Add e2lib.join(), a function that joins path components

Inspired by Python's os.path.join

Signed-off-by: Tobias Ulmer <tu@emlix.com>

diff --git a/generic/e2lib.lua b/generic/e2lib.lua
index 277a26fd999b1517e62c712a9e82d80420b4bc10..1f7ec7fabb948c0f1d5c0af8233257b7646c531b 100644 (file)
--- a/generic/e2lib.lua
+++ b/generic/e2lib.lua
@@ -665,6 +665,55 @@ function e2lib.basename(path)
     return base
 end
 
+--- Return a file path joined from the supplied components.
+-- This function is modelled after Python's os.path.join, but missing some
+-- features and handles edge cases slightly different. It only knows about
+-- UNIX-style forward slash separators. Joining an empty string at the end will
+-- result in a trailing separator to be added, following Python's behaviour.
+-- The function does not fail under normal circumstances.
+--
+-- @param p1 A potentially empty path component (string). This argument is
+--           mandatory.
+-- @param p2 A potentially empty, optional path component (string).
+-- @param ... Further path components, following the same rule as "p2".
+-- @return A joined path (string), which may be empty.
+function e2lib.join(p1, p2, ...)
+       assert(type(p1) == "string")
+       assert(p2 == nil or type(p2) == "string")
+
+       local sep = "/"
+       local args = {p1, p2, ...}
+       local buildpath = ""
+       local sepnext = false
+
+       for _,component in ipairs(args) do
+               assert(type(component) == "string")
+
+               if sepnext then
+                       -- If the previous or next component already
+                       -- has a separator in the right place, we don't
+                       -- need to add one. We do however not go to the
+                       -- trouble removing multiple separators.
+                       if buildpath:sub(-1) == sep or
+                               component:sub(1) == sep then
+                               -- do nothing
+                       else
+                               buildpath = buildpath .. sep
+                       end
+               end
+
+               buildpath = buildpath .. component
+
+               if component:len() > 0 then
+                       sepnext = true
+               else
+                       sepnext = false
+               end
+       end
+
+       return buildpath
+end
+
 function e2lib.is_backup_file(path)
     return string.find(path, "~$") or string.find(path, "^#.*#$")
 end