Add RAR/CBR support

src/archive.cr

@@ -0,0 +1,53 @@
+require "zip"
+require "archive"
+
+# A unified class to handle all supported archive formats. It uses the ::Zip
+#   module in crystal standard library if the target file is a zip archive.
+#   Otherwise it uses `archive.cr`.
+class ArchiveFile
+  def initialize(@filename : String)
+    if [".cbz", ".zip"].includes? File.extname filename
+      @archive_file = Zip::File.new filename
+    else
+      @archive_file = Archive::File.new filename
+    end
+  end
+
+  def self.open(filename : String, &)
+    s = self.new filename
+    yield s
+    s.close
+  end
+
+  def close
+    if @archive_file.is_a? Zip::File
+      @archive_file.as(Zip::File).close
+    end
+  end
+
+  # Lists all file entries
+  def entries
+    ary = [] of Zip::File::Entry | Archive::Entry
+    @archive_file.entries.map do |e|
+      if (e.is_a? Zip::File::Entry && e.file?) ||
+         (e.is_a? Archive::Entry && e.info.file?)
+        ary.push e
+      end
+    end
+    ary
+  end
+
+  def read_entry(e : Zip::File::Entry | Archive::Entry) : Bytes?
+    if e.is_a? Zip::File::Entry
+      data = nil
+      e.open do |io|
+        slice = Bytes.new e.uncompressed_size
+        bytes_read = io.read_fully? slice
+        data = slice if bytes_read
+      end
+      data
+    else
+      e.read
+    end
+  end
+end