        // had to be read from the calldata.
+        const tokenIn = decoded.details.find((d) => d.label === "Token In");
+        if (
+            tokenIn &&
+            tokenIn.value !== "ETH (native)" &&
+            !decoded.details.some((d) => d.label === "Amount")
+        ) {
+            pendingTxDetails.amount = "Unknown (could not be decoded)";
+            pendingTxDetails.token = null;
+            pendingTxDetails.tokenSymbol = null;
+        }
     }
 
     // Carry decoded calldata info through to success/error views

src/popup/views/txStatus.js

@@ -91,12 +91,17 @@ function startWait(txInfo, txHash, broadcastTime, pollNow) {
     // native currency of txInfo.chainId, the network the transaction was sent
     // on, not the active network's: the active network can change, in
     // Settings or when the user approves a site's request, while this screen
-    // is open or before a later popup resumes it.
-    const symbol =
-        txInfo.token === "ETH"
-            ? nativeCurrencyByChainId(txInfo.chainId)
-            : displaySymbol(txInfo.tokenSymbol || "?");
-    $("wait-tx-summary").textContent = txInfo.amount + " " + symbol;
+    // is open or before a later popup resumes it. A null token is a swap whose
+    // amount was not decoded (see showTxApproval() in approval.js): the amount
+    // says so, and no symbol follows it.
+    let symbol = "";
+    if (txInfo.token === "ETH") {
+        symbol = nativeCurrencyByChainId(txInfo.chainId);
+    } else if (txInfo.token !== null) {
+        symbol = displaySymbol(txInfo.tokenSymbol || "?");
+    }
+    $("wait-tx-summary").textContent =
+        txInfo.amount + (symbol ? " " + symbol : "");
     $("wait-tx-to").innerHTML = toAddressHtml(txInfo.to);
     $("wait-tx-hash").innerHTML = txHashHtml(txHash);
     attachCopyHandlers("view-wait-tx");
@@ -231,10 +236,13 @@ function restoreWait() {
 function showSuccess(txInfo, txHash, blockNumber) {
     endWait();
 
-    const symbol =
-        txInfo.token === "ETH"
-            ? nativeCurrencyByChainId(txInfo.chainId)
-            : displaySymbol(txInfo.tokenSymbol || "?");
+    // As on the wait screen, a null token has no symbol.
+    let symbol = "";
+    if (txInfo.token === "ETH") {
+        symbol = nativeCurrencyByChainId(txInfo.chainId);
+    } else if (txInfo.token !== null) {
+        symbol = displaySymbol(txInfo.tokenSymbol || "?");
+    }
     state.viewData = {
         amount: txInfo.amount,
         symbol: symbol,
@@ -294,7 +302,8 @@ function renderSuccess() {
     } else {
         summarySection.classList.remove("hidden");
         toSection.classList.remove("hidden");
-        $("success-tx-summary").textContent = d.amount + " " + d.symbol;
+        $("success-tx-summary").textContent =
+            d.amount + (d.symbol ? " " + d.symbol : "");
         $("success-tx-to").innerHTML = toAddressHtml(d.to);
     }
 
@@ -317,10 +326,13 @@ function renderSuccess() {
 function showError(txInfo, txHash, message) {
     endWait();
 
-    const symbol =
-        txInfo.token === "ETH"
-            ? nativeCurrencyByChainId(txInfo.chainId)
-            : displaySymbol(txInfo.tokenSymbol || "?");
+    // As on the wait screen, a null token has no symbol.
+    let symbol = "";
+    if (txInfo.token === "ETH") {
+        symbol = nativeCurrencyByChainId(txInfo.chainId);
+    } else if (txInfo.token !== null) {
+        symbol = displaySymbol(txInfo.tokenSymbol || "?");
+    }
     state.viewData = {
         amount: txInfo.amount,
         symbol: symbol,
@@ -334,7 +346,8 @@ function showError(txInfo, txHash, message) {
 function renderError() {
     const d = state.viewData;
     if (!d || !d.message) return;
-    $("error-tx-summary").textContent = d.amount + " " + d.symbol;
+    $("error-tx-summary").textContent =
+        d.amount + (d.symbol ? " " + d.symbol : "");
     $("error-tx-to").innerHTML = toAddressHtml(d.to);
     $("error-tx-message").textContent = d.message;
 

src/shared/uniswap.js

@@ -53,6 +53,11 @@ function formatAmount(raw, decimals) {
 // on a scale — not as a token name, and not as a quantity.
 const UNNAMED_CURRENCY = "Unknown (not named in the calldata)";
 
