Issue when uploading a file with multipart/form-data with Chrome but trying to upload a directory instead of a file

先从 lib/plug/conn.ex 中的 Plug.Conn.read_multipart_from_buffer_or_adapter/4 和 read_part_headers/2 开始，然后检查 lib/plug/parsers/multipart.ex。使用提供的 curl 请求重现格式错误的目录上传，并跟踪 {:error, :closed} 的处理方式。当服务器返回适当的错误响应而不是崩溃时，即表示完成。

[debug] ** (Plug.Parsers.ParseError) malformed request, a MatchError exception was raised with message "no match of right hand side value: {:error, :closed}"
    (plug) lib/plug/conn.ex:1045: Plug.Conn.read_multipart_from_buffer_or_adapter/4
    (plug) lib/plug/conn.ex:936: Plug.Conn.read_part_headers/2
    (plug) lib/plug/parsers/multipart.ex:64: Plug.Parsers.MULTIPART.parse_multipart/2
    (plug) lib/plug/parsers/multipart.ex:34: Plug.Parsers.MULTIPART.parse/5
    (plug) lib/plug/parsers.ex:271: Plug.Parsers.reduce/7
    (app) lib/app_web/endpoint.ex:1: AppWeb.Endpoint.plug_builder_call/2
    (app) lib/plug/debugger.ex:122: AppWeb.Endpoint."call (overridable 3)"/2
    (app) lib/app_web/endpoint.ex:1: AppWeb.Endpoint.call/2
    (plug) lib/plug/adapters/cowboy/handler.ex:16: Plug.Adapters.Cowboy.Handler.upgrade/4
    (cowboy) /Sites/api/deps/cowboy/src/cowboy_protocol.erl:442: :cowboy_protocol.execute/4

Since plug crashes the server doesn't even return error 500, I would prefer to be able to return a proper response saying that the file seem invalid or something.

As a curl request from Chrome inspector:

curl 'http://127.0.0.1:4000/app/batch' -H 'Accept: application/vnd.api+json' -H 'Referer: http://app.test:4200/submit?batch=true' -H 'Origin: http://app.test:4200' -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36' -H 'Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryUhoiSH3D5xDbVVAz' --data-binary $'------WebKitFormBoundaryUhoiSH3D5xDbVVAz\r\nContent-Disposition: form-data; name="file"; filename="Flow Chart.gstencil"\r\nContent-Type: application/octet-stream\r\n\r\n\r\n------WebKitFormBoundaryUhoiSH3D5xDbVVAz--\r\n' --compressed

I'm using Plug version 1.6.2