Add a compat function to check how much disk space is free.

Closes ticket 16734.

configure.ac

@@ -406,6 +406,7 @@ AC_CHECK_FUNCS(
         rint \
         sigaction \
         socketpair \
+	statvfs \
         strlcat \
         strlcpy \
 	strnlen \
@@ -916,6 +917,7 @@ AC_CHECK_HEADERS(
         sys/resource.h \
         sys/select.h \
         sys/socket.h \
+	sys/statvfs.h \
 	sys/sysctl.h \
         sys/syslimits.h \
         sys/time.h \

src/common/compat.c

@@ -68,6 +68,9 @@
 #ifdef HAVE_CRT_EXTERNS_H
 #include <crt_externs.h>
 #endif
+#ifdef HAVE_SYS_STATVFS_H
+#include <sys/statvfs.h>
+#endif
 
 #ifdef _WIN32
 #include <conio.h>
@@ -3374,3 +3377,42 @@ tor_getpass(const char *prompt, char *output, size_t buflen)
 #endif
 }
 
+/** Return the amount of free disk space we have permission to use, in
+ * bytes. Return -1 if the amount of free space can't be determined. */
+int64_t
+tor_get_avail_disk_space(const char *path)
+{
+#ifdef HAVE_STATVFS
+  struct statvfs st;
+  int r;
+  memset(&st, 0, sizeof(st));
+
+  r = statvfs(path, &st);
+  if (r < 0)
+    return -1;
+
+  int64_t result = st.f_bavail;
+  if (st.f_frsize) {
+    result *= st.f_frsize;
+  } else if (st.f_bsize) {
+    result *= st.f_bsize;
+  } else {
+    return -1;
+  }
+
+  return result;
+#elif defined(_WIN32)
+  ULARGE_INTEGER freeBytesAvail;
+  BOOL ok;
+
+  ok = GetDiskFreeSpaceEx(path, &freeBytesAvail, NULL, NULL);
+  if (!ok) {
+    return -1;
+  }
+  return (int64_t)freeBytesAvail;
+#else
+  (void)path;
+  errno = ENOSYS;
+  return -1;
+#endif
+}

src/common/compat.h

@@ -405,6 +405,8 @@ int tor_fd_setpos(int fd, off_t pos);
 int tor_fd_seekend(int fd);
 int tor_ftruncate(int fd);
 
+int64_t tor_get_avail_disk_space(const char *path);
+
 #ifdef _WIN32
 #define PATH_SEPARATOR "\\"
 #else

src/test/test_util.c

@@ -4347,6 +4347,30 @@ test_util_writepid(void *arg)
   tor_free(contents);
 }
 
+static void
+test_util_get_avail_disk_space(void *arg)
+{
+  (void) arg;
+  int64_t val;
+
+  /* No answer for nonexistent directory */
+  val = tor_get_avail_disk_space("/akljasdfklsajdklasjkldjsa");
+  tt_int_op(val, OP_EQ, -1);
+
+  /* Try the current directory */
+  val = tor_get_avail_disk_space(".");
+
+#if !defined(HAVE_STATVFS) && !defined(_WIN32)
+  tt_i64_op(val, OP_EQ, -1); /* You don't have an implementation for this */
+#else
+  tt_i64_op(val, OP_GT, 0); /* You have some space. */
+  tt_i64_op(val, OP_LT, ((int64_t)1)<<56); /* You don't have a zebibyte */
+#endif
+
+ done:
+  ;
+}
+
 struct testcase_t util_tests[] = {
   UTIL_LEGACY(time),
   UTIL_TEST(parse_http_time, 0),
@@ -4414,6 +4438,7 @@ struct testcase_t util_tests[] = {
   UTIL_TEST(hostname_validation, 0),
   UTIL_TEST(ipv4_validation, 0),
   UTIL_TEST(writepid, 0),
+  UTIL_TEST(get_avail_disk_space, 0),
   END_OF_TESTCASES
 };