Add simplistic reimplementation of strcasestr to compat library

While all systems that I have access to support strcasestr, it is
in fact not part of POSIX. So here's a fallback reimplementation
based on POSIX functions.

Signed-off-by: Dirk Hohndel <hohndel@infradead.org>

Tested-by: Tomas Carnecky <tom@dbservice.com> (on OpenSolaris snv_134)

compat/Makefile.local

@@ -8,3 +8,7 @@ notmuch_compat_srcs :=
 ifneq ($(HAVE_GETLINE),1)
 notmuch_compat_srcs += $(dir)/getline.c $(dir)/getdelim.c
 endif
+
+ifneq ($(HAVE_STRCASESTR),1)
+notmuch_compat_srcs += $(dir)/strcasestr.c
+endif

compat/compat.h

@@ -38,4 +38,8 @@ getdelim (char **lineptr, size_t *n, int delimiter, FILE *fp);
 
 #endif /* !HAVE_GETLINE */
 
+#if !HAVE_STRCASESTR
+char* strcasestr(const char *haystack, const char *needle);
+#endif /* !HAVE_STRCASESTR */
+
 #endif /* NOTMUCH_COMPAT_H */

compat/have_strcasestr.c

@@ -0,0 +1,10 @@
+#define _GNU_SOURCE
+#include <strings.h>
+
+int main()
+{
+    char *found;
+    const char *haystack, *needle;
+
+    found = strcasestr(haystack, needle);
+}

compat/strcasestr.c

@@ -0,0 +1,40 @@
+/*
+ * slow simplistic reimplementation of strcasestr for systems that
+ * don't include it in their library
+ *
+ * based on a GPL implementation in OpenTTD found under GPL v2
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation, version 2.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+   02110-1301, USA.  */
+
+/* Imported into notmuch by Dirk Hohndel - original author unknown. */
+
+#include <string.h>
+
+#include "compat.h"
+
+char *strcasestr(const char *haystack, const char *needle)
+{
+	size_t hay_len = strlen(haystack);
+	size_t needle_len = strlen(needle);
+	while (hay_len >= needle_len) {
+		if (strncasecmp(haystack, needle, needle_len) == 0)
+		    return (char *) haystack;
+
+		haystack++;
+		hay_len--;
+	}
+
+	return NULL;
+}

configure

@@ -310,6 +310,17 @@ else
 fi
 rm -f compat/have_getline
 
+printf "Checking for strcasestr... "
+if ${CC} -o compat/have_strcasestr compat/have_strcasestr.c > /dev/null 2>&1
+then
+    printf "Yes.\n"
+    have_strcasestr=1
+else
+    printf "No (will use our own instead).\n"
+    have_strcasestr=0
+fi
+rm -f compat/have_strcasestr
+
 cat <<EOF
 
 All required packages were found. You may now run the following
@@ -384,6 +395,10 @@ zsh_completion_dir = \$(prefix)/share/zsh/functions/Completion/Unix
 # build its own version)
 HAVE_GETLINE = ${have_getline}
 
+# Whether the strcasestr function is available (if not, then notmuch will
+# build its own version)
+HAVE_STRCASESTR = ${have_strcasestr}
+
 # Flags needed to compile and link against Xapian
 XAPIAN_CXXFLAGS = ${xapian_cxxflags}
 XAPIAN_LDFLAGS = ${xapian_ldflags}
@@ -405,9 +420,10 @@ VALGRIND_CFLAGS = ${valgrind_cflags}
 # Combined flags for compiling and linking against all of the above
 CONFIGURE_CFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)      \\
 		   \$(TALLOC_CFLAGS) -DHAVE_VALGRIND=\$(HAVE_VALGRIND)   \\
-		   \$(VALGRIND_CFLAGS)
+		   \$(VALGRIND_CFLAGS) -DHAVE_STRCASESTR=\$(HAVE_STRCASESTR)
 CONFIGURE_CXXFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)    \\
 		     \$(TALLOC_CFLAGS) -DHAVE_VALGRIND=\$(HAVE_VALGRIND) \\
-		     \$(VALGRIND_CFLAGS) \$(XAPIAN_CXXFLAGS)
+		     \$(VALGRIND_CFLAGS) \$(XAPIAN_CXXFLAGS)             \\
+                     -DHAVE_STRCASESTR=\$(HAVE_STRCASESTR)
 CONFIGURE_LDFLAGS =  \$(GMIME_LDFLAGS) \$(TALLOC_LDFLAGS) \$(XAPIAN_LDFLAGS)
 EOF