Select Zip64 extensions a little more aggressively.

 * Compressed files close to 4GiB (in case compression makes file larger)

 * Include encryption overhead when checking whether file is too big.

 * Clarify comments

Suggested by a conversation on info-zip-dev mailing list.

diff --git a/libarchive/archive_write_set_format_zip.c b/libarchive/archive_write_set_format_zip.c
index 0399b7b793db1fbd7a0e349866b16ea2e1e2323e..bad577132773fa62e39ee3d509b3c2b89736f856 100644 (file)
--- a/libarchive/archive_write_set_format_zip.c
+++ b/libarchive/archive_write_set_format_zip.c
@@ -715,9 +715,20 @@ archive_write_zip_header(struct archive_write *a, struct archive_entry *entry)
                                zip->entry_compressed_size += additional_size;
                }
 
-               if ((zip->flags & ZIP_FLAG_FORCE_ZIP64) /* User asked. */
-                   || (zip->entry_uncompressed_size > 0xffffffffLL)) {
-                                                       /* Large entry. */
+               /*
+                * Set Zip64 extension in any of the following cases
+                * (this was suggested by discussion on info-zip-dev
+                * mailing list):
+                *  = Zip64 is being forced by user
+                *  = File is over 4GiB uncompressed
+                *    (including encryption header, if any)
+                *  = File is over 3.75GiB and is being compressed
+                *    (compression might make file larger)
+                */
+               if ((zip->flags & ZIP_FLAG_FORCE_ZIP64)
+                   || (zip->entry_uncompressed_size + additional_size > 0xffffffffLL)
+                   || (zip->entry_uncompressed_size > 0xf0000000LL
+                       && zip->entry_compression != COMPRESSION_STORE)) {
                        zip->entry_uses_zip64 = 1;
                        version_needed = 45;
                }
@@ -725,9 +736,11 @@ archive_write_zip_header(struct archive_write *a, struct archive_entry *entry)
                /* We may know the size, but never the CRC. */
                zip->entry_flags |= ZIP_ENTRY_FLAG_LENGTH_AT_END;
        } else {
-               /* Prefer deflate if it's available, because deflate
-                * has a clear end-of-data marker that makes
-                * length-at-end more reliable. */
+               /* We don't know the size.  In this case, we prefer
+                * deflate (it has a clear end-of-data marker which
+                * makes length-at-end more reliable) and will
+                * enable Zip64 extensions unless we're told not to.
+                */
                zip->entry_compression = COMPRESSION_DEFAULT;
                zip->entry_flags |= ZIP_ENTRY_FLAG_LENGTH_AT_END;
                if ((zip->flags & ZIP_FLAG_AVOID_ZIP64) == 0) {