+// The same refusal when a V4 swap action could not be read (see
+// decodeExactly()). That action names both of its currencies, so saying the
+// calldata did not name one would be false.
+const UNDECODED_CURRENCY = "Unknown (could not be decoded)";
+
 // Explicit presence, never truthiness. Every gate in this file that guards a
 // decoded value goes through here: an address is never falsy once set, but an
 // amount of 0n is, and a gate that cannot tell a genuine zero from an absent
@@ -295,6 +300,24 @@ function v4ExactInAmount(raw) {
     return raw === 0n ? OPEN_DELTA : raw;
 }
 
+// The V4 swap actions are read only in the parameter structs V4Router has
+// deployed on mainnet and Sepolia. v4-periphery `main` has since added a
+// `minHopPriceX36` field to all four (`src/interfaces/IV4Router.sol`), and
+// reading a shape nobody has deployed would be guessing. ethers alone would
+// read the newer structs anyway: it takes whatever word sits where a
+// deployed field would be, ignores bytes left over, and holds back an error
+// in a field until that field is used. The newer multi-hop exact-in struct
+// then yields the offset of its hop-price array as `amountIn`. So a decode
+// counts only when encoding the result again gives back the same bytes;
+// otherwise this throws, and decodeV4Swap() marks the step as not decoded.
+function decodeExactly(types, data) {
+    const decoded = coder.decode(types, data);
+    if (coder.encode(types, decoded) !== data) {
+        throw new Error("Not in the deployed V4 parameter shape.");
+    }
+    return decoded;
+}
+
 // Decode V4_SWAP (command 0x10) input bytes.
 // The input is ABI-encoded as (bytes actions, bytes[] params).
 // We extract token addresses from SETTLE (input) and TAKE (output) sub-actions,
@@ -309,6 +332,10 @@ function decodeV4Swap(input) {
         let takeToken = null;
         let amountIn = null;
         let amountOutMin = null;
+        // Set when a swap action's parameters are not in the deployed shape
+        // (see decodeExactly()), so nothing was read from that action. SETTLE
+        // and TAKE may still name both currencies.
+        let swapUndecoded = false;
 
         for (let i = 0; i < actions.length; i++) {
             const actionId = actions[i];
@@ -337,7 +364,7 @@ function decodeV4Swap(input) {
                         //   tuple(address,uint24,int24,address,bytes)[] path,
                         //   uint128 amountIn, uint128 amountOutMin)
                         try {
-                            const s = coder.decode(
+                            const s = decodeExactly(
                                 [
                                     "tuple(address,tuple(address,uint24,int24,address,bytes)[],uint128,uint128)",
                                 ],
@@ -355,13 +382,13 @@ function decodeV4Swap(input) {
                                 amountOutMin = s[0][3];
                             }
                         } catch {
-                            // Fall through — SETTLE/TAKE will provide tokens
+                            swapUndecoded = true;
                         }
                     } else {
                         // ExactInputSingleParams: (tuple(address,address,uint24,int24,address) poolKey,
                         //   bool zeroForOne, uint128 amountIn, uint128 amountOutMin, bytes hookData)
                         try {
-                            const s = coder.decode(
+                            const s = decodeExactly(
                                 [
                                     "tuple(tuple(address,address,uint24,int24,address),bool,uint128,uint128,bytes)",
                                 ],
@@ -384,7 +411,7 @@ function decodeV4Swap(input) {
                                 amountOutMin = s[0][3];
                             }
                         } catch {
-                            // Fall through
+                            swapUndecoded = true;
                         }
                     }
                 } else if (
@@ -393,7 +420,7 @@ function decodeV4Swap(input) {
                 ) {
                     if (actionId === V4_SWAP_EXACT_OUT) {
                         try {
-                            const s = coder.decode(
+                            const s = decodeExactly(
                                 [
                                     "tuple(address,tuple(address,uint24,int24,address,bytes)[],uint128,uint128)",
                                 ],
@@ -405,11 +432,11 @@ function decodeV4Swap(input) {
                                 settleToken = path[path.length - 1][0];
                             }
                         } catch {
-                            // Fall through
+                            swapUndecoded = true;
                         }
                     } else {
                         try {
-                            const s = coder.decode(
+                            const s = decodeExactly(
                                 [
                                     "tuple(tuple(address,address,uint24,int24,address),bool,uint128,uint128,bytes)",
                                 ],
@@ -426,7 +453,7 @@ function decodeV4Swap(input) {
                                     ? poolKey[1]
                                     : poolKey[0];
                         } catch {
-                            // Fall through
+                            swapUndecoded = true;
                         }
                     }
                 }
@@ -440,6 +467,7 @@ function decodeV4Swap(input) {
             tokenOut: takeToken,
             amountIn,
             amountOutMin,
+            swapUndecoded,
         };
     } catch {
         return null;
@@ -465,6 +493,7 @@ function decode(data, toAddress, sources) {
         let minOutput = null;
         let hasUnwrapWeth = false;
         let hasV2ExactOut = false;
+        let swapUndecoded = false;
         const commandNames = [];
 
