Add support for byte arrrays

A log entry containing a byte encoded message would cause jq to return
an error `cannot add <string> to array`. This converts the message into
a string before adding it to the log stream.

Change-type: minor

format.jq

@@ -16,10 +16,37 @@ def fmt_unit($entry):
   +"]"
 ;
 
+# Convert a byte array into a string
+# Source: https://stackoverflow.com/a/48431552
+
+def btostring:
+	[foreach .[] as $item (
+    	[0, 0]
+    	;
+    	if .[0] > 0 then [.[0] - 1, .[1] * 64 + ($item % 64)]
+    	elif $item >= 240 then [3, $item % 8]
+    	elif $item >= 224 then [2, $item % 16]
+    	elif $item >= 192 then [1, $item % 32]
+    	elif $item < 128 then [0, $item]
+    	else error("Malformed UTF-8 bytes")
+    	end
+    	;
+    	if .[0] == 0 then .[1] else empty end
+	)] | implode
+
+
+def fmt_message($msg):
+	if $msg | type == "array" then
+		$msg | btostring
+	else
+		$msg
+	end
+;
+
 # Select fields from the journalctl output and tranform to
 # a human readable format
 def fmt_entry($entry):
-  [fmt_date($entry.__REALTIME_TIMESTAMP), fmt_unit($entry), .MESSAGE] | join(" ")
+  [fmt_date($entry.__REALTIME_TIMESTAMP), fmt_unit($entry), fmt_message(.MESSAGE)] | join(" ")
 ;
 
 # Process the entry