1 files changed, 26 insertions, 16 deletions
diff --git a/data/sample.lua b/data/sample.lua
index 6c09442b5..9d6bf0fc7 100644
--- a/data/sample.lua
+++ b/data/sample.lua
@@ -2,7 +2,8 @@
 -- that is very similar to that of pandoc's HTML writer.
 -- There is one new feature: code blocks marked with class 'dot'
 -- are piped through graphviz and images are included in the HTML
--- output using 'data:' URLs.
+-- output using 'data:' URLs. The image format can be controlled
+-- via the `image_format` metadata field.
 --
 -- Invoke with: pandoc -t sample.lua
 --
@@ -12,6 +13,28 @@
 -- produce informative error messages if your code contains
 -- syntax errors.
 
+local pipe = pandoc.pipe
+local stringify = (require "pandoc.utils").stringify
+
+-- The global variable PANDOC_DOCUMENT contains the full AST of
+-- the document which is going to be written. It can be used to
+-- configure the writer.
+local meta = PANDOC_DOCUMENT.meta
+
+-- Chose the image format based on the value of the
+-- `image_format` meta value.
+local image_format = meta.image_format
+  and stringify(meta.image_format)
+  or "png"
+local image_mime_type = ({
+    jpeg = "image/jpeg",
+    jpg = "image/jpeg",
+    gif = "image/gif",
+    png = "image/png",
+    svg = "image/svg+xml",
+  })[image_format]
+  or error("unsupported image format `" .. img_format .. "`")
+
 -- Character escaping
 local function escape(s, in_attribute)
   return s:gsub("[<>&\"']",
@@ -44,19 +67,6 @@ local function attributes(attr)
   return table.concat(attr_table)
 end
 
--- Run cmd on a temporary file containing inp and return result.
-local function pipe(cmd, inp)
-  local tmp = os.tmpname()
-  local tmph = io.open(tmp, "w")
-  tmph:write(inp)
-  tmph:close()
-  local outh = io.popen(cmd .. " " .. tmp,"r")
-  local result = outh:read("*all")
-  outh:close()
-  os.remove(tmp)
-  return result
-end
-
 -- Table to store footnotes, so they can be included at the end.
 local notes = {}
 
@@ -217,8 +227,8 @@ function CodeBlock(s, attr)
   -- If code block has class 'dot', pipe the contents through dot
   -- and base64, and include the base64-encoded png as a data: URL.
   if attr.class and string.match(' ' .. attr.class .. ' ',' dot ') then
-    local png = pipe("base64", pipe("dot -Tpng", s))
-    return '<img src="data:image/png;base64,' .. png .. '"/>'
+    local img = pipe("base64", {}, pipe("dot", {"-T" .. image_format}, s))
+    return '<img src="data:' .. image_mime_type .. ';base64,' .. img .. '"/>'
   -- otherwise treat as code (one could pipe through a highlighter)
   else
     return "<pre><code" .. attributes(attr) .. ">" .. escape(s) ..