cli: implement new 'flattened JSON' mode.

Much nicer for grepping, since `{ "foo": { "bar": [7] } }` is turned into
`foo.bar[0]=7`.

Changelog-Added: cli: New `--flat` mode for easy grepping.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

cli/lightning-cli.c

@@ -78,6 +78,49 @@ static size_t human_readable(const char *buffer, const jsmntok_t *t, char term)
 	abort();
 }
 
+/* Returns number of tokens digested */
+static size_t flat_json(const char *prefix,
+			const char *buffer, const jsmntok_t *t)
+{
+	size_t i, n;
+	char *p;
+
+	switch (t->type) {
+	case JSMN_PRIMITIVE:
+	case JSMN_STRING:
+		printf("%s=%.*s\n",
+		       prefix, t->end - t->start, buffer + t->start);
+		return 1;
+	case JSMN_ARRAY:
+		n = 1;
+		for (i = 0; i < t->size; i++) {
+			p = tal_fmt(NULL, "%s[%zi]", prefix, i);
+			n += flat_json(p, buffer, t + n);
+			tal_free(p);
+		}
+		return n;
+	case JSMN_OBJECT:
+		n = 1;
+		for (i = 0; i < t->size; i++) {
+			if (streq(prefix, ""))
+				p = tal_fmt(NULL, "%.*s",
+					    t[n].end - t[n].start,
+					    buffer + t[n].start);
+			else
+				p = tal_fmt(NULL, "%s.%.*s", prefix,
+					    t[n].end - t[n].start,
+					    buffer + t[n].start);
+			n++;
+			n += flat_json(p, buffer, t + n);
+			tal_free(p);
+		}
+		return n;
+	case JSMN_UNDEFINED:
+		break;
+	}
+	abort();
+}
+
 static int compare_tok(const jsmntok_t *a, const jsmntok_t *b,
 		       const char *buffer)
 {
@@ -184,6 +227,7 @@ enum format {
 	JSON,
 	HUMAN,
 	HELPLIST,
+	FLAT,
 	DEFAULT_FORMAT,
 	RAW
 };
@@ -194,6 +238,12 @@ static char *opt_set_human(enum format *format)
 	return NULL;
 }
 
+static char *opt_set_flat(enum format *format)
+{
+	*format = FLAT;
+	return NULL;
+}
+
 static char *opt_set_json(enum format *format)
 {
 	*format = JSON;
@@ -454,6 +504,8 @@ int main(int argc, char *argv[])
 			   "<command> [<params>...]", "Show this message. Use the command help (without hyphens -- \"lightning-cli help\") to get a list of all RPC commands");
 	opt_register_noarg("-H|--human-readable", opt_set_human, &format,
 			   "Human-readable output (default for 'help')");
+	opt_register_noarg("-F|--flat", opt_set_flat, &format,
+			   "Flatten output ('x.y.x=' format)");
 	opt_register_noarg("-J|--json", opt_set_json, &format,
 			   "JSON output (default unless 'help')");
 	opt_register_noarg("-R|--raw", opt_set_raw, &format,
@@ -624,6 +676,9 @@ int main(int argc, char *argv[])
 		case HUMAN:
 			human_readable(resp, result, '\n');
 			break;
+		case FLAT:
+			flat_json("", resp, result);
+			break;
 		case JSON:
 			print_json(resp, result, "");
 			printf("\n");

tests/test_misc.py

@@ -1063,6 +1063,17 @@ def test_cli(node_factory):
     assert [l for l in lines if l.startswith('help=')] == []
     assert [l for l in lines if l.startswith('format-hint=')] == []
 
+    # Flat format is great for grep.  LONG LIVE UNIX!
+    out = subprocess.check_output(['cli/lightning-cli',
+                                   '--network={}'.format(TEST_NETWORK),
+                                   '--lightning-dir={}'
+                                   .format(l1.daemon.lightning_dir),
+                                   '-F',
+                                   'help']).decode('utf-8')
+    lines = out.splitlines()
+    # Everything is a help[XX]= line, except format-hint.
+    assert [l for l in lines if not re.search(r'^help\[[0-9]*\].', l)] == ['format-hint=simple']
+
 
 def test_daemon_option(node_factory):
     """