Support config file line continuation

1. Allow to use the line continuation, which is indicated by \ before the new line character, in config files.
2. Add a new testcase "247-config-line-continuation.t" for
    a). testing line continuation
    b). making sure string escaping still works
    c). testing line continuations within a string
    b). testing line continuations with too many lines

docs/userguide

@@ -1078,6 +1078,19 @@ show_marks yes|no
 show_marks yes
 --------------
 
+[[line_continuation]]
+
+=== Line continuation
+
+Config files support line continuation, which is indicated by \ before the
+new line character.
+
+*Examples*:
+-------------------
+bindsym Mod1+f \
+fullscreen toggle
+-------------------
+
 == Configuring i3bar
 
 The bar at the bottom of your monitor is drawn by a separate process called

src/config_parser.c

@@ -837,11 +837,11 @@ static char *migrate_config(char *input, off_t size) {
  */
 bool parse_file(const char *f, bool use_nagbar) {
     SLIST_HEAD(variables_head, Variable) variables = SLIST_HEAD_INITIALIZER(&variables);
-    int fd, ret, read_bytes = 0;
+    int fd;
     struct stat stbuf;
     char *buf;
     FILE *fstr;
-    char buffer[1026], key[512], value[512];
+    char buffer[4096], key[512], value[512], *continuation = NULL;
 
     if ((fd = open(f, O_RDONLY)) == -1)
         die("Could not open configuration file: %s\n", strerror(errno));
@@ -850,27 +850,30 @@ bool parse_file(const char *f, bool use_nagbar) {
         die("Could not fstat file: %s\n", strerror(errno));
 
     buf = scalloc((stbuf.st_size + 1) * sizeof(char));
-    while (read_bytes < stbuf.st_size) {
-        if ((ret = read(fd, buf + read_bytes, (stbuf.st_size - read_bytes))) < 0)
-            die("Could not read(): %s\n", strerror(errno));
-        read_bytes += ret;
-    }
-
-    if (lseek(fd, 0, SEEK_SET) == (off_t)-1)
-        die("Could not lseek: %s\n", strerror(errno));
 
     if ((fstr = fdopen(fd, "r")) == NULL)
         die("Could not fdopen: %s\n", strerror(errno));
 
     while (!feof(fstr)) {
-        if (fgets(buffer, 1024, fstr) == NULL) {
+        if (!continuation)
+            continuation = buffer;
+        if (fgets(continuation, sizeof(buffer) - (continuation - buffer), fstr) == NULL) {
             if (feof(fstr))
                 break;
             die("Could not read configuration file\n");
         }
+        if (buffer[strlen(buffer) - 1] != '\n') {
+            ELOG("Use continuation with too many lines\n");
+        }
+        continuation = strstr(buffer, "\\\n");
+        if (continuation) {
+            continue;
+        }
+
+        strncpy(buf + strlen(buf), buffer, strlen(buffer) + 1);
 
         /* sscanf implicitly strips whitespace. Also, we skip comments and empty lines. */
-        if (sscanf(buffer, "%s %[^\n]", key, value) < 1 ||
+        if (sscanf(buffer, "%511s %511[^\n]", key, value) < 1 ||
             key[0] == '#' || strlen(key) < 3)
             continue;
 

