feat(tempo): add split payments for charge

.changeset/quiet-cooks-smile.md

@@ -0,0 +1,5 @@
+---
+'mppx': patch
+---
+
+Added split-payment support to Tempo charge requests, including client transaction construction and stricter server verification for split transfers.

src/server/Mppx.test.ts

@@ -1567,6 +1567,77 @@ describe('cross-route credential replay via scope binding flaw', () => {
     // The result should be 200 (matched to cheap), not routed to expensive.
     expect(result.status).toBe(200)
   })
+
+  test('rejects no-splits credential replayed at splits route', async () => {
+    // Method whose schema transform moves splits into methodDetails.
+    const splitsMethod = Method.from({
+      name: 'mock',
+      intent: 'charge',
+      schema: {
+        credential: { payload: z.object({ token: z.string() }) },
+        request: z.pipe(
+          z.object({
+            amount: z.string(),
+            currency: z.string(),
+            decimals: z.number(),
+            recipient: z.string(),
+            splits: z.optional(z.array(z.object({ amount: z.string(), recipient: z.string() }))),
+          }),
+          z.transform(({ amount, currency, decimals, recipient, splits }) => ({
+            methodDetails: {
+              amount: String(Number(amount) * 10 ** decimals),
+              currency,
+              recipient,
+              ...(splits && { splits }),
+            },
+          })),
+        ),
+      },
+    })
+
+    const splitsServerMethod = Method.toServer(splitsMethod, {
+      async verify() {
+        return mockReceipt()
+      },
+    })
+
+    const handler = Mppx.create({ methods: [splitsServerMethod], realm, secretKey })
+
+    // Get a challenge from a route with no splits
+    const noSplitsHandle = handler.charge({
+      amount: '1',
+      currency: '0x0000000000000000000000000000000000000001',
+      decimals: 6,
+      expires: new Date(Date.now() + 60_000).toISOString(),
+      recipient: '0x0000000000000000000000000000000000000002',
+    })
+    const noSplitsResult = await noSplitsHandle(new Request('https://example.com/no-splits'))
+    expect(noSplitsResult.status).toBe(402)
+    if (noSplitsResult.status !== 402) throw new Error()
+
+    const noSplitsChallenge = Challenge.fromResponse(noSplitsResult.challenge)
+    const credential = Credential.from({
+      challenge: noSplitsChallenge,
+      payload: { token: 'valid' },
+    })
+
+    // Present at a route that requires splits
+    const splitsHandle = handler.charge({
+      amount: '1',
+      currency: '0x0000000000000000000000000000000000000001',
+      decimals: 6,
+      expires: new Date(Date.now() + 60_000).toISOString(),
+      recipient: '0x0000000000000000000000000000000000000002',
+      splits: [{ amount: '0.2', recipient: '0x0000000000000000000000000000000000000003' }],
+    })
+    const result = await splitsHandle(
+      new Request('https://example.com/with-splits', {
+        headers: { Authorization: Credential.serialize(credential) },
+      }),
+    )
+
+    expect(result.status).toBe(402)
+  })
 })
 
 describe('withReceipt', () => {

src/server/Mppx.ts

@@ -389,6 +389,29 @@ function createMethodFn(parameters: createMethodFn.Parameters): createMethodFn.R
                 return { challenge: response, status: 402 }
               }
             }
+
+            // Compare payment-relevant methodDetails fields (memo, splits).
+            // These are excluded from the top-level field check above but
+            // affect verification semantics — a credential issued for a
+            // no-splits route must not be accepted on a splits route.
+            for (const field of ['memo', 'splits'] as const) {
+              const routeVal = routeDetails[field]
+              const echoedVal = echoedDetails[field]
+              if (
+                routeVal !== undefined &&
+                JSON.stringify(routeVal) !== JSON.stringify(echoedVal)
+              ) {
+                const response = await transport.respondChallenge({
+                  challenge,
+                  input,
+                  error: new Errors.InvalidChallengeError({
+                    id: credential.challenge.id,
+                    reason: `credential ${field} does not match this route's requirements`,
+                  }),
+                })
+                return { challenge: response, status: 402 }
+              }
+            }
           }
         }
 

src/tempo/Methods.test.ts

@@ -51,6 +51,85 @@ describe('charge', () => {
     expect(result.success).toBe(true)
   })
 
