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supports upper/lower case file names. This is a convenience for
users of systems (such as Unix) which store filenames in upper
and lower case.
+ The receiver should accommodate file names in lower and upper
case.
+ When transmitting files between different operating systems,
file names must be acceptable to both the sender and receiving
operating systems.
If directories are included, they are delimited by /; i.e.,
"subdir/foo" is acceptable, "subdir\foo" is not.
Length The file length and each of the succeeding fields are optional.[3]
The length field is stored in the block as a decimal string counting
the number of data bytes in the file. The file length does not
include any CPMEOF (^Z) or other garbage characters used to pad the
last block.
If the file being transmitted is growing during transmission, the
length field should be set to at least the final expected file
length, or not sent.
The receiver stores the specified number of characters, discarding
any padding added by the sender to fill up the last block.
Modification Date The mod date is optional, and the filename and length
may be sent without requiring the mod date to be sent.
Iff the modification date is sent, a single space separates the
modification date from the file length.
The mod date is sent as an octal number giving the time the contents
of the file were last changed, measured in seconds from Jan 1 1970
Universal Coordinated Time (GMT). A date of 0 implies the
modification date is unknown and should be left as the date the file
is received.
This standard format was chosen to eliminate ambiguities arising from
transfers between different time zones.
__________
3. Fields may not be skipped.
Chapter 5 XMODEM Protocol Enhancements
X/YMODEM Protocol Reference 10-27-87 14
Mode Iff the file mode is sent, a single space separates the file mode
from the modification date. The file mode is stored as an octal
string. Unless the file originated from a Unix system, the file mode
is set to 0. rb(1) checks the file mode for the 0x8000 bit which
indicates a Unix type regular file. Files with the 0x8000 bit set
are assumed to have been sent from another Unix (or similar) system
which uses the same file conventions. Such files are not translated
in any way.
Serial Number Iff the serial number is sent, a single space separates the
serial number from the file mode. The serial number of the
transmitting program is stored as an octal string. Programs which do
not have a serial number should omit this field, or set it to 0. The
receiver's use of this field is optional.
Other Fields YMODEM was designed to allow additional header fields to be
added as above without creating compatibility problems with older
YMODEM programs. Please contact Omen Technology if other fields are
needed for special application requirements.
The rest of the block is set to nulls. This is essential to preserve
upward compatibility.[4]
If the filename block is received with a CRC or other error, a
retransmission is requested. After the filename block has been received,
it is ACK'ed if the write open is successful. If the file cannot be
opened for writing, the receiver cancels the transfer with CAN characters
as described above.
The receiver then initiates transfer of the file contents according to the
standard XMODEM/CRC protocol.
After the file contents have been transmitted, the receiver again asks for