utility added to make sure file handles can't be left open

make-epub.lua

@@ -162,21 +162,19 @@ local function download_pages(config)
       local temporary_html_file_name = utility.tmp_file_name()
       os.execute("curl " .. download_url:enquote() .. " > " .. temporary_html_file_name)
 
-      local html_file, err = io.open(temporary_html_file_name, "r")
+      utility.open(temporary_html_file_name, "r", "Could not download " .. download_url:enquote())(function(html_file)
-      if not html_file then error("Could not download " .. download_url:enquote()) end
+        local raw_html = html_file:read("*all")
-      local raw_html = html_file:read("*a")
-      html_file:close()
-      os.execute("rm " .. temporary_html_file_name)
 
         local parser = htmlparser.parse(raw_html)
         local content_tag = parser:select(".article > div > div") -- TODO add ability to set selector in config!
         local text = content_tag[1]:getcontent()
 
-      local page_file, err = io.open(section_dir .. page .. ".html", "w")
+        utility.open(section_dir .. page .. ".html", "w")(function(page_file)
-      if not page_file then error(err) end
           page_file:write(text .. "\n")
-      page_file:close()
+        end)
+      end)
 
+      os.execute("rm " .. temporary_html_file_name)
       os.execute("sleep " .. tostring(math.random(5))) -- avoid rate limiting
     end
   end
@@ -201,12 +199,9 @@ local function concatenate_pages(config)
 
   for section = config.sections.start, config.sections.finish do
     local section_dir = working_dir .. path_separator .. tostring(section) .. path_separator
-    local section_file, err = io.open(working_dir .. path_separator .. tostring(section) .. ".md", "w")
+    utility.open(working_dir .. path_separator .. tostring(section) .. ".md", "w")(function(section_file)
-    if not section_file then error(err) end
-
       for page = 1, config.page_counts[section - (config.sections.start - 1)] do
-      local page_file, err = io.open(section_dir .. page .. ".md", "r")
+        utility.open(section_dir .. page .. ".md", "r")(function(page_file)
-      if not page_file then error(err) end
           if config.sections.automatic_naming then
             local naming_patterns = {
               "^Prologue$",
@@ -224,20 +219,19 @@ local function concatenate_pages(config)
               line = page_file:read("*line")
             end
           else
-        section_file:write(page_file:read("*a"))
+            section_file:write(page_file:read("*all"))
           end
           section_file:write("\n") -- guarantees no accidental line collisions
-      page_file:close()
+        end)
       end
-    section_file:close()
+    end)
   end
 end
 
 local function write_markdown_file(config)
   local working_dir = get_base_file_name(config)
 
-  local markdown_file, err = io.open(get_base_file_name(config) .. ".md", "w")
+  utility.open(get_base_file_name(config) .. ".md", "w")(function(markdown_file)
-  if not markdown_file then error(err) end
     markdown_file:write(format_metadata(config))
     markdown_file:write(copyright_warning)
 
@@ -250,17 +244,16 @@ local function write_markdown_file(config)
       markdown_file:write("\n\n")
 
       local section_file_name = working_dir .. path_separator .. tostring(section)
-    local section_file, err = io.open(section_file_name .. ".md", "r")
+      utility.open(section_file_name .. ".md", "r")(function(section_file)
-    if not section_file then error(err) end
+        markdown_file:write(section_file:read("*all"))
-    markdown_file:write(section_file:read("*a"))
+      end)
-    section_file:close()
     end
 
     markdown_file:write("\n\n# Ebook Creation Metadata\n\n")
     markdown_file:write(copyright_warning)
     markdown_file:write("This ebook was created using the following config:\n\n")
     markdown_file:write("```json\n" .. config.config_file_text .. "\n```\n")
-  markdown_file:close()
+  end)
 end
 
 local function make_epub(config)
@@ -305,10 +298,9 @@ local function argparse(arguments, positional_arguments)
 end
 
 local function main(arguments)
-  local config_file, err = io.open(arguments.json_file_name, "r")
+  local config = utility.open(arguments.json_file_name, "r")(function(config_file)
-  if not config_file then error(err) end
+    return load_config(config_file:read("*all"))
-  local config = load_config(config_file:read("*all"))
+  end)
-  config_file:close()
 
   local actions = {
     download = download_pages,

utility-functions.lua

@@ -100,6 +100,17 @@ utility.tmp_file_name = function()
   return "." .. utility.uuid() .. ".tmp"
 end
 
+-- io.open, but errors are immediately thrown, and the file is closed for you
+utility.open = function(file_name, mode, custom_error_message)
+  local file, err = io.open(file_name, mode)
+  if not file then error(custom_error_message or err) end
+  return function(fn)
+    local result = fn(file)
+    file:close()
+    return result
+  end
+end
+
 utility.escape_quotes = function(input)
   -- the order of these commands is important and must be preserved
   input = input:gsub("\\", "\\\\")