fix: a V4 step of chained swap actions shows what the user receives (closes #563)

A V4 step's input side is the currency SETTLE or SETTLE_ALL names, else
the one currency some swap action spends and none buys; its output side
is the currency TAKE or TAKE_ALL names, else the one some swap action
buys and none spends. Amount and Min. received come from those actions,
summed when several exact-in actions each state one. A step with an
unread swap action is named only by SETTLE, SETTLE_ALL, TAKE and
TAKE_ALL, and shows no figure. A side a step with a swap action leaves
unknown shows no other step's token or figure. Before, the first swap
action set both sides, SETTLE_ALL and TAKE_ALL went unread, and a
SWAP_EXACT_OUT was read as spending its path's last currency.

Model: opus-5-5

tests/uniswap.test.js

@@ -107,6 +107,7 @@ function encodeV4Swap(actions, params) {
 // V4 inner action IDs, as src/shared/uniswap.js names them.
 const V4_SWAP_EXACT_IN = 0x07;
 const V4_SWAP_EXACT_IN_SINGLE_ID = 0x06;
+const V4_SWAP_EXACT_OUT_SINGLE_ID = 0x08;
 const V4_SETTLE_ID = 0x0b;
 const V4_TAKE_ID = 0x0e;
 const ZERO_ADDR = "0x0000000000000000000000000000000000000000";
@@ -163,6 +164,31 @@ function encodeV4ExactInSingle(currency0, currency1, amountIn, amountOutMin) {
     );
 }
 
+// Helper: V4 ExactOutputSingleParams —
+//   (tuple(address,address,uint24,int24,address) poolKey, bool zeroForOne,
+//    uint128 amountOut, uint128 amountInMaximum, bytes hookData)
+function encodeV4ExactOutSingle(
+    currency0,
+    currency1,
+    amountOut,
+    amountInMaximum,
+) {
+    return coder.encode(
+        [
+            "tuple(tuple(address,address,uint24,int24,address),bool,uint128,uint128,bytes)",
+        ],
+        [
+            [
+                [currency0, currency1, 100, 1, ZERO_ADDR],
+                true, // zeroForOne: in = currency0, out = currency1
+                amountOut,
+                amountInMaximum,
+                "0x",
+            ],
+        ],
+    );
+}
+
 // Each V4 swap action's parameters in two shapes: the struct V4Router has
 // deployed on mainnet and Sepolia, and the one v4-periphery `main` has since
 // moved to, which adds a `minHopPriceX36` field. Each swaps WETH for USDC.
@@ -267,9 +293,7 @@ function v4SwapCalldata(actionId, swapParams) {
     );
 }
 
-// V4 SETTLE_ALL (currency, maxAmount) and TAKE_ALL (currency, minAmount). The
-// decoder reads neither, so in a V4_SWAP of a swap action and these, only the
-// swap action names the currencies.
+// V4 SETTLE_ALL (currency, maxAmount) and TAKE_ALL (currency, minAmount).
 const V4_SETTLE_ALL_ID = 0x0c;
 const V4_TAKE_ALL_ID = 0x0f;
 function encodeV4SettleAll(currency, maxAmount) {
@@ -279,6 +303,12 @@ function encodeV4TakeAll(currency, minAmount) {
     return coder.encode(["address", "uint256"], [currency, minAmount]);
 }
 
+// V4 CLOSE_CURRENCY (currency), which the decoder does not read.
+const V4_CLOSE_CURRENCY_ID = 0x12;
+function encodeV4CloseCurrency(currency) {
+    return coder.encode(["address"], [currency]);
+}
+
 function detail(result, label) {
     return result.details.find((d) => d.label === label);
 }
@@ -358,10 +388,9 @@ describe("uniswap decoder", () => {
         },
     );
 
-    // Only the unread swap action names the currencies here. The token lines
-    // must not say the calldata did not name them.
