Add compat/snprintf.c for systems that return bogus

Some systems (namely HPUX and Windows) return -1 when maxsize in snprintf()
and in vsnprintf() is reached. So replace snprintf() and vsnprintf()
functions with our own ones that return correct value upon overflow.

[jc: verified that review comments by J6t have been incorporated, and
 tightened the check to verify the resulting buffer contents, suggested
 by Wayne Davison]

Signed-off-by: Michal Rokos <michal.rokos@nextsoft.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -3,6 +3,10 @@ all::
 
 # Define V=1 to have a more verbose compile.
 #
+# Define SNPRINTF_RETURNS_BOGUS if your are on a system which snprintf()
+# or vsnprintf() return -1 instead of number of characters which would
+# have been written to the final string if enough space had been available.
+#
 # Define FREAD_READS_DIRECTORIES if your are on a system which succeeds
 # when attempting to read from an fopen'ed directory.
 #
@@ -629,6 +633,10 @@ endif
 ifdef NO_C99_FORMAT
 	BASIC_CFLAGS += -DNO_C99_FORMAT
 endif
+ifdef SNPRINTF_RETURNS_BOGUS
+	COMPAT_CFLAGS += -DSNPRINTF_RETURNS_BOGUS
+	COMPAT_OBJS += compat/snprintf.o
+endif
 ifdef FREAD_READS_DIRECTORIES
 	COMPAT_CFLAGS += -DFREAD_READS_DIRECTORIES
 	COMPAT_OBJS += compat/fopen.o

compat/snprintf.c

@@ -0,0 +1,40 @@
+#include "../git-compat-util.h"
+
+#undef vsnprintf
+int git_vsnprintf(char *str, size_t maxsize, const char *format, va_list ap)
+{
+	char *s;
+	int ret;
+
+	ret = vsnprintf(str, maxsize, format, ap);
+	if (ret != -1)
+		return ret;
+
+	s = NULL;
+	if (maxsize < 128)
+		maxsize = 128;
+
+	while (ret == -1) {
+		maxsize *= 4;
+		str = realloc(s, maxsize);
+		if (! str)
+			break;
+		s = str;
+		ret = vsnprintf(str, maxsize, format, ap);
+	}
+	free(s);
+	return ret;
+}
+
+int git_snprintf(char *str, size_t maxsize, const char *format, ...)
+{
+	va_list ap;
+	int ret;
+
+	va_start(ap, format);
+	ret = git_vsnprintf(str, maxsize, format, ap);
+	va_end(ap);
+
+	return ret;
+}
+

config.mak.in

@@ -46,3 +46,4 @@ NO_MKDTEMP=@NO_MKDTEMP@
 NO_ICONV=@NO_ICONV@
 OLD_ICONV=@OLD_ICONV@
 NO_DEFLATE_BOUND=@NO_DEFLATE_BOUND@
+SNPRINTF_RETURNS_BOGUS=@SNPRINTF_RETURNS_BOGUS@

configure.ac

@@ -326,6 +326,40 @@ else
 	NO_C99_FORMAT=
 fi
 AC_SUBST(NO_C99_FORMAT)
+#
+# Define SNPRINTF_RETURNS_BOGUS if your are on a system which snprintf()
+# or vsnprintf() return -1 instead of number of characters which would
+# have been written to the final string if enough space had been available.
+AC_CACHE_CHECK([whether snprintf() and/or vsnprintf() return bogus value],
+ [ac_cv_snprintf_returns_bogus],
+[
+AC_RUN_IFELSE(
+	[AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT
+		#include "stdarg.h"
+
+		int test_vsnprintf(char *str, size_t maxsize, const char *format, ...)
+		{
+		  int ret;
+		  va_list ap;
+		  va_start(ap, format);
+		  ret = vsnprintf(str, maxsize, format, ap);
+		  va_end(ap);
+		  return ret;
+		}],
+		[[char buf[6];
+		  if (test_vsnprintf(buf, 3, "%s", "12345") != 5
+		      || strcmp(buf, "12")) return 1;
+		  if (snprintf(buf, 3, "%s", "12345") != 5
+		      || strcmp(buf, "12")) return 1]])],
+	[ac_cv_snprintf_returns_bogus=no],
+	[ac_cv_snprintf_returns_bogus=yes])
+])
+if test $ac_cv_snprintf_returns_bogus = yes; then
+	SNPRINTF_RETURNS_BOGUS=UnfortunatelyYes
+else
+	SNPRINTF_RETURNS_BOGUS=
+fi
+AC_SUBST(SNPRINTF_RETURNS_BOGUS)
 
 
 ## Checks for library functions.

git-compat-util.h

@@ -209,6 +209,15 @@ void *gitmemmem(const void *haystack, size_t haystacklen,
 extern FILE *git_fopen(const char*, const char*);
 #endif
 
+#ifdef SNPRINTF_RETURNS_BOGUS
+#define snprintf git_snprintf
+extern int git_snprintf(char *str, size_t maxsize,
+			const char *format, ...);
+#define vsnprintf git_vsnprintf
+extern int git_vsnprintf(char *str, size_t maxsize,
+			 const char *format, va_list ap);
+#endif
+
 #ifdef __GLIBC_PREREQ
 #if __GLIBC_PREREQ(2, 1)
 #define HAVE_STRCHRNUL