Proper PHP way to parse email attachments from EML

问题:

I have a file containing an email in "plain text MIME message format". I am not sure if this is the EML format. The email contains an attachment and I want to extract the attachment and create those files again. This is how the attachment part looks like -

...
...
Receive, deliver details
...
...
From: sac ascsac <[e-mail]>

Date: Thu, 20 Jan 2011 18:05:16 +0530

Message-ID: <[e-mail]>

Subject: Test attachments

To: [e-mail]

Content-Type: multipart/mixed; boundary=20cf3054ac85d97721049a465e12



--20cf3054ac85d97721049a465e12

Content-Type: multipart/alternative; boundary=20cf3054ac85d97717049a465e10



--20cf3054ac85d97717049a465e10

Content-Type: text/plain; charset=ISO-8859-1



hello this is a test mail. It contains two attachments



--20cf3054ac85d97717049a465e10

Content-Type: text/html; charset=ISO-8859-1



hello this is a test mail. It contains two attachments<br>


--20cf3054ac85d97717049a465e10--

--20cf3054ac85d97721049a465e12

Content-Type: text/plain; charset=US-ASCII; name="simple_test.txt"

Content-Disposition: attachment; filename="simple_test.txt"

Content-Transfer-Encoding: base64

X-Attachment-Id: f_gj5n2yx60



aGVsbG8gd29ybGQKYWMgYXNj
...
encoded things here
...
ZyBmZyAKCjIKNDIzCnQ2Mwo=

--20cf3054ac85d97721049a465e12

Content-Type: application/x-httpd-php; name="oscomm_backup_code.php"

Content-Disposition: attachment; filename="oscomm_backup_code.php"

Content-Transfer-Encoding: base64

X-Attachment-Id: f_gj5n5gxn1



PD9waHAKCg ...
...
encoded things here
...
X2xpbmsoRklMRU5BTUVfQkFDS1VQKSk7Cgo/Pgo=
--20cf3054ac85d97721049a465e12--

I can see that the part between X-Attachment-Id: f_gj5n2yx60 and ZyBmZyAKCjIKNDIzCnQ2Mwo=, both including is the content of the first attachment. I want to parse those attachments (file names and contents and create those files).

I got this file after parsing a dbx format file using a DBX Parser class available in PHP classes.

I searched in many places and did not find much discussion regarding this here in SO other than Script to parse emails for attachments. May be I missed some terms while searching. In that answer it is mentioned -

you can use the boundries to extract the base64 encoded information

But I am not sure which are the boundaries and how exactly to use the boundaries? There already must be some libraries or some well defined method of doing this. I guess I will commit many mistakes if I try reinventing the wheel here.

回答1:

There's an PHP Mailparse extension, have you tried it?

The manual way would be, process the mail line by line. When you hit your first Content-Type header (this one in your example): Content-Type: multipart/mixed; boundary=20cf3054ac85d97721049a465e12

You have the boundary. This string is used as the boundary between your multiple parts (that's why they call it multipart). Everytime a line starts with the dashes and this string, a new part begin. In your example: --20cf3054ac85d97721049a465e12

Every part will start with headers, a blank line, and content. By looking at the content-type of the headers you can determine which are attachments, what their type is and their filename. Read the whole content, strip the spaces, base64_decode it, and you've got the binary contents of the file. Does this help?