detect.go

package enmime

import (
	"net/textproto"
	"strings"
)

// detectMultipartMessage returns true if the message has a recognized multipart Content-Type header
func detectMultipartMessage(root *Part) bool {
	// Parse top-level multipart
	ctype := root.Header.Get(hnContentType)
	mediatype, _, _, err := ParseMediaType(ctype)

	// According to rfc2046#section-5.1.7 all other multipart should
	// be treated as multipart/mixed
	return err == nil && strings.HasPrefix(mediatype, ctMultipartPrefix)
}

// detectAttachmentHeader returns true, if the given header defines an attachment. First it checks
// if the Content-Disposition header defines either an attachment part or an inline part with at
// least one parameter. If this test is false, the Content-Type header is checked for attachment,
// but not inline. Email clients use inline for their text bodies.
//
// Valid Attachment-Headers:
//
//  - Content-Disposition: attachment; filename="frog.jpg"
//  - Content-Disposition: inline; filename="frog.jpg"
//  - Content-Type: attachment; filename="frog.jpg"
func detectAttachmentHeader(header textproto.MIMEHeader) bool {
	mediatype, params, _, _ := ParseMediaType(header.Get(hnContentDisposition))
	if strings.ToLower(mediatype) == cdAttachment ||
		(strings.ToLower(mediatype) == cdInline && len(params) > 0) {
		return true
	}

	mediatype, _, _, _ = ParseMediaType(header.Get(hnContentType))
	return strings.ToLower(mediatype) == cdAttachment
}

// detectTextHeader returns true, if the the MIME headers define a valid 'text/plain' or 'text/html'
// part.  If the emptyContentTypeIsPlain argument is set to true, a missing Content-Type header will
// result in a positive plain part detection.
func detectTextHeader(header textproto.MIMEHeader, emptyContentTypeIsText bool) bool {
	ctype := header.Get(hnContentType)
	if ctype == "" && emptyContentTypeIsText {
		return true
	}

	if mediatype, _, _, err := ParseMediaType(ctype); err == nil {
		switch mediatype {
		case ctTextPlain, ctTextHTML:
			return true
		}
	}

	return false
}

// detectBinaryBody returns true if the mail header defines a binary body.
func detectBinaryBody(root *Part) bool {
	if detectTextHeader(root.Header, true) {
		// It is text/plain, but an attachment.
		// Content-Type: text/plain; name="test.csv"
		// Content-Disposition: attachment; filename="test.csv"
		// Check for attachment only, or inline body is marked
		// as attachment, too.
		mediatype, _, _, _ := ParseMediaType(root.Header.Get(hnContentDisposition))
		return strings.ToLower(mediatype) == cdAttachment
	}

	isBin := detectAttachmentHeader(root.Header)
	if !isBin {
		// This must be an attachment, if the Content-Type is not
		// 'text/plain' or 'text/html'.
		// Example:
		// Content-Type: application/pdf; name="doc.pdf"
		mediatype, _, _, _ := ParseMediaType(root.Header.Get(hnContentType))
		mediatype = strings.ToLower(mediatype)
		if mediatype != ctTextPlain && mediatype != ctTextHTML {
			return true
		}
	}

	return isBin
}