122 lines
2.7 KiB
Go
122 lines
2.7 KiB
Go
package backendutil
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import (
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"bytes"
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"errors"
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"io"
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"mime"
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nettextproto "net/textproto"
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"strings"
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"github.com/emersion/go-imap"
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"github.com/emersion/go-message/textproto"
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)
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var errNoSuchPart = errors.New("backendutil: no such message body part")
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func multipartReader(header textproto.Header, body io.Reader) *textproto.MultipartReader {
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contentType := header.Get("Content-Type")
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if !strings.HasPrefix(strings.ToLower(contentType), "multipart/") {
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return nil
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}
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_, params, err := mime.ParseMediaType(contentType)
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if err != nil {
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return nil
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}
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return textproto.NewMultipartReader(body, params["boundary"])
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}
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// FetchBodySection extracts a body section from a message.
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func FetchBodySection(header textproto.Header, body io.Reader, section *imap.BodySectionName) (imap.Literal, error) {
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// First, find the requested part using the provided path
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for i := 0; i < len(section.Path); i++ {
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n := section.Path[i]
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mr := multipartReader(header, body)
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if mr == nil {
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// First part of non-multipart message refers to the message itself.
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// See RFC 3501, Page 55.
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if len(section.Path) == 1 && section.Path[0] == 1 {
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break
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}
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return nil, errNoSuchPart
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}
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for j := 1; j <= n; j++ {
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p, err := mr.NextPart()
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if err == io.EOF {
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return nil, errNoSuchPart
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} else if err != nil {
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return nil, err
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}
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if j == n {
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body = p
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header = p.Header
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break
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}
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}
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}
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// Then, write the requested data to a buffer
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b := new(bytes.Buffer)
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resHeader := header
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if section.Fields != nil {
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// Copy header so we will not change value passed to us.
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resHeader = header.Copy()
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if section.NotFields {
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for _, fieldName := range section.Fields {
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resHeader.Del(fieldName)
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}
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} else {
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fieldsMap := make(map[string]struct{}, len(section.Fields))
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for _, field := range section.Fields {
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fieldsMap[nettextproto.CanonicalMIMEHeaderKey(field)] = struct{}{}
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}
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for field := resHeader.Fields(); field.Next(); {
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if _, ok := fieldsMap[field.Key()]; !ok {
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field.Del()
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}
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}
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}
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}
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// Write the header
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err := textproto.WriteHeader(b, resHeader)
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if err != nil {
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return nil, err
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}
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switch section.Specifier {
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case imap.TextSpecifier:
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// The header hasn't been requested. Discard it.
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b.Reset()
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case imap.EntireSpecifier:
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if len(section.Path) > 0 {
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// When selecting a specific part by index, IMAP servers
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// return only the text, not the associated MIME header.
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b.Reset()
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}
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}
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// Write the body, if requested
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switch section.Specifier {
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case imap.EntireSpecifier, imap.TextSpecifier:
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if _, err := io.Copy(b, body); err != nil {
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return nil, err
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}
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}
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var l imap.Literal = b
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if section.Partial != nil {
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l = bytes.NewReader(section.ExtractPartial(b.Bytes()))
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}
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return l, nil
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}
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