feat(2.0): seroval json mode by lxsmnsyc · Pull Request #2042 · solidjs/solid-start

lxsmnsyc · 2026-01-04T00:55:26Z

Pretty straight forward. Adds an opt-in mode to use json mode (set by default) for seroval streaming, this is because the js stream is affected by CSP.

Also adds streaming support for client-to-server communication (except for url-encoded requests), assuming that the browser it comes from supports it.

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pkg-pr-new · 2026-01-04T00:56:11Z

Open in StackBlitz

npm i https://pkg.pr.new/solidjs/solid-start/@solidjs/start@2042

npm i https://pkg.pr.new/solidjs/solid-start/@solidjs/vite-plugin-nitro-2@2042

commit: fce37a8

lxsmnsyc · 2026-01-04T00:57:07Z

packages/start/src/config/index.ts

  middleware?: string;
+  serialization?: {
+    // This only matters for server function responses
+    mode?: 'js' | 'json';


When possible, add a plugins option here that we can load into the serializer. The only problem is how do we bridge it from the config to the runtime (do we need a "runtime" config API?)

The non-magical way I could think of is to add this as an option to createHandler in entry-server.tsx 🤔

either that or an "entry" file for configs I suppose.

Wouldn't we be able to set an environment variable, then use something like

const serialization = import.meta.env.VITE_SOLIDSTART_SERIALIZATION; if (["js", "json"].includes(serialization ?? "js")) { // initialize seroval mode } else if (serialization) { const [serializer, deserializer] = await import(serialization); }

@atk Not exactly this API in mind. I'm not trying to override seroval, I'm more of trying to think of an idea to allow incorporating 3P seroval plugins

lxsmnsyc · 2026-01-04T00:57:46Z

packages/start/src/server/serialization.ts

+  URLSearchParamsPlugin,
+  URLPlugin,
+];
+const MAX_SERIALIZATION_DEPTH_LIMIT = 64;


Seroval has a default limit of 1000, but that's because of my poor judgment. Will probably port this default back.

lxsmnsyc · 2026-01-04T01:46:46Z

packages/start/src/server/server-runtime.ts

+          // TODO(Alexis): move to serializeToJSONStream
+          body: await serializeToJSONString(args),
+          // duplex: 'half',
+          // body: serializeToJSONStream(args),


bleeding edge. TypeScript doesn't have the duplex property defined yet so this one is invalid for now. On top of that, this doesn't actually "stream" as in the server responds immediately on request. What the browser does currently is buffer the entire stream then sends in bulk (technically speaking, duplex: half describes this behavior, duplex: full describes the desired behavior).

Once all browsers are ready for this (and also TypeScript), we can swap to duplex: full

lxsmnsyc · 2026-01-04T04:16:49Z

packages/start/src/server/server-functions-handler.ts

-      });
+    } else if (contentType?.startsWith('application/json')) {
+      parsed = await event.request.json() as any[];
+    } else if (request.headers.has('x-serialized')) {


We no longer use the application/json mime type for seroval

We wanted to distinguish seroval-based body from JSON body. Did I just add a new feature?

lxsmnsyc · 2026-01-15T03:29:04Z

packages/start/src/server/server-runtime.ts

    ...options,
+    // TODO(Alexis): move to serializeToJSONStream
+    body: await serializeToJSONString(args),
+    // duplex: 'half',


microsoft/TypeScript-DOM-lib-generator#1729

tracking

katywings · 2026-01-15T23:14:20Z

Testing this branch on my project and uploading files through formData via https://github.com/hattipjs/hattip/tree/main/packages/base/multipart results in the following error 🙈:
[unhandledRejection] Error: Invalid content type

The error is throwed at this line: https://github.com/hattipjs/hattip/blob/15aa5ae4dec4478aa07785c85b2c85d4a753d0af/packages/base/multipart/src/form-data.ts#L79

It looks like with the changes in this branch, the upload doesn't set proper multipart boundaries anymore 🤔. The condition leading to the throw is !match.directives.boundary (https://github.com/hattipjs/hattip/blob/15aa5ae4dec4478aa07785c85b2c85d4a753d0af/packages/base/multipart/src/form-data.ts#L77C3-L77C29) - meaning: the content-type header misses the boundary flag 😅. E.g. the header should look as something like:

Content-Type: multipart/form-data; 
          boundary=gc0p4Jq0M2Yt08jU534c0p

(Reference: https://www.w3.org/Protocols/rfc1341/7_2_Multipart.html)

lxsmnsyc · 2026-01-16T02:26:38Z

Seemed like explicit definition of multipart/form-data overrides the derived content-type fetch does under the hood. Anyways fixed

brenelz · 2026-02-08T00:12:32Z

Whats the latest on this pr?

lxsmnsyc · 2026-02-09T08:50:17Z

@brenelz nothing much, but I haven't tested since the last commit lol

Copilot

Pull request overview

This PR introduces a new Seroval serialization layer for server functions with an opt-in response mode (js vs json, defaulting to json) to improve CSP compatibility, and expands the server-function transport to support more body types.

Changes:

Bumped seroval / seroval-plugins to ^1.5.0.
Added a new serialization module plus shared body-format helpers to support JS-stream vs JSON-stream response deserialization and additional body types (FormData, File, Blob, ArrayBuffer, Uint8Array, etc.).
Added new e2e/demo routes and tests for server-function round trips.

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 16 comments.