+  test('schema: validates request with splits', () => {
+    const result = Methods.charge.schema.request.safeParse({
+      amount: '1',
+      currency: '0x20c0000000000000000000000000000000000001',
+      decimals: 6,
+      recipient: '0x1234567890abcdef1234567890abcdef12345678',
+      splits: [
+        {
+          amount: '0.25',
+          recipient: '0xabcdefabcdefabcdefabcdefabcdefabcdefabcd',
+        },
+        {
+          amount: '0.1',
+          memo: '0x1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef',
+          recipient: '0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb',
+        },
+      ],
+    })
+    expect(result.success).toBe(true)
+    if (!result.success) return
+
+    expect(result.data.methodDetails?.splits).toEqual([
+      {
+        amount: '250000',
+        recipient: '0xabcdefabcdefabcdefabcdefabcdefabcdefabcd',
+      },
+      {
+        amount: '100000',
+        memo: '0x1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef',
+        recipient: '0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb',
+      },
+    ])
+  })
+
+  test('schema: rejects empty splits', () => {
+    const result = Methods.charge.schema.request.safeParse({
+      amount: '1',
+      currency: '0x20c0000000000000000000000000000000000001',
+      decimals: 6,
+      recipient: '0x1234567890abcdef1234567890abcdef12345678',
+      splits: [],
+    })
+    expect(result.success).toBe(false)
+  })
+
+  test('schema: rejects more than 10 splits', () => {
+    const result = Methods.charge.schema.request.safeParse({
+      amount: '11',
+      currency: '0x20c0000000000000000000000000000000000001',
+      decimals: 6,
+      recipient: '0x1234567890abcdef1234567890abcdef12345678',
+      splits: Array.from({ length: 11 }, (_, index) => ({
+        amount: '0.1',
+        recipient: `0x${(index + 1).toString(16).padStart(40, '0')}`,
+      })),
+    })
+    expect(result.success).toBe(false)
+  })
+
+  test('schema: rejects split totals greater than or equal to amount', () => {
+    const result = Methods.charge.schema.request.safeParse({
+      amount: '1',
+      currency: '0x20c0000000000000000000000000000000000001',
+      decimals: 6,
+      recipient: '0x1234567890abcdef1234567890abcdef12345678',
+      splits: [
+        {
+          amount: '0.5',
+          recipient: '0xabcdefabcdefabcdefabcdefabcdefabcdefabcd',
+        },
+        {
+          amount: '0.5',
+          recipient: '0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb',
+        },
+      ],
+    })
+    expect(result.success).toBe(false)
+  })
+
   test('schema: rejects invalid request', () => {
     const result = Methods.charge.schema.request.safeParse({
       amount: '1',

src/tempo/Methods.ts

@@ -1,9 +1,18 @@
-import type { Account } from 'viem'
+import type { Account, Address } from 'viem'
 import { parseUnits } from 'viem'
 
 import * as Method from '../Method.js'
 import * as z from '../zod.js'
 
+const split = z.object({
+  amount: z.amount(),
+  memo: z.optional(z.hash()),
+  recipient: z.pipe(
+    z.string(),
+    z.transform((v) => v as Address),
+  ),
+})
+
 /**
  * Tempo charge intent for one-time TIP-20 token transfers.
  *
@@ -20,31 +29,58 @@ export const charge = Method.from({
       ]),
     },
     request: z.pipe(
-      z.object({
-        amount: z.amount(),
-        chainId: z.optional(z.number()),
-        currency: z.string(),
-        decimals: z.number(),
-        description: z.optional(z.string()),
-        externalId: z.optional(z.string()),
-        feePayer: z.optional(
-          z.pipe(
-            z.union([z.boolean(), z.custom<Account>()]),
-            z.transform((v): boolean => (typeof v === 'object' ? true : v)),
+      z
+        .object({
+          amount: z.amount(),
+          chainId: z.optional(z.number()),
+          currency: z.string(),
+          decimals: z.number(),
+          description: z.optional(z.string()),
+          externalId: z.optional(z.string()),
+          feePayer: z.optional(
+            z.pipe(
+              z.union([z.boolean(), z.custom<Account>()]),
+              z.transform((v): boolean => (typeof v === 'object' ? true : v)),
+            ),
           ),
+          memo: z.optional(z.hash()),
+          recipient: z.optional(z.string()),
+          splits: z.optional(z.array(split).check(z.minLength(1), z.maxLength(10))),
+        })
+        .check(
+          z.refine(({ amount, decimals, splits }) => {
+            if (!splits) return true
+
+            const totalAmount = parseUnits(amount, decimals)
+            const splitTotal = splits.reduce(
+              (sum, split) => sum + parseUnits(split.amount, decimals),
+              0n,
+            )
+
+            return (
+              splits.every((split) => parseUnits(split.amount, decimals) > 0n) &&
+              splitTotal < totalAmount
+            )
+          }, 'Invalid splits'),
         ),
-        memo: z.optional(z.hash()),
-        recipient: z.optional(z.string()),
-      }),
-      z.transform(({ amount, chainId, decimals, feePayer, memo, ...rest }) => ({
+      z.transform(({ amount, chainId, decimals, feePayer, memo, splits, ...rest }) => ({
         ...rest,
         amount: parseUnits(amount, decimals).toString(),
-        ...(chainId !== undefined || feePayer !== undefined || memo !== undefined
+        ...(chainId !== undefined ||
+        feePayer !== undefined ||
+        memo !== undefined ||
+        splits !== undefined
           ? {
               methodDetails: {
                 ...(chainId !== undefined && { chainId }),
                 ...(feePayer !== undefined && { feePayer }),
                 ...(memo !== undefined && { memo }),
+                ...(splits !== undefined && {
+                  splits: splits.map((split) => ({
+                    ...split,
+                    amount: parseUnits(split.amount, decimals).toString(),
+                  })),
+                }),
               },
             }
           : {}),