         // THE INVARIANT: an amount and the token it is counted in always come
@@ -567,7 +596,20 @@ function decode(data, toAddress, sources) {
 
                 if (cmdId === 0x10) {
                     const v4 = decodeV4Swap(inputs[i]);
-                    if (v4) {
+                    if (v4 && v4.swapUndecoded) {
+                        // The unread swap action named this step's currencies
+                        // and amounts, so the step is marked and still sets
+                        // both sides as a swap step does. A side its SETTLE or
+                        // TAKE did not name is set undetermined, not left to
+                        // an earlier or later step's token and figure.
+                        swapUndecoded = true;
+                        commandNames[i] += " (could not be decoded)";
+                        if (!inputEstablished) {
+                            setInput(v4.tokenIn, v4.amountIn);
+                        }
+                        outputToken = v4.tokenOut;
+                        minOutput = v4.amountOutMin;
+                    } else if (v4) {
                         setInputOnce(v4.tokenIn, v4.amountIn);
                         // Always update output: last swap step wins. A step
                         // that carries the Min. received figure but decoded no
@@ -591,16 +633,19 @@ function decode(data, toAddress, sources) {
             }
         }
 
-        // Resolve token info. A null token on either side means the calldata
-        // named no currency for it; tokenInfo() refuses rather than calling it
-        // ETH. UNWRAP_WETH turns WETH into ETH, so it makes the output ETH
-        // when the output side is WETH, or when no step set the output side.
-        // Any other output keeps its own token and figure: a swap that buys
-        // USDC and then unwraps the WETH it did not spend receives USDC.
+        // Resolve token info. A null token on either side means no step named
+        // a currency for it, or a V4 step whose swap action went unread left
+        // it undetermined; tokenInfo() refuses rather than calling it ETH.
+        // UNWRAP_WETH turns WETH into ETH, so it makes the output ETH when the
+        // output side is WETH, or when no step set the output side. A step
+        // whose swap action went unread did set it, to undetermined. Any other
+        // output keeps its own token and figure: a swap that buys USDC and
+        // then unwraps the WETH it did not spend receives USDC.
         const outputIsWeth =
             present(outputToken) &&
             WETH_ADDRESSES.includes(outputToken.toLowerCase());
-        const outputUnset = !present(outputToken) && !present(minOutput);
+        const outputUnset =
+            !present(outputToken) && !present(minOutput) && !swapUndecoded;
         const inInfo = tokenInfo(inputToken, sources);
         const outInfo =
             hasUnwrapWeth && (outputIsWeth || outputUnset)
@@ -640,7 +685,10 @@ function decode(data, toAddress, sources) {
             // rather than going missing or naming a token by default. Same
             // wording as the Token Out refusal below: the two sides of this
             // screen must not describe the same condition in two ways.
-            details.push({ label: "Token In", value: UNNAMED_CURRENCY });
+            details.push({
+                label: "Token In",
+                value: swapUndecoded ? UNDECODED_CURRENCY : UNNAMED_CURRENCY,
+            });
         }
 
         if (present(inputAmount)) {
@@ -703,7 +751,10 @@ function decode(data, toAddress, sources) {
             // rather than going missing or naming a token by default, and a
             // Min. received figure below it is never attached to a token the
             // calldata did not state.
-            details.push({ label: "Token Out", value: UNNAMED_CURRENCY });
+            details.push({
+                label: "Token Out",
+                value: swapUndecoded ? UNDECODED_CURRENCY : UNNAMED_CURRENCY,
+            });
         }
 
         if (present(minOutput)) {