Implement custom boundary generator using crypto API (node and browser)

Author: octet-stream

lib/Encoder.test.ts

@@ -22,7 +22,7 @@ test("Accepts custom boundary as the second argument", t => {
 
   const encoder = new Encoder(new FormData(), expected)
 
-  t.is(encoder.boundary, expected)
+  t.is(encoder.boundary, `form-data-boundary-${expected}`)
 })
 
 test("Has content-type string", t => {
@@ -36,7 +36,10 @@ test("Has content-type string with custom boundary string", t => {
 
   const encoder = new Encoder(new FormData(), expected)
 
-  t.is(encoder.boundary, expected)
+  t.is(
+    encoder.contentType,
+    `multipart/form-data; boundary=form-data-boundary-${expected}`
+  )
 })
 
 test("Has correct headers", async t => {
@@ -246,7 +249,8 @@ test("Yields every appended File", async t => {
 test(
   "Throws TypeError when the first argument is not a FormData instance",
   t => {
-    const trap = () => new Encoder({} as any)
+    // @ts-expect-error
+    const trap = () => new Encoder({})
 
     t.throws(trap, {
       instanceOf: TypeError,
@@ -256,7 +260,8 @@ test(
 )
 
 test("Throws TypeError when given boundary is not a string", t => {
-  const trap = () => new Encoder(new FormData(), 42 as any)
+  // @ts-expect-error
+  const trap = () => new Encoder(new FormData(), 42)
 
   t.throws(trap, {
     instanceOf: TypeError,

lib/Encoder.ts

@@ -64,7 +64,7 @@ export class Encoder {
    *
    * const encoder = new Encoder(fd)
    */
-  constructor(form: FormDataLike, boundary: string = createBoundary()) {
+  constructor(form: FormDataLike, boundary: string = createBoundary(8)) {
     if (!isFormData(form)) {
       throw new TypeError("Expected first argument to be a FormData instance.")
     }
@@ -73,7 +73,7 @@ export class Encoder {
       throw new TypeError("Expected boundary to be a string.")
     }
 
-    this.boundary = boundary
+    this.boundary = `form-data-boundary-${boundary}`
     this.contentType = `multipart/form-data; boundary=${this.boundary}`
 
     this.#encoder = new TextEncoder()

lib/util/createBoundary.ts

@@ -1,11 +1,10 @@
-import {customAlphabet} from "nanoid"
-
-const alphabet = "0123456789abcdefghijklmnopqrstuvwxyz"
-const generate = customAlphabet(alphabet, 16)
+import {randomBytes} from "crypto"
 
 /**
  * Generates a boundary string for FormData encoder.
  */
-const createBoundary = (): string => `form-data-boundary-${generate()}`
+const createBoundary = (size: number): string => (
+  randomBytes(size).toString("hex")
+)
 
 export default createBoundary

package.json

@@ -58,8 +58,5 @@
     "ts-node": "10.0.0",
     "ttypescript": "1.5.12",
     "typescript": "4.3.4"
-  },
-  "dependencies": {
-    "nanoid": "3.1.23"
   }
 }