src/tempo/client/Charge.ts

@@ -11,6 +11,7 @@ import * as Client from '../../viem/Client.js'
 import * as z from '../../zod.js'
 import * as Attribution from '../Attribution.js'
 import * as AutoSwap from '../internal/auto-swap.js'
+import * as Charge_internal from '../internal/charge.js'
 import * as defaults from '../internal/defaults.js'
 import * as Methods from '../Methods.js'
 
@@ -54,18 +55,37 @@ export function charge(parameters: charge.Parameters = {}) {
       const { request } = challenge
       const { amount, methodDetails } = request
       const currency = request.currency as Address
-      const recipient = request.recipient as Address
+
+      if (parameters.expectedRecipients) {
+        const allowed = new Set(parameters.expectedRecipients.map((a) => a.toLowerCase()))
+        const splits = methodDetails?.splits as readonly { recipient: string }[] | undefined
+        if (splits) {
+          for (const split of splits) {
+            if (!allowed.has(split.recipient.toLowerCase()))
+              throw new Error(`Unexpected split recipient: ${split.recipient}`)
+          }
+        }
+      }
 
       const memo = methodDetails?.memo
         ? (methodDetails.memo as Hex.Hex)
         : Attribution.encode({ serverId: challenge.realm, clientId })
-
-      const transferCall = Actions.token.transfer.call({
-        amount: BigInt(amount),
-        memo,
-        to: recipient,
-        token: currency,
+      const transfers = Charge_internal.getTransfers({
+        amount,
+        methodDetails: {
+          ...methodDetails,
+          memo,
+        },
+        recipient: request.recipient as Address,
       })
+      const transferCalls = transfers.map((transfer) =>
+        Actions.token.transfer.call({
+          amount: BigInt(transfer.amount),
+          ...(transfer.memo && { memo: transfer.memo as Hex.Hex }),
+          to: transfer.recipient as Address,
+          token: currency,
+        }),
+      )
 
       const autoSwap = AutoSwap.resolve(
         context?.autoSwap ?? parameters.autoSwap,
@@ -82,7 +102,14 @@ export function charge(parameters: charge.Parameters = {}) {
           })
         : undefined
 
-      const calls = [...(swapCalls ?? []), transferCall]
+      const calls = [...(swapCalls ?? []), ...transferCalls]
+
+      const validBefore = (() => {
+        const defaultExpiry = Math.floor(Date.now() / 1000) + 25
+        if (!challenge.expires) return defaultExpiry
+        const challengeExpiry = Math.floor(new Date(challenge.expires).getTime() / 1000)
+        return Math.min(defaultExpiry, challengeExpiry)
+      })()
 
       if (mode === 'push') {
         const { receipts } = await sendCallsSync(client, {
@@ -104,6 +131,7 @@ export function charge(parameters: charge.Parameters = {}) {
         calls,
         ...(methodDetails?.feePayer && { feePayer: true }),
         nonceKey: 'expiring',
+        validBefore,
       } as never)
       // FIXME: figure out gas estimation issue for fee payer tx
       prepared.gas = prepared.gas! + 5_000n
@@ -131,6 +159,11 @@ export declare namespace charge {
     autoSwap?: AutoSwap | undefined
     /** Client identifier used to derive the client fingerprint in attribution memos. */
     clientId?: string | undefined
+    /**
+     * Allowlist of expected split recipient addresses. When set, the client
+     * rejects any challenge whose split recipients are not in this list.
+     */
+    expectedRecipients?: readonly Address[] | undefined
     /**
      * Controls how the charge transaction is submitted.
      *