allow eml export when attachments have no name (#5199)

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

- [x] ✅ Yes, it's included

#### Type of change

- [x] 🐛 Bugfix

#### Test Plan

- [x] ⚡ Unit test
- [x] 💚 E2E

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 - Handle the case where an email or event cannot be retrieved from Exchange due to an `ErrorCorruptData` error. Corso will skip over the item but report it in the backup summary.
 - Emails attached within other emails are now correctly exported
+- Gracefully handle email and post attachments without name when exporting to eml
 
 ## [v0.19.0] (beta) - 2024-02-06
 

src/internal/converters/eml/eml.go

@@ -171,6 +171,13 @@ func getFileAttachment(ctx context.Context, attachment models.Attachmentable) (*
 	}
 
 	name := ptr.Val(attachment.GetName())
+	if len(name) == 0 {
+		// Graph as of now does not let us create any attachments
+		// without a name, but we have run into instances where we have
+		// see attachments without a name, possibly from old
+		// data. This is for those cases.
+		name = "Unnamed"
+	}
 
 	contentID, err := attachment.GetBackingStore().Get("contentId")
 	if err != nil {
@@ -472,6 +479,9 @@ func FromJSONPostToEML(
 			}
 
 			name := ptr.Val(attachment.GetName())
+			if len(name) == 0 {
+				name = "Unnamed"
+			}
 
 			contentID, err := attachment.GetBackingStore().Get("contentId")
 			if err != nil {

src/internal/converters/eml/eml_test.go

@@ -162,6 +162,44 @@ func (suite *EMLUnitSuite) TestConvert_edge_cases() {
 				require.NoError(suite.T(), err, "setting attachment content")
 			},
 		},
+		{
+			name: "attachment without name",
+			transform: func(msg models.Messageable) {
+				attachments := msg.GetAttachments()
+				attachments[1].SetName(ptr.To(""))
+
+				// This test has to be run on a non inline attachment
+				// as inline attachments use contentID instead of name
+				// even when there is a name.
+				assert.False(suite.T(), ptr.Val(attachments[1].GetIsInline()))
+			},
+		},
+		{
+			name: "attachment with nil name",
+			transform: func(msg models.Messageable) {
+				attachments := msg.GetAttachments()
+				attachments[1].SetName(nil)
+
+				// This test has to be run on a non inline attachment
+				// as inline attachments use contentID instead of name
+				// even when there is a name.
+				assert.False(suite.T(), ptr.Val(attachments[1].GetIsInline()))
+			},
+		},
+		{
+			name: "multiple attachments without name",
+			transform: func(msg models.Messageable) {
+				attachments := msg.GetAttachments()
+				attachments[1].SetName(ptr.To(""))
+				attachments[2].SetName(ptr.To(""))
+
+				// This test has to be run on a non inline attachment
+				// as inline attachments use contentID instead of name
+				// even when there is a name.
+				assert.False(suite.T(), ptr.Val(attachments[1].GetIsInline()))
+				assert.False(suite.T(), ptr.Val(attachments[2].GetIsInline()))
+			},
+		},
 	}
 
 	for _, test := range tests {

src/internal/converters/eml/testdata/email-with-attachments.json

@@ -104,6 +104,19 @@
       "contentId": null,
       "contentLocation": null,
       "contentBytes": "W1BhdGhzXQpQcmVmaXggPSAuLgo="
+    },
+    {
+      "@odata.type": "#microsoft.graph.fileAttachment",
+      "@odata.mediaContentType": "application/octet-stream",
+      "id": "ZZMkAGJiZmE2NGU4LTQ4YjktNDI1Mi1iMWQzLTQ1MmMxODJkZmQyNABGAAAAAABFdiK7oifWRb4ADuqgSRcnBwBBFDg0JJk7TY1fmsJrh7tNAAAAAAEJAABBFDg0JJk7TY1fmsJrh7tNAAEwbDEWAAABEgAQAD3rU0iyzCdHgz0xmOrWc9g=",
+      "lastModifiedDateTime": "2023-11-16T05:42:47Z",
+      "name": "qt2.conf",
+      "contentType": "application/octet-stream",
+      "size": 156,
+      "isInline": false,
+      "contentId": null,
+      "contentLocation": null,
+      "contentBytes": "Z1BhdGhzXQpQcmVmaXggPSAuLgo="
     }
   ]
 }