1 files changed, 70 insertions, 0 deletions
diff --git a/lib/asn1kit/berstring.rb b/lib/asn1kit/berstring.rb
new file mode 100644
index 0000000..23b9e93
--- /dev/null
+++ b/lib/asn1kit/berstring.rb
@@ -0,0 +1,70 @@
+module ASN1Kit
+  module BERString
+    TAG_CLASS_MAP = {
+      UNIVERSAL: 0x00,
+      APPLICATION: 0x40,
+      CONTEXT_SPECIFIC: 0x80,
+      PRIVATE: 0xC0
+    }
+
+    refine(String) do
+      def put_object(tc, tn, len, encoding)
+        force_encoding("BINARY")
+        constructed = encoding == :constructed
+        if tn < 0x1f
+          self << (TAG_CLASS_MAP[tc] | (constructed ? 0x20 : 0x00) | tn)
+        else
+          self << (TAG_CLASS_MAP[tc] | (constructed ? 0x20 : 0x00) | 0x1f)
+          self << [tn].pack("w")
+        end
+        if len && len < 0x80
+          self << len
+        elsif !len
+          self << 0x80
+        else
+          d = len.digits(256)
+          self << (0x80 | d.size)
+          self << d.reverse.pack("C")
+        end
+      end
+
+      def put_eoc
+        force_encoding("BINARY")
+        self << 0x00
+        self << 0x00
+      end
+
+      # Returns an array: [tag_class, is_constructed, tag_number, hlen, len]
+      # where
+      #   tag_class:: one of :UNIVERSAL, :APPLICATION, :CONTEXT_SPECIFIC, :PRIVATE
+      #   is_constructed:: true of false
+      #   tag_number:: an Integer
+      #   hlen:: header octets length
+      #   len:: content octets length
+      def get_object(offset = 0)
+        h = getbyte(offset) or
+          raise RangeError, "end of string reached"
+        hlen = 1
+        tag_class = [:UNIVERSAL, :APPLICATION, :CONTEXT_SPECIFIC, :PRIVATE][h >> 6]
+        constructed = h & 0x20 == 0x20
+        tag_number = h & 0x1f
+        if tag_number == 0x1f
+          tag_number = unpack("@#{offset + hlen} w")[0] or
+            raise RangeError, "end of string reached"
+          hlen += (tag_number.bit_length / 8r).ceil
+        end
+        len = getbyte(offset + hlen) or
+          raise RangeError, "end of string reached"
+        hlen += 1
+        if len > 0x80
+          blen = len - 0x80
+          d = unpack("@#{offset + hlen} C#{blen}")
+          d[-1] or raise RangeError, "end of string reached"
+          len = d.inject(0) { |sum, i| (sum << 8) + i }
+          hlen += blen
+        end
+        [tag_class, tag_number, constructed, hlen, len]
+      end
+    end
+  end
+end