wildebeest/backend/src/utils/body.ts

// Extract the request body as the type `T`. Use this function when the requset
// can be url encoded, form data or JSON. However, not working for formData
// containing binary data (like File).
export async function readBody<T>(request: Request): Promise<T> {
	let form = null
	const contentType = request.headers.get('content-type')
	if (contentType === null) {
		throw new Error('invalid request')
	}
	if (contentType.startsWith('application/json')) {
		return request.json<T>()
	} else if (
		contentType.includes('charset') &&
		contentType.includes('multipart/form-data') &&
		contentType.includes('boundary')
	) {
		form = await localFormDataParse(request)
	} else {
		form = await request.formData()
	}

	const out: any = {}

	for (const [key, value] of form) {
		if (key.endsWith('[]')) {
			// The `key[]` notiation is used when sending an array of values.

			const key2 = key.replace('[]', '')
			const outArr: unknown[] = (out[key2] ??= [])
			outArr.push(value)
		} else {
			out[key] = value
		}
	}
	return out as T
}

export async function localFormDataParse(request: Request): Promise<FormData> {
	const contentType = request.headers.get('content-type')
	if (contentType === null) {
		throw new Error('invalid request')
	}

	console.log('will attempt local parse of form data')
	const rBody = await request.text()
	const enc = new TextEncoder()
	const bodyArr = enc.encode(rBody)
	const boundary = getBoundary(contentType)
	console.log(`Got boundary ${boundary}`)
	const parts = parse(bodyArr, boundary)
	console.log(`parsed ${parts.length} parts`)
	const dec = new TextDecoder()
	const form: FormData = new FormData()
	for (const part of parts) {
		const value = dec.decode(part.data)
		form.append(part.name || 'null', value)
	}

	return form
}

// temporary code to deal with EW bug
/**
 * Multipart Parser (Finite State Machine)
 * usage:
 * const multipart = require('./multipart.js');
 * const body = multipart.DemoData(); 							   // raw body
 * const body = Buffer.from(event['body-json'].toString(),'base64'); // AWS case
 * const boundary = multipart.getBoundary(event.params.header['content-type']);
 * const parts = multipart.Parse(body,boundary);
 * each part is:
 * { filename: 'A.txt', type: 'text/plain', data: <Buffer 41 41 41 41 42 42 42 42> }
 *  or { name: 'key', data: <Buffer 41 41 41 41 42 42 42 42> }
 */

type Part = {
	contentDispositionHeader: string
	contentTypeHeader: string
	part: number[]
}

type Input = {
	filename?: string
	name?: string
	type: string
	data: Uint8Array
}

enum ParsingState {
	INIT,
	READING_HEADERS,
	READING_DATA,
	READING_PART_SEPARATOR,
}

export function parse(multipartBodyBuffer: Uint8Array, boundary: string): Input[] {
	let lastline = ''
	let contentDispositionHeader = ''
	let contentTypeHeader = ''
	let state: ParsingState = ParsingState.INIT
	let buffer: number[] = []
	const allParts: Input[] = []

	let currentPartHeaders: string[] = []

	for (let i = 0; i < multipartBodyBuffer.length; i++) {
		const oneByte: number = multipartBodyBuffer[i]
		const prevByte: number | null = i > 0 ? multipartBodyBuffer[i - 1] : null
		// 0x0a => \n
		// 0x0d => \r
		const newLineDetected: boolean = oneByte === 0x0a && prevByte === 0x0d
		const newLineChar: boolean = oneByte === 0x0a || oneByte === 0x0d

		if (!newLineChar) lastline += String.fromCharCode(oneByte)
		if (ParsingState.INIT === state && newLineDetected) {
			// searching for boundary
			if ('--' + boundary === lastline) {
				state = ParsingState.READING_HEADERS // found boundary. start reading headers
			}
			lastline = ''
		} else if (ParsingState.READING_HEADERS === state && newLineDetected) {
			// parsing headers. Headers are separated by an empty line from the content. Stop reading headers when the line is empty
			if (lastline.length) {
				currentPartHeaders.push(lastline)
			} else {
				// found empty line. search for the headers we want and set the values
				for (const h of currentPartHeaders) {
					if (h.toLowerCase().startsWith('content-disposition:')) {
						contentDispositionHeader = h
					} else if (h.toLowerCase().startsWith('content-type:')) {
						contentTypeHeader = h
					}
				}
				state = ParsingState.READING_DATA
				buffer = []
			}
			lastline = ''
		} else if (ParsingState.READING_DATA === state) {
			// parsing data
			if (lastline.length > boundary.length + 4) {
				lastline = '' // mem save
			}
			if ('--' + boundary === lastline) {
				const j = buffer.length - lastline.length
				const part = buffer.slice(0, j - 1)

				allParts.push(process({ contentDispositionHeader, contentTypeHeader, part }))
				buffer = []
				currentPartHeaders = []
				lastline = ''
				state = ParsingState.READING_PART_SEPARATOR
				contentDispositionHeader = ''
				contentTypeHeader = ''
			} else {
				buffer.push(oneByte)
			}
			if (newLineDetected) {
				lastline = ''
			}
		} else if (ParsingState.READING_PART_SEPARATOR === state) {
			if (newLineDetected) {
				state = ParsingState.READING_HEADERS
			}
		}
	}
	return allParts
}

//  read the boundary from the content-type header sent by the http client
//  this value may be similar to:
//  'multipart/form-data; boundary=----WebKitFormBoundaryvm5A9tzU1ONaGP5B',
export function getBoundary(header: string): string {
	const items = header.split(';')
	if (items) {
		for (let i = 0; i < items.length; i++) {
			const item = new String(items[i]).trim()
			if (item.indexOf('boundary') >= 0) {
				const k = item.split('=')
				return new String(k[1]).trim().replace(/^["']|["']$/g, '')
			}
		}
	}
	return ''
}

function process(part: Part): Input {
	// will transform this object:
	// { header: 'Content-Disposition: form-data; name="uploads[]"; filename="A.txt"',
	// info: 'Content-Type: text/plain',
	// part: 'AAAABBBB' }
	// into this one:
	// { filename: 'A.txt', type: 'text/plain', data: <Buffer 41 41 41 41 42 42 42 42> }
	const obj = function (str: string) {
		const k = str.split('=')
		const a = k[0].trim()

		const b = JSON.parse(k[1].trim())
		const o = {}
		Object.defineProperty(o, a, {
			value: b,
			writable: true,
			enumerable: true,
			configurable: true,
		})
		return o
	}
	const header = part.contentDispositionHeader.split(';')

	const filenameData = header[2]
	let input = {}
	if (filenameData) {
		input = obj(filenameData)
		const contentType = part.contentTypeHeader.split(':')[1].trim()
		Object.defineProperty(input, 'type', {
			value: contentType,
			writable: true,
			enumerable: true,
			configurable: true,
		})
	}
	// always process the name field
	Object.defineProperty(input, 'name', {
		value: header[1].split('=')[1].replace(/"/g, ''),
		writable: true,
		enumerable: true,
		configurable: true,
	})

	Object.defineProperty(input, 'data', {
		value: Uint8Array.from(part.part),
		writable: true,
		enumerable: true,
		configurable: true,
	})
	return input as Input
}