Add function encoder

lib/abi_coder_rb.rb

@@ -10,6 +10,7 @@
 require_relative "abi_coder_rb/encode"
 
 require_relative "periphery/event_decoder"
+require_relative "periphery/function_encoder"
 
 module AbiCoderRb
   class DecodingError < StandardError; end

lib/periphery/function_encoder.rb

@@ -0,0 +1,25 @@
+require "digest/keccak"
+
+module FunctionEncoder
+  extend AbiCoderRb
+
+  class << self
+    def encode_function(function_signature, params)
+      # check the method_signature by regex
+      raise "Invalid function signature" unless function_signature.match?(/^\w+\(.+\)$/)
+
+      # e.g. baz(uint32,bool) => (uint32,bool)
+      types_str = "(#{function_signature.match(/\((.*)\)/)[1]})"
+      "0x#{function_id(function_signature)}#{bin_to_hex(encode(types_str, params))}"
+    end
+
+    private
+
+    # This is derived as the first 4 bytes of the Keccak hash of the ASCII form of the signature like `baz(uint32,bool)`.
+    def function_id(function_signature)
+      # remove blank spaces
+      function_signature = function_signature.gsub(/\s+/, "")
+      Digest::Keccak.hexdigest(function_signature, 256)[0, 8]
+    end
+  end
+end

spec/function_encoding_spec.rb

@@ -0,0 +1,8 @@
+require "spec_helper"
+
+RSpec.describe FunctionEncoder do
+  it "can encode function" do
+    result = FunctionEncoder.encode_function("baz(uint32,bool)", [69, true])
+    expect(result).to eq "0xcdcd77c000000000000000000000000000000000000000000000000000000000000000450000000000000000000000000000000000000000000000000000000000000001"
+  end
+end

spec/packed_encoding_spec.rb

@@ -202,5 +202,21 @@
     expect(
       encode("int128", 17, true)
     ).to eq hex("00000000000000000000000000000011")
+
+    transactions = [
+      { operation: 0, to: "0xa89005ab7d7fd81A94c8A8e0799648248CeE6934", value: 1, data: "".b },
+      { operation: 0, to: "0xc1b5bcbc94e6127ac3ee4054d0664e4f6afe45d3", value: 1, data: "".b }
+    ]
+    result = transactions.map do |tx|
+      encode(
+        %w[uint8 address uint256 uint256 bytes],
+        [tx[:operation], tx[:to], tx[:value], tx[:data].length, tx[:data]],
+        true
+      )
+    end.join
+
+    expect(result).to eq(
+      hex("00a89005ab7d7fd81a94c8a8e0799648248cee69340000000000000000000000000000000000000000000000000000000000000001000000000000000000000000000000000000000000000000000000000000000000c1b5bcbc94e6127ac3ee4054d0664e4f6afe45d300000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000000")
+    )
   end
 end