serialize before validate!

[j-ibarra]

Fix: Serialize request body before validation to support custom types

Problem

When using custom transformers (introduced in #2281 and #2383) with types like Decimal, there was a type mismatch between the TypeScript interface and the OpenAPI schema validation:

• OpenAPI Schema: Defines the field as string with format decimal
• TypeScript Type: Uses custom type Decimal (generated via typeTransformers)
• Runtime Value: Contains a Decimal instance before serialization

This caused validation failures because the validator expected a string but received a Decimal object.

Solution

Reordered the request processing pipeline to serialize before validate:

Before:

if (opts.requestValidator) {
  await opts.requestValidator(opts); // ❌ Validates Decimal object against string schema
}

if (opts.body && opts.bodySerializer) {
  opts.body = opts.bodySerializer(opts.body); // Converts Decimal to string
}

After:

if (opts.body && opts.bodySerializer) {
  opts.body = opts.bodySerializer(opts.body); // ✅ Converts Decimal to string first
}

if (opts.requestValidator) {
  await opts.requestValidator(opts); // ✅ Validates serialized string
}

Usage

With this fix, users can now use custom types with proper serialization:

// Client configuration
const client = createClient({
  bodySerializer: (body: any) => JSON.parse(JSON.stringify(body))
});

// Works correctly with custom types
const response = await client.POST('/api/endpoint', {
  body: {
    amount: new Decimal('123.45') // Serialized to "123.45" before validation
  }
});

This ensures compatibility between custom TypeScript types and OpenAPI schema validation while maintaining type safety throughout the request lifecycle.

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[mrlubos]

@j-ibarra how will your approach validate when I pass an object body such as

{
  foo: 1,
}

that foo is a number and not string?

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commit: fe7f809

[codecov]

Codecov Report

❌ Patch coverage is 11.11111% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 23.61%. Comparing base (a312623) to head (fe7f809).

Files with missing lines	Patch %	Lines
...src/plugins/@hey-api/client-axios/bundle/client.ts	0.00%	3 Missing ⚠️
.../src/plugins/@hey-api/client-next/bundle/client.ts	0.00%	3 Missing ⚠️
...src/plugins/@hey-api/client-fetch/bundle/client.ts	33.33%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2573   +/-   ##
=======================================
  Coverage   23.61%   23.61%           
=======================================
  Files         363      363           
  Lines       36504    36504           
  Branches     1562     1562           
=======================================
  Hits         8622     8622           
  Misses      27869    27869           
  Partials       13       13           

Flag	Coverage Δ
unittests	23.61% <11.11%> (ø)

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[j-ibarra]

how will your approach validate when I pass an object body such as

{
foo: 1,
}
that foo is a number and not string?

In this case keep the same behavior

When I declare type Decimal from decimal.js, with the custom transform type, in the request the zod throw error because the gen is type string (this is good)

the decimal lib serialize the type to string, example

const value = {
    food: new Decimal(100)
}

or

const value = {
    food: new Decimal("100")
}

the Zod generated is

food: z.string()

for this reason a thing that we need the parser before the validation

using in the body paser

JSON.parse(JSON.stringify(data))

The result is

const value = {
    food: "100.00"
}

The response flow is

• response
• validate body
• parse body

the request flow should be

• parse body
• validate body
• request

[mrlubos]

If your body serializer turns an object with an array into a serialized string body, how will you validate using Zod that the array has at least 3 entries?

[j-ibarra]

If your body serializer turns an object with an array into a serialized string body, how will you validate using Zod that the array has at least 3 entries?

using

JSON.parse(JSON.stringify(data))

the object return the primitive type, arrays could be validate with zod normally

other example

using

JSON.parse(JSON.stringify(data))

class MyEncryptedDate {
    private value: string;

    constructor(encrypted:string) {
        this.value = new Date(encryptionHelper(encrypted))
    }
    
    toJSON() {
        return new Date(this.value);
    }
}

type dto = {
value: MyEncryptedDate,
values: MyEncryptedDate[]
}

const body = JSON.parse(JSON.stringify(data))

The type of the body should be

type dto = {
value: Date,
values: Date[]
}