bug: nonce on all operation to prevent id collision

2 files changed, 14 insertions, 4 deletions

diff --git a/entity/dag/operation.go b/entity/dag/operation.go
index b0a78de6..94974a82 100644
--- a/entity/dag/operation.go
+++ b/entity/dag/operation.go
@@ -10,13 +10,23 @@ import (
 // data structure and storage.
 type Operation interface {
 	// Id return the Operation identifier
+	//
 	// Some care need to be taken to define a correct Id derivation and enough entropy in the data used to avoid
 	// collisions. Notably:
-	// - the Id of the first Operation will be used as the Id of the Entity. Collision need to be avoided across entities of the same type
-	//   (example: no collision within the "bug" namespace).
+	// - the Id of the first Operation will be used as the Id of the Entity. Collision need to be avoided across entities
+	//   of the same type (example: no collision within the "bug" namespace).
 	// - collisions can also happen within the set of Operations of an Entity. Simple Operation might not have enough
 	//   entropy to yield unique Ids (example: two "close" operation within the same second, same author).
-	// A common way to derive an Id will be to use the DeriveId function on the serialized operation data.
+	//   If this is a concern, it is recommended to include a piece of random data in the operation's data, to guarantee
+	//   a minimal amount of entropy and avoid collision.
+	//
+	//   Author's note: I tried to find a clever way around that inelegance (stuffing random useless data into the stored
+	//   structure is not exactly elegant) but I failed to find a proper way. Essentially, anything that would reuse some
+	//   other data (parent operation's Id, lamport clock) or the graph structure (depth) impose that the Id would only
+	//   make sense in the context of the graph and yield some deep coupling between Entity and Operation. This in turn
+	//   make the whole thing even less elegant.
+	//
+	// A common way to derive an Id will be to use the entity.DeriveId() function on the serialized operation data.
 	Id() entity.Id
 	// Validate check if the Operation data is valid
 	Validate() error
diff --git a/entity/id.go b/entity/id.go
index b602452e..c8dbdb94 100644
--- a/entity/id.go
+++ b/entity/id.go
@@ -18,7 +18,7 @@ const UnsetId = Id("unset")
 // Id is an identifier for an entity or part of an entity
 type Id string
 
-// DeriveId generate an Id from some data, taken from a root part of the entity.
+// DeriveId generate an Id from the serialization of the object or part of the object.
 func DeriveId(data []byte) Id {
 	// My understanding is that sha256 is enough to prevent collision (git use that, so ...?)
 	// If you read this code, I'd be happy to be schooled.