logv: unescape "\n" and "\\" in the log

Double escape node alias in the log, to print weird node alias
in escaped form.

Fix #4912

lightningd/lightningd.c

@@ -1266,11 +1266,12 @@ int main(int argc, char *argv[])
 	 * formatting.  json_escape() avoids printing weird characters in our
 	 * log.  And tal_hex() is a helper from utils which returns a hex string;
 	 * it's assumed that the argument was allocated with tal or tal_arr
-	 * so it can use tal_bytelen() to get the length. */
+	 * so it can use tal_bytelen() to get the length.
+	 * Double json_escape is needed, because logv unescapes \\ and \n. */
 	log_info(ld->log, "--------------------------------------------------");
 	log_info(ld->log, "Server started with public key %s, alias %s (color #%s) and lightningd %s",
 		 type_to_string(tmpctx, struct node_id, &ld->id),
-		 json_escape(tmpctx, (const char *)ld->alias)->s,
+		 json_escape(tmpctx, json_escape(tmpctx, (const char *)ld->alias)->s)->s,
 		 tal_hex(tmpctx, ld->rgb), version());
 	ld->state = LD_STATE_RUNNING;
 

lightningd/log.c

@@ -560,6 +560,24 @@ void logv(struct logger *log, enum log_level level,
 		if (l->log[i] < ' ' || l->log[i] >= 0x7f)
 			l->log[i] = '?';
 
+	/* Replace "\n" with line breaks and "\\" with "\" in the log, if they exist. */
+	char *write_ptr = l->log;
+	for (size_t i=0; i<log_len; i++) {
+		if (l->log[i] == '\\' && i < log_len-1 && l->log[i+1] == 'n') {
+			// Replace \n with line break.
+			*write_ptr = '\n';
+			i++;
+		} else if (l->log[i] == '\\' && i < log_len-1 && l->log[i+1] == '\\') {
+			// Replace \\ with \.
+			*write_ptr = '\\';
+			i++;
+		} else {
+			*write_ptr = l->log[i];
+		}
+		write_ptr++;
+	}
+	*write_ptr = 0x00;
+
 	maybe_print(log, l);
 
 	add_entry(log, &l);

tests/test_misc.py

@@ -2027,7 +2027,8 @@ def mock_fail(*args):
     l1.daemon.start(wait_for_initialized=False, stderr_redir=True)
     l1.daemon.wait_for_logs([r'getblockhash [a-z0-9]* exited with status 1',
                              r'Unable to estimate any fees',
-                             r'BROKEN.*we have been retrying command for --bitcoin-retry-timeout={} seconds'.format(timeout)])
+                             r'BROKEN',
+                             r'we have been retrying command for --bitcoin-retry-timeout={} seconds'.format(timeout)])
     # Will exit with failure code.
     assert l1.daemon.wait() == 1
 

tests/test_plugin.py

@@ -1575,7 +1575,11 @@ def test_libplugin(node_factory):
     # Test commands
     assert l1.rpc.call("helloworld") == {"hello": "NOT FOUND"}
     l1.daemon.wait_for_log("get_ds_bin_done: 00010203")
-    l1.daemon.wait_for_log("BROKEN.* Datastore gave nonstring result.*00010203")
+    l1.daemon.wait_for_logs([
+        r'BROKEN',
+        r'Datastore gave nonstring result',
+        r'00010203',
+    ])
     assert l1.rpc.call("helloworld", {"name": "test"}) == {"hello": "test"}
     l1.stop()
     l1.daemon.opts["plugin"] = plugin