testcases/t/247-config-line-continuation.t

@@ -0,0 +1,201 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • http://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • http://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • http://build.i3wm.org/docs/ipc.html
+#   (or docs/ipc)
+#
+# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+#   (unless you are already familiar with Perl)
+#
+# Checks that the line continuation are parsed correctly
+#
+
+use i3test i3_autostart => 0;
+
+# starts i3 with the given config, opens a window, returns its border style
+sub launch_get_border {
+    my ($config) = @_;
+
+    my $pid = launch_with_config($config);
+
+    my $i3 = i3(get_socket_path(0));
+    my $tmp = fresh_workspace;
+
+    my $window = open_window(name => '"special title"');
+
+    my @content = @{get_ws_content($tmp)};
+    cmp_ok(@content, '==', 1, 'one node on this workspace now');
+    my $border = $content[0]->{border};
+
+    exit_gracefully($pid);
+
+    return $border;
+}
+
+#####################################################################
+# test string escaping
+#####################################################################
+
+my $config = <<'EOT';
+# i3 config file (v4)
+font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+
+set $vartest \"special title\"
+for_window [title="$vartest"] border none
+EOT
+
+is(launch_get_border($config), 'none', 'no border');
+
+#####################################################################
+# test the line continuation
+#####################################################################
+
+$config = <<'EOT';
+# i3 config file (v4)
+font \
+-misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+
+# Use line contiuation with too many lines (>4096 characters).
+# This config is invalid. Use it to ensure no buffer overflow.
+bindsym Mod1+b \
+0001-This is a very very very very very very very very very very very very very very very very very long cmd \
+0002-This is a very very very very very very very very very very very very very very very very very long cmd \
+0003-This is a very very very very very very very very very very very very very very very very very long cmd \
+0004-This is a very very very very very very very very very very very very very very very very very long cmd \
+0005-This is a very very very very very very very very very very very very very very very very very long cmd \
+0006-This is a very very very very very very very very very very very very very very very very very long cmd \
+0007-This is a very very very very very very very very very very very very very very very very very long cmd \
+0008-This is a very very very very very very very very very very very very very very very very very long cmd \
+0009-This is a very very very very very very very very very very very very very very very very very long cmd \
+0010-This is a very very very very very very very very very very very very very very very very very long cmd \
+0011-This is a very very very very very very very very very very very very very very very very very long cmd \
+0012-This is a very very very very very very very very very very very very very very very very very long cmd \
+0013-This is a very very very very very very very very very very very very very very very very very long cmd \
+0014-This is a very very very very very very very very very very very very very very very very very long cmd \
+0015-This is a very very very very very very very very very very very very very very very very very long cmd \
+0016-This is a very very very very very very very very very very very very very very very very very long cmd \
+0017-This is a very very very very very very very very very very very very very very very very very long cmd \
+0018-This is a very very very very very very very very very very very very very very very very very long cmd \
+0019-This is a very very very very very very very very very very very very very very very very very long cmd \
+0020-This is a very very very very very very very very very very very very very very very very very long cmd \
+0021-This is a very very very very very very very very very very very very very very very very very long cmd \
+0022-This is a very very very very very very very very very very very very very very very very very long cmd \
+0023-This is a very very very very very very very very very very very very very very very very very long cmd \
+0024-This is a very very very very very very very very very very very very very very very very very long cmd \
+0025-This is a very very very very very very very very very very very very very very very very very long cmd \
+0026-This is a very very very very very very very very very very very very very very very very very long cmd \
+0027-This is a very very very very very very very very very very very very very very very very very long cmd \
+0028-This is a very very very very very very very very very very very very very very very very very long cmd \
+0029-This is a very very very very very very very very very very very very very very very very very long cmd \
+0030-This is a very very very very very very very very very very very very very very very very very long cmd \
+0031-This is a very very very very very very very very very very very very very very very very very long cmd \
+0032-This is a very very very very very very very very very very very very very very very very very long cmd \
+0033-This is a very very very very very very very very very very very very very very very very very long cmd \
+0034-This is a very very very very very very very very very very very very very very very very very long cmd \
+0035-This is a very very very very very very very very very very very very very very very very very long cmd \
+0036-This is a very very very very very very very very very very very very very very very very very long cmd \
+0037-This is a very very very very very very very very very very very very very very very very very long cmd \
+0038-This is a very very very very very very very very very very very very very very very very very long cmd \
+0039-This is a very very very very very very very very very very very very very very very very very long cmd \
+0040-This is a very very very very very very very very very very very very very very very very very long cmd \
+0041-This is a very very very very very very very very very very very very very very very very very long cmd \
+0042-This is a very very very very very very very very very very very very very very very very very long cmd \
+0043-This is a very very very very very very very very very very very very very very very very very long cmd \
+0044-This is a very very very very very very very very very very very very very very very very very long cmd \
