haven::write_xpt() produces malformed LABELV8 header for long variable labels (incompatible with SAS)

[ankonyeni]

There is a discrepancy between haven::write_xpt() and the SAS autocall macro loc2xpt when writing XPT v8 datasets that contain variable/column labels longer than 40 characters. An XPT file produced by write_xpt() cannot be read by SAS — SAS reports an error when attempting to import the file.

The XPT V8/V9 specification states that long labels are placed in a labelrecords section whose header looks like:

"HEADER RECORD*******LABELV8 HEADER RECORD!!!!!!!nnnnn "

where nnnnn is the number of variables for which long labels will be defined.

When I write a dataset with a single column whose label exceeds 40 characters using haven::write_xpt(), the LABELV8 header in the produced file looks like this:

"HEADER RECORD*******LABELV8 HEADER RECORD!!!!!!! 1 0 "

When the same dataset is written using the SAS autocall macro loc2xpt, the LABELV8 header looks like this:

"HEADER RECORD*******LABELV8 HEADER RECORD!!!!!!!1 "

The LABELV8 header generated by write_xpt() is not consistent with the XPT V8/V9 specification and differs from the header produced by loc2xpt. This inconsistency appears to be the cause of the SAS read error.

# Minimal example (replace path/filenames as needed)
library(haven)

df <- data.frame(x = 1)

# label longer than 40 characters
attr(df$x, "label") <- "This is a very long variable label that exceeds forty characters"

# write XPT (to current working directory)
haven::write_xpt(df, "test_longlabel.xpt")

Steps to reproduce

1. Create a dataset with at least one variable whose label is > 40 characters (example above).
2. Call haven::write_xpt() to write a v8 XPT file.
3. Inspect the LABELV8 header in the file (open in hex/text viewer).
4. Attempt to read the XPT file in SAS using xpt2loc macro — SAS fails to read it (error).

This issue prevents interoperability with SAS when writing XPT v8 files that include variable labels longer than 40 characters.