Add support for reading exif tags from IO objects

- Updated `README.md` to include instructions for reading metadata from IO objects.
- Modified `lib/exiftool.rb` to handle IO objects as input, allowing ExifTool to infer file type from content.
- Utilized `Open3.popen3` for executing shell commands, ensuring proper process management and error handling.
- Added a test case in `test/exiftool_test.rb`.

Author: bogdan

README.md

@@ -83,6 +83,16 @@ e.files_with_results
 # => ["path/to/iPhone 4S.jpg", "path/to/Droid X.jpg", …
 ```
 
+### Reading from IO
+
+You can pass an IO object to read metadata from standard input. ExifTool will infer the file type from content:
+
+```ruby
+io = File.open('test/IMG_2452.jpg', 'rb')
+e = Exiftool.new(io)
+e[:make] # => "Canon"
+```
+
 ### Dates without timezones
 
 It seems that most exif dates don't include timezone offsets, without which forces us to assume the

lib/exiftool.rb

@@ -2,6 +2,7 @@
 
 require 'json'
 require 'shellwords'
+require 'open3'
 require 'exiftool/result'
 require 'forwardable'
 require 'pathname'
@@ -30,7 +31,20 @@ def self.exiftool_installed?
 
   # This is a string, not a float, to handle versions like "9.40" properly.
   def self.exiftool_version
-    @exiftool_version ||= `#{command} -ver 2> /dev/null`.chomp
+    return @exiftool_version if defined?(@exiftool_version) && @exiftool_version
+
+    stdout_str = ''
+    begin
+      Open3.popen3(command, '-ver') do |_stdin, stdout, _stderr, wait_thr|
+        stdout_str = stdout.read.to_s.chomp
+        # Ensure the process is reaped
+        wait_thr.value
+      end
+    rescue Errno::ENOENT
+      stdout_str = ''
+    end
+
+    @exiftool_version = stdout_str
   end
 
   def self.expand_path(filename)
@@ -47,16 +61,45 @@ def self.expand_path(filename)
 
   def initialize(filenames, exiftool_opts = '')
     @file2result = {}
+    io_input = nil
+    if filenames.is_a?(IO)
+      io_input = filenames
+      filenames = ['-']
+    end
+
     filenames = [filenames] if filenames.is_a?(String) || filenames.is_a?(Pathname)
     return if filenames.empty?
 
-    escaped_filenames = filenames.map do |f|
-      Shellwords.escape(self.class.expand_path(f.to_s))
-    end.join(' ')
-    # I'd like to use -dateformat, but it doesn't support timezone offsets properly,
-    # nor sub-second timestamps.
-    cmd = "#{self.class.command} #{exiftool_opts} -j -coordFormat \"%.8f\" #{escaped_filenames} 2> /dev/null"
-    json = `#{cmd}`.chomp
+    expanded_filenames = filenames.map do |f|
+      f == '-' ? '-' : self.class.expand_path(f.to_s)
+    end
+    args = [
+      self.class.command,
+      *Shellwords.split(exiftool_opts),
+      '-j',
+      '-coordFormat', '%.8f',
+      *expanded_filenames
+    ]
+
+    json = ''
+    begin
+      Open3.popen3(*args) do |stdin, stdout, _stderr, wait_thr|
+        if io_input
+          # Reading first 64KB.
+          # It is enough to parse exif tags.
+          # https://en.wikipedia.org/wiki/Exif#Technical_2
+          while (chunk = io_input.read(1 << 16))
+            stdin.write(chunk)
+          end
+          stdin.close
+        end
+        json = stdout.read.to_s.chomp
+        wait_thr.value
+      end
+    rescue Errno::ENOENT
+      json = ''
+    end
+
     raise ExiftoolNotInstalled if json == ''
 
     JSON.parse(json).each do |raw|

test/exiftool_test.rb

@@ -80,6 +80,17 @@
     validate_result(e, 'test/utf8.jpg')
   end
 
+  it 'supports an IO object as a constructor arg' do
+    File.open('test/IMG_2452.jpg', 'rb') do |io|
+      e = Exiftool.new(io)
+      _(e.errors?).must_be_false
+      h = e.to_hash
+      _(h[:file_type]).must_equal 'JPEG'
+      _(h[:mime_type]).must_equal 'image/jpeg'
+      _(h[:make]).must_equal 'Canon'
+    end
+  end
+
   describe 'single-get' do
     it 'responds with known correct responses' do
       Dir['test/*.jpg'].each do |filename|