+0045-This is a very very very very very very very very very very very very very very very very very long cmd \
+0046-This is a very very very very very very very very very very very very very very very very very long cmd \
+0047-This is a very very very very very very very very very very very very very very very very very long cmd \
+0048-This is a very very very very very very very very very very very very very very very very very long cmd \
+0049-This is a very very very very very very very very very very very very very very very very very long cmd \
+0050-This is a very very very very very very very very very very very very very very very very very long cmd \
+0051-This is a very very very very very very very very very very very very very very very very very long cmd \
+0052-This is a very very very very very very very very very very very very very very very very very long cmd \
+0053-This is a very very very very very very very very very very very very very very very very very long cmd \
+0054-This is a very very very very very very very very very very very very very very very very very long cmd \
+0055-This is a very very very very very very very very very very very very very very very very very long cmd \
+0056-This is a very very very very very very very very very very very very very very very very very long cmd \
+0057-This is a very very very very very very very very very very very very very very very very very long cmd \
+0058-This is a very very very very very very very very very very very very very very very very very long cmd \
+0059-This is a very very very very very very very very very very very very very very very very very long cmd \
+0060-This is a very very very very very very very very very very very very very very very very very long cmd \
+0061-This is a very very very very very very very very very very very very very very very very very long cmd \
+0062-This is a very very very very very very very very very very very very very very very very very long cmd \
+0063-This is a very very very very very very very very very very very very very very very very very long cmd \
+0064-This is a very very very very very very very very very very very very very very very very very long cmd \
+0065-This is a very very very very very very very very very very very very very very very very very long cmd \
+0066-This is a very very very very very very very very very very very very very very very very very long cmd \
+0067-This is a very very very very very very very very very very very very very very very very very long cmd \
+0068-This is a very very very very very very very very very very very very very very very very very long cmd \
+0069-This is a very very very very very very very very very very very very very very very very very long cmd \
+0070-This is a very very very very very very very very very very very very very very very very very long cmd \
+0071-This is a very very very very very very very very very very very very very very very very very long cmd \
+0072-This is a very very very very very very very very very very very very very very very very very long cmd \
+0073-This is a very very very very very very very very very very very very very very very very very long cmd \
+0074-This is a very very very very very very very very very very very very very very very very very long cmd \
+0075-This is a very very very very very very very very very very very very very very very very very long cmd \
+0076-This is a very very very very very very very very very very very very very very very very very long cmd \
+0077-This is a very very very very very very very very very very very very very very very very very long cmd \
+0078-This is a very very very very very very very very very very very very very very very very very long cmd \
+0079-This is a very very very very very very very very very very very very very very very very very long cmd \
+0080-This is a very very very very very very very very very very very very very very very very very long cmd \
+0081-This is a very very very very very very very very very very very very very very very very very long cmd \
+0082-This is a very very very very very very very very very very very very very very very very very long cmd \
+0083-This is a very very very very very very very very very very very very very very very very very long cmd \
+0084-This is a very very very very very very very very very very very very very very very very very long cmd \
+0085-This is a very very very very very very very very very very very very very very very very very long cmd \
+0086-This is a very very very very very very very very very very very very very very very very very long cmd \
+0087-This is a very very very very very very very very very very very very very very very very very long cmd \
+0088-This is a very very very very very very very very very very very very very very very very very long cmd \
+0089-This is a very very very very very very very very very very very very very very very very very long cmd \
+0090-This is a very very very very very very very very very very very very very very very very very long cmd \
+0091-This is a very very very very very very very very very very very very very very very very very long cmd \
+0092-This is a very very very very very very very very very very very very very very very very very long cmd \
+0093-This is a very very very very very very very very very very very very very very very very very long cmd \
+0094-This is a very very very very very very very very very very very very very very very very very long cmd \
+0095-This is a very very very very very very very very very very very very very very very very very long cmd \
+0096-This is a very very very very very very very very very very very very very very very very very long cmd \
+0097-This is a very very very very very very very very very very very very very very very very very long cmd \
+0098-This is a very very very very very very very very very very very very very very very very very long cmd \
+0099-This is a very very very very very very very very very very very very very very very very very long cmd
+
+# Use line continuation for variables
+set \
+$vartest \
+\"special title\"
+
+# Use line continuation for commands
+for_window \
+[title="$vartest"] \
+border \
+none
+
+EOT
+
+is(launch_get_border($config), 'none', 'no border');
+
+#####################################################################
+# test the line continuation within a string
+#####################################################################
+
+$config = <<'EOT';
+# i3 config file (v4)
+font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+
+set \
+$vartest \
+\"special \
+title\"
+for_window [title="$vartest"] border none
+EOT
+
+is(launch_get_border($config), 'none', 'no border');
+
+
+done_testing;