+    // SETTLE_ALL and TAKE_ALL name both sides as SETTLE and TAKE do.
     test.each(V4_SWAP_ACTION_SHAPES)(
-        "a V4 $action in the newer shape, then SETTLE_ALL and TAKE_ALL, says both tokens could not be decoded",
+        "a V4 $action in the newer shape, then SETTLE_ALL and TAKE_ALL, takes both tokens from them",
         ({ id, newer }) => {
             const data = buildExecute(
                 "0x10",
@@ -381,6 +410,27 @@ describe("uniswap decoder", () => {
             expect(detail(result, "Steps").value).toBe(
                 "V4 Swap (could not be decoded)",
             );
+            expect(detail(result, "Token In").address).toBe(WETH_ADDR);
+            expect(detail(result, "Token Out").address).toBe(USDC_ADDR);
+            expect(detail(result, "Amount")).toBeUndefined();
+            expect(detail(result, "Min. received")).toBeUndefined();
+        },
+    );
+
+    // Only the unread swap action names the currencies here. The token lines
+    // must not say the calldata did not name them.
+    test.each(V4_SWAP_ACTION_SHAPES)(
+        "a V4 step of only a $action in the newer shape says both tokens could not be decoded",
+        ({ id, newer }) => {
+            const data = buildExecute(
+                "0x10",
+                [encodeV4Swap(new Uint8Array([id]), [newer])],
+                9999999999n,
+            );
+            const result = uniswap.decode(data, ROUTER_ADDR);
+            expect(detail(result, "Steps").value).toBe(
+                "V4 Swap (could not be decoded)",
+            );
             expect(detail(result, "Token In").value).toBe(
                 "Unknown (could not be decoded)",
             );
@@ -394,7 +444,7 @@ describe("uniswap decoder", () => {
     // action names. The V3 step's WETH and its Min. received figure were
     // shown instead.
     test.each(V4_SWAP_ACTION_SHAPES)(
-        "a V3 step, then a V4 $action in the newer shape and TAKE_ALL, does not show the V3 step's output",
+        "a V3 step, then a V4 step of only a $action in the newer shape, does not show the V3 step's output",
         ({ id, newer }) => {
             const data = buildExecute(
                 solidityPacked(["uint8", "uint8"], [0x00, 0x10]),
@@ -403,10 +453,7 @@ describe("uniswap decoder", () => {
                         USDT_ADDR,
                         WETH_ADDR,
                     ]),
-                    encodeV4Swap(new Uint8Array([id, V4_TAKE_ALL_ID]), [
-                        newer,
-                        encodeV4TakeAll(USDC_ADDR, 990000n),
-                    ]),
+                    encodeV4Swap(new Uint8Array([id]), [newer]),
                 ],
                 9999999999n,
             );
@@ -423,15 +470,12 @@ describe("uniswap decoder", () => {
     // The user pays the V4 step's WETH, which only its unread swap action
     // names. The V3 step's USDC and its amount were shown instead.
     test.each(V4_SWAP_ACTION_SHAPES)(
-        "a V4 $action in the newer shape and SETTLE_ALL, then a V3 step, does not show the V3 step's input",
+        "a V4 step of only a $action in the newer shape, then a V3 step, does not show the V3 step's input",
         ({ id, newer }) => {
             const data = buildExecute(
                 solidityPacked(["uint8", "uint8"], [0x10, 0x00]),
                 [
-                    encodeV4Swap(new Uint8Array([id, V4_SETTLE_ALL_ID]), [
-                        newer,
-                        encodeV4SettleAll(WETH_ADDR, ONE_WETH),
-                    ]),
+                    encodeV4Swap(new Uint8Array([id]), [newer]),
                     encodeV3SwapExactIn(
                         USER_ADDR,
                         990000n,
@@ -458,10 +502,7 @@ describe("uniswap decoder", () => {
         const data = buildExecute(
             solidityPacked(["uint8", "uint8"], [0x10, 0x0c]),
             [
-                encodeV4Swap(new Uint8Array([id, V4_TAKE_ALL_ID]), [
-                    newer,
-                    encodeV4TakeAll(USDC_ADDR, 990000n),
-                ]),
+                encodeV4Swap(new Uint8Array([id]), [newer]),
                 encodeWrapEth(USER_ADDR, 0n), // UNWRAP_WETH, same encoding
             ],
             9999999999n,
@@ -1124,6 +1165,419 @@ describe("uniswap decoder", () => {
         expect(detail(result, "Min. received").value).toBe("0.9900 USDC");
     });
 
+    // https://git.eeqj.de/sneak/AutistMask/issues/563 — a V4 step of several
+    // swap actions. The screen showed the first action's output as Token Out.
