exp/lighthorizon: Prototyping support for XDR serialization

exp/lighthorizon/index/Gemfile

@@ -0,0 +1,7 @@
+source 'https://rubygems.org'
+
+gem 'xdrgen', git:'https://github.com/stellar/xdrgen.git', ref: 'master'
+gem 'pry'
+gem 'octokit'
+gem 'netrc'
+gem 'rake'

exp/lighthorizon/index/Rakefile

@@ -0,0 +1,53 @@
+require 'bundler'
+Bundler.setup()
+require 'pry'
+
+namespace :xdr do
+
+  HORIZON_XDR = [
+    "xdr/LightHorizon-types.x"
+  ]
+  LOCAL_XDR_PATHS = HORIZON_XDR.map{ |src| "xdr/" + File.basename(src) }
+
+  task :update => [:download, :generate]
+
+  task :download do
+    require 'octokit'
+    require 'base64'
+    FileUtils.mkdir_p "xdr"
+    FileUtils.rm_rf "xdr/*.x"
+
+    client = Octokit::Client.new(:netrc => true)
+
+    HORIZON_XDR.each do |src|
+      local_path = "xdr/" + File.basename(src)
+      encoded    = client.contents("stellar/go/exp/lighthorizon", path: src).content
+      decoded    = Base64.decode64 encoded
+
+      IO.write(local_path, decoded)
+    end
+  end
+
+  task :generate do
+    require "pathname"
+    require "xdrgen"
+    require 'fileutils'
+
+    compilation = Xdrgen::Compilation.new(
+      LOCAL_XDR_PATHS,
+      output_dir: "xdr",
+      namespace:  "xdr",
+      language:   :go
+    )
+    compilation.compile
+
+    xdr_generated = IO.read("xdr/xdr_generated.go")
+    IO.write("xdr/xdr_generated.go", <<~EOS)
+      //lint:file-ignore S1005 The issue should be fixed in xdrgen. Unfortunately, there's no way to ignore a single file in staticcheck.
+      //lint:file-ignore U1000 fmtTest is not needed anywhere, should be removed in xdrgen.
+      #{xdr_generated}
+    EOS
+
+    system("gofmt -w xdr/xdr_generated.go")
+  end
+end

exp/lighthorizon/index/main.go

@@ -1,11 +1,11 @@
 package index
 
 import (
-	"bufio"
 	"bytes"
 	"io"
-	"strconv"
 	"sync"
+
+	"github.com/stellar/go/exp/lighthorizon/index/xdr"
 )
 
 const CheckpointIndexVersion = 1
@@ -18,44 +18,16 @@ type CheckpointIndex struct {
 }
 
 func NewCheckpointIndexFromBytes(b []byte) (*CheckpointIndex, error) {
-	buf := bytes.NewBuffer(b)
-	r := bufio.NewReader(buf)
-
-	firstCheckpointString, err := r.ReadString(0x00)
-	if err != nil {
-		return nil, err
-	}
-
-	// Remove trailing 0x00 byte
-	firstCheckpointString = firstCheckpointString[:len(firstCheckpointString)-1]
-
-	firstCheckpoint, err := strconv.ParseUint(firstCheckpointString, 10, 32)
-	if err != nil {
-		return nil, err
-	}
-
-	lastCheckpointString, err := r.ReadString(0x00)
-	if err != nil {
-		return nil, err
-	}
-
-	// Remove trailing 0x00 byte
-	lastCheckpointString = lastCheckpointString[:len(lastCheckpointString)-1]
-
-	lastCheckpoint, err := strconv.ParseUint(lastCheckpointString, 10, 32)
-	if err != nil {
-		return nil, err
-	}
-
-	bitmap, err := io.ReadAll(r)
+	xdrCheckpoint := xdr.CheckpointIndex{}
+	err := xdrCheckpoint.UnmarshalBinary(b)
 	if err != nil {
 		return nil, err
 	}
 
 	return &CheckpointIndex{
-		bitmap:          bitmap,
-		firstCheckpoint: uint32(firstCheckpoint),
-		lastCheckpoint:  uint32(lastCheckpoint),
+		bitmap:          xdrCheckpoint.Bitmap,
+		firstCheckpoint: uint32(xdrCheckpoint.FirstCheckpoint),
+		lastCheckpoint:  uint32(xdrCheckpoint.LastCheckpoint),
 	}, nil
 }
 
@@ -243,13 +215,17 @@ func (i *CheckpointIndex) Buffer() *bytes.Buffer {
 	i.mutex.RLock()
 	defer i.mutex.RUnlock()
 
-	var b bytes.Buffer
-	b.WriteString(strconv.FormatUint(uint64(i.firstCheckpoint), 10))
-	b.WriteByte(0)
-	b.WriteString(strconv.FormatUint(uint64(i.lastCheckpoint), 10))
-	b.WriteByte(0)
-	b.Write(i.bitmap)
-	return &b
+	xdrCheckpoint := xdr.CheckpointIndex{
+		FirstCheckpoint: xdr.Uint32(i.firstCheckpoint),
+		LastCheckpoint:  xdr.Uint32(i.lastCheckpoint),
+		Bitmap:          i.bitmap,
+	}
+
+	b, err := xdrCheckpoint.MarshalBinary()
+	if err != nil {
+		panic(err)
+	}
+	return bytes.NewBuffer(b)
 }
 
 // Flush flushes the index data to byte slice in index format.

exp/lighthorizon/index/xdr/LightHorizon-types.x

@@ -0,0 +1,17 @@
+// Copyright 2022 Stellar Development Foundation and contributors. Licensed
+// under the Apache License, Version 2.0. See the COPYING file at the root
+// of this distribution or at http://www.apache.org/licenses/LICENSE-2.0
+
+namespace stellar
+{
+
+typedef unsigned int uint32;
+typedef opaque Value<>;
+
+struct CheckpointIndex {
+    uint32 firstCheckpoint;
+    uint32 lastCheckpoint;
+    opaque bitmap<>;
+};
+
+}