common: new function command_log to log something about a specific command.

Needs implementations for lightningd and libplugin, since they both use this
infrastructure.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/json_command.h

@@ -6,6 +6,7 @@
 #include <ccan/compiler/compiler.h>
 #include <common/json_parse.h>
 #include <common/jsonrpc_errors.h>
+#include <common/status_levels.h>
 
 struct command;
 struct command_result;
@@ -33,6 +34,11 @@ command_fail_badparam(struct command *cmd,
 			    json_tok_full(buffer, tok));
 }
 
+/* Do some logging (complaining!) about this command misuse */
+void command_log(struct command *cmd, enum log_level level,
+		 const char *fmt, ...)
+	PRINTF_FMT(3, 4);
+
 /* Also caller supplied: is this invoked simply to get usage? */
 bool command_usage_only(const struct command *cmd);
 

lightningd/jsonrpc.c

@@ -1483,6 +1483,20 @@ bool command_dev_apis(const struct command *cmd)
 	return cmd->ld->developer;
 }
 
+void command_log(struct command *cmd, enum log_level level,
+		 const char *fmt, ...)
+{
+	const char *msg;
+	va_list ap;
+
+	va_start(ap, fmt);
+	msg = tal_vfmt(cmd, fmt, ap);
+	log_(cmd->ld->log, level, NULL, level >= LOG_UNUSUAL,
+	     "JSON COMMAND %s: %s",
+	     cmd->json_cmd->name, msg);
+	va_end(ap);
+}
+
 void command_set_usage(struct command *cmd, const char *usage TAKES)
 {
 	usage = tal_strdup(cmd->ld, usage);

plugins/libplugin.c

@@ -631,6 +631,19 @@ bool command_check_only(const struct command *cmd)
 	return cmd->check;
 }
 
+void command_log(struct command *cmd, enum log_level level,
+		 const char *fmt, ...)
+{
+	const char *msg;
+	va_list ap;
+
+	va_start(ap, fmt);
+	msg = tal_vfmt(cmd, fmt, ap);
+	plugin_log(cmd->plugin, level, "JSON COMMAND %s: %s",
+		   cmd->methodname, msg);
+	va_end(ap);
+}
+
 struct command_result *command_check_done(struct command *cmd)
 {
 	assert(command_check_only(cmd));