fix: Encode data message content as raw JSON

When encoding a data message, the content should
remain unmodified. When it is typed as a `[]byte`,
it ends up getting encoded in base64. Typing it as
`json.RawMessage` ensures the content is
unmodified when marshaled into JSON.

Signed-off-by: Link Dupont <link@sub-pop.net>

CONTRIBUTING.md

@@ -79,7 +79,7 @@ You should see the message logged to the output of `sub` in [Terminal
 Now publish a data message containing the string "hello" to the `echo` worker.
 
 ```
-echo "hello" | \
+echo '"hello"' | \
 go run ./cmd/yggctl generate data-message --directive echo - | \
 pub -broker tcp://localhost:1883 -topic yggdrasil/$(hostname)/data/in
 ```
@@ -253,7 +253,7 @@ Similarly, a data message can be published to a client using `yggctl generate`
 and `pub`.
 
 ```
-echo "hello" | \
+echo '"hello"' | \
 yggctl generate data-message --directive echo - | \
 pub -broker tcp://localhost:1883 -topic yggdrasil/$(hostname)/data/in
 ```
@@ -264,7 +264,7 @@ It is also possible to send data directly to a worker. This method does not publ
 a message to the MQTT broker. Instead, it calls a D-Bus method:
 
 ```bash
-echo -n "hello" | yggctl dispatch -w "echo" -
+echo -n '"hello"' | yggctl dispatch -w "echo" -
 ```
 
 # Code Guidelines

messages.go

@@ -118,7 +118,7 @@ type Data struct {
 	Sent       time.Time         `json:"sent"`
 	Directive  string            `json:"directive"`
 	Metadata   map[string]string `json:"metadata"`
-	Content    []byte            `json:"content"`
+	Content    json.RawMessage   `json:"content"`
 }
 
 // A WorkerMessage represents the structure of a journal entry in the