From 115d085befc8d040bc6855c6baa83485c901a956 Mon Sep 17 00:00:00 2001
From: Lordfirespeed <28568841+Lordfirespeed@users.noreply.github.com>
Date: Tue, 20 Aug 2024 14:17:21 +0100
Subject: [PATCH] feat: basic `multipart/form-data` parser

---
 src/parsers/multipart-form-data.ts        | 159 ++++++++++++++++++++++
 tests/parsers/multipart-form-data.test.ts |  71 ++++++++++
 2 files changed, 230 insertions(+)
 create mode 100644 src/parsers/multipart-form-data.ts
 create mode 100644 tests/parsers/multipart-form-data.test.ts

diff --git a/src/parsers/multipart-form-data.ts b/src/parsers/multipart-form-data.ts
new file mode 100644
index 0000000..cc3b4bb
--- /dev/null
+++ b/src/parsers/multipart-form-data.ts
@@ -0,0 +1,159 @@
+import { ClientError } from '@otterhttp/errors'
+
+import type { ParsedHeaders } from '@/parsers/http-headers'
+import { type ParsedMultipartDataPart, parseMultipart } from '@/parsers/multipart'
+
+export type ParsedFormFieldValue = {
+  fieldName: string
+  type: 'field-value'
+  value: {
+    headers: ParsedHeaders
+    content: Buffer
+  }
+}
+
+export type ParsedFormFieldFile = {
+  filename: string
+  headers: ParsedHeaders
+  content: Buffer
+}
+
+export type ParsedFormFieldFileList = {
+  fieldName: string
+  type: 'field-file-list'
+  files: ParsedFormFieldFile[]
+}
+
+export type ParsedMultipartFormData = Record<string, ParsedFormFieldValue | ParsedFormFieldFileList>
+
+export function isParsedFormFieldValue(
+  value: ParsedFormFieldValue | ParsedFormFieldFileList,
+): value is ParsedFormFieldValue {
+  return value.type === 'field-value'
+}
+
+export function isParsedFormFieldFileList(
+  value: ParsedFormFieldValue | ParsedFormFieldFileList,
+): value is ParsedFormFieldFileList {
+  return value.type === 'field-file-list'
+}
+
+function getFilesFromMixed(mixedContent: Buffer, boundary: string): ParsedFormFieldFile[] {
+  const parts = parseMultipart(mixedContent, boundary)
+  const files: ParsedFormFieldFile[] = []
+
+  for (const part of parts) {
+    const contentDisposition = part.headers['content-disposition']
+    if (contentDisposition != null && Object.hasOwn(contentDisposition.parameters, 'filename')) {
+      files.push({
+        filename: contentDisposition.parameters.filename,
+        headers: part.headers,
+        content: part.content,
+      })
+      continue
+    }
+
+    const contentType = part.headers['content-type']
+    if (contentType != null && Object.hasOwn(contentType.parameters, 'name')) {
+      files.push({
+        filename: contentType.parameters.name,
+        headers: part.headers,
+        content: part.content,
+      })
+      continue
+    }
+
+    // ignore any parts with no clear filename specified
+    void undefined
+  }
+
+  return files
+}
+
+function addFormData(part: ParsedMultipartDataPart, dest: ParsedMultipartFormData): void {
+  function fail(): never {
+    throw new ClientError('Invalid multipart form-data', {
+      code: 'ERR_INVALID_FORM_DATA',
+    })
+  }
+
+  const contentDisposition = part.headers['content-disposition']
+  if (contentDisposition == null) fail()
+  if (contentDisposition.type !== 'form-data') fail()
+  if (!Object.hasOwn(contentDisposition.parameters, 'name')) fail()
+  const name = contentDisposition.parameters.name
+
+  if (Object.hasOwn(contentDisposition.parameters, 'filename')) {
+    // get file from part
+    const filename = contentDisposition.parameters.filename
+    const file: ParsedFormFieldFile = {
+      filename: filename,
+      headers: part.headers,
+      content: part.content,
+    }
+
+    if (Object.hasOwn(dest, name) && dest[name] != null) {
+      const existingEntry = dest[name]
+      // don't overwrite pre-existing values
