2 files changed, 88 insertions, 38 deletions

diff --git a/cli/js/web/fetch.ts b/cli/js/web/fetch.ts
index 47ed1a7d1..045d1afcd 100644
--- a/cli/js/web/fetch.ts
+++ b/cli/js/web/fetch.ts
@@ -2,15 +2,15 @@
 import { notImplemented } from "../util.ts";
 import { isTypedArray } from "./util.ts";
 import * as domTypes from "./dom_types.d.ts";
-import { TextDecoder, TextEncoder } from "./text_encoding.ts";
+import { TextEncoder } from "./text_encoding.ts";
 import { DenoBlob, bytesSymbol as blobBytesSymbol } from "./blob.ts";
 import { read } from "../ops/io.ts";
 import { close } from "../ops/resources.ts";
 import { fetch as opFetch, FetchResponse } from "../ops/fetch.ts";
 import * as Body from "./body.ts";
-import { DomFileImpl } from "./dom_file.ts";
 import { getHeaderValueParams } from "./util.ts";
 import { ReadableStreamImpl } from "./streams/readable_stream.ts";
+import { MultipartBuilder } from "./fetch/multipart.ts";
 
 const NULL_BODY_STATUS = [101, 204, 205, 304];
 const REDIRECT_STATUS = [301, 302, 303, 307, 308];
@@ -232,45 +232,14 @@ export async function fetch(
           body = init.body[blobBytesSymbol];
           contentType = init.body.type;
         } else if (init.body instanceof FormData) {
-          let boundary = "";
+          let boundary;
           if (headers.has("content-type")) {
             const params = getHeaderValueParams("content-type");
-            if (params.has("boundary")) {
-              boundary = params.get("boundary")!;
-            }
-          }
-          if (!boundary) {
-            boundary =
-              "----------" +
-              Array.from(Array(32))
-                .map(() => Math.random().toString(36)[2] || 0)
-                .join("");
-          }
-
-          let payload = "";
-          for (const [fieldName, fieldValue] of init.body.entries()) {
-            let part = `\r\n--${boundary}\r\n`;
-            part += `Content-Disposition: form-data; name=\"${fieldName}\"`;
-            if (fieldValue instanceof DomFileImpl) {
-              part += `; filename=\"${fieldValue.name}\"`;
-            }
-            part += "\r\n";
-            if (fieldValue instanceof DomFileImpl) {
-              part += `Content-Type: ${
-                fieldValue.type || "application/octet-stream"
-              }\r\n`;
-            }
-            part += "\r\n";
-            if (fieldValue instanceof DomFileImpl) {
-              part += new TextDecoder().decode(fieldValue[blobBytesSymbol]);
-            } else {
-              part += fieldValue;
-            }
-            payload += part;
+            boundary = params.get("boundary")!;
           }
-          payload += `\r\n--${boundary}--`;
-          body = new TextEncoder().encode(payload);
-          contentType = "multipart/form-data; boundary=" + boundary;
+          const multipartBuilder = new MultipartBuilder(init.body, boundary);
+          body = multipartBuilder.getBody();
+          contentType = multipartBuilder.getContentType();
         } else {
           // TODO: ReadableStream
           notImplemented();
diff --git a/cli/js/web/fetch/multipart.ts b/cli/js/web/fetch/multipart.ts
index 792f9b5ee..654d4a0ea 100644
--- a/cli/js/web/fetch/multipart.ts
+++ b/cli/js/web/fetch/multipart.ts
@@ -1,5 +1,8 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
 
+import { Buffer } from "../../buffer.ts";
+import { bytesSymbol } from "../blob.ts";
+import { DomFileImpl } from "../dom_file.ts";
 import { DenoBlob } from "../blob.ts";
 import { TextEncoder, TextDecoder } from "../text_encoding.ts";
 import { getHeaderValueParams } from "../util.ts";
@@ -14,6 +17,84 @@ interface MultipartHeaders {
   disposition: Map<string, string>;
 }
 
+export class MultipartBuilder {
+  readonly boundary: string;
+  readonly formData: FormData;
+  readonly writer: Buffer;
+  constructor(formData: FormData, boundary?: string) {
+    this.boundary = boundary ?? this.#createBoundary();
+    this.formData = formData;
+    this.writer = new Buffer();
+  }
+
+  getContentType(): string {
+    return `multipart/form-data; boundary=${this.boundary}`;
+  }
+
+  getBody(): Uint8Array {
+    for (const [fieldName, fieldValue] of this.formData.entries()) {
+      if (fieldValue instanceof DomFileImpl) {
+        this.#writeFile(fieldName, fieldValue);
+      } else this.#writeField(fieldName, fieldValue as string);
+    }
+
+    this.writer.writeSync(encoder.encode(`\r\n--${this.boundary}--`));
+
+    return this.writer.bytes();
+  }
+
+  #createBoundary = (): string => {
+    return (
+      "----------" +
+      Array.from(Array(32))
+        .map(() => Math.random().toString(36)[2] || 0)
+        .join("")
+    );
+  };
+
+  #writeHeaders = (headers: string[][]): void => {
+    let buf = this.writer.empty() ? "" : "\r\n";
+
+    buf += `--${this.boundary}\r\n`;
+    for (const [key, value] of headers) {
+      buf += `${key}: ${value}\r\n`;
+    }
+    buf += `\r\n`;
+
+    this.writer.write(encoder.encode(buf));
+  };
+
+  #writeFileHeaders = (
+    field: string,
+    filename: string,
+    type?: string
+  ): void => {
+    const headers = [
+      [
+        "Content-Disposition",
+        `form-data; name="${field}"; filename="${filename}"`,
+      ],
+      ["Content-Type", type || "application/octet-stream"],
+    ];
+    return this.#writeHeaders(headers);
+  };
+
+  #writeFieldHeaders = (field: string): void => {
+    const headers = [["Content-Disposition", `form-data; name="${field}"`]];
+    return this.#writeHeaders(headers);
+  };
+
+  #writeField = (field: string, value: string): void => {
+    this.#writeFieldHeaders(field);
+    this.writer.writeSync(encoder.encode(value));
+  };
+
+  #writeFile = (field: string, value: DomFileImpl): void => {
+    this.#writeFileHeaders(field, value.name, value.type);
+    this.writer.writeSync(value[bytesSymbol]);
+  };
+}
+
 export class MultipartParser {
   readonly boundary: string;
   readonly boundaryChars: Uint8Array;