Attachments failed to replicate when deleted and recreated

[sethrosetter]

This also fails with Android (1.3.1-30) and .NET (1.3.1-13)

Failing test - https://github.com/couchbaselabs/mobile-testkit/blob/feature/add-multiple-sg-replication-test/testsuites/listener/shared/client_sg/attachments.py#L14-L86

Steps to reproduce:

1. Start continuous replication between LiteServ and Sync Gateway
2. Add a few docs with large attachements to LiteServ
3. Immediately after delete the docs on LiteServ
4. Recreate the docs on LiteServ with the same id and attachment (rev = 3-xxxxx)
5. The recreated attachement docs do not sync to sync gateway

Expected: Recreated attachment docs would sync
Actual: They do not

I am seeing these errors in the logs

14:21:50.655‖ WARNING: CBLRestPusher[http://192.168.0.49:4985/db]: _bulk_docs got an error: {
    error = "bad_request";
    id = "large_attach_0";
    reason = "Missing digest in stub attachment \"golden_gate_large.jpg\"";
    status = 400;
} {at __40-[CBLRestPusher uploadBulkDocs:changes:]_block_invoke:402}
14:21:50.655‖ WARNING: CBLRestPusher[http://192.168.0.49:4985/db]: _bulk_docs got an error: {
    error = "bad_request";
    id = "large_attach_1";
    reason = "Missing digest in stub attachment \"golden_gate_large.jpg\"";
    status = 400;

---

• Version: 1.3.1-6
• Client OS: Mac OSX
• Server: Sync Gateway 1.3.1-16

[borrrden]

https://github.com/couchbaselabs/mobile-testkit/blob/feature/add-multiple-sg-replication-test/testsuites/listener/shared/client_sg/attachments.py#L82 I don't think this is valid. Purged docs do not replicate

[borrrden]

Analysis:

couchbase-lite-ios/Source/CBLDatabase+Attachments.m

Line 303 in 2d6e635

return @{@"stub": @YES, @"revpos": @(revPos)};

this is the offending area. Include the digest here (it is already on attachment in this case, but need to confirm that this is a valid thing to do. It seems that there is already a stub in this case so really the attachment doesn't need mutating I think?) and the test can proceed. .NET will pass the test with this change and a small .NET specific one.

[snej]

I'm not clear how that line relates to this bug. If the doc was deleted and then recreated, doesn't the new revision's attachment have a revpos=3? If so, it wouldn't hit the offending line.

[borrrden]

It doesn't. It still has revpos=1 (in some cases...)

[borrrden]

Analysis: The following sequence triggers this behavior:

1. PUT document with attachment
2. DELETE document
3. PUT document with attachment and no rev-id

In particular the third call without the revid causes the process attachments method to get a nil previous revision and default to generation 1

[pasin]

Once couchbase/couchbase-lite-net#790 is merged, I can port the fix to the iOS platform.