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feat: add transformRequest option for custom request streams #604

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feat: add transformRequest option for custom request streams #604

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7b5cdc7
feat: add transformRequest option for custom request streams
ZawaPaP Jan 31, 2026
da7d4a0
docs: add type test and README for transformRequest
ZawaPaP Jan 31, 2026
ba39e00
remove type option to fix the place
ZawaPaP Jan 31, 2026
36ca0ad
Update README.md
mcollina Feb 9, 2026
1c2341c
add test and error handling
ZawaPaP Feb 11, 2026
38aac28
Merge branch 'feature/support-gcf' of https://github.com/ZawaPaP/fast…
ZawaPaP Feb 11, 2026
88a2615
simplify error handling
ZawaPaP Feb 11, 2026
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20 changes: 20 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -114,6 +114,26 @@ try {

```

You can provide a custom stream using the `transformRequest` option. This is useful for environments like Google Cloud Functions where the request body has already been consumed:

```js
const { Readable } = require('node:stream')

// In environments like Google Cloud Functions/Firebase, `request.rawBody`
// contains the full raw request body buffer/string.
fastify.register(require('@fastify/multipart'), {
transformRequest: (request) => Readable.from(request.rawBody)
})

// In a standard Fastify/Node.js server, `request.raw` is already a readable
// stream for the incoming HTTP request, so you can usually omit
// `transformRequest` entirely or simply return `request.raw`:
//
// fastify.register(require('@fastify/multipart'), {
// transformRequest: (request) => request.raw
// })
```

Additionally, you can pass per-request options to the `req.file`, `req.files`, `req.saveRequestFiles` or `req.parts` function.

```js
Expand Down
14 changes: 10 additions & 4 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ const { generateId } = require('./lib/generateId')
const createError = require('@fastify/error')
const streamToNull = require('./lib/stream-consumer')
const deepmergeAll = require('@fastify/deepmerge')({ all: true })
const { PassThrough, Readable } = require('node:stream')
const { PassThrough, Readable, pipeline } = require('node:stream')
const { pipeline: pump } = require('node:stream/promises')
const secureJSON = require('secure-json-parse')

Expand All @@ -26,6 +26,7 @@ const InvalidMultipartContentTypeError = createError('FST_INVALID_MULTIPART_CONT
const InvalidJSONFieldError = createError('FST_INVALID_JSON_FIELD_ERROR', 'a request field is not a valid JSON as declared by its Content-Type', 406)
const FileBufferNotFoundError = createError('FST_FILE_BUFFER_NOT_FOUND', 'the file buffer was not found', 500)
const NoFormData = createError('FST_NO_FORM_DATA', 'FormData is not available', 500)
const InvalidTransformRequestError = createError('FST_INVALID_TRANSFORM_REQUEST', 'transformRequest must return a readable stream', 500)

function setMultipart (req, _payload, done) {
req[kMultipart] = true
Expand Down Expand Up @@ -171,6 +172,8 @@ function fastifyMultipart (fastify, options, done) {
? options.throwFileSizeLimit
: true

const transformRequest = typeof options.transformRequest === 'function' ? options.transformRequest : (request) => request

fastify.decorate('multipartErrors', {
PartsLimitError,
FilesLimitError,
Expand Down Expand Up @@ -297,7 +300,12 @@ function fastifyMultipart (fastify, options, done) {
process.nextTick(() => cleanup(err))
})

request.pipe(bb)
const stream = transformRequest(request)
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Copilot AI Feb 4, 2026

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When transformRequest returns a different stream than the original request, event listeners for 'close' and 'error' are only attached to the original request object (lines 275-276, outside this diff). This means errors or close events from the transformed stream won't trigger cleanup, potentially leading to resource leaks.

Consider also attaching event listeners to the transformed stream when it differs from the original request, similar to how event listeners are attached to the request object.

Suggested change
const stream = transformRequest(request)
const stream = transformRequest(request)
if (stream !== request && typeof stream?.on === 'function') {
stream.on('close', cleanup)
stream.on('error', cleanup)
}

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@mcollina mcollina Feb 9, 2026

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this is correct to fix, but possibly with a different implementation

if (!stream || typeof stream.pipe !== 'function') throw new InvalidTransformRequestError()

pipeline(stream, bb, (err) => {
cleanup(err)
})

function onField (name, fieldValue, fieldnameTruncated, valueTruncated, encoding, contentType) {
// don't overwrite prototypes
Expand Down Expand Up @@ -435,8 +443,6 @@ function fastifyMultipart (fastify, options, done) {
}

function cleanup (err) {
request.unpipe(bb)

if ((err || request.aborted) && currentFile) {
currentFile.destroy()
currentFile = null
Expand Down
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