Add `su_save` (#274)

* Add `su_save`

* Increase load priority

Some default plugins like `autoreload` expect the file to be available 
after the save, so we try to run before it.

* Avoid using `--keep-cwd` as it needs a recent version of `pkexec`

2 files changed, 116 insertions, 0 deletions

diff --git a/manifest.json b/manifest.json
index 81e06c9..4397258 100644
--- a/manifest.json
+++ b/manifest.json
@@ -1277,6 +1277,14 @@
       "mod_version": "3"
     },
     {
+      "description": "Save files that require root permissions. Needs `pkexec`.",
+      "version": "1.0",
+      "path": "plugins/su_save.lua",
+      "id": "su_save",
+      "name": "Save as Super User",
+      "mod_version": "3"
+    },
+    {
       "description": "Takes an SVG screenshot. Only browsers seem to support the generated SVG properly.",
       "version": "0.1",
       "path": "plugins/svg_screenshot.lua",
diff --git a/plugins/su_save.lua b/plugins/su_save.lua
new file mode 100644
index 0000000..4091f4a
--- /dev/null
+++ b/plugins/su_save.lua
@@ -0,0 +1,108 @@
+-- mod-version:3 priority:99
+local core = require "core"
+local common = require "core.common"
+local command = require "core.command"
+local config = require "core.config"
+local Doc = require "core.doc"
+
+
+-- When pkexec version >= 121 is more widespread,
+-- change to "pkexec --keep-cwd cp '%s' '%s'"
+local default_command = "pkexec sh -c \"cd $PWD; cp '%s' '%s'\""
+config.plugins.su_save = common.merge({
+  enabled = true,
+  save_command = default_command,
+  config_spec = {
+    name = "Super User Save",
+    {
+      label = "Enabled",
+      description = "Disable or enable the automatic save as super user.",
+      path = "enabled",
+      type = "toggle",
+      default = true
+    },
+    {
+      label = "Save command",
+      description = "Command used to save the temporary file (first '%s') over the original file (second '%s').",
+      path = "save_command",
+      type = "string",
+      default = default_command
+    },
+  }
+}, config.plugins.su_save)
+
+
+local doc_save = Doc.save
+local function su_save(doc, filename, abs_filename, ...)
+  if not config.plugins.su_save then
+    return error("Bad su_save plugin configuration")
+  end
+
+  local old_clean_change_id = doc.clean_change_id
+
+  -- Override io.open to check for permission errors
+  local io_open = io.open
+  local temp_filename, save_location
+  local io_open_valid = true
+  io.open = function(...)
+    -- Only override the first io.open call. Hopefully this works well enough.
+    io.open = io_open
+
+    -- In case Doc.save crashes before even getting to the first io.open,
+    -- we need to use the original one.
+    if not io_open_valid then return io_open(...) end
+
+    local fp, error_msg, error_code = io_open(...)
+    -- If there was an access issue with open, save to a temporary file
+    if error_code == 13 then -- 13 seems to be EACCES, to verify use `errno -l`
+      save_location = select(1, ...)
+      temp_filename = core.temp_filename()
+      core.log_quiet('Trying to save "%s" as super user using "%s" as temporary file', save_location, temp_filename)
+      return io_open(temp_filename, select(2, ...))
+    end
+
+    return fp, error_msg, error_code
+  end
+
+  -- Call original Doc:save, now with custom io.open
+  local ok, result = pcall(doc_save, doc, filename, abs_filename, ...)
+  io_open_valid = false
+
+  if temp_filename then
+    if ok then
+      -- This is using the blocking os.execute to simplify error management
+      local success, exit_type, exit_code = os.execute(string.format(config.plugins.su_save.save_command, temp_filename, save_location))
+      if not success then
+        -- Restore change_id because save failed
+        doc.clean_change_id = old_clean_change_id
+        -- 126 means "dismissed" for pkexec. TODO: Should this be configurable?
+        if exit_type == "exit" and exit_code == 126 then
+          return error(string.format('Unable to save "%s" with super user permissions (dismissed)', save_location))
+        end
+        return error(string.format('Unable to save "%s" with super user permissions (%s code %d)', save_location, exit_type, exit_code))
+      end
+    end
+    os.remove(temp_filename)
+  end
+
+  if not ok then
+    -- Propagate error
+    return error(result)
+  end
+
+  return result
+end
+
+function Doc:save(...)
+  if not (config.plugins.su_save and config.plugins.su_save.enabled) then
+    return doc_save(self, ...)
+  end
+  return su_save(self, ...)
+end
+
+command.add("core.docview!", {
+  ["su-save:save-as-super-user"] = function(dv)
+    su_save(dv.doc)
+    core.log('Saved "%s"', dv.doc.filename)
+  end
+})