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imapserver: implement PREVIEW extension (RFC 8970), and store previews in message database

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We were already generating previews of plain text parts for the webmail
interface, but we didn't store them, so were generating the previews each time
messages were listed.

Now we store previews in the database for faster handling. And we also generate
previews for html parts if needed. We use the first part that has textual
content.

For IMAP, the previews can be requested by an IMAP client. When we get the
"LAZY" variant, which doesn't require us to generate a preview, we generate it
anyway, because it should be fast enough. So don't make clients first ask for
"PREVIEW (LAZY)" and then again a request for "PREVIEW".

We now also generate a preview when a message is added to the account. Except
for imports. It would slow us down, the previews aren't urgent, and they will
be generated on-demand at first-request.
This commit is contained in:
Mechiel Lukkien
2025-03-28 16:57:44 +01:00
parent 8b418a9ca2
commit aa631c604c
23 changed files with 735 additions and 187 deletions
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27
store/account.go
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@ -560,6 +560,18 @@ type Message struct {
TrainedJunk *bool // If nil, no training done yet. Otherwise, true is trained as junk, false trained as nonjunk.
MsgPrefix []byte // Typically holds received headers and/or header separator.
// If non-nil, a preview of the message based on text and/or html parts of the
// message. Used in the webmail and IMAP PREVIEW extension. If non-nil, it is empty
// if no preview could be created, or the message has not textual content or
// couldn't be parsed.
// Previews are typically created when delivering a message, but not when importing
// messages, for speed. Previews are generated on first request (in the webmail, or
// through the IMAP fetch attribute "PREVIEW" (without "LAZY")), and stored with
// the message at that time.
// The preview is at most 256 characters (can be more bytes), with detected quoted
// text replaced with "[..."].
Preview *string
// ParsedBuf message structure. Currently saved as JSON of message.Part because bstore
// cannot yet store recursive types. Created when first needed, and saved in the
// database.
@ -2126,6 +2138,9 @@ type AddOpts struct {
JunkFilter *junk.Filter
SkipTraining bool
// If true, a preview will be generated if the Message doesn't already have one.
SkipPreview bool
}
// todo optimization: when moving files, we open the original, call MessageAdd() which hardlinks it and close the file gain. when passing the filename, we could just use os.Link, saves 2 syscalls.
@ -2255,6 +2270,8 @@ func (a *Account) MessageAdd(log mlog.Log, tx *bstore.Tx, mb *Mailbox, m *Messag
if err := json.Unmarshal(m.ParsedBuf, &p); err != nil {
log.Errorx("unmarshal parsed message, continuing", err, slog.String("parse", ""))
} else {
mr := FileMsgReader(m.MsgPrefix, msgFile)
p.SetReaderAt(mr)
part = &p
}
return part
@ -2269,6 +2286,16 @@ func (a *Account) MessageAdd(log mlog.Log, tx *bstore.Tx, mb *Mailbox, m *Messag
m.PrepareThreading(log, part)
}
if !opts.SkipPreview && m.Preview == nil {
if p := getPart(); p != nil {
s, err := p.Preview(log)
if err != nil {
return fmt.Errorf("generating preview: %v", err)
}
m.Preview = &s
}
}
// Assign to thread (if upgrade has completed).
noThreadID := opts.SkipThreads
if m.ThreadID == 0 && !opts.SkipThreads && getPart() != nil {