[lxsmnsyc]

The 1.x version of #2359.

Problem

On 1.x, a file only reaches a server function inside a FormData that is the only argument. Anything else goes through seroval, which has no plugin for Blob or File, so these calls fail with SerovalUnsupportedTypeError:

await upload(file);                    // a File as the only argument
await upload(file, { tags: ["a"] });
await upload({ file });
await upload(formData, 1);

Change

This is the same design as #2359:

• Client: when the arguments hold files, server-runtime.ts sends multipart form data, with an x-serialized-form header.
  • The serialized arguments go in the args field, and each file goes in its own file<i> part.
  • A seroval plugin created for the call replaces each file with its part's index, wherever seroval finds it: arguments, arrays, objects, Map, Set, FormData entries.
• Server: server-handler.ts reads that form with readUploadArgs. A plugin created for that request turns each index back into its part, and rejects a missing part, a bad index, or a missing args field.
• Other bodies are read without that plugin, so an index in a plain body fails to deserialize.
• Calls without files are sent as before, with x-serialized: true.

serializeToJSONString and deserializeFromJSONString take per-call plugins, tried before the built-in ones.

uploads.ts carries the same note as #2359 comparing this with seroval's binary mode.

Limits

These are the same as #2359:

• The body is read with request.formData(), with no total size limit.
• Files arrive as File values.
• GET server functions can't carry files.

Verification

• 8 new tests in runtime/uploads.test.ts go through the real handler (toWebHandler) with the client's request. They cover:
  • a file as the only argument;
  • files next to and inside other arguments, including a Map and a FormData;
  • a file used twice;
  • a cross-realm blob;
  • a call without files staying as text;
  • the three rejections.
• New server-function-upload route plus a Cypress test.
• packages/start: 129 tests, typecheck and build pass.
• apps/tests: unit (2) passes. Cypress: 20 of 21 pass, including the new test. The one failure, server-function.cy.ts › "should reject the promise when the response is a 5xx without an X-Error header", fails the same way on clean 1.x.

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Latest commit: 45cb05c

The changes in this PR will be included in the next version bump.

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Name	Type
@solidjs/start	Minor

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