Shim IO#pread when not supported

Typically on Windows.

.github/workflows/ci.yml

@@ -8,26 +8,35 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
-    name: "Ruby ${{ matrix.ruby }} / Failure allowed: ${{ matrix.experimental }}"
+    runs-on: ${{ matrix.os }}-latest
+    name: "Ruby ${{ matrix.ruby }} / ${{ matrix.os }} / Failure allowed: ${{ matrix.experimental }}"
     continue-on-error: ${{ matrix.experimental }}
     timeout-minutes: 5
 
     strategy:
       fail-fast: false
       matrix:
+        os: ["ubuntu"]
         ruby: ["2.6", "2.7", "3.0", "3.1", "3.2"]
         experimental: [false]
         include:
+          - ruby: "3.2"
+            os: "windows"
+            experimental: false
           - ruby: "ruby-head"
+            os: "ubuntu"
             experimental: true
           - ruby: "truffleruby-head"
+            os: "ubuntu"
             experimental: true
           - ruby: "jruby-head"
+            os: "ubuntu"
             experimental: true
           - ruby: "jruby-9.3.9.0"
+            os: "ubuntu"
             experimental: true
           - ruby: "jruby-9.4.0.0"
+            os: "ubuntu"
             experimental: true
     steps:
       - uses: actions/checkout@v3

lib/mini_mime.rb

@@ -85,14 +85,40 @@ def fetch(key, &blk)
       end
     end
 
+    if ::File.method_defined?(:pread)
+      PReadFile = ::File
+    else
+      # For Windows support
+      class PReadFile
+        def initialize(filename)
+          @mutex = Mutex.new
+          # We must open the file in binary mode
+          # otherwise Ruby's automatic line terminator
+          # translation will skew the row size
+          @file = ::File.open(filename, 'rb')
+        end
+
+        def readline(*args)
+          @file.readline(*args)
+        end
+
+        def pread(size, offset)
+          @mutex.synchronize do
+            @file.seek(offset, IO::SEEK_SET)
+            @file.read(size)
+          end
+        end
+      end
+    end
+
     class RandomAccessDb
       MAX_CACHED = 100
 
       def initialize(path, sort_order)
         @path = path
-        @file = File.open(@path)
+        @file = PReadFile.new(@path)
 
-        @row_length = @file.readline.length
+        @row_length = @file.readline("\n").length
         @file_length = File.size(@path)
         @rows = @file_length / @row_length
 

test/mini_mime_test.rb

@@ -57,6 +57,8 @@ def should_prioritize_extensions_correctly
 
   if defined? MIME::Types
     def test_full_parity_with_mime_types
+      skip("Windows MIME::Types isn't reliable") if RUBY_PLATFORM.match?(/windows/i)
+
       exts = Set.new
       MIME::Types.each do |type|
         type.extensions.each { |ext| exts << ext }