Add group mailbox export (#5153)

<!-- PR description-->

* Add EML exports for group mailbox.
* Tested E2E manually along with unit tests added in this PR.
* Will follow it up with a sanity test PR.
---

#### Does this PR need a docs update or release note?

- [x] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [ ] ⛔ No

#### Type of change

<!--- Please check the type of change your PR introduces: --->
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* #<issue>

#### Test Plan

<!-- How will this be tested prior to merging.-->
- [x] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Update repo init configuration to reduce the total number of GET requests sent
   to the object store when using corso. This affects repos that have many
   backups created in them per day the most.
+- Group mailbox emails can now be exported as `.eml` files.
 
 ### Fixed
 - Retry transient 400 "invalidRequest" errors during onedrive & sharepoint backup.

src/cli/export/groups.go

@@ -7,7 +7,6 @@ import (
 	"github.com/alcionai/corso/src/cli/flags"
 	"github.com/alcionai/corso/src/cli/utils"
 	"github.com/alcionai/corso/src/pkg/control"
-	"github.com/alcionai/corso/src/pkg/selectors"
 )
 
 // called by export.go to map subcommands to provider-specific handling.
@@ -93,10 +92,6 @@ func exportGroupsCmd(cmd *cobra.Command, args []string) error {
 	sel := utils.IncludeGroupsRestoreDataSelectors(ctx, opts)
 	utils.FilterGroupsRestoreInfoSelectors(sel, opts)
 
-	// TODO(pandeyabs): Exclude conversations from export since they are not
-	// supported yet. https://github.com/alcionai/corso/issues/4822
-	sel.Exclude(sel.Conversation(selectors.Any()))
-
 	acceptedGroupsFormatTypes := []string{
 		string(control.DefaultFormat),
 		string(control.JSONFormat),

src/internal/m365/collection/groups/export.go

@@ -5,19 +5,24 @@ import (
 	"context"
 	"encoding/json"
 	"io"
+	"strings"
 	"time"
 
 	"github.com/alcionai/clues"
 	"github.com/microsoftgraph/msgraph-sdk-go/models"
 
 	"github.com/alcionai/corso/src/internal/common/ptr"
+	"github.com/alcionai/corso/src/internal/converters/eml"
 	"github.com/alcionai/corso/src/internal/data"
+	groupMeta "github.com/alcionai/corso/src/internal/m365/collection/groups/metadata"
 	"github.com/alcionai/corso/src/pkg/control"
 	"github.com/alcionai/corso/src/pkg/export"
 	"github.com/alcionai/corso/src/pkg/fault"
+	"github.com/alcionai/corso/src/pkg/logger"
 	"github.com/alcionai/corso/src/pkg/metrics"
 	"github.com/alcionai/corso/src/pkg/path"
 	"github.com/alcionai/corso/src/pkg/services/m365/api"
+	"github.com/alcionai/corso/src/pkg/services/m365/api/graph/metadata"
 )
 
 func NewExportCollection(
@@ -26,7 +31,19 @@ func NewExportCollection(
 	backupVersion int,
 	cec control.ExportConfig,
 	stats *metrics.ExportStats,
+	cat path.CategoryType,
 ) export.Collectioner {
+	var streamItems export.ItemStreamer
+
+	switch cat {
+	case path.ChannelMessagesCategory:
+		streamItems = streamChannelMessages
+	case path.ConversationPostsCategory:
+		streamItems = streamConversationPosts
+	default:
+		return nil
+	}
+
 	return export.BaseCollection{
 		BaseDir:           baseDir,
 		BackingCollection: backingCollections,
@@ -37,8 +54,12 @@ func NewExportCollection(
 	}
 }
 
