Large RPC requests

Vercel limits the request body of a Function to 4.5 MB. On a Reactive Resume installation hosted on Vercel, larger RPC requests, such as big file uploads or assistant attachments, are first uploaded to private Blob storage. The server then restores the original request and runs it with the usual authentication, validation and limits. The web app does this for you: it stages any RPC request body of 3 MiB or more, and sends smaller bodies directly. You only need this page if you write your own client for /api/rpc against a Vercel installation.

Scope

Item	Value
Applies to	`POST /api/rpc/...` only
Does not apply to	The REST API (`/api/openapi`) and MCP (`/mcp`). Their bodies stay subject to the 4.5 MB limit on Vercel.
Available on	Installations running on Vercel with Blob storage (`STORAGE_BACKEND=blob`, the default there). Everywhere else the prepare step returns `404` and you send the request directly. Staging also needs Redis; without it the prepare step returns `503`.
Maximum staged size	160 MiB of serialized request bytes, including base64 and RPC framing
Lifetimes	Upload URL: 5 minutes. Staging reference: 10 minutes.
Use count	One. The reference is used up as soon as a finalize request passes the user and path checks, whether the RPC call then succeeds or fails.
Rate limit	30 prepare requests per user per minute

Protocol

1. Prepare

Tell the server what you are about to send.

POST /api/storage/stage
Content-Type: application/json
x-api-key: YOUR_API_KEY

{ "path": "/api/rpc/storage/uploadFile", "contentType": "multipart/form-data; boundary=...", "size": 10485861 }

Field	Type	Description
`path`	string	Pathname and query string of the original RPC request. Must start with `/api/rpc`.
`contentType`	string	The original request’s `Content-Type` header, including any multipart boundary.
`size`	integer	Exact byte length of the serialized original body. At most 167,772,160 (160 MiB).

Authenticate with an x-api-key header, an OAuth bearer token or a session cookie. If the request carries an Origin header, it must match the installation’s own origin. Response 200:

{ "id": "3f2b9c1e-6a0d-4a57-9d0a-3c1f7b8e2d44", "url": "https://..." }

If you get 404, the installation doesn’t stage bodies (for example, it runs in Docker). Send the original request unchanged, and skip staging for later requests too.

2. Upload

Upload the exact body bytes to the URL from step 1.

PUT <url from step 1>
Content-Type: application/octet-stream

<exact serialized body bytes>

Don’t send your Reactive Resume credentials to this URL. The body must be exactly size bytes, sent as application/octet-stream.

3. Finalize

Send the original request with an empty body and the staging reference in the x-resume-staged-body header:

POST /api/rpc/storage/uploadFile
x-api-key: YOUR_API_KEY
x-resume-staged-body: 3f2b9c1e-6a0d-4a57-9d0a-3c1f7b8e2d44

Use the same path (including the query string) and the same user as in step 1. The server replaces the body with the staged bytes, sets Content-Type to the stored contentType, deletes the staged object and returns the normal RPC response.

Errors

Status	Step	Cause
`400`	Prepare	Invalid JSON, a `path` outside `/api/rpc` or on another origin, or `size` above the maximum.
`400`	Finalize	Malformed reference, a method other than `POST`, staging not available on this installation, or the staged object is missing.
`401`	Prepare, finalize	Not authenticated, or the `Origin` header doesn’t match.
`403`	Finalize	The reference belongs to another user or another path.
`404`	Prepare	Staging isn’t available on this installation.
`409`	Finalize	A parallel request already used the reference.
`410`	Finalize	The reference expired or was already used.
`413`	Finalize	The uploaded byte count differs from `size`.
`429`	Prepare	Rate limit exceeded.
`503`	Prepare	Redis isn’t available.

A reference can’t be retried. If a finalize response is lost, check whether the change was saved before you stage and send the request again.

Using the API: the REST API, which most integrations should use.
Deploying to Vercel: hosting requirements, including Blob storage and Redis.

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Scope

Protocol

1. Prepare

2. Upload

3. Finalize

Errors

​Scope

​Protocol

​1. Prepare

​2. Upload

​3. Finalize

​Errors

​Related pages

Scope

Protocol

1. Prepare

2. Upload

3. Finalize

Errors

Related pages