hpack: implement HPACK encoding (only "Literal Header Field without Indexing")

1 files changed, 57 insertions, 0 deletions

diff --git a/lib/plum/hpack/encoder.rb b/lib/plum/hpack/encoder.rb
new file mode 100644
index 0000000..4a04eb7
--- /dev/null
+++ b/lib/plum/hpack/encoder.rb
@@ -0,0 +1,57 @@
+module Plum
+  module HPACK
+    class Encoder
+      attr_reader :context
+
+      def initialize(dynamic_table_limit)
+        @context = Context.new(dynamic_table_limit)
+      end
+
+      # currently only support 0x0000XXXX type (without indexing)
+      # and not huffman
+      # +---+---+---+---+---+---+---+---+
+      # | 0 | 0 | 0 | 0 |       0       |
+      # +---+---+-----------------------+
+      # | H |     Name Length (7+)      |
+      # +---+---------------------------+
+      # |  Name String (Length octets)  |
+      # +---+---------------------------+
+      # | H |     Value Length (7+)     |
+      # +---+---------------------------+
+      # | Value String (Length octets)  |
+      # +-------------------------------+
+      def encode(headers)
+        out = "".b
+        headers.each do |name, value|
+          name = name.to_s; value = value.to_s
+          out << "\x00"
+          out << encode_integer(name.bytesize, 7)
+          out << name
+          out << encode_integer(value.bytesize, 7)
+          out << value
+        end
+
+        out
+      end
+
+      private
+      def encode_integer(value, prefix_length)
+        mask = (1 << prefix_length) - 1
+
+        if value < mask
+          [value].pack("C").b
+        else
+          bytes = [mask]
+          value -= mask
+          while value >= mask
+            bytes << (value % 0b10000000) + 0b10000000
+            value >>= 7
+          end
+          bytes << value
+ 
+          bytes.pack("C*").b
+        end
+      end
+    end
+  end
+end