Creating index with "ddoc":"" makes DB read-only

[ermouth]

Expected Behavior

CouchDB should prevent creation of Mango index ddoc with the _design/ _id.

Current Behavior

POST-ing JSON body with "ddoc":"" field to /db/_index creates a ddoc, which seems non-deletable, effectively breaks replication and makes DB non-writable (both PUT and POST fail with 500).

Steps to Reproduce

1. Open Fauxton
2. Create a DB
3. Open Mango query tab and then Mango indexes
4. Create index with any name and "ddoc":"" field

Context

I was creating Mango index editor in Couch Photon, and noticed the issue during UI tests.

Your Environment

• Version used: CouchDB 2.1.2 single node
• Browser Name and version: Chrome 66
• Operating System and version (desktop or mobile): Xenial

[wohali]

@ermouth I think this was fixed for 2.2.0, see #961

[wohali]

if not let me know and we can reopen

[ermouth]

#961 is unrelated. Letting you know it is not fixed in 2.2.x branch. Just built 2.2.0 from sources to check it.

[wohali]

Confirmed:

$ curl -X PUT localhost:15984/abc
{"error":"file_exists","reason":"The database could not be created, the file already exists."}
$ curl -X POST -H "Content-Type: application/json" localhost:15984/abc/_index -d '{"ddoc":"", "index":{"fields": ["food"]}}'
{"result":"created","id":"_design/","name":"3c4336c43e5e1a54362c91818f3909a95ba10120"}
$ curl localhost:15984/abc/_design
{"error":"not_found","reason":"missing"}
$ curl localhost:15984/abc/_design/
{"error":"not_found","reason":"missing"}
$ curl localhost:15984/abc/_all_docs
{"total_rows":3,"offset":0,"rows":[
{"id":"_design/","key":"_design/","value":{"rev":"1-b17f56e26b76133f3c9dc111f6222da6"}},
{"id":"a","key":"a","value":{"rev":"1-73a83873149212c382ed9432f4df7b3a"}},
{"id":"b","key":"b","value":{"rev":"1-0f07c7dbc9a29f0d0c2729f9c61f5411"}}
]}

[nickva]

This still happens. With auto-indexer (ken) it's even worse as it will start crashing as well and flooding the logs with failures that look like:

[error] 2021-11-04T17:19:00.390502Z [email protected] emulator -------- Error in process <0.16318.0> on node '[email protected]' with exit value:
{{nocatch,{illegal_docid,<<"Illegal document id `_design/`">>}},[{couch_doc,validate_docid,1,[{file,"src/couch_doc.erl"},{line,213}]},{couch_doc,transfer_fields,3,[{file,"src/couch_doc.erl"},{line,252}]},{ken_server,'-update_db_indexes/2-fun-1-',4,[{file,"src/ken_server.erl"},{line,280}]},{lists,foldl,3,[{file,"lists.erl"},{line,1263}]},{ken_server,update_db_indexes,2,[{file,"src/ken_server.erl"},{line,279}]}]}

[jaydoane]

It appears that #3990 fixes this issue, so closing as resolved.