lib/icu/Compare: add fallback using strcasecmp() and strcasestr()

NEWS

@@ -3,6 +3,7 @@ ver 0.20.11 (not yet released)
   - curl: support Content-Type application/xml
 * decoder
   - ffmpeg: more reliable song duration
+* fix case insensitive search without libicu
 
 ver 0.20.10 (2017/08/24)
 * decoder

configure.ac

@@ -241,6 +241,7 @@ AC_CHECK_FUNCS(getpwnam_r getpwuid_r)
 AC_CHECK_FUNCS(initgroups)
 AC_CHECK_FUNCS(fnmatch)
 AC_CHECK_FUNCS(strndup)
+AC_CHECK_FUNCS(strcasestr)
 
 if test x$host_is_linux = xyes; then
 	MPD_OPTIONAL_FUNC(eventfd, eventfd, USE_EVENTFD)

src/lib/icu/CaseFold.hxx

@@ -23,6 +23,10 @@
 #include "check.h"
 #include "Compiler.h"
 
+#if defined(HAVE_ICU) || defined(_WIN32)
+#define HAVE_ICU_CASE_FOLD
+#endif
+
 template<typename T> class AllocatedString;
 
 gcc_nonnull_all

src/lib/icu/Compare.cxx

@@ -24,18 +24,43 @@
 
 #include <string.h>
 
+#ifdef HAVE_ICU_CASE_FOLD
+
 IcuCompare::IcuCompare(const char *_needle) noexcept
 	:needle(IcuCaseFold(_needle)) {}
 
+#else
+
+IcuCompare::IcuCompare(const char *_needle) noexcept
+	:needle(AllocatedString<>::Duplicate(_needle)) {}
+
+#endif
+
 bool
 IcuCompare::operator==(const char *haystack) const noexcept
 {
+#ifdef HAVE_ICU_CASE_FOLD
 	return StringIsEqual(IcuCaseFold(haystack).c_str(), needle.c_str());
+#else
+	return strcasecmp(haystack, needle.c_str());
+#endif
 }
 
 bool
 IcuCompare::IsIn(const char *haystack) const noexcept
 {
+#ifdef HAVE_ICU_CASE_FOLD
 	return StringFind(IcuCaseFold(haystack).c_str(),
 			  needle.c_str()) != nullptr;
+#elif defined(HAVE_STRCASESTR)
+	return strcasestr(haystack, needle.c_str()) != nullptr;
+#else
+	/* poor man's strcasestr() */
+	for (const size_t length = strlen(needle.c_str());
+	     *haystack != 0; ++haystack)
+		if (strncasecmp(haystack, needle.c_str(), length) == 0)
+			return true;
+
+	return false;
+#endif
 }