[RFC PATCH] configure: check for POSIX.1-2008 realpath(3) implementation.

[Tomi Ollila <tomi.ollila@iki.fi>]

Check whether realpath(3) supports the resolved_path == NULL feature,
standardized in POSIX.1-2008.

This is tested by executing the realpath(3) with NULL as second
argument and the program is expected to SIGSEGV in case the
feature is not supported.

If the feature is not supported the compatibility code calls realpath(3)
with second argument pointing to buffer with MAX_PATH in size. With
this more systems are supported; those that have POSIX.1-2008 -capable
realpath(3) and those that have MAX_PATH defined and realpath(3) does
not exceed that limit.
---

I tested running configure and then make test; then make clean,
edited Makefile.config POSIX_2008_REALPATH = 0 and make clean
again. then tested sigsegv'ing with (memcpy(0, 0, 4)...


 configure        | 32 ++++++++++++++++++++++++++++++--
 notmuch-config.c | 21 ++++++++++++++++++++-
 2 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/configure b/configure
index 13b6062..8174219 100755
--- a/configure
+++ b/configure
@@ -454,6 +454,29 @@ echo $util_byte_order
 
 rm -f _byteorder _byteorder.c
 
+printf "Checking for posix 2008 realpath()... "
+# resolved_path == NULL is standardized in POSIX.1-2008
+cat > _posix_2008_realpath.c <<EOF
+#define _BSD_SOURCE
+#include <limits.h>
+#include <stdlib.h>
+#include <signal.h>
+void exit1(int sig) { exit(1); }
+int main () {
+ signal(SIGSEGV, exit1);
+ int main () { realpath (".", (char*)0); return 0;
+}
+EOF
+${CC} ${CFLAGS} _posix_2008_realpath.c -o _posix_2008_realpath > /dev/null 2>&1
+if ./_posix_2008_realpath; then
+	echo Yes.
+	posix_2008_realpath=1
+else
+	echo No.
+	posix_2008_realpath=0
+fi
+rm -f _posix_2008_realpath _posix_2008_realpath.c
+
 if [ $errors -gt 0 ]; then
     cat <<EOF
 
@@ -718,6 +741,9 @@ libdir = ${LIBDIR:=\$(prefix)/lib}
 # byte order within a 32 bit word. 1234 = little, 4321 = big, 0 = guess
 UTIL_BYTE_ORDER = ${util_byte_order}
 
+# Whether realpath(3) supports resolved_path == NULL feature
+POSIX_2008_REALPATH = ${posix_2008_realpath}
+
 # Whether libdir is in a path configured into ldconfig
 LIBDIR_IN_LDCONFIG = ${libdir_in_ldconfig}
 
@@ -824,7 +850,8 @@ CONFIGURE_CFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)      \\
 		   -DSTD_GETPWUID=\$(STD_GETPWUID)                       \\
 		   -DSTD_ASCTIME=\$(STD_ASCTIME)                         \\
 		   -DHAVE_XAPIAN_COMPACT=\$(HAVE_XAPIAN_COMPACT)	 \\
-		   -DUTIL_BYTE_ORDER=\$(UTIL_BYTE_ORDER)
+		   -DUTIL_BYTE_ORDER=\$(UTIL_BYTE_ORDER)		 \\
+		   -DPOSIX_2008_REALPATH=\$(POSIX_2008_REALPATH)
 
 CONFIGURE_CXXFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)    \\
 		     \$(TALLOC_CFLAGS) -DHAVE_VALGRIND=\$(HAVE_VALGRIND) \\
@@ -834,7 +861,8 @@ CONFIGURE_CXXFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)    \\
 		     -DSTD_GETPWUID=\$(STD_GETPWUID)                     \\
 		     -DSTD_ASCTIME=\$(STD_ASCTIME)                       \\
 		     -DHAVE_XAPIAN_COMPACT=\$(HAVE_XAPIAN_COMPACT)       \\
-		     -DUTIL_BYTE_ORDER=\$(UTIL_BYTE_ORDER)
+		     -DUTIL_BYTE_ORDER=\$(UTIL_BYTE_ORDER)		 \\
+		     -DPOSIX_2008_REALPATH=\$(POSIX_2008_REALPATH)
 
 CONFIGURE_LDFLAGS =  \$(GMIME_LDFLAGS) \$(TALLOC_LDFLAGS) \$(XAPIAN_LDFLAGS)
 EOF
diff --git a/notmuch-config.c b/notmuch-config.c
index 8d28653..14d0e5c 100644
--- a/notmuch-config.c
+++ b/notmuch-config.c
@@ -454,10 +454,26 @@ notmuch_config_save (notmuch_config_t *config)
     }
 
     /* Try not to overwrite symlinks. */
+#if POSIX_2008_REALPATH
     filename = realpath (config->filename, NULL);
+#else
+    /* compatibility with minor effort, not elegance, is the ruling factor
+       in these (two) else branches... */
+    char resolved_path[PATH_MAX];
+    filename = realpath (config->filename, resolved_path);
+#endif
     if (! filename) {
 	if (errno == ENOENT) {
+#if POSIX_2008_REALPATH
 	    filename = strdup (config->filename);
+#else
+	    /* ... this is the other else... */
+	    resolved_path[sizeof resolved_path - 1] = '\0';
+	    strncpy(resolved_path, config->filename, sizeof resolved_path);
+	    /* "faking" out of memory in case path too long -- close enough? */
+	    filename = resolved_path[sizeof resolved_path - 1]?
+		resolved_path: NULL;
+#endif
 	    if (! filename) {
 		fprintf (stderr, "Out of memory.\n");
 		g_free (data);
@@ -480,12 +496,15 @@ notmuch_config_save (notmuch_config_t *config)
 		     filename, error->message);
 	}
 	g_error_free (error);
+#if POSIX_2008_REALPATH
 	free (filename);
+#endif
 	g_free (data);
 	return 1;
     }
-
+#if POSIX_2008_REALPATH
     free (filename);
+#endif
     g_free (data);
     return 0;
 }
-- 
1.8.5.3