Use saner defaults

So that most of the time users won't need to use any switches.

--pretty-print has been inverted into jq's --compact-output,
and --auto-id has been replaced with barely, if-at-all useful
--null-as-id.

json-rpc-shell.adoc

@@ -27,11 +27,13 @@ processor.
 Usage
 ~~~~~
 Three things may appear on the internal command line, in a sequence.  The first
-one must always be the name of the JSON-RPC method to call, as a bare word,
-separated from the rest by white space.  Following that, you may enter two kinds
-of JSON values.  If it is a string, a number, or a null value, it is taken as
-the "id" to use for the request.  If it is an object or an array, it constitutes
-the method parameters.  Booleans may appear in neither.
+one is always the name of the JSON-RPC method to call, as a bare word, separated
+from the rest by white space.  Following that, you may enter three kinds of JSON
+values.  If it is an object or an array, it constitutes the method parameters.
+If it is a string or a number, it is taken as the "id" to use for the request,
+which would be chosen for you automatically if left unspecified.  Finally,
+a null value indicates that the request should be sent as a notification,
+lacking the ID completely.  Booleans cannot be used for anything.
 
 The response to the method call may be piped through external commands, the same
 way you would do it in a Unix shell.
@@ -43,9 +45,9 @@ Options
 -------
 Controlling Output
 ~~~~~~~~~~~~~~~~~~
-*-p*, *--pretty*::
-	Pretty-print responses, adding spaces and newlines where appropriate
-	to improve readability.
+*-c*, *--compact-output*::
+	Do not pretty-print responses.  Normally, spaces and newlines are added
+	where appropriate to improve readability.
 
 *--color* _WHEN_::
 	By default, when the output of the program is a terminal, JSON responses
@@ -61,11 +63,10 @@ Controlling Output
 
 Protocol
 ~~~~~~~~
-*-a*, *--auto-id*::
-	Choose message IDs automatically, in an increasing sequence.  Normally you
-	need to enter the ID on the command line manually, so as to distinguish
-	notifications from other requests.  Even with this option enabled, you can
-	still specify the ID, if you wish.
+*-n*, *--null-as-id*::
+	Normally, entering a null JSON value on the command line causes
+	a notification to be sent.  With this option, it is sent as the "id"
+	field of a normal request, which is discouraged by the specification.
 
 *-t*, *--trust-all*::
 	Trust all SSL/TLS certificates.  Useful in case that the certificate is
@@ -131,10 +132,12 @@ Examples
 Running some queries against json-rpc-test-server, included in the source
 distribution of this program (public services are hard to find):
 
-Pretty-printing and Manual IDs
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- $ json-rpc-shell -p ws://localhost:1234
- json-rpc> date 1
+Methods Without Parameters
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+ $ json-rpc-shell ws://localhost:1234
+ json-rpc> ping
+ "pong"
+ json-rpc> date
  {
    "year": 2020,
    "month": 9,
@@ -150,7 +153,7 @@ Notifications never produce a response, not even when the method is not known
 to the server:
 
  $ json-rpc-shell ws://localhost:1234
- json-rpc> notify {"events": ["conquest", "war", "famine", "death"]}
+ json-rpc> notify {"events": ["conquest", "war", "famine", "death"]} null
  [Notification]
 
 Piping In and Out
@@ -158,7 +161,7 @@ Piping In and Out
 GNU Readline always repeats the prompt, which makes this a bit less useful
 for invoking from other programs:
 
- $ echo 'ping | jq ascii_upcase' | json-rpc-shell -a ws://localhost:1234
+ $ echo 'ping | jq ascii_upcase' | json-rpc-shell ws://localhost:1234
  json-rpc> ping | jq ascii_upcase
  "PONG"
 

json-rpc-shell.c

@@ -932,11 +932,11 @@ static struct app_context
 
 	struct config config;               ///< Program configuration
 	enum color_mode color_mode;         ///< Colour output mode
-	bool pretty_print;                  ///< Whether to pretty print
+	bool compact;                       ///< Whether to not pretty print
 	bool verbose;                       ///< Print requests
 	bool trust_all;                     ///< Don't verify peer certificates
 
-	bool auto_id;                       ///< Use automatically generated ID's
+	bool null_as_id;                    ///< JSON null is used as an ID
 	int64_t next_id;                    ///< Next autogenerated ID
 
 	iconv_t term_to_utf8;               ///< Terminal encoding to UTF-8
@@ -2845,7 +2845,7 @@ process_response (struct app_context *ctx, const json_t *id, struct str *buf,
 	if (result)
 	{
 		int flags = JSON_ENCODE_ANY;
-		if (ctx->pretty_print)
+		if (!ctx->compact)
 			flags |= JSON_INDENT (2);
 
 		char *utf8 = json_dumps (result, flags);
@@ -3041,9 +3041,16 @@ process_input (char *user_input, void *user_data)
 		*target = json_incref (args[i]);
 	}
 
-	if (!id && ctx->auto_id)
+	if (!id)
 		id = json_integer (ctx->next_id++);
 
+	// Use nulls to send notifications, unless a special switch is used
+	if (!ctx->null_as_id && json_is_null (id))
+	{
+		json_decref (id);
+		id = NULL;
+	}
+
 	make_json_rpc_call (ctx, method, id, params, pipeline);
 
 fail_parse:
@@ -3341,15 +3348,12 @@ parse_program_arguments (struct app_context *ctx, int argc, char **argv,
 		{ 'd', "debug", NULL, 0, "run in debug mode" },
 		{ 'h', "help", NULL, 0, "display this help message and exit" },
 		{ 'V', "version", NULL, 0, "output version information and exit" },
-		// TODO: consider making this the default and instead adding
-		// an option to accept JSON null as an id.
-		{ 'a', "auto-id", NULL, 0, "automatic `id' fields" },
+		{ 'n', "null-as-id", NULL, 0, "JSON null is used as an `id'" },
 		{ 'o', "origin", "O", 0, "set the HTTP Origin header" },
-		// TODO: consider inverting this to -c/--compact-output
-		{ 'p', "pretty", NULL, 0, "pretty-print the responses" },
+		{ 'c', "compact-output", NULL, 0, "do not pretty-print responses" },
 		{ 't', "trust-all", NULL, 0, "don't care about SSL/TLS certificates" },
 		{ 'v', "verbose", NULL, 0, "print raw requests and responses" },
-		{ 'c', "color", "WHEN", OPT_LONG_ONLY,
+		{ 'C', "color", "WHEN", OPT_LONG_ONLY,
 		  "colorize output: never, always, or auto" },
 		{ 'w', "write-default-cfg", "FILENAME",
 		  OPT_OPTIONAL_ARG | OPT_LONG_ONLY,
@@ -3375,12 +3379,12 @@ parse_program_arguments (struct app_context *ctx, int argc, char **argv,
 		exit (EXIT_SUCCESS);
 
 	case 'o': *origin = optarg;         break;
-	case 'a': ctx->auto_id      = true; break;
-	case 'p': ctx->pretty_print = true; break;
+	case 'n': ctx->null_as_id   = true; break;
+	case 'c': ctx->compact      = true; break;
 	case 't': ctx->trust_all    = true; break;
 	case 'v': ctx->verbose      = true; break;
 
-	case 'c':
+	case 'C':
 		if      (!strcasecmp (optarg, "never"))
 			ctx->color_mode = COLOR_NEVER;
 		else if (!strcasecmp (optarg, "always"))