feat(GODT-2802): IMAP Serivce

Handles all IMAP related tasks. Unlike the previous iteration, this new
service automatically adds and removes users from Gluon by interfacing
with server manager.

internal/services/imapservice/sync_attachment_downloader.go

@@ -0,0 +1,115 @@
+// Copyright (c) 2023 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package imapservice
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+
+	"github.com/ProtonMail/gluon/async"
+	"github.com/ProtonMail/gluon/logging"
+	"github.com/ProtonMail/go-proton-api"
+)
+
+type attachmentResult struct {
+	attachment []byte
+	err        error
+}
+
+type attachmentJob struct {
+	id     string
+	size   int64
+	result chan attachmentResult
+}
+
+type attachmentDownloader struct {
+	workerCh chan attachmentJob
+	cancel   context.CancelFunc
+}
+
+func attachmentWorker(ctx context.Context, client APIClient, work <-chan attachmentJob) {
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case job, ok := <-work:
+			if !ok {
+				return
+			}
+			var b bytes.Buffer
+			b.Grow(int(job.size))
+			err := client.GetAttachmentInto(ctx, job.id, &b)
+			select {
+			case <-ctx.Done():
+				close(job.result)
+				return
+			case job.result <- attachmentResult{attachment: b.Bytes(), err: err}:
+				close(job.result)
+			}
+		}
+	}
+}
+
+func (s *syncJob) newAttachmentDownloader(ctx context.Context, client APIClient, workerCount int) *attachmentDownloader {
+	workerCh := make(chan attachmentJob, (workerCount+2)*workerCount)
+	ctx, cancel := context.WithCancel(ctx)
+	for i := 0; i < workerCount; i++ {
+		workerCh = make(chan attachmentJob)
+		async.GoAnnotated(ctx, s.panicHandler, func(ctx context.Context) { attachmentWorker(ctx, client, workerCh) }, logging.Labels{
+			"sync": fmt.Sprintf("att-downloader %v", i),
+		})
+	}
+
+	return &attachmentDownloader{
+		workerCh: workerCh,
+		cancel:   cancel,
+	}
+}
+
+func (a *attachmentDownloader) getAttachments(ctx context.Context, attachments []proton.Attachment) ([][]byte, error) {
+	resultChs := make([]chan attachmentResult, len(attachments))
+	for i, id := range attachments {
+		resultChs[i] = make(chan attachmentResult, 1)
+		select {
+		case a.workerCh <- attachmentJob{id: id.ID, result: resultChs[i], size: id.Size}:
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		}
+	}
+
+	result := make([][]byte, len(attachments))
+	var err error
+	for i := 0; i < len(attachments); i++ {
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case r := <-resultChs[i]:
+			if r.err != nil {
+				err = fmt.Errorf("failed to get attachment %v: %w", attachments[i], r.err)
+			}
+			result[i] = r.attachment
+		}
+	}
+
+	return result, err
+}
+
+func (a *attachmentDownloader) close() {
+	a.cancel()
+}