augeas backend: remove some race conditions in set method

1 files changed, 17 insertions, 4 deletions

diff --git a/acf2/persistence/backends/augeas.lua b/acf2/persistence/backends/augeas.lua
index f883409..fbe993e 100644
--- a/acf2/persistence/backends/augeas.lua
+++ b/acf2/persistence/backends/augeas.lua
@@ -46,6 +46,11 @@ local function key(mode)
    return mode == '@' and '.' or mode:sub(2, -1)
 end
 
+local function append_key_pred(path, mode, value)
+   return append_pred(path, key(mode).." = '"..value.."'")
+end
+
+
 local function conv_path(path)
    local res = '/files'
    if #path == 0 then return res, nil, {} end
@@ -69,7 +74,7 @@ local function conv_path(path)
 	    res = append_pred(res, comp)
 	 else
 	    assert(type(comp) == 'string' and comp:match('^[%w _-]+$'))
-	    res = append_pred(res, key(mode).." = '"..comp.."'")
+	    res = append_key_pred(res, mode, comp)
 	    table.insert(keys, key(mode))
 	 end
 	 mode = nil
@@ -186,10 +191,18 @@ function backend:set(mods)
 	 if count > 0 and not new then return apath, keys end
 
 	 if key_mode(pmode) then
-	    ppath = insert(parent, true)
+	    local cpath = pmode == '@' and append_key_pred(
+	       ppath, '@', ''
+	    ) or append_pred(ppath, 'count('..key(pmode)..') = 0')
+
+	    count = #self.aug:match(cpath)
+	    assert(count < 2)
+	    if count == 0 then cpath = insert(parent, true) end
+
 	    local key = key(pmode)
-	    self.aug:set(ppath..'/'..key, name)
-	    return append_pred(ppath, key), keys
+	    self.aug:set(cpath..'/'..key, name)
+
+	    return append_key_pred(ppath, pmode, name), keys
 	 end
 
 	 if #matches == 0 then