Unexpected EOF while decrypting a file

[3c7]

Hey all,

while I cannot rule out I just made a stupid mistake - this is basically my first go "project" - i cannot get my head around why the created reader is not able to read the decrypted data in the following scenario (links to code and the relevant test case):

• A note is generated with dummy title and text
• An attachment is generated with dummy content
• Both get encryted
• Some debug output
• Both get decrypted ⚡

While the note text can be decrypted, during the decryption of the attachment file, the following error is caught in the test:

model_test.go:303: error after reading 0 bytes from decryption reader of attachment 0: unexpected EOF

The function in question is a wrapper around the decryption function which can be found here. The first call to age.Decrypt results in a successful decyption of the note's text. Afterwards a loop iterates over the file attachments of a note and the second call results in the mentioned error. I debugged the code multiple times, but still fail to understand why this happens, so I hope to get some hints what to look for here.

The test routine for reference:

func TestAttachmentEncryption(t *testing.T) {
	note := model.NewNote("Title", "Note")
	attachment := model.NewAttachment("attachment.txt", []byte("This is some data."))
	note.Attachments = append(note.Attachments, attachment)

	i1, err := age.ParseX25519Identity(key)
	if err != nil {
		t.Fatalf("Could not parse identity: %v", err)
	}
	r1 := i1.Recipient()

	enc, err := note.ToEncryptedNote(*r1)
	if err != nil {
		t.Fatal(err)
	}
	j, err := enc.Json()
	if err != nil {
		t.Fatal(err)
	}
	t.Logf(">>> DEBUG: Encrypted note: %s", string(j))
	dec, err := enc.ToDecryptedNote(i1)  // <- error is "generated" here; the function calls 
	if err != nil {
		t.Fatal(err)
	}

	j2, err := json.Marshal(dec)
	if err != nil {
		t.Fatal(err)
	}
	t.Logf(">>> DEBUG: Decrypted note: %s", string(j2))

	if len(dec.Attachments[0].Content) != len(attachment.Content) {
		t.Fatal("Content length mismatch")
	}

	for i := range dec.Attachments[0].Content {
		if dec.Attachments[0].Content[i] != attachment.Content[i] {
			t.Fatalf("Mismatch of content at pos %d.", i)
		}
	}
}

[magical]

In your attachment encryption loop, you call defer w.Close().

https://github.com/3c7/age-encrypted-notebook/blob/1e57ce9cd739e1b2ed6604aff48ba32732ef5de3/internal/model/model.go#L194

These deferred calls run at the end of the function, not at the end of each loop iteration, so the writer is not being properly closed before you append the ciphertext to the encryptedAttachments list.

[3c7]

Thank you very much. Lesson learned!

PASS
ok  	github.com/3c7/aen/internal/model	0.290s

[FiloSottile]

This is a common Go gotcha, you might want to set up staticcheck in your editor, which can flag use of defer in a loop and other similar issues.