cups/cups-failover-backend.patch

diff -up cups-2.4.0/backend/failover.c.failover cups-2.4.0/backend/failover.c
--- cups-2.4.0/backend/failover.c.failover	2021-12-15 11:06:14.274967317 +0100
+++ cups-2.4.0/backend/failover.c	2021-12-15 11:06:14.274967317 +0100
@@ -0,0 +1,837 @@
+/*
+ * Failover Backend for the Common UNIX Printing System (CUPS).
+ *
+ * Copyright (c) 2014, Red Hat, Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * * Neither the name of Red Hat, Inc. nor the names of its contributors
+ *   may be used to endorse or promote products derived from this software
+ *   without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT,
+ * INC.  BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+ * USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * Original version by Clark Hale, Red Hat, Inc.
+ *
+ * This backend presents a fake printer that will choose the first
+ * available printer from a list of IPP URIs.
+ *
+ * Option failover contains a comma separated list of IPP URIs.  The
+ * URIs are attempted in-order.
+ *
+ * Option failover-retries contains an integer that indicates how many
+ * times to iterate through the failover list before completely
+ * failing.
+ *
+ * Contents:
+ *   main()                   - Checks each printer in a failover list, and
+ *                              sends job data to the first available printer
+ *   move_job()               - Sends and IPP Move-Job request
+ *   check_printer()          - Checks a printer's attributes to see
+ *                              if it's enabled and accepting jobs
+ *   read_config()            - Read the backends configuration from
+ *                              options
+ *   get_printer_attributes() - Sends an IPP Get-Attributes request to
+ *                              a URI
+ *   sigterm_handler()        - Handle SIGTERM that cancels the job
+ *   password_cb()            - Password call back used to disable password
+ *                              prompt
+ */
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <cups/http-private.h>
+#include <cups/http.h>
+#include "backend-private.h"
+
+/*
+ * Return Values
+ */
+typedef enum fo_state_e
+{
+  FO_PRINTER_GOOD = 0,
+  FO_PRINTER_BAD,
+  FO_PRINTER_BUSY,
+  FO_AUTH_REQUIRED
+} fo_state_t;
+
+/*
+ * Constants
+ */
+#define FAILOVER_DEFAULT_RETRIES        (3)
+#define FAILOVER_PASSWORD_RETRIES_MAX   (3)
+
+/*
+ * Local Functions
+ */
+static       int   check_printer(const char *device_uri);
+static       int   read_config(cups_array_t *printer_array, int *retries,
+                               const char *options);
+static       int   get_printer_attributes(const char *device_uri,
+                                          ipp_t **attributes);
+static       int   move_job(int jobid, const char *dest);
+static       void  sigterm_handler(int sig);
+static const char *password_cb(const char *);
+
+/*
+ * Global Variables
+ */
+static int         job_canceled = 0;     /* Job canceled */
+static char       *password = NULL;      /* password for device */
+static int         password_retries = 0;
+static const char *auth_info_required = "none";
+
+/*
+ * 'main()' - Checks each printer in a failover list, and
+ *            sends job data to the first available printer
+ * Usage:
+ *    printer-uri job-id user title copies options [file]
+ *
+ *    The printer-uri option is not used, but it still required to fit
+ *    to the backend(7) standards.
+ */
+int
+main(int argc, char *argv[])
+{
+  const char   *selected_uri = NULL;      /* URI of selected printer     */
+  const char   *tmp_device_uri;           /* Device URI to check         */
+  cups_array_t *printer_array;            /* Array of available printers */
+  int           printer_count = 0;        /* current printer array index */
+  int           retry_max = 1;            /* maximum retries before exit */
+  int           retry_count = 0;          /* current retry number        */
+  int           auth_failed_count = 0;    /* auth failures per loop      */
+  int           rc = CUPS_BACKEND_OK;
+#if defined(HAVE_SIGACTION) && !defined(HAVE_SIGSET)
+  struct        sigaction action;       /* Actions for POSIX signals */
+#endif /* HAVE_SIGACTION && !HAVE_SIGSET */
+
+ /*
+  * Check args
+  */
+  if (argc == 1)
+  {
+   /*
+    * print out discovery data
+    */
+    char *backendName;
+
+    if ((backendName = strrchr(argv[0], '/')) != NULL)
+      backendName++;
+    else
+      backendName = argv[0];
+
+    _cupsLangPrintf(stderr,"network %s \"Unknown\" \"%s (%s)\"\n",
+                    backendName,
+                    _cupsLangString(cupsLangDefault(), _("Failover Printer")),
+                    backendName);
+
+    return (CUPS_BACKEND_OK);
+  }
+  else if (argc < 6)
+  {
+    _cupsLangPrintf(stderr,
+                    _("Usage: %s job-id user title copies options [file]"),
+                    argv[0]);
+    return (CUPS_BACKEND_STOP);
+  }
+
+  fprintf(stderr, "DEBUG: Failover backend starting up.\n");
+
+ /*
+  * Don't buffer status messages
+  */
+  setbuf(stderr, NULL);
+
+ /*
+  * Ignore SIGPIPE and catch SIGTERM signals...
+  */
+#ifdef HAVE_SIGSET
+  sigset(SIGPIPE, SIG_IGN);
+  sigset(SIGTERM, sigterm_handler);
+#elif defined(HAVE_SIGACTION)
+  memset(&action, 0, sizeof(action));
+  action.sa_handler = SIG_IGN;
+  sigaction(SIGPIPE, &action, NULL);
+
+  sigemptyset(&action.sa_mask);
+  sigaddset(&action.sa_mask, SIGTERM);
+  action.sa_handler = sigterm_handler;
+  sigaction(SIGTERM, &action, NULL);
+#else
+  signal(SIGPIPE, SIG_IGN);
+  signal(SIGTERM, sigterm_handler);
+#endif /* HAVE_SIGSET */
+
+  printer_array = cupsArrayNew(NULL, NULL);
+
+ /*
+  * Read Configuration
+  */
+  if ((rc = read_config(printer_array, &retry_max,
+                        argv[5])) != CUPS_BACKEND_OK)
+  {
+    fprintf(stderr, "ERROR: Failed to read configuration options!\n");
+    goto cleanup;
+  }
+
+ /*
+  * Main Retry Loop
+  */
+  for (retry_count = 0; retry_count < retry_max; retry_count++)
+  {
+    fprintf(stderr, "DEBUG: Retry loop #%d\n", retry_count + 1);
+
+   /*
+    * Reset Counters
+    */
+    printer_count = 0;
+    auth_failed_count = 0;
+
+    tmp_device_uri = (char *)cupsArrayFirst(printer_array);
+
+    do
+    {
+      if (job_canceled)
+      {
+        fprintf(stderr, "DEBUG: Job Canceled\n");
+        goto cleanup;
+      }
+
+      fprintf(stderr,"DEBUG: Checking printer #%d: %s\n",
+              printer_count+1, tmp_device_uri);
+
+      rc = check_printer(tmp_device_uri);
+
+      // Printer is available and not busy.
+      if ( rc == FO_PRINTER_GOOD )
+      {
+        selected_uri = tmp_device_uri;
+        break;
+      }
+      // Printer is busy
+      else if (rc == FO_PRINTER_BUSY)
+      {
+        fprintf(stderr, "DEBUG: Waiting for job to complete.\n");
+        sleep(2);
+        continue;
+      }
+      // Authorization is required to access the printer.
+      else if (rc == FO_AUTH_REQUIRED)
+      {
+        auth_failed_count++;
+        fprintf(stderr, "DEBUG: auