Update strings.go

strings.go

@@ -8,3 +8,33 @@ func TrimStringFromQuery(s, substr string) string {
 	}
 	return s
 }
+
+func Strpos(haystack, needle string, offset int) int {
+    length := len(haystack)
+    if length == 0 || offset >= length || -offset > length {
+        return -1
+    }
+
+    if offset < 0 {
+        offset += length
+    }
+
+    for i := offset; i <= length-len(needle); i++ {
+        if haystack[i:i+len(needle)] == needle {
+            return i
+        }
+    }
+
+    return -1
+}
+
+
+func Substr(str string, start uint, length int) string {
+    if int(start) >= len(str) || length == 0 {
+        return ""
+    }
+    if length < 0 || int(start)+length > len(str) {
+        return str[start:]
+    }
+    return str[start : start+uint(length)]
+}