Tickets :: Comment on [#25] error :source-ing files with "variable length" record format

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Comment	> Motivation for this ticket. > > The problem with sourcing appears whenever a vim plugin is copied to > VMS via FTP. If it is dropped into [plugin] or [ftplugin] or > [autoload] it then crashes when it is sourced. > > -------------------- > Details > > Here are some notes I have compiled on copying files from Windows to > VMS via FTP. > > Binary FTP > First of all, binary-FTP-copying is of out of question. The file > created on the VMS is padded to the next higher multiple of 512 > bytes, which is very ugly. This also shows when the file is > opened in vim. (Other than that, the file thus copied is nicely > readable on the VMS by vim, and sourcing it works -- if its > fileformat on Windows was "unix".) The rest of this therefore > discusses ASCII FTP. > > ASCII FTP > A file on the local (Windows) machine either has the DOS or UNIX > fileformat. In the former case, the lines are separated by > 0d0a, in the latter case only by 0a. Obviously, the former is > native, the other is alien to Windows. > > When the file is ASCII-FTP copied to VMS, it is converted to an > RMS file with variable-length record format and > carriage-return-carriage-control record attributes. The FTP knows > it is copying a file from Windows to VMS, and thus presumes > that the original (Windows) file uses 0d0a sequences as line > separators. (Which assumption is wrong if the fileformat is Unix.) > > Whatever the fileformat was on Windows, the resultant file has > now been converted to an RMS file, whose each line (record) has > an attribute specifying its length. The record attributes are > "Carriage return carriage control". This would suggest there are > still some "carriage returns" between records (xxd reports line > feeds, "0a"s), but this may just be a trick of OpenVMS: > > Wikipedia: "OpenVMS uses a record-based file system, which > stores text files as one record per line. In most file formats, > no line terminators are actually stored, but the Record > Management Services facility can transparently add a terminator to > each line when it is retrieved by an application." > > This is where the original fileformat makes a difference: a > multi-line file with fileformat=dos has been converted to a > multi-record RMS file, with records starting wherever 0d0a > sequences were found. A multi-line file with fileformat=unix was also > converted, but since there were no 0d0a sequences, it only > contains a single record on VMS. xxd sees them identically: for the > multi-record "dos" file it displays "0a"s where records break; > for the single-record "unix" file it displays "0a"s which have > not been recognised as line terminators and are "still present" > in the single record. > > Example: let's suppose a Windows file contains the text "a\nb". > The "dos" representation would be 61-0d-0a-62, and this would be > converted to a 2-record file: the first record would have length > 1 (the byte 61), the second record would also have length 1 > (the byte 62), and xxd would show 61-0a-62. The "unix" > representation would be 61-0a-62, and this would be converted to a > single-record file: the record would have length 3 (61-0a-62), > and xxd would also show 61-0a-62. > > Now we use vim to open the file. The "dos" file is read as a > multi-line file, with "0a"s used as separators. Good. The "unix" > file is read as a one-liner. That's also fine with vim, which > notices the "0a"s and considers them line separators. Also good. > > In both cases vim detected the fileformat as "unix" (since there > were no 0d0a sequences). If we were to save either of the files > using the VMS vim, it would become an RMS file with Stream_LF > record format (and the same carriage-return-carriage-control > record attributes). > > Paradoxically, there is a problem when sourcing the multi-record, > originally-dos-fileformat files -- while sourcing the > single-record, originally-unix-fileformat file succeeds. Perhaps > this is a vim bug. > > When sourcing the file, vim apparently does not recognise the > record limits and simply concatenates the records without putting > the 0a bytes in between. Thus, the whole text becomes a mess (the > lines are not separated at all). > > On the contrary, the originally-unix-fileformat file works > because after vim reads it as a one-liner, it detects the "0a"s, > separates the lines, and sources it correctly. > > Conclusion > The above would suggest it is best to use fileformat=unix when > FTP copying. However, there is a serious problem with this: if > the file is longer than 32767 bytes, the file is truncated > because at most 32768 bytes can be put into a single RMS-file record. > (And we are creating a single-file record, as described above.) > What's worse, no warning/error is issued when this happens > during the ASCII-FTP copy. > > Thus, it is best and safest to use the dos fileformat, ASCII FTP > copy, and then change the file's record format to Stream_LF > using convert/fdl. > > >
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