+      if (!isParsedFormFieldFileList(existingEntry)) return
+      existingEntry.files.push(file)
+      return
+    }
+
+    dest[name] = {
+      fieldName: name,
+      type: 'field-file-list',
+      files: [file],
+    } satisfies ParsedFormFieldFileList
+
+    return
+  }
+
+  const contentType = part.headers['content-type']
+  if (contentType != null && contentType.mediaType === 'multipart/mixed') {
+    // get files from multipart/mixed
+    if (!Object.hasOwn(contentType.parameters, 'boundary')) fail()
+    const files = getFilesFromMixed(part.content, contentType.parameters.boundary)
+
+    if (Object.hasOwn(dest, name) && dest[name] != null) {
+      const existingEntry = dest[name]
+      // don't overwrite pre-existing values
+      if (!isParsedFormFieldFileList(existingEntry)) return
+      existingEntry.files.push(...files)
+      return
+    }
+
+    dest[name] = {
+      fieldName: name,
+      type: 'field-file-list',
+      files: files,
+    } satisfies ParsedFormFieldFileList
+
+    return
+  }
+
+  // otherwise, consider the part to be a value specifier
+  // don't overwrite pre-existing values
+  if (Object.hasOwn(dest, name) && dest[name] != null) return
+
+  dest[name] = {
+    fieldName: name,
+    type: 'field-value',
+    value: {
+      headers: part.headers,
+      content: part.content,
+    },
+  } satisfies ParsedFormFieldValue
+}
+
+/**
+ * @see [RFC 7578](https://datatracker.ietf.org/doc/html/rfc7578)
+ */
+export function parseMultipartFormData(body: Buffer, boundary: string): ParsedMultipartFormData {
+  const parts = parseMultipart(body, boundary)
+  const parsedFormData: ParsedMultipartFormData = {}
+  for (const part of parts) {
+    addFormData(part, parsedFormData)
+  }
+  return parsedFormData
+}
diff --git a/tests/parsers/multipart-form-data.test.ts b/tests/parsers/multipart-form-data.test.ts
new file mode 100644
index 0000000..288ab0c
--- /dev/null
+++ b/tests/parsers/multipart-form-data.test.ts
@@ -0,0 +1,71 @@
+import { expect, it } from 'vitest'
+
+import {ParsedFormFieldFileList, parseMultipartFormData} from "@/parsers/multipart-form-data";
+
+it('should parse valid multipart form data with a single part', () => {
+  const multipart = [
+    'preamble',
+    '--boundary',
+    'content-disposition: form-data; name=foo',
+    'content-type: application/json',
+    '',
+    '{ "foo": "bar" }',
+    '--boundary',
+    '',
+    'epilogue',
+  ].join('\r\n')
+
+  expect(parseMultipartFormData(Buffer.from(multipart), 'boundary')).toMatchObject({
+    foo: {
+      fieldName: "foo",
+      type: "field-value",
+      value: {
+        headers: {},
+        content: Buffer.from('{ "foo": "bar" }')
+      }
+    }
+  })
+})
+
+it('should parse valid multipart form data with multiple parts', () => {
+  const multipart = [
+    'preamble',
+    '--boundary',
+    'content-disposition: form-data; name=foo',
+    'x-content-type: application/json',
+    '',
+    '{ "foo": "bar" }',
+    '--boundary',
+    'content-length: 6',
+    'content-disposition: form-data; name=bar; filename=baz',
+    '',
+    'foo bar baz',
+    '',
+    '--boundary',
+    '',
+    'epilogue',
+  ].join('\r\n')
+
+  const result = parseMultipartFormData(Buffer.from(multipart), 'boundary')
+  expect(result).toMatchObject({
+    foo: {
+      fieldName: "foo",
+      type: "field-value",
+      value: {
+        headers: {},
+        content: Buffer.from('{ "foo": "bar" }')
+      }
+    },
+    bar: {
+      fieldName: "bar",
+      type: "field-file-list",
+      files: [
+        {
+          filename: "baz",
+          content: Buffer.from("foo bar baz\r\n"),
+          headers: {}
+        }
+      ]
+    }
+  })
+})
\ No newline at end of file