@grest-ts/http-file

HTTP codecs for file uploads and downloads in the Grest framework. Handles multipart FormData encoding for uploads and binary response streaming for downloads — automatically, on both client and server.

In-memory files — when to use

Both GGFileUpload and GGFileDownload buffer the entire file in Node.js process memory. On upload, Busboy collects all chunks into a Buffer; on download, the full file is written to the response at once. This is simple and works great for prototyping, internal tools, and smaller applications.

For production systems handling large files or high throughput, consider uploading directly to an object store (S3, GCS, R2, etc.) — for example via presigned URLs — and passing only the resulting key/URL through your API. This keeps memory usage predictable and avoids OOM under load.

Quick Example

import { httpSchema } from "@grest-ts/http"
import { GGFileUpload, GGFileDownload } from "@grest-ts/http-file"
import { GGContractClass, IsObject, IsString, IsArray, VALIDATION_ERROR, SERVER_ERROR } from "@grest-ts/schema"
import { IsFile } from "@grest-ts/schema-file"

const FileApiContract = new GGContractClass("FileApi", {
    upload: {
        input: IsObject({ file: IsFile, description: IsString.orUndefined }),
        success: IsObject({ fileName: IsString, size: IsNumber }),
        errors: [VALIDATION_ERROR]
    },
    uploadBatch: {
        input: IsObject({
            files: IsArray(IsFile),
            metadata: IsObject({ tags: IsArray(IsString) })
        }),
        success: IsObject({ count: IsNumber }),
        errors: [VALIDATION_ERROR]
    },
    download: {
        input: IsObject({ id: IsString }),
        success: IsFile,
        errors: [SERVER_ERROR]
    }
})

export const FileApi = httpSchema(FileApiContract)
    .pathPrefix("api/files")
    .routes({
        upload:      GGFileUpload.POST("upload"),
        uploadBatch: GGFileUpload.POST("upload-batch"),
        download:    GGFileDownload.GET("download")
    })

That's it — the codecs handle multipart encoding, binary streaming, content headers, and filename preservation on both sides.

GGFileUpload

Codec for uploading files from client to server via multipart/form-data.

import { GGFileUpload } from "@grest-ts/http-file"

GGFileUpload.POST(path)

How it works

Client side: Splits the input into a FormData body:

• A __json field containing all non-file data as JSON
• Each file field appended as a binary part with its filename and MIME type
• Content-Type header is not set explicitly — fetch() auto-detects the multipart boundary

Server side: Uses Busboy for streaming multipart parsing:

• Extracts the __json field and parses it
• Collects each file part into a GGFile via the schema's decodeFromRaw()
• Reassembles the full input object with files at their original paths
• Handles array fields (e.g. files.0, files.1) via wildcard matching

Usage rules

Rule	Reason
Only POST is supported	Multipart upload requires a request body
Input must contain at least one file field	Use GGRpc.POST for JSON-only routes
Output is standard JSON	Use GGFileDownload for file responses

Mixed file + JSON data

Files and JSON data are sent together in a single request. The codec automatically separates them:

const IsUploadRequest = IsObject({
    file: IsFile,                          // sent as binary part
    description: IsString.orUndefined,     // sent in __json
    tags: IsArray(IsString)                // sent in __json
})

File arrays

Arrays of files work naturally:

const IsBatchRequest = IsObject({
    files: IsArray(IsFile),                // each file sent as files.0, files.1, ...
    metadata: IsObject({ category: IsString })
})

GGFileDownload

Codec for downloading files from server to client as binary HTTP responses.

import { GGFileDownload } from "@grest-ts/http-file"

GGFileDownload.GET(path)
GGFileDownload.POST(path)

How it works

Server side: Sends the file as a binary response:

• Content-Type set from the file's MIME type
• Content-Length set from file size
• Content-Disposition set with the filename (URL-encoded)
• Error responses are sent as JSON with the appropriate status code

Client side: Parses the binary response:

• Reads arrayBuffer() from the response
• Extracts filename from Content-Disposition header
• Creates a GGFile instance via the schema's decodeFromRaw()
• JSON error responses are parsed normally

Usage rules

Rule	Reason
GET or POST supported	GET for simple lookups, POST for complex queries
Output must be a file schema (e.g. IsFile)	Use GGRpc.GET/POST for JSON responses
Input must be JSON-only	File download routes accept JSON input, not file uploads

GET vs POST downloads

.routes({
    // GET — parameters sent as query string
    downloadById: GGFileDownload.GET("download"),

    // POST — parameters sent as JSON body
    generateReport: GGFileDownload.POST("generate-report")
})

Use GET for simple key-based lookups. Use POST when the request body is complex.

Service Implementation

Services return GGFile for downloads and receive GGFile for uploads — no transport details leak into business logic:

import { GGFile } from "@grest-ts/schema-file"

class FileService implements IFileApi {
    async upload(request: { file: GGFile, description?: string }) {
        const bytes = await request.file.buffer()
        await storage.save(request.file.name, bytes)
        return { fileName: request.file.name, size: request.file.size }
    }

    async download(request: { id: string }): Promise<GGFile> {
        const data = await storage.load(request.id)
        return GGFile.fromBuffer(data.bytes, data.name, data.mimeType)
    }
}

Browser Support

The package has separate entry points for Node.js and browsers:

Entry	Client	Server
Node.js (default)	Full support	Full support
Browser (browser)	Full support	Throws error

Browser builds only include client-side codecs (request building and response parsing). Server-side codecs (createForServer) throw an error in the browser since they depend on Node.js APIs (http.IncomingMessage, Busboy).

This is handled automatically by bundlers via the browser export condition — no configuration needed.

Path Parameters

Upload routes support path parameters:

.routes({
    uploadAvatar: GGFileUpload.POST("users/:userId/avatar")
})

// Client call:
await api.uploadAvatar({ userId: "123", avatar: file })
// → POST /api/files/users/123/avatar