move to using canonicaljson for bundle output

Author: garethr

README.md

@@ -45,7 +45,6 @@ structure based on the current specification and would allow for building a cust
 user interface for generating `bundle.json` files.
 
 ```python
-import json
 from cnab import Bundle, InvocationImage
 
 bundle = Bundle(
@@ -60,7 +59,7 @@ bundle = Bundle(
     ],
 )
 
-print(json.dumps(bundle.to_dict(), indent=4))
+print(bundle.to_json())
 ```
 
 ## Running CNABs

cnab/test_types.py

@@ -51,6 +51,12 @@ def test_convert_bundle_to_dict(self, bundle):
     def test_bundle_description_blank(self, bundle):
         assert not bundle.description
 
+    def test_convert_bundle_to_json(self, bundle):
+        assert isinstance(bundle.to_json(), str)
+
+    def test_convert_bundle_to_pretty_json(self, bundle):
+        assert isinstance(bundle.to_json(pretty=True), str)
+
 
 def test_read_bundle():
     with open("fixtures/helloworld/bundle.json") as f:

cnab/types.py

@@ -1,3 +1,5 @@
+import canonicaljson  # type: ignore
+
 from dataclasses import dataclass, field
 from typing import Optional, Any, List, Union, Dict, TypeVar, Callable, Type, cast
 
@@ -416,3 +418,10 @@ def to_dict(self) -> dict:
         result["schemaVersion"] = from_str(self.schema_version)
         result["version"] = from_str(self.version)
         return clean(result)
+
+    def to_json(self, pretty: bool = False) -> str:
+        if pretty:
+            func = canonicaljson.encode_pretty_printed_json
+        else:
+            func = canonicaljson.encode_canonical_json
+        return func(self.to_dict()).decode()

poetry.lock

@@ -11,6 +11,7 @@ keywords = ["cnab"]
 [tool.poetry.dependencies]
 python = "^3.7"
 docker = { version = "^3.6", optional = true }
+canonicaljson = "^1.1"
 
 [tool.poetry.extras]
 docker = ["docker"]