Add Protocol Error JSON Schema

protocol-spec/json-schema/ProtocolError.schema.json

@@ -0,0 +1,44 @@
+{
+    "definitions": {},
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "$id": "urn:cadmium:1",
+    "type": "object",
+    "title": "Protocol Error Schema",
+    "required": [
+      "errCode",
+      "errText"
+    ],
+    "additionalProperties": false,
+    "properties": {
+      "errCode": {
+        "$id": "#/properties/errCode",
+        "type": "integer",
+        "title": "Error Code",
+        "description": "Error code (defined in extensions, may be same per extensions)",
+        "examples": [
+          0,
+          1,
+          2,
+          3,
+          4
+        ]
+      },
+      "errText": {
+        "$id": "#/properties/errText",
+        "type": "string",
+        "title": "Error Text",
+        "description": "Explanation of error in human-readable view",
+        "examples": [
+          "Incorrect type of message (type isn't implemented in the server)",
+          "Rate-limit exceed"
+        ],
+        "pattern": "^(.*)$"
+      },
+      "errPayload": {
+        "$id": "#/properties/errPayload",
+        "type": "object",
+        "title": "Error Payload",
+        "description": "Advanced error information (fields defined in extensions)"
+      }
+    }
+  }