Introduce FormDataEncoder.contentLength property. Make sure readonly properties actually read-only in runtime.

Author: octet-stream

lib/Encoder.test.ts

@@ -19,7 +19,30 @@ import {FormDataEncoder} from "./Encoder"
 test("Has boundary string", t => {
   const encoder = new FormDataEncoder(new FormData())
 
-  t.true(typeof encoder.boundary === "string")
+  t.true("boundary" in encoder)
+  t.is(typeof encoder.boundary, "string")
+})
+
+test("boundary property is read-only", t => {
+  const encoder = new FormDataEncoder(new FormData())
+
+  const {boundary: expected} = encoder
+
+  // @ts-expect-error
+  try { encoder.boundary = "some string" } catch { /* noop */ }
+
+  t.is(encoder.boundary, expected)
+})
+
+test("boundary property cannot be deleted", t => {
+  const encoder = new FormDataEncoder(new FormData())
+
+  const {boundary: expected} = encoder
+
+  // @ts-expect-error
+  try { delete encoder.boundary } catch { /* noop */ }
+
+  t.is(encoder.boundary, expected)
 })
 
 test("Accepts custom boundary as the second argument", t => {
@@ -33,9 +56,33 @@ test("Accepts custom boundary as the second argument", t => {
 test("Has content-type string", t => {
   const encoder = new FormDataEncoder(new FormData())
 
+  t.true("contentType" in encoder)
+  t.is(typeof encoder.contentType, "string")
   t.true(encoder.contentType.startsWith("multipart/form-data; boundary="))
 })
 
+test("contentType property is read-only", t => {
+  const encoder = new FormDataEncoder(new FormData())
+
+  const {contentType: expected} = encoder
+
+  // @ts-expect-error
+  try { encoder.contentType = "application/json" } catch { /* noop */ }
+
+  t.is(encoder.contentType, expected)
+})
+
+test("contentType cannot be deleted", t => {
+  const encoder = new FormDataEncoder(new FormData())
+
+  const {contentType: expected} = encoder
+
+  // @ts-expect-error
+  try { delete encoder.contentType } catch { /* noop */ }
+
+  t.is(encoder.contentType, expected)
+})
+
 test("Has content-type string with custom boundary string", t => {
   const expected = "BoundaryString123"
 
@@ -47,6 +94,40 @@ test("Has content-type string with custom boundary string", t => {
   )
 })
 
+test("Has contentLength property", async t => {
+  const encoder = new FormDataEncoder(new FormData())
+
+  t.true("contentLength" in encoder)
+  t.is(typeof encoder.contentLength, "string")
+  t.is(
+    encoder.contentLength,
+
+    await readStream(encoder).then(({length}) => `${length}`)
+  )
+})
+
+test("contentLength property is read-only", t => {
+  const encoder = new FormDataEncoder(new FormData())
+
+  const {contentLength: expected} = encoder
+
+  // @ts-expect-error
+  try { encoder.contentLength = String(Date.now()) } catch { /* noop */ }
+
+  t.is(encoder.contentLength, expected)
+})
+
+test("contentLength property cannot be deleted", t => {
+  const encoder = new FormDataEncoder(new FormData())
+
+  const {contentLength: expected} = encoder
+
+  // @ts-expect-error
+  try { encoder.contentLength = String(Date.now()) } catch { /* noop */ }
+
+  t.is(encoder.contentLength, expected)
+})
+
 test("Has correct headers", async t => {
   const encoder = new FormDataEncoder(new FormData())
 

lib/Encoder.ts

@@ -8,25 +8,7 @@ import {FormDataLike} from "./FormDataLike"
 import {FileLike} from "./FileLike"
 
 export class FormDataEncoder {
-  /**
-   * Returns boundary string
-   */
-  readonly boundary: string
-
-  /**
-   * Returns Content-Type header for multipart/form-data
-   */
-  readonly contentType: string
-
-  /**
-   * Returns headers object with Content-Type and Content-Length header
-   */
-  readonly headers: {
-    "Content-Type": string
-    "Content-Length": string
-  }
-
-  readonly #CRLF: string
+  readonly #CRLF: string = "\r\n"
 
   readonly #CRLF_BYTES: Uint8Array
 
@@ -37,7 +19,7 @@ export class FormDataEncoder {
   /**
    * TextEncoder instance
    */
-  readonly #encoder: TextEncoder
+  readonly #encoder = new TextEncoder()
 
   /**
    * Returns form-data footer bytes
@@ -49,6 +31,29 @@ export class FormDataEncoder {
    */
   readonly #form: FormDataLike
 
+  /**
+   * Returns boundary string
+   */
+  readonly boundary: string
+
+  /**
+   * Returns Content-Type header
+   */
+  readonly contentType: string
+
+  /**
+   * Returns Content-Length header
+   */
+  readonly contentLength: string
+
+  /**
+   * Returns headers object with Content-Type and Content-Length header
+   */
+  readonly headers: {
+    "Content-Type": string
+    "Content-Length": string
+  }
+
   /**
    * Creates a multipart/form-data encoder.
    *
@@ -75,23 +80,34 @@ export class FormDataEncoder {
       throw new TypeError("Expected boundary to be a string.")
     }
 
-    this.boundary = `form-data-boundary-${boundary}`
-    this.contentType = `multipart/form-data; boundary=${this.boundary}`
-
-    this.#encoder = new TextEncoder()
+    // ? Should I preserve FormData entries in array instead?
+    // ? That way it will be immutable, but require to allocate a new array
+    // ? and go through entries during initialization.
+    this.#form = form
 
-    this.#CRLF = "\r\n"
     this.#CRLF_BYTES = this.#encoder.encode(this.#CRLF)
     this.#CRLF_BYTES_LENGTH = this.#CRLF_BYTES.byteLength
 
-    this.#form = form
+    this.boundary = `form-data-boundary-${boundary}`
+    this.contentType = `multipart/form-data; boundary=${this.boundary}`
+
     this.#footer = this.#encoder.encode(
       `${this.#DASHES}${this.boundary}${this.#DASHES}${this.#CRLF.repeat(2)}`
     )
 
+    this.contentLength = String(this.getContentLength())
+
     this.headers = Object.freeze({
       "Content-Type": this.contentType,
-      "Content-Length": String(this.getContentLength())
+      "Content-Length": this.contentLength
+    })
+
+    // Make sure following properties read/only in runtime.
+    Object.defineProperties(this, {
+      boundary: {writable: false, configurable: false},
+      contentType: {writable: false, configurable: false},
+      contentLength: {writable: false, configurable: false},
+      headers: {writable: false, configurable: false}
     })
   }