+    // Every step below pays USDT and receives USDC, so it reads Swap USDT →
+    // USDC whichever kind of swap actions it holds and in whatever order they
+    // are written. Each is tried with three endings: SETTLE_ALL and TAKE_ALL,
+    // SETTLE and TAKE, and CLOSE_CURRENCY for each currency, which leaves the
+    // sides to the swap actions alone.
+    const V4_STEP_ENDINGS = [
+        {
+            ending: "SETTLE_ALL and TAKE_ALL",
+            ids: [V4_SETTLE_ALL_ID, V4_TAKE_ALL_ID],
+            params: [
+                encodeV4SettleAll(USDT_ADDR, 1000000000n),
+                encodeV4TakeAll(USDC_ADDR, 990000000n),
+            ],
+        },
+        {
+            ending: "SETTLE and TAKE",
+            ids: [V4_SETTLE_ID, V4_TAKE_ID],
+            params: [encodeV4Settle(USDT_ADDR), encodeV4Take(USDC_ADDR)],
+        },
+        {
+            ending: "CLOSE_CURRENCY",
+            ids: [
+                V4_CLOSE_CURRENCY_ID,
+                V4_CLOSE_CURRENCY_ID,
+                V4_CLOSE_CURRENCY_ID,
+            ],
+            params: [
+                encodeV4CloseCurrency(USDT_ADDR),
+                encodeV4CloseCurrency(WETH_ADDR),
+                encodeV4CloseCurrency(USDC_ADDR),
+            ],
+        },
+    ];
+    // 1,000 USDT for at least 0.5 WETH
+    const USDT_FOR_WETH_IN = {
+        id: V4_SWAP_EXACT_IN_SINGLE_ID,
+        param: encodeV4ExactInSingle(
+            USDT_ADDR,
+            WETH_ADDR,
+            1000000000n,
+            500000000000000000n,
+        ),
+    };
+    // 0.5 WETH for at least 990 USDC
+    const WETH_FOR_USDC_IN = {
+        id: V4_SWAP_EXACT_IN_SINGLE_ID,
+        param: encodeV4ExactInSingle(
+            WETH_ADDR,
+            USDC_ADDR,
+            500000000000000000n,
+            990000000n,
+        ),
+    };
+    // exactly 0.5 WETH for at most 1,000 USDT
+    const USDT_FOR_WETH_OUT = {
+        id: V4_SWAP_EXACT_OUT_SINGLE_ID,
+        param: encodeV4ExactOutSingle(
+            USDT_ADDR,
+            WETH_ADDR,
+            500000000000000000n,
+            1000000000n,
+        ),
+    };
+    // exactly 990 USDC for at most 0.5 WETH
+    const WETH_FOR_USDC_OUT = {
+        id: V4_SWAP_EXACT_OUT_SINGLE_ID,
+        param: encodeV4ExactOutSingle(
+            WETH_ADDR,
+            USDC_ADDR,
+            990000000n,
+            500000000000000000n,
+        ),
+    };
+    // 400 USDT for at least 396 USDC
+    const USDT_FOR_USDC_IN = {
+        id: V4_SWAP_EXACT_IN_SINGLE_ID,
+        param: encodeV4ExactInSingle(
+            USDT_ADDR,
+            USDC_ADDR,
+            400000000n,
+            396000000n,
+        ),
+    };
+    // 600 USDT through WETH for at least 594 USDC
+    const USDT_FOR_USDC_THROUGH_WETH_IN = {
+        id: V4_SWAP_EXACT_IN,
+        param: encodeV4ExactIn(
+            USDT_ADDR,
+            [WETH_ADDR, USDC_ADDR],
+            600000000n,
+            594000000n,
+        ),
+    };
+    // the open delta of USDT through WETH for at least 594 USDC
+    const USDT_OPEN_DELTA_FOR_USDC_THROUGH_WETH_IN = {
+        id: V4_SWAP_EXACT_IN,
+        param: encodeV4ExactIn(
+            USDT_ADDR,
+            [WETH_ADDR, USDC_ADDR],
+            0n,
+            594000000n,
+        ),
+    };
+    // Amount is the amountIn of the action that spends USDT, or the sum when
+    // several exact-in actions each state one. Min. received is the same for
+    // the actions that buy USDC. The decoder reads no amount from an exact-out
+    // action, and an open delta is not a stated amount.
