resolves asciidoctor#540 allow image type to be specified using forma…

…t attribute

lib/asciidoctor-pdf/asciidoctor_ext/image.rb

@@ -2,17 +2,17 @@ module Asciidoctor
 module Image
   class << self
     def image_type path
-      (::File.extname path).downcase[1..-1]
+      (::File.extname path)[1..-1].downcase
     end
   end
 
   def image_type
-    ::File.extname(inline? ? target : (attr 'target')).downcase[1..-1]
+    (attr 'format', nil, false) || ::File.extname(inline? ? target : (attr 'target'))[1..-1].downcase
   end
 
   def target_with_image_type
     image_path = inline? ? (target) : (attr 'target')
-    [image_path, (::File.extname image_path).downcase[1..-1]]
+    [image_path, (attr 'format', nil, false) || (::File.extname image_path)[1..-1].downcase]
   end
 end
 end

lib/asciidoctor-pdf/converter.rb

@@ -798,7 +798,7 @@ def convert_image node
       warn %(asciidoctor: WARNING: GIF image format not supported. Please convert #{target} to PNG.)
     end
 
-    unless (image_path = resolve_image_path node, target) && (::File.readable? image_path)
+    unless (image_path = resolve_image_path node, target, image_type) && (::File.readable? image_path)
       valid_image = false
       warn %(asciidoctor: WARNING: image to embed not found or not readable: #{image_path || target})
     end
@@ -1510,7 +1510,7 @@ def convert_inline_image node
         warn %(asciidoctor: WARNING: GIF image format not supported. Please convert #{target} to PNG.) unless scratch?
         valid = false
       end
-      unless (image_path = resolve_image_path node, target) && (::File.readable? image_path)
+      unless (image_path = resolve_image_path node, target, image_type) && (::File.readable? image_path)
         warn %(asciidoctor: WARNING: image to embed not found or not readable: #{image_path || target}) unless scratch?
         valid = false
       end
@@ -2517,7 +2517,7 @@ def resolve_imagesdir doc
   def resolve_image_path node, image_path = nil, image_type = nil
     imagesdir = resolve_imagesdir(doc = node.document)
     image_path ||= node.attr 'target'
-    image_type ||= ::Asciidoctor::Image.image_type image_path
+    image_type ||= ((node.attr 'format', nil, false) || (::Asciidoctor::Image.image_type image_path))
     # handle case when image is a URI
     if (node.is_uri? image_path) || (imagesdir && (node.is_uri? imagesdir) &&
         (image_path = (node.normalize_web_path image_path, imagesdir, false)))
@@ -2532,7 +2532,7 @@ def resolve_image_path node, image_path = nil, image_type = nil
       else
         ::OpenURI
       end
-      tmp_image = ::Tempfile.new ['image-', %(.#{image_type})]
+      tmp_image = ::Tempfile.new ['image-', %(.#{image_type || 'jpg'})]
       tmp_image.binmode if (binary = image_type != 'svg')
       begin
         open(image_path, (binary ? 'rb' : 'r')) {|fd| tmp_image.write(fd.read) }
@@ -2560,7 +2560,7 @@ def resolve_background_image doc, theme, key
       return bg_image if bg_image == 'none'
 
       if (bg_image.include? ':') && bg_image =~ ImageAttributeValueRx
-        # QUESTION should we support width and height in this case?
+        # QUESTION should we support width, height, and format in this case?
         bg_image = $1
       end