Detect whether zlib is new enough. Based on patch from Oliver Jowett.
diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index d2c3d18..4aa1eea 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -74,3 +74,5 @@
* Added Swap(), SwapElements(), and RemoveLast() to Reflection interface.
Alexander Melnikov <alm@sibmail.ru>
* HPUX support.
+ Oliver Jowett <oliver.jowett@gmail.com>
+ * Detect whether zlib is new enough in configure script.
diff --git a/configure.ac b/configure.ac
index 754a190..eb81a7e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -82,14 +82,38 @@
AC_FUNC_STRTOD
AC_CHECK_FUNCS([ftruncate memset mkdir strchr strerror strtol])
+# Check for zlib.
HAVE_ZLIB=0
-AS_IF([test "$with_zlib" != no],
- [AC_SEARCH_LIBS([zlibVersion], [z],
- [AC_DEFINE([HAVE_ZLIB], [1], [Enable classes using zlib compression.])
- HAVE_ZLIB=1],
- [if test "$with_zlib" != check; then
- AC_MSG_FAILURE([--with-zlib was given, but test for zlib failed])
- fi])])
+AS_IF([test "$with_zlib" != no], [
+ AC_MSG_CHECKING([zlib version])
+
+ # First check the zlib header version.
+ AC_COMPILE_IFELSE(
+ AC_LANG_PROGRAM([[
+ #include <zlib.h>
+ #if !defined(ZLIB_VERNUM) || (ZLIB_VERNUM < 0x1204)
+ # error zlib version too old
+ #endif
+ ]], []), [
+ AC_MSG_RESULT([ok (1.2.0.4 or later)])
+
+ # Also need to add -lz to the linker flags and make sure this succeeds.
+ AC_SEARCH_LIBS([zlibVersion], [z], [
+ AC_DEFINE([HAVE_ZLIB], [1], [Enable classes using zlib compression.])
+ HAVE_ZLIB=1
+ ], [
+ AS_IF([test "$with_zlib" != check], [
+ AC_MSG_FAILURE([--with-zlib was given, but no working zlib library was found])
+ ])
+ ])
+ ], [
+ AS_IF([test "$with_zlib" = check], [
+ AC_MSG_RESULT([headers missing or too old (requires 1.2.0.4)])
+ ], [
+ AC_MSG_FAILURE([--with-zlib was given, but zlib headers were not present or were too old (requires 1.2.0.4)])
+ ])
+ ])
+])
AM_CONDITIONAL([HAVE_ZLIB], [test $HAVE_ZLIB = 1])
AS_IF([test "$with_protoc" != "no"], [