fix(tools): bound internal request serialization

apps/sim/tools/index.test.ts

@@ -3973,13 +3973,21 @@ describe('Internal Route Trust', () => {
   })
 
   it('rejects oversized operation input before invoking the in-process handler', async () => {
+    const later = vi.fn()
     const mockTool = {
       id: 'test_oversized_operation_input',
       name: 'Test Oversized Operation Input',
       description: 'Rejects operation input above the shared tool admission limit',
       version: '1.0.0',
       params: { payload: { type: 'string', required: true } },
-      operation: { input: (params: { payload: string }) => params },
+      operation: {
+        input: (params: { payload: string }) => ({
+          payload: params.payload,
+          get later() {
+            return later()
+          },
+        }),
+      },
     }
     ;(tools as Record<string, unknown>).test_oversized_operation_input = mockTool
 
@@ -3995,6 +4003,7 @@ describe('Internal Route Trust', () => {
         error: expect.stringContaining('Request body size limit exceeded (10MB)'),
       })
       expect(mockExecuteInternalToolOperation).not.toHaveBeenCalled()
+      expect(later).not.toHaveBeenCalled()
     } finally {
       Reflect.deleteProperty(tools, 'test_oversized_operation_input')
     }

apps/sim/tools/index.ts

@@ -2688,7 +2688,19 @@ async function executeDeclaredInternalOperation({
   if (privateToolMetadataType) {
     headers.set(PRIVATE_TOOL_METADATA_REQUEST_HEADER, privateToolMetadataType)
   }
-  validateRequestBodySize(JSON.stringify(operationInput), requestId, toolId)
+  const { stringifyRequestWithinLimit } = await import('@/tools/request-body-size.server')
+  try {
+    stringifyRequestWithinLimit(operationInput, MAX_REQUEST_BODY_SIZE_BYTES)
+  } catch (error) {
+    if (isPayloadSizeLimitError(error)) {
+      logger.error(`[${requestId}] Request body size exceeds limit for ${toolId}:`, {
+        bodySizeLowerBound: error.observedBytes,
+        maxSize: error.maxBytes,
+      })
+      throw new Error(BODY_SIZE_LIMIT_ERROR_MESSAGE)
+    }
+    throw error
+  }
   const deadline = serializeExecutionDeadlineHeader(signal)
   if (deadline) headers.set(INTERNAL_EXECUTION_DEADLINE_HEADER, deadline)
   const billingAttribution = context.billingAttribution

apps/sim/tools/request-body-size.server.test.ts

@@ -0,0 +1,68 @@
+/**
+ * @vitest-environment node
+ */
+import { describe, expect, it, vi } from 'vitest'
+import { PayloadSizeLimitError } from '@/lib/core/utils/stream-limits'
+import { stringifyRequestWithinLimit } from '@/tools/request-body-size.server'
+
+describe('stringifyRequestWithinLimit', () => {
+  it.each([
+    { 'escaped"key\n': '\u0000é😀\ud800', empty: {}, array: [1, null, true] },
+    { missing: undefined, array: [undefined, () => 1, Symbol('omitted'), Number.NaN] },
+    { date: new Date('2026-01-01T00:00:00Z'), boxed: [Object(1), Object('é'), Object(false)] },
+  ])('preserves native JSON and its exact UTF-8 limit for %j', (value) => {
+    const expected = JSON.stringify(value)
+    const bytes = Buffer.byteLength(expected, 'utf8')
+    expect(stringifyRequestWithinLimit(value, bytes)).toBe(expected)
+    expect(() => stringifyRequestWithinLimit(value, bytes - 1)).toThrow(PayloadSizeLimitError)
+  })
+
+  it('invokes getters, toJSON and boxed conversions only once', () => {
+    const getter = vi.fn(() => ({ toJSON }))
+    const toJSON = vi.fn(() => 'value')
+    const numberConversion = vi.fn(() => 3)
+    const stringConversion = vi.fn(() => 'text')
+    const value = {
+      get data() {
+        return getter()
+      },
+      number: Object.assign(Object(1), { [Symbol.toPrimitive]: numberConversion }),
+      string: Object.assign(Object('original'), { [Symbol.toPrimitive]: stringConversion }),
+    }
+
+    expect(stringifyRequestWithinLimit(value, 100)).toBe(
+      '{"data":"value","number":3,"string":"text"}'
+    )
+    for (const hook of [getter, toJSON, numberConversion, stringConversion]) {
+      expect(hook).toHaveBeenCalledTimes(1)
+    }
+  })
+
+  it('stops native traversal before later getters on oversized strings', () => {
+    const later = vi.fn()
+    const value = {
+      large: '\u0000'.repeat(100),
+      get later() {
+        return later()
+      },
+    }
+
+    expect(() => stringifyRequestWithinLimit(value, 50)).toThrow(PayloadSizeLimitError)
+    expect(later).not.toHaveBeenCalled()
+  })
+
+  it('preserves native omissions, shared objects, cycle errors and bigint conversion errors', () => {
+    const shared = { a: 1 }
+    expect(stringifyRequestWithinLimit([shared, shared], 100)).toBe(
+      JSON.stringify([shared, shared])
+    )
+    expect(stringifyRequestWithinLimit(undefined, 100)).toBeUndefined()
+    const cycle: { self?: unknown } = {}
+    cycle.self = cycle
+    expect(() => stringifyRequestWithinLimit(cycle, 100)).toThrow(TypeError)
+    const number = Object.assign(Object(1), { [Symbol.toPrimitive]: () => 1n })
+    expect(() => JSON.stringify(number)).toThrow(TypeError)
+    expect(() => stringifyRequestWithinLimit(number, 100)).toThrow(TypeError)
+    expect(() => stringifyRequestWithinLimit(1n, 100)).toThrow(TypeError)
+  })
+})

