quote Content-Type boundary param if needed as per RFC 2616

Author: zefir-git

src/Multipart.ts

@@ -439,10 +439,32 @@ export class Multipart implements Part {
         return Multipart.combineArrays(result);
     }
 
+    private static boundaryShouldBeQuoted(boundary: Uint8Array): boolean {
+        for (const byte of boundary) {
+            if (
+                byte === Multipart.HT
+                || byte === Multipart.SP
+                || byte === 0x22
+                || byte === 0x28
+                || byte === 0x29
+                || byte === 0x2c
+                || byte === 0x2f
+                || (byte >= Multipart.COLON && byte <= 0x40)
+                || (byte >= 0x5b && byte <= 0x5d)
+                || byte === 0x7b
+                || byte === 0x7d
+            ) return true;
+        }
+        return false;
+    }
+
     /**
      * Set the `Content-Type` header of this multipart based on {@link mediaType} and {@link boundary}.
      */
     private setHeaders() {
-        this.headers.set("Content-Type", this.#mediaType + "; boundary=" + new TextDecoder().decode(this.#boundary));
+        const shouldQuoteBoundary = Multipart.boundaryShouldBeQuoted(this.#boundary);
+        const boundaryString = new TextDecoder().decode(this.#boundary);
+        const boundary = shouldQuoteBoundary ? `"${boundaryString.replace(/"/g, '\\"')}"` : boundaryString;
+        this.headers.set("Content-Type", this.#mediaType + "; boundary=" + boundary);
     }
 }