uploads: allow uploading .zip, .rar., and .7z files from disk.

Allow uploading .zip, .rar, and .7z files from disk. The archive will be extracted and the images
inside will be uploaded.

This only works for archive files uploaded from disk, not from a source URL.

Post source URLs will look something like this: "file://foo.zip/1.jpg", "file://foo.zip/2.jpg", etc.
Sometimes artists uses Shift JIS or other encodings instead of UTF-8 for filenames. In these cases
we just assume the filename is UTF-8 and replace invalid characters with '?', so filenames might be
wrong in some cases.

There are various protections to prevent uploading malicious archive files:

* Archives with more than 100 files aren't allowed.
* Archives that decompress to more than 100MB aren't allowed.
* Archives with filenames containing '..' components aren't allowed (e.g. '../../../../../etc/passwd').
* Archives with filenames containing absolute paths aren't allowed (e.g. '/etc/passwd').
* Archives containing symlinks aren't allowed (e.g. 'foo -> /etc/passwd').
* Archive types other than .zip, .rar, and .7z aren't allowed (e.g. .tar.gz, .cpio).
* File permissions, owners, and other metadata are ignored.

Partial fix for #5340: Add support for extracting archive attachments from certain sources

app/logical/danbooru/archive.rb

@@ -107,10 +107,15 @@ module Danbooru
     ensure
       archive&.close
     end
-    alias_method :entries, :each_entry
 
-    # Extract the files in the archive to a directory. Subdirectories inside the archive are ignored; all files are
-    # extracted to a single top-level directory.
+    # XXX You can't call `extract!` on these entries because libarchive doesn't let you extract an entry after you iterate past it.
+    #
+    # @return [Array<Danbooru::Archive::Entry>] The list of entries in the archive.
+    def entries
+      @entries ||= each_entry.to_a
+    end
+
+    # Extract the files in the archive to a directory.
     #
     # If a block is given, extract the archive to a temp directory and delete the directory after the block finishes.
     # Otherwise, extract to a temp directory and return the directory. The caller should delete the directory afterwards.
@@ -135,15 +140,20 @@ module Danbooru
 
     # Extract the archive to a directory. See `extract!` for details.
     def extract_to!(directory, flags: DEFAULT_FLAGS)
-      entries.map do |entry|
+      each_entry.map do |entry|
         raise Danbooru::Archive::Error, "Can't extract archive containing absolute path (path: '#{entry.pathname_utf8}')" if entry.pathname_utf8.starts_with?("/")
         raise Danbooru::Archive::Error, "'#{entry.pathname_utf8}' is not a regular file" if !entry.file?
 
-        path = "#{directory}/#{entry.pathname_utf8.tr("/", "_")}"
+        path = "#{directory}/#{entry.pathname_utf8}"
         entry.extract!(path, flags: flags)
       end
     end
 
+    # @return [Integer] The number of files in the archive.
+    def file_count
+      @file_count ||= entries.count
+    end
+
     # @return [Integer] The total decompressed size of all files in the archive.
     def uncompressed_size
       @uncompressed_size ||= entries.sum(&:size)
@@ -151,7 +161,7 @@ module Danbooru
 
     # @return [Boolean] True if any entry in the archive satisfies the condition; otherwise false.
     def exists?(&block)
-      entries.with_index { |entry, index| return true if yield entry, index + 1 }
+      each_entry.with_index { |entry, index| return true if yield entry, index + 1 }
       false
     end
 
@@ -162,7 +172,7 @@ module Danbooru
 
     # @return [String] The archive format as returned by libarchive ("RAR", "ZIP", etc).
     def format
-      @format ||= entries.lazy.map(&:format).first
+      @format ||= each_entry.lazy.map(&:format).first
     end
 
     # Print the archive contents in `ls -l` format.
@@ -205,9 +215,15 @@ module Danbooru
       entry.pathname_utf8
     end
 
-    # @return [String] The pathname encoded as UTF-8 instead of ASCII-8BIT. May be wrong if the original pathname wasn't UTF-8.
+    # @see https://security.snyk.io/research/zip-slip-vulnerability
+    # @return [Boolean] True if the pathname contains any ".." components, e.g. "../../../../../etc/passwd"
+    def directory_traversal?
+      entry.pathname.split("/").compact_blank.grep("..").any?
+    end
+
+    # @return [String, nil] The pathname encoded as UTF-8 instead of ASCII-8BIT. May be wrong if the original pathname wasn't UTF-8.
     def pathname_utf8
-      pathname.encode("UTF-8", invalid: :replace, undef: :replace, replace: "?")
+      pathname&.encode("UTF-8", invalid: :replace, undef: :replace, replace: "?")
     end
 
     # @return [String] The archive entry format ("RAR", "ZIP", etc).