apps/sim/tools/request-body-size.server.ts

@@ -0,0 +1,88 @@
+import { types } from 'node:util'
+import { assertKnownSizeWithinLimit } from '@/lib/core/utils/stream-limits'
+
+/**
+ * Uses native JSON traversal with an incremental UTF-8 budget, stopping before
+ * the complete oversized JSON string is allocated. Getters and toJSON retain
+ * native invocation semantics; allocations inside those hooks are not bounded.
+ */
+export function stringifyRequestWithinLimit(value: unknown, maxBytes: number): string | undefined {
+  let bytes = 0
+  const containers = new WeakMap<object, number>()
+  const charge = (size: number): void => {
+    bytes += size
+    assertKnownSizeWithinLimit(bytes, maxBytes, 'Request body')
+  }
+  const chargeString = (text: string): void => {
+    charge(2)
+    for (let index = 0; index < text.length; index++) {
+      const code = text.charCodeAt(index)
+      if (code === 0x22 || code === 0x5c) {
+        charge(2)
+      } else if (code < 0x20) {
+        charge(code === 8 || code === 9 || code === 10 || code === 12 || code === 13 ? 2 : 6)
+      } else if (code < 0x80) {
+        charge(1)
+      } else if (code < 0x800) {
+        charge(2)
+      } else if (code >= 0xd800 && code <= 0xdfff) {
+        const next = text.charCodeAt(index + 1)
+        if (code <= 0xdbff && next >= 0xdc00 && next <= 0xdfff) {
+          charge(4)
+          index++
+        } else {
+          charge(6)
+        }
+      } else {
+        charge(3)
+      }
+    }
+  }
+  const nativeJson = JSON as typeof JSON & {
+    isRawJSON?: (input: unknown) => input is { rawJSON: string }
+  }
+
+  const serialized = JSON.stringify(value, function (this: object, key, input: unknown) {
+    /** Native stringify unboxes these after calling the replacer. */
+    let current = input
+    if (types.isNumberObject(current)) current = +current
+    else if (types.isStringObject(current)) current = String(current)
+    else if (types.isBooleanObject(current)) current = Boolean.prototype.valueOf.call(current)
+    else if (types.isBigIntObject(current)) current = BigInt.prototype.valueOf.call(current)
+
+    const arrayItem = Array.isArray(this)
+    const omitted =
+      current === undefined || typeof current === 'function' || typeof current === 'symbol'
+    if (omitted && !arrayItem) return current
+
+    const entries = containers.get(this)
+    if (entries !== undefined) {
+      if (entries > 0) charge(1)
+      if (!arrayItem) {
+        chargeString(key)
+        charge(1)
+      }
+      containers.set(this, entries + 1)
+    }
+
+    if (omitted || current === null) charge(4)
+    else if (typeof current === 'string') chargeString(current)
+    else if (typeof current === 'number')
+      charge(Number.isFinite(current) ? String(current).length : 4)
+    else if (typeof current === 'boolean') charge(current ? 4 : 5)
+    else if (typeof current === 'object') {
+      if (nativeJson.isRawJSON?.(current)) {
+        charge(Buffer.byteLength(current.rawJSON, 'utf8'))
+      } else {
+        charge(2)
+        containers.set(current, 0)
+      }
+    }
+    return current
+  })
+
+  if (serialized !== undefined) {
+    assertKnownSizeWithinLimit(Buffer.byteLength(serialized, 'utf8'), maxBytes, 'Request body')
+  }
+  return serialized
+}