TIP: 402 Title: General Platform UNC Support Version: $Revision: 1.2 $ Author: Jan Nijtmans State: Draft Type: Project Vote: Pending Created: 16-Jul-2011 Post-History: Discussions-To: Tcl Core list Keywords: Tcl Tcl-Version: 8.7 ~ Abstract Both Windows and Cygwin interpret paths starting with '''//''' as a special prefix, indicating that the path has the form: '''//server/share/file_path'''. Windows has built-in handling of such paths built-in. UNIX doesn't have this. It could be implemented through a VFS extension, but there is one problem: File normalization on UNIX collapes multiple slashes into a single slash, so this would convert the UNC path into a normal path. This makes it impossible to implement a VFS extension which uses '''//''' as prefix, implementing connection to a Samba server using the UNC path format. ~ Rationale At the moment, Cygwin and Windows have built-in a special case that paths starting with double-slash will not be collapsed into a single slash. UNIX does not do that. This change will allow a single uniform format for accessing (Samba) shares on external machines using the path format '''//server/share/file_path'''. On Windows and Cygwin this already works, because it is built-in Windows functionality. On UNIX a VFS extension could be developed which does the same. ~ Specification This document proposes: * Extend the special case built-in for Windows and Cygwin to UNIX, so paths starting with double-slash will no longer normalize to paths starting with a single slash. > '''POTENTIAL INCOMPATIBILITY''' * As '''//''' becomes a special prefix, the '''file split''' will return '''//''' as its first list element when the original path starts with a double slash. ~ Compatibility On UNIX, this means that paths like '''//usr/bin/tclsh''' might no longer do what it did earlier, if a VFS exists which uses '''//''' as path prefix. If no such VFS exists, it will probably still work, only comparing normalized paths will no longer regard '''//''' as equal to '''/'''. Handling of multiple slashes in other locations of the string will not change. So normalizing '''/foo//bar''' will still give '''/foo/bar'''. The most likely cause of multiple slashes appearing in a path is because of appending a file name to a path which already ends with a slash, e.g. |set dir "somedir/" |set path $dir/filename Of course, the '''file join''' command does not have this danger: |set dir "somedir/" |set path [file join $dir filename] On Windows and Cygwin, there is no change in behavior at all. ~ Alternatives Variations are possible in the handling of paths starting with 3 or more slashes. The current TIP implementation collapes more than 2 slashes to exactly 2 slashes, as the current Windows and Cygwin implementations do. ~ Reference Implementation A reference implementation is available at http://core.tcl.tk/tcl in branch ''jn-unc-vfs''. ~ Copyright This document has been placed in the public domain.