Transaction messages/comments metadata

CIP-0020/CIP-0020.md

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+---
+CIP: 20
+Title: Transaction message/comment metadata
+Authors: Martin Lang <martin@martinlang.at>, Ola Ahlman <ola@ahlnet.nu>, Andrew Westberg <andrewwestberg@gmail.com>
+Comments-URI: no comments yet
+Status: Draft
+Type: Informational
+Created: 2021-06-13
+License: CC-BY-4.0
+---
+
+# Abstract
+
+This proposal describes a basic JSON schema to add messages/comments/memos as transaction metadata by using the metadatum label **674**.
+Adding informational text, invoice-numbers or similar to a transaction on the cardano blockchain.
+
+# Motivation
+
+We have the utilities on the cardano blockchain now since the introduction of the "allegra-era". A simple consens about adding messages, comments or memos to transactions is still missing.
+So the CIP authors came together to form a first implementation of this. It is straight and simple, additional keys and content can be added later.
+The IOG main wallet `Daedalus` can now also directly show attached metadata information in the transaction details view. This CIP is the missing link to bring it together.
+
+Current Tools/Sites/Explorers that have implemented it already or have plans to implement it:
+* [CNTools](https://cardano-community.github.io/guild-operators/#/Scripts/cntools)
+* [JorManager](https://bitbucket.org/muamw10/jormanager/)
+* [StakePoolOperator Scripts](https://github.com/gitmachtl/scripts)
+* [Cardanoscan.io](https://cardanoscan.io)
+* [AdaStat.net](https://adastat.net)
+
+# Specification
+
+The specification for the individual strings follow the general design specification for JSON metadata, which is already implemented and in operation on the cardano blockchain.
+The used metadatum label is **`"674":`**, this number was choosen because it is the T9 encoding of the string "msg".
+The message content has the key **`"msg":`** and consists of an array of individual **message-strings**. 
+The number of theses **message-strings** must be at least one for a single message, more for multiple messages/lines. Each of theses individual **message-strings** array entries must be at most 64 bytes when UTF-8 encoded.
+
+Format:
+``` 
+{ 
+  "674":
+         { "msg": 
+                  [ 
+                    "message-string 1" //Optional: ,"message-string 2","message-string 3" ...
+                  ]
+         }
+}
+```
+
+
+
+Example for a single message/comment/memo:
+``` json
+{ 
+  "674":
+         { "msg": 
+                  [ 
+                    "This is a comment for the transaction xyz, thank you very much!"
+                  ]
+         }
+}
+```
+
+Example for multiple messages/comments/memos:
+``` json
+{ 
+  "674":
+         { "msg": 
+                  [ 
+                    "Invoice-No: 1234567890",
+                    "Customer-No: 555-1234",
+                    "P.S.: i will shop again at your store :-)"
+                  ]
+         }
+}
+```
+Example above in Daedalus currently (could be improved if CIP is implemented):
+![image](https://user-images.githubusercontent.com/47434720/121822100-85b38a80-cc9d-11eb-9d13-1869746a69b2.png)
+
+
+# Rationale
+
+This design is simple, so many tools on the cardano blockchain can implement it easily. The array type was choosen to have consistency, no need to switch between a string or
+an array format, or testing against a string or array format. Updates in the future are possible, like adding a versioning key `"ver":`, adding a key `"utxo":` to provide specific data for every tx-out#idx in the transaction, making subarrays in the message-strings, etc. But for now, we need a common agreement to provide general messages/comments/memos with this CIP.
+
+# Copyright
+
+This CIP is licensed under [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/legalcode)