fix: fallback fall through behavior when allowlist is set

.changeset/popular-walls-begin.md

@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Fixed issue where `fallback` transports would fall through when other transports do not support the JSON-RPC method (has set up a method allowlist on the transport).

src/clients/transports/createTransport.ts

@@ -79,6 +79,7 @@ export function createTransport<
   return {
     config: {
       key,
+      methods,
       name,
       request,
       retryCount,

src/clients/transports/fallback.test.ts

@@ -4,6 +4,7 @@ import { createHttpServer } from '~test/src/utils.js'
 import { getBlockNumber } from '../../actions/public/getBlockNumber.js'
 import { localhost } from '../../chains/index.js'
 import {
+  InternalRpcError,
   MethodNotSupportedRpcError,
   UserRejectedRequestError,
 } from '../../errors/rpc.js'
@@ -31,6 +32,7 @@ test('default', () => {
     {
       "config": {
         "key": "fallback",
+        "methods": undefined,
         "name": "Fallback",
         "request": [Function],
         "retryCount": 3,
@@ -45,6 +47,7 @@ test('default', () => {
           {
             "config": {
               "key": "http",
+              "methods": undefined,
               "name": "HTTP JSON-RPC",
               "request": [Function],
               "retryCount": 0,
@@ -61,6 +64,7 @@ test('default', () => {
           {
             "config": {
               "key": "http",
+              "methods": undefined,
               "name": "HTTP JSON-RPC",
               "request": [Function],
               "retryCount": 0,
@@ -267,6 +271,46 @@ describe('request', () => {
     expect(await transport.request({ method: 'eth_c' })).toBe('0x2')
   })
 
+  test('methods.include (error)', async () => {
+    const server1 = await createHttpServer((_req, res) => {
+      res.writeHead(200, {
+        'Content-Type': 'application/json',
+      })
+      res.end(
+        JSON.stringify({
+          error: { code: InternalRpcError.code, message: 'sad times' },
+        }),
+      )
+    })
+    const server2 = await createHttpServer((_req, res) => {
+      res.writeHead(200, {
+        'Content-Type': 'application/json',
+      })
+      res.end(JSON.stringify({ result: '0x2' }))
+    })
+
+    const transport = fallback([
+      http(server1.url, { methods: { include: ['eth_a', 'eth_b'] } }),
+      http(server2.url, { methods: { exclude: ['eth_a'] } }),
+      http(server2.url, { methods: { include: ['eth_b'] } }),
+    ])({
+      chain: localhost,
+    })
+
+    await expect(() =>
+      transport.request({ method: 'eth_a' }),
+    ).rejects.toThrowErrorMatchingInlineSnapshot(`
+      [InternalRpcError: An internal error was received.
+
+      URL: http://localhost
+      Request body: {"method":"eth_a"}
+
+      Details: sad times
+      Version: [email protected]]
+    `)
+    expect(await transport.request({ method: 'eth_b' })).toBe('0x2')
+  })
+
   test('error (rpc)', async () => {
     let count = 0
     const server1 = await createHttpServer((_req, res) => {
@@ -556,6 +600,7 @@ describe('client', () => {
         "request": [Function],
         "transport": {
           "key": "fallback",
+          "methods": undefined,
           "name": "Fallback",
           "onResponse": [Function],
           "request": [Function],
@@ -566,6 +611,7 @@ describe('client', () => {
             {
               "config": {
                 "key": "http",
+                "methods": undefined,
                 "name": "HTTP JSON-RPC",
                 "request": [Function],
                 "retryCount": 0,
@@ -582,6 +628,7 @@ describe('client', () => {
             {
               "config": {
                 "key": "http",
+                "methods": undefined,
                 "name": "HTTP JSON-RPC",
                 "request": [Function],
                 "retryCount": 0,

src/clients/transports/fallback.ts

@@ -122,6 +122,8 @@ export function fallback<const transports extends readonly Transport[]>(
         key,
         name,
         async request({ method, params }) {
+          let includes: boolean | undefined
+
           const fetch = async (i = 0): Promise<any> => {
             const transport = transports[i]({
               ...rest,
@@ -158,6 +160,16 @@ export function fallback<const transports extends readonly Transport[]>(
               // If we've reached the end of the fallbacks, throw the error.
               if (i === transports.length - 1) throw err
 
+              // Check if at least one other transport includes the method
+              includes ??= transports.slice(i + 1).some((transport) => {
+                const { include, exclude } =
+                  transport({ chain }).config.methods || {}
+                if (include) return include.includes(method)
+                if (exclude) return !exclude.includes(method)
+                return true
+              })
+              if (!includes) throw err
+
               // Otherwise, try the next fallback.
               return fetch(i + 1)
             }