[egl] shader: fix reliance on null terminated strings

Compiled in resources often will not contain a null terminator, as such
we must not use functions that rely on it. This implements a memsearch
function that performs like strstr on a buffer instead of a null
terminated string.

common/include/common/stringutils.h

@@ -37,4 +37,10 @@ bool str_containsValue(const char * list, char delimiter, const char * value);
 // Local implementation of strdup
 char * lg_strdup(const char *s);
 
+// search a non null terminated buffer for a value
+const char * memsearch(
+    const char * haystack, size_t haystackSize,
+    const char * needle  , size_t needleSize  ,
+    const char * offset);
+
 #endif

common/src/stringutils.c

@@ -26,6 +26,7 @@
 #include <errno.h>
 
 #include "common/stringutils.h"
+#include "common/debug.h"
 
 int valloc_sprintf(char ** str, const char * format, va_list ap)
 {
@@ -110,3 +111,24 @@ char * lg_strdup(const char *s)
   memcpy(out, s, len);
   return out;
 }
+
+const char * memsearch(
+    const char * haystack, size_t haystackSize,
+    const char * needle  , size_t needleSize  ,
+    const char * offset)
+{
+  int i = 0;
+  if (offset)
+  {
+    DEBUG_ASSERT(offset >= haystack);
+    DEBUG_ASSERT(offset < haystack + haystackSize);
+    i = offset - haystack;
+  }
+
+  const int searchSize = haystackSize - needleSize + 1;
+  for(; i < searchSize; ++i)
+    if (memcmp(haystack + i, needle, needleSize) == 0)
+      return haystack + i;
+
+  return NULL;
+}