Create /var/cache/ddclient if it doesn't exist

Fixes #76

Makefile.am

@@ -70,7 +70,8 @@ AM_PL_LOG_FLAGS = -Mstrict -w \
 	-I'$(abs_top_srcdir)'/t/lib
 handwritten_tests = \
 	t/geturl_connectivity.pl \
-	t/parse_assignments.pl
+	t/parse_assignments.pl \
+	t/write_cache.pl
 generated_tests = \
 	t/version.pl
 TESTS = $(handwritten_tests) $(generated_tests)

configure.ac

@@ -37,6 +37,8 @@ AC_SUBST([PERL])
 # package doesn't depend on all of them, so their availability can't
 # be assumed.
 m4_foreach_w([_m], [
+    File::Basename
+    File::Path
     version=0.77
   ], [AX_PROG_PERL_MODULES([_m], [],
          [AC_MSG_ERROR([missing required Perl module _m])])])
@@ -45,6 +47,8 @@ m4_foreach_w([_m], [
 # then some tests will fail. Only prints a warning if not installed.
 m4_foreach_w([_m], [
     Data::Dumper
+    File::Spec::Functions
+    File::Temp
     Test::More
   ], [AX_PROG_PERL_MODULES([_m], [],
          [AC_MSG_WARN([some tests will fail due to missing module _m])])])

ddclient.in

@@ -22,6 +22,8 @@ package ddclient;
 require v5.10.1;
 use strict;
 use warnings;
+use File::Basename;
+use File::Path qw(make_path);
 use Getopt::Long;
 use Sys::Hostname;
 use IO::Socket;
@@ -997,6 +999,16 @@ sub write_cache {
 
     ## write the updates and other entries to the cache file.
     if ($file) {
+        (undef, my $dir) = fileparse($file);
+        make_path($dir, { error => \my $err }) if !-d $dir;
+        if ($err && @$err) {
+            for my $diag (@$err) {
+                my ($f, $msg) = %$diag;
+                warning("Failed to create cache file directory: %s: %s", $f, $msg);
+            }
+            return;
+        }
+
         $saved_cache = undef;
         local *FD;
         if (!open(FD, "> $file")) {

t/write_cache.pl

@@ -0,0 +1,46 @@
+use Test::More;
+use File::Spec::Functions;
+use File::Temp;
+eval { require Test::MockModule; } or plan(skip_all => $@);
+SKIP: { eval { require Test::Warnings; } or skip($@, 1); }
+eval { require 'ddclient'; } or BAIL_OUT($@);
+
+my $warning;
+
+my $module = Test::MockModule->new('ddclient');
+$module->redefine('warning', sub {
+    BAIL_OUT("warning already logged") if defined($warning);
+    $warning = sprintf(shift, @_);
+});
+my $tmpdir = File::Temp->newdir();
+my $dir = $tmpdir->dirname();
+diag("temporary directory: $dir");
+
+sub tc {
+    return {
+        name => shift,
+        f => shift,
+        warning_regex => shift,
+    };
+}
+
+my @test_cases = (
+    tc("create cache file",    catfile($dir, 'a', 'b', 'cachefile'),        undef),
+    tc("overwrite cache file", catfile($dir, 'a', 'b', 'cachefile'),        undef),
+    tc("bad directory",        catfile($dir, 'a', 'b', 'cachefile', 'bad'), qr/File exists/),
+);
+
+for my $tc (@test_cases) {
+    $warning = undef;
+    ddclient::write_cache($tc->{f});
+    subtest $tc->{name} => sub {
+        if (defined($tc->{warning_regex})) {
+            like($warning, $tc->{warning_regex}, "expected warning message");
+        } else {
+            ok(!defined($warning), "no warning");
+            ok(-f $tc->{f}, "cache file exists");
+        }
+    };
+}
+
+done_testing();