19.4. Data File Transfer

As mentioned before a data file is transferred using the command below.

From RFC1179:

The data file may contain any 8 bit values at all. The total number of bytes in the stream may be sent as the first operand, otherwise the field should be cleared to 0. The name of the data file should start with ASCII "dfA". This should be followed by a three digit job number. The job number should be followed by the host name which has constructed the data file. Interpretation of the contents of the data file is determined by the contents of the corresponding control file.

There are several surprises in RFC1179.

1. Apparently a job should only consist of a single data file. This is a severe limitation, and in fact the BSD lpr and other print spoolers process jobs with multiple data files. By convention, these data files have names of the form dfA, dfB, ... dfZ, dfa, dfz.

2. The RFC does not specify that the control file and data file job numbers must be identical. Most implementations follow this convention, which simplifies life tremendously.

3. The RFC does not specify that the control file and data file job host names must be identical. Most implementations follow this convention, which simplifies life tremendously.

4. A zero length data file does not cause a data transfer to take place. LPRng modifies this action to be slightly different. When a zero length data file transfer is indicated, all of the input until the connection is closed is used as the contents of the data file.

   When piping into the lpr program, this can be very useful as it eliminates the need to create temporary files on the local host. Note that some print spoolers do not use this interpretation, and this option should be used carefully.