Show a summary per file

File	Description
pnpm-lock.yaml	Updates lockfile for `seroval`/`seroval-plugins` upgrade.
packages/start/package.json	Bumps `seroval` and `seroval-plugins` dependency ranges.
packages/start/src/config/index.ts	Adds `serialization.mode` option and injects `SEROVAL_MODE` define.
packages/start/src/server/serialization.ts	Introduces streaming serializer/deserializer utilities for JS and JSON modes.
packages/start/src/server/server-functions-shared.ts	Adds body-format header constants + helpers for encoding/decoding request/response bodies.
packages/start/src/server/server-runtime.ts	Updates client runtime to use the new serialization/body extraction helpers.
packages/start/src/server/server-functions-handler.ts	Updates server handler to use the new serialization + body extraction helpers.
apps/tests/src/routes/server-function-ping.tsx	Adds a basic server-function route for testing.
apps/tests/src/routes/server-function-form-data.tsx	Adds a FormData/File server-function route for testing.
apps/tests/src/routes/server-function-blob.tsx	Adds a Blob server-function route for testing.
apps/tests/src/e2e/server-function.test.ts	Adds new e2e tests for ping and FormData server functions.
.changeset/plenty-geese-enter.md	Adds changeset entry for the feature.

Files not reviewed (1)

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packages/start/src/server/server-functions-handler.ts

apps/tests/src/routes/server-function-blob.tsx

Copilot · 2026-02-19T19:53:35Z

apps/tests/src/e2e/server-function.test.ts

+  test("should build with a server function w/ form data", async ({ page }) => {
+    await page.goto("http://localhost:3000/server-function-form-data");
+    await expect(page.locator("#server-fn-test")).toContainText('{"result":true}');
+  });


A new Blob server-function route was added (/server-function-blob), but there is no e2e coverage for it here. Consider adding an e2e test for the blob round-trip (or removing the route if it's not intended to be exercised) so the new body-format handling stays covered.

Suggested change

});

});

test("should build with a server function w/ blob data", async ({ page }) => {

await page.goto("http://localhost:3000/server-function-blob");

await expect(page.locator("#server-fn-test")).toContainText('{"result":true}');

});

packages/start/src/server/server-runtime.ts

packages/start/src/config/index.ts

apps/tests/src/routes/server-function-form-data.tsx

Copilot · 2026-02-19T19:53:38Z

packages/start/src/server/server-functions-shared.ts

+export const enum BodyFormat {
+  Seroval = "0",
+  String = "1",
+  FormData = "2",
+  URLSearchParams = "3",
+  Blob = "4",
+  File = "5",
+  ArrayBuffer = "6",
+  Uint8Array = "7",
+}


BodyFormat is declared as a const enum, but this package is built with tsc + isolatedModules: true (and likely esbuild for TS transpilation). const enum will cause compilation/transpilation failures in isolated module builds. Use a regular enum, or replace it with a const object (as const) plus a string-literal union type.

packages/start/src/server/server-functions-shared.ts

katywings · 2026-02-21T16:19:57Z

packages/start/src/server/serialization.ts

+  });
+}
+
+class SerovalChunkReader {


Just to get a better understanding of the thinking here, why should this and getHeadersAndBody be part of SolidStart and not Seroval directly?

The encoding is specific to Start. Seroval isn't tied to the Web APIs

lxsmnsyc commented Jan 4, 2026

View reviewed changes

lxsmnsyc mentioned this pull request Jan 4, 2026

feat(1.0): seroval json #2043

Merged

lxsmnsyc commented Jan 4, 2026

View reviewed changes

lxsmnsyc changed the title ~~feat: seroval json mode~~ feat(2.0): seroval json mode Jan 14, 2026

lxsmnsyc force-pushed the feat-seroval-json branch from 7932c2f to 25b3f44 Compare January 15, 2026 03:13

lxsmnsyc commented Jan 15, 2026

View reviewed changes

lxsmnsyc force-pushed the feat-seroval-json branch from 820baec to db436df Compare February 9, 2026 11:29

atilafassina requested review from Copilot and katywings February 19, 2026 19:45

atilafassina approved these changes Feb 19, 2026

View reviewed changes

lxsmnsyc added 11 commits February 19, 2026 20:45

add seroval json mode

3eca797

Update server-runtime.ts

b22bb73

Create plenty-geese-enter.md

1d5c88a

Fix client-server comms

91c17a4

Add tests

d90c103

Add new header

935ffa0

Update server-functions-handler.ts

31c15ab

Clone requests/responses

ff263f7

Add more formats

e11dfb3

Fix File encoding

932dcd2

Update server-functions-handler.ts

8cb05af

lxsmnsyc added 9 commits February 19, 2026 20:45

Update server-runtime.ts

bfaf652

Fix FormData missing boundary

df68b5b

Add form-data test

e3ce6db

fix tests

99966a2

Bump seroval to 1.5.0

265cf07

Bump seroval-plugins

7ad4f09

Add bidirectional encoding

c4c02ba

Fix error

a56ba83

Update server-functions-shared.ts

0defa47

atilafassina force-pushed the feat-seroval-json branch from db436df to 0defa47 Compare February 19, 2026 19:45

Copilot started reviewing on behalf of atilafassina February 19, 2026 19:45 View session

Copilot AI reviewed Feb 19, 2026

View reviewed changes

fix copilot suggestions

fce37a8

katywings reviewed Feb 21, 2026

View reviewed changes

-  });
+  });
+  test("should build with a server function w/ blob data", async ({ page }) => {
+    await page.goto("http://localhost:3000/server-function-blob");
+    await expect(page.locator("#server-fn-test")).toContainText('{"result":true}');
+  });

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