ptg10805159Section 21.5 Source Code 801
48 /*
49 * Structure describing a print request.
50 */
51 struct printreq {
52 uint32_t size; /* size in bytes */
53 uint32_t flags; /* see below */
54 char usernm[USERNM_MAX]; /* user’s name */
55 char jobnm[JOBNM_MAX]; /* job’s name */
56 };
57 /*
58 * Request flags.
59 */
60 #define PR_TEXT 0x01 /* treat file as plain text */61 /*
62 * The response from the spooling daemon to the print command.
63 */
64 struct printresp {
65 uint32_t retcode; /* 0=success, !0=error code */
66 uint32_t jobid; /* job ID */
67 char msg[MSGLEN_MAX]; /* error message */
68 };
69 #endif /* _PRINT_H */[48 – 69] Theprintreqandprintrespstructures define the protocol between the
print command and the printer spooling daemon. Theprintcommand sends
aprintreqstructurespecifying the size of the job in bytes, job characteristics,
the user name, and the job name to the printer spooling daemon. The daemon
responds with aprintrespstructurecontaining a return code, the job ID,
and an error message if the request failed.
ThePR_TEXTjob characteristic indicates that the file being printed should be
treated as plaintext (instead of PostScript). We define a bitmask of flags
instead of defining a separate field for each flag. Although only one flag value
is currently defined, we could extend the protocol in the future to add more
characteristics. For example, we could add a flag to request double-sided
printing. Wehave room for 31 additional flags without requiring that we
change the size of the structure. Changing the size of the structuremeans that
we might introduce a compatibility problem between the client and the server
unless we upgrade both at the same time. An alternative approach is to add a
version number to the messages to allow the structures to change with each
version.
Note that we define all integers in the protocol structures with an explicit size.
This helps avoid misaligned structureelements when a client has a different
long integer size than the server.