+    const V4_STEPS = [
+        {
+            step: "USDT for WETH exact-in, then WETH for USDC exact-in",
+            swaps: [USDT_FOR_WETH_IN, WETH_FOR_USDC_IN],
+            amount: "1000.0000 USDT",
+            min: "990.0000 USDC",
+        },
+        {
+            step: "WETH for USDC exact-in, then USDT for WETH exact-in",
+            swaps: [WETH_FOR_USDC_IN, USDT_FOR_WETH_IN],
+            amount: "1000.0000 USDT",
+            min: "990.0000 USDC",
+        },
+        {
+            step: "WETH for USDC exact-out, then USDT for WETH exact-out",
+            swaps: [WETH_FOR_USDC_OUT, USDT_FOR_WETH_OUT],
+            amount: undefined,
+            min: undefined,
+        },
+        {
+            step: "USDT for WETH exact-out, then WETH for USDC exact-out",
+            swaps: [USDT_FOR_WETH_OUT, WETH_FOR_USDC_OUT],
+            amount: undefined,
+            min: undefined,
+        },
+        {
+            step: "USDT for WETH exact-in, then WETH for USDC exact-out",
+            swaps: [USDT_FOR_WETH_IN, WETH_FOR_USDC_OUT],
+            amount: "1000.0000 USDT",
+            min: undefined,
+        },
+        {
+            step: "WETH for USDC exact-out, then USDT for WETH exact-in",
+            swaps: [WETH_FOR_USDC_OUT, USDT_FOR_WETH_IN],
+            amount: "1000.0000 USDT",
+            min: undefined,
+        },
+        {
+            step: "USDT for WETH exact-out, then WETH for USDC exact-in",
+            swaps: [USDT_FOR_WETH_OUT, WETH_FOR_USDC_IN],
+            amount: undefined,
+            min: "990.0000 USDC",
+        },
+        {
+            step: "USDT for USDC, then USDT for USDC through WETH, both exact-in",
+            swaps: [USDT_FOR_USDC_IN, USDT_FOR_USDC_THROUGH_WETH_IN],
+            amount: "1000.0000 USDT",
+            min: "990.0000 USDC",
+        },
+        {
+            step: "USDT for USDC, then the open delta of USDT for USDC through WETH, both exact-in",
+            swaps: [USDT_FOR_USDC_IN, USDT_OPEN_DELTA_FOR_USDC_THROUGH_WETH_IN],
+            amount: undefined,
+            min: "990.0000 USDC",
+        },
+    ];
+    test.each(
+        V4_STEPS.flatMap((step) =>
+            V4_STEP_ENDINGS.map((ending) => ({ ...step, ...ending })),
+        ),
+    )(
+        "a V4 step of $step, then $ending, reads Swap USDT → USDC",
+        ({ swaps, ids, params, amount, min }) => {
+            const data = buildExecute(
+                "0x10",
+                [
+                    encodeV4Swap(
+                        new Uint8Array([...swaps.map((s) => s.id), ...ids]),
+                        [...swaps.map((s) => s.param), ...params],
+                    ),
+                ],
+                9999999999n,
+            );
+
+            const result = uniswap.decode(data, ROUTER_ADDR);
+            expect(result.name).toBe("Swap USDT → USDC");
+            expect(detail(result, "Token In").address).toBe(USDT_ADDR);
+            expect(detail(result, "Token Out").address).toBe(USDC_ADDR);
+            expect(detail(result, "Amount")?.value).toBe(amount);
+            expect(detail(result, "Min. received")?.value).toBe(min);
+        },
+    );
+
+    // A step with a swap action that could not be read is named only by its
+    // SETTLE_ALL, TAKE_ALL, SETTLE and TAKE, and states no figure: its readable
+    // USDT for WETH action names neither side. The unread action is
+    // V4_SWAP_ACTION_SHAPES[0].newer, WETH for USDC exact-in in the newer
+    // shape.
+    test.each([
+        {
+            ...V4_STEP_ENDINGS[0],
+            tokenIn: `USDT (${USDT_ADDR})`,
+            tokenOut: `USDC (${USDC_ADDR})`,
+        },
+        {
+            ...V4_STEP_ENDINGS[1],
+            tokenIn: `USDT (${USDT_ADDR})`,
+            tokenOut: `USDC (${USDC_ADDR})`,
+        },
+        {
+            ...V4_STEP_ENDINGS[2],
+            tokenIn: "Unknown (could not be decoded)",
+            tokenOut: "Unknown (could not be decoded)",
+        },
+    ])(
+        "a V4 step of a readable swap action and an unread one, then $ending, shows no figure",
+        ({ ids, params, tokenIn, tokenOut }) => {
+            const data = buildExecute(
+                "0x10",
+                [
+                    encodeV4Swap(
+                        new Uint8Array([
+                            USDT_FOR_WETH_IN.id,
+                            V4_SWAP_ACTION_SHAPES[0].id,
+                            ...ids,
+                        ]),
+                        [
+                            USDT_FOR_WETH_IN.param,
+                            V4_SWAP_ACTION_SHAPES[0].newer,
+                            ...params,
+                        ],
+                    ),
+                ],
+                9999999999n,
+            );
+
+            const result = uniswap.decode(data, ROUTER_ADDR);
+            expect(detail(result, "Steps").value).toBe(
+                "V4 Swap (could not be decoded)",
+            );
+            expect(detail(result, "Token In").value).toBe(tokenIn);
+            expect(detail(result, "Token Out").value).toBe(tokenOut);
+            expect(detail(result, "Amount")).toBeUndefined();
+            expect(detail(result, "Min. received")).toBeUndefined();
+        },
+    );
+
+    // A V4 step that spends WETH on USDC and on DAI. Its swap actions buy two
+    // currencies that none of them spends, and CLOSE_CURRENCY, which the
+    // decoder does not read, names no side, so its output side is unknown.
+    const WETH_FOR_USDC_AND_DAI = encodeV4Swap(
+        new Uint8Array([
+            V4_SWAP_EXACT_IN_SINGLE_ID,
+            V4_SWAP_EXACT_IN_SINGLE_ID,
+            V4_CLOSE_CURRENCY_ID,
+            V4_CLOSE_CURRENCY_ID,
+            V4_CLOSE_CURRENCY_ID,
+        ]),
+        [
+            // 0.25 WETH for at least 495 USDC
+            encodeV4ExactInSingle(
+                WETH_ADDR,
+                USDC_ADDR,
+                250000000000000000n,
+                495000000n,
+            ),
+            // 0.25 WETH for at least 495 DAI
+            encodeV4ExactInSingle(
+                WETH_ADDR,
+                DAI_ADDR,
+                250000000000000000n,
+                495000000000000000000n,
+            ),
+            encodeV4CloseCurrency(WETH_ADDR),
+            encodeV4CloseCurrency(USDC_ADDR),
+            encodeV4CloseCurrency(DAI_ADDR),
+        ],
+    );
+
+    // The user ends with USDC and DAI, not the V3 step's WETH. That WETH and
+    // the V3 step's Min. received figure were shown instead.
+    test("a V3 step, then a V4 step whose swap actions buy two currencies, does not show the V3 step's output", () => {
+        const data = buildExecute(
+            solidityPacked(["uint8", "uint8"], [0x00, 0x10]),
+            [
+                encodeV3SwapExactIn(
+                    USER_ADDR,
+                    1000000000n,
+                    500000000000000000n,
+                    [USDT_ADDR, WETH_ADDR],
+                ),
+                WETH_FOR_USDC_AND_DAI,
+            ],
+            9999999999n,
+        );
+        const result = uniswap.decode(data, ROUTER_ADDR);
+        expect(result.name).toBe("Uniswap Swap");
+        expect(detail(result, "Token In").address).toBe(
+            USDT_ADDR.toLowerCase(),
+        );
+        expect(detail(result, "Amount").value).toBe("1000.0000 USDT");
+        expect(detail(result, "Token Out").value).toBe(
+            "Unknown (not named in the calldata)",
+        );
+        expect(detail(result, "Min. received")).toBeUndefined();
+    });
+
+    // The input side of the same gap: the V4 step's swap actions spend USDC
+    // and DAI, two currencies that none of them buys, and nothing names its
+    // input side. The V3 step's WETH and its amount were shown instead.
+    test("a V4 step whose swap actions spend two currencies, then a V3 step, does not show the V3 step's input", () => {
+        const data = buildExecute(
+            solidityPacked(["uint8", "uint8"], [0x10, 0x00]),
+            [
+                encodeV4Swap(
+                    new Uint8Array([
+                        V4_SWAP_EXACT_IN_SINGLE_ID,
+                        V4_SWAP_EXACT_IN_SINGLE_ID,
+                        V4_CLOSE_CURRENCY_ID,
+                        V4_CLOSE_CURRENCY_ID,
+                        V4_CLOSE_CURRENCY_ID,
+                    ]),
+                    [
+                        // 500 USDC for at least 0.25 WETH
+                        encodeV4ExactInSingle(
+                            USDC_ADDR,
+                            WETH_ADDR,
+                            500000000n,
+                            250000000000000000n,
+                        ),
+                        // 500 DAI for at least 0.25 WETH
+                        encodeV4ExactInSingle(
+                            DAI_ADDR,
+                            WETH_ADDR,
+                            500000000000000000000n,
+                            250000000000000000n,
+                        ),
+                        encodeV4CloseCurrency(USDC_ADDR),
+                        encodeV4CloseCurrency(DAI_ADDR),
+                        encodeV4CloseCurrency(WETH_ADDR),
+                    ],
+                ),
+                encodeV3SwapExactIn(
+                    USER_ADDR,
+                    500000000000000000n,
+                    990000000n,
+                    [WETH_ADDR, USDT_ADDR],
+                ),
+            ],
+            9999999999n,
+        );
+        const result = uniswap.decode(data, ROUTER_ADDR);
+        expect(result.name).toBe("Uniswap Swap");
+        expect(detail(result, "Token In").value).toBe(
+            "Unknown (not named in the calldata)",
+        );
+        expect(detail(result, "Amount")).toBeUndefined();
+        expect(detail(result, "Token Out").address).toBe(
+            USDT_ADDR.toLowerCase(),
+        );
+        expect(detail(result, "Min. received").value).toBe("990.0000 USDT");
+    });
+
+    // UNWRAP_WETH makes Token Out ETH when no step set the output side. A V4
+    // step with a swap action did set it, to unknown here.
+    test("an UNWRAP_WETH after a V4 step whose swap actions buy two currencies does not make Token Out ETH", () => {
+        const data = buildExecute(
+            solidityPacked(["uint8", "uint8"], [0x10, 0x0c]),
+            [
+                WETH_FOR_USDC_AND_DAI,
+                encodeWrapEth(USER_ADDR, 0n), // UNWRAP_WETH, same encoding
+            ],
+            9999999999n,
+        );
+        const result = uniswap.decode(data, ROUTER_ADDR);
+        expect(detail(result, "Token Out").value).toBe(
+            "Unknown (not named in the calldata)",
+        );
+    });
+
+    // The router works through an exact-out path from its last entry back to
+    // its first: the WETH entry buys the USDC, then the USDT entry buys that
+    // WETH. The user pays the first entry's USDT, not the last entry's WETH.
+    test("a two-hop V4 exact-out action shows its first path entry as Token In", () => {
+        const data = buildExecute(
+            "0x10",
+            [
+                encodeV4Swap(new Uint8Array([0x09]), [
+                    // SWAP_EXACT_OUT: exactly 990 USDC for at most 1,000 USDT
+                    coder.encode(
+                        [`tuple(address,${PATH_KEY}[],uint128,uint128)`],
+                        [
+                            [
+                                USDC_ADDR,
+                                [
+                                    [USDT_ADDR, 100, 1, ZERO_ADDR, "0x"],
+                                    [WETH_ADDR, 100, 1, ZERO_ADDR, "0x"],
+                                ],
+                                990000000n,
+                                1000000000n,
+                            ],
+                        ],
+                    ),
+                ]),
+            ],
+            9999999999n,
+        );
+
+        const result = uniswap.decode(data, ROUTER_ADDR);
+        expect(result.name).toBe("Swap USDT → USDC");
+        expect(detail(result, "Token In").address).toBe(USDT_ADDR);
+        expect(detail(result, "Token Out").address).toBe(USDC_ADDR);
+    });
+
     // https://git.eeqj.de/sneak/AutistMask/issues/415 — the router's V2
     // exact-in reads an amountIn of zero as universal-router
     // Constants.ALREADY_PAID: an earlier step sent the tokens to the pair, and