Use CRC32 for the replication protocol

It's about 7 times faster than SHA1, and has similar or better
characteristics for identifying file changes.

src/lavinmq/clustering.cr

@@ -4,7 +4,8 @@ require "digest/sha1"
 
 module LavinMQ
   module Clustering
-    Start = Bytes['R'.ord, 'E'.ord, 'P'.ord, 'L'.ord, 'I'.ord, 1, 0, 0]
+    Start100 = Bytes['R'.ord, 'E'.ord, 'P'.ord, 'L'.ord, 'I'.ord, 1, 0, 0]
+    Start    = Bytes['R'.ord, 'E'.ord, 'P'.ord, 'L'.ord, 'I'.ord, 1, 0, 1]
 
     class Error < Exception; end
 

src/lavinmq/clustering/client.cr

@@ -125,9 +125,9 @@ module LavinMQ
 
       private def sync_files(socket, lz4)
         Log.info { "Waiting for list of files" }
-        sha1 = Digest::SHA1.new
-        remote_hash = Bytes.new(sha1.digest_size)
-        local_hash = Bytes.new(sha1.digest_size)
+        crc32 = Digest::CRC32.new
+        remote_hash = Bytes.new(crc32.digest_size)
+        local_hash = Bytes.new(crc32.digest_size)
         files_to_delete = ls_r(@data_dir)
         missing_files = Array(String).new
         loop do
@@ -139,9 +139,9 @@ module LavinMQ
           path = File.join(@data_dir, filename)
           files_to_delete.delete(path)
           if File.exists? path
-            sha1.file(path)
-            sha1.final(local_hash)
-            sha1.reset
+            crc32.file(path)
+            crc32.final(local_hash)
+            crc32.reset
             if local_hash != remote_hash
               Log.info { "Mismatching hash: #{path}" }
               move_to_backup path

src/lavinmq/clustering/server.cr

@@ -14,7 +14,7 @@ module LavinMQ
     # When a follower connects:
     # It sends a static header (wrong header disconnects the client)
     # It sends its password (servers closes the connection if the password is wrong)
-    # Server sends a list of files in its data directory and the sha1 hash of those files
+    # Server sends a list of files in its data directory and the crc32 hash of those files
     # Client requests files that is missing or has mismatching checksums of
     # In the meantime the server queues up changes (all publishes/consumes are paused)
     # When client doesn't request more files starts to stream changes
@@ -72,12 +72,12 @@ module LavinMQ
       end
 
       def files_with_hash(& : Tuple(String, Bytes) -> Nil)
-        sha1 = Digest::SHA1.new
-        hash = Bytes.new(sha1.digest_size)
-        @files.each_key do |path|
-          sha1.file path
-          sha1.final hash
-          sha1.reset
+        crc32 = Digest::CRC32.new
+        hash = Bytes.new(crc32.digest_size)
+        @files.each do |path, mfile|
+          crc32.file path
+          crc32.final hash
+          crc32.reset
           yield({path, hash})
         end
       end