我尝试解析TXT文件中的Mimefile，格式如下

Content-Type: multipart/related; boundary="MIMEBoundary"
MIME-Version: 1.0
Content-Description: This Transmission File is created with Pegasus Test Suite
X-eFileRoutingCode: MEF
Content-Transfer-Encoding: Binary
Content-Location: manifest_xml

--MIMEBoundary
Content-Type: text/xml; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

<?xml version='1.0' encoding='UTF-8'?>
<SOAP:Envelope xmlns="http://www.efiles.id/efile" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/" xmlns:efile="http://www.efiles.id/efile" xsi:schemaLocation="http://schemas.xmlsoap.org/soap/envelope/ ../message/SOAP.xsd http://www.files./efile ../message/efileMessage.xsd"><SOAP:Header><IFATransmissionHeader><MessageId>012342018ABCDEFGHIJK</MessageId><TransmissionTs>2018-07-01T09:51:56-05:00</TransmissionTs><TransmitterDetail><ETIN>XXXXX</ETIN></TransmitterDetail></IFATransmissionHeader></SOAP:Header><SOAP:Body><TransmissionManifest><SubmissionDataList><Cnt>1</Cnt><SubmissionData><SubmissionId>0123452018OPQRSTUVWX</SubmissionId><ElectronicPostmarkTs>2018-07-01T09:51:56-05:00</ElectronicPostmarkTs></SubmissionData></SubmissionDataList></TransmissionManifest></SOAP:Body></SOAP:Envelope>
--MIMEBoundary
Content-Type: application/octet-stream
MIME-Version: 1.0
Content-Transfer-Encoding: base64

UEsDBBQAAAAAAOh2lFQAAAAAAAAAAAAAAAALAAAAYXR0YWNobWVudC9QSwMEFAAAAAAA6HaUVAAA
AAAAAAAAAAAAAAQAAAB4bWwvUEsDBBQAAAAAAOh2lFT0i/87pT0AAKU9AAAVAAAAYXR0YWNobWVu
dC9zYW1wbGUucGRmJVBERi0yLjAKJbq63toKMSAwIG9iajw8L1R5cGUvQ2F0YWxvZy9QYWdlcyAy
IDAgUi9NZXRhZGF0YSAxMiAwIFI+PgplbmRvYmoKMiAwIG9iajw8L1R5cGUvUGFnZXMvS2lkc1sz
IDAgUl0vQ291bnQgMT4+CmVuZG9iagoxMiAwIG9iajw8L1R5cGUvTWV0YWRhdGEvU3VidHlwZS9Y

--MIMEBoundary--

我想分离XML并将其编码为单独字符串，我是如何创建这样一个解码器的

class NewlineSafeBytesParser(email.parser.BytesParser):
    def parse(self, fp, headersonly=False):
        from io import TextIOWrapper
        fp = TextIOWrapper(fp, encoding='ascii', errors='surrogateescape', newline='')
        try:
            return self.parser.parse(fp, headersonly)
        finally:
            fp.detach()

# Subclassing:
parser = NewlineSafeBytesParser()

但我得到了一个损坏的解码结果，如何将编码的zip文件（Base64）编码与txt文件分开，以便可以单独解码？