-// streamItems streams the items in the backingCollection into the export stream chan
-func streamItems(
+//-------------------------------------------------------------
+// Channel Messages
+//-------------------------------------------------------------
+
+// streamChannelMessages streams the items in the backingCollection into the export stream chan
+func streamChannelMessages(
 	ctx context.Context,
 	drc []data.RestoreCollection,
 	backupVersion int,
@@ -198,3 +219,145 @@ func makeMinimumChannelMesasge(item models.ChatMessageable) minimumChannelMessag
 		Subject:              ptr.Val(item.GetSubject()),
 	}
 }
+
+//-------------------------------------------------------------
+// Conversation Posts
+//-------------------------------------------------------------
+
+// streamConversationPosts adds the post items into the export stream channel.
+func streamConversationPosts(
+	ctx context.Context,
+	drc []data.RestoreCollection,
+	backupVersion int,
+	cec control.ExportConfig,
+	ch chan<- export.Item,
+	stats *metrics.ExportStats,
+) {
+	defer close(ch)
+
+	errs := fault.New(false)
+
+	for _, rc := range drc {
+		for item := range rc.Items(ctx, errs) {
+			ictx := clues.Add(
+				ctx,
+				"path_short_ref", rc.FullPath().ShortRef(),
+				"stream_item_id", item.ID())
+
+			// Trim .data suffix from itemID. Also, we don't expect .meta files
+			// here since details are not persisted for metadata files.
+			trimmedID := strings.TrimSuffix(item.ID(), metadata.DataFileSuffix)
+			exportName := trimmedID + ".eml"
+
+			postMetadata, err := fetchAndReadMetadata(ictx, trimmedID, rc)
+			if err != nil {
+				ch <- export.Item{
+					ID:    item.ID(),
+					Error: err,
+				}
+
+				continue
+			}
+
+			reader := item.ToReader()
+			content, err := io.ReadAll(reader)
+
+			reader.Close()
+
+			if err != nil {
+				ch <- export.Item{
+					ID:    item.ID(),
+					Error: err,
+				}
+
+				continue
+			}
+
+			// Convert JSON to eml.
+			email, err := eml.FromJSONPostToEML(ictx, content, postMetadata)
+			if err != nil {
+				err = clues.Wrap(err, "converting JSON to eml")
+
+				logger.CtxErr(ictx, err).Info("processing collection item")
+
+				ch <- export.Item{
+					ID:    item.ID(),
+					Error: err,
+				}
+
+				continue
+			}
+
+			emlReader := io.NopCloser(bytes.NewReader([]byte(email)))
+
+			stats.UpdateResourceCount(path.ConversationPostsCategory)
+			body := metrics.ReaderWithStats(emlReader, path.ConversationPostsCategory, stats)
+
+			ch <- export.Item{
+				ID:   item.ID(),
+				Name: exportName,
+				Body: body,
+			}
+		}
+
+		items, recovered := errs.ItemsAndRecovered()
+
+		// Return all the items that we failed to source from the persistence layer
+		for _, item := range items {
+			ch <- export.Item{
+				ID:    item.ID,
+				Error: &item,
+			}
+		}
+
+		for _, err := range recovered {
+			ch <- export.Item{
+				Error: err,
+			}
+		}
+	}
+}
+
+func fetchAndReadMetadata(
+	ctx context.Context,
+	itemID string,
+	fin data.FetchItemByNamer,
+) (groupMeta.ConversationPostMetadata, error) {
+	metaName := itemID + metadata.MetaFileSuffix
+
+	ctx = clues.Add(ctx, "meta_file_name", metaName)
+
+	meta, err := fin.FetchItemByName(ctx, metaName)
+	if err != nil {
+		return groupMeta.ConversationPostMetadata{},
+			clues.WrapWC(ctx, err, "fetching metadata")
+	}
+
+	metaReader := meta.ToReader()
+	defer metaReader.Close()
+
+	metaFormatted, err := readMetadata(metaReader)
+	if err != nil {
+		return groupMeta.ConversationPostMetadata{},
+			clues.WrapWC(ctx, err, "deserializing metadata")
+	}
+
+	return metaFormatted, nil
+}
+
+// getMetadata reads and parses the metadata info for an item
+func readMetadata(metaRC io.ReadCloser) (groupMeta.ConversationPostMetadata, error) {
+	var meta groupMeta.ConversationPostMetadata
+
+	metaraw, err := io.ReadAll(metaRC)
+	if err != nil {
+		return groupMeta.ConversationPostMetadata{}, err
+	}
+
+	err = json.Unmarshal(metaraw, &meta)
+	if err != nil {
+		return groupMeta.ConversationPostMetadata{}, err
+	}
+
+	return meta, nil
+}