[GitHub] S-Aggarwal opened a new issue #782: Using custom revision numbers when creating documents

[gi...@git.apache.org]

S-Aggarwal opened a new issue #782: Using custom revision numbers when creating documents
URL: https://github.com/apache/couchdb/issues/782
 
 
   <!--- Provide a general summary of the issue in the Title above -->
   
   We were using our own revision numbers with couchDB 1.6 to mask the number of edits made on a document. This was achieved by adding a "_rev" property to the JSON document we inserted into the database and making an API request with a _rev parameter (as if performing an update). The revision number was generated using the following Go code:
   
   ```go
   // randomRev produces a deterministic revision number from the plaintext, 1-2^16, and a hash
   // After compaction, the number of revisions for a doc is now masked on the server
   // Input should be the document
   func randomRev(doc interface{}) string {
   	encoded, err := json.Marshal(doc)
   	if err != nil {
   		log.Error(errors.Trace(err))
   		return ""
   	}
   	multihash, err := mh.Sum(append([]byte("revsalt"), encoded...), mh.SHA1, 16)
   	if err != nil {
   		log.Error(errors.Trace(err))
   		return ""
   	}
   	revNum := binary.BigEndian.Uint16(multihash[15:17]) // two bytes ie 0-2^16
   	return strconv.Itoa(int(revNum)) + "-" + multihash.HexString()[4:]
   }
   ```
   
   In Couch 1.6, couch treated the document creation as an update and then the revision number was just an increment of what we provided (eg if we gave _rev=41543-c1a310b73245bfac2a69583319a2470c, then after completion the stored document had _rev=41544-<some hash value hexstring>).
   
   In Couch 2.1, this generally doesn't work for the most part and Couch gives us a Document update conflict but what's strange is it seems to work sometimes. 
   Eg
   While inserting 
   ```json
   {
   	"_id": "randomid10",
   	"_rev": "64769-1a0347892643024c68e945015bfd0141",
   	"par" : "test"
   }
   ```
   we get a 409: Document update conflict.
   
   But when inserting
   ```json
   {
   	"_id": "randomid123",
   	"_rev": "41543-c1a310b73245bfac2a69583319a2470c",
   	"par": "test"
   }
   ```
   the document is successfully created. Also adding this same document to a different database (or even the same one after wiping it completely) gives back an update conflict.
   
   I am not sure what is happening behind the scenes here but there seems to be some kind of bug here.
   
 
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