The CUPS filter and backend APIs define standard exit codes and provide access to the backchannel data stream. They are only used when writing backends, filters, and port monitors.
The <cups/backend.h> and <cups/cups.h> header files must be included to use the CUPS_BACKEND_ constants and cupsBackChannel functions, respectively.
Programs using these functions must be linked to the CUPS library: libcups.a, libcups.so.2, libcups.2.dylib, libcups_s.a, or libcups2.lib depending on the platform. The following command compiles myprogram.c using GCC and the CUPS library:
gcc -o myprogram myprogram.c -lcups
All of these functions require CUPS 1.2 or higher.
Read data from the backchannel. Reads up to "bytes" bytes from the backchannel. The "timeout" parameter controls how many seconds to wait for the data - use 0.0 to return immediately if there is no data, -1.0 to wait for data indefinitely.
ssize_t
cupsBackChannelRead(
char * buffer,
size_t bytes,
double timeout);
| Name | Description |
|---|---|
| buffer | Buffer to read |
| bytes | Bytes to read |
| timeout | Timeout in seconds |
Bytes read or -1 on error
Write data to the backchannel. Writes "bytes" bytes to the backchannel. The "timeout" parameter controls how many seconds to wait for the data to be written - use 0.0 to return immediately if the data cannot be written, -1.0 to wait indefinitely.
ssize_t
cupsBackChannelWrite(
const char * buffer,
size_t bytes,
double timeout);
| Name | Description |
|---|---|
| buffer | Buffer to write |
| bytes | Bytes to write |
| timeout | Timeout in seconds |
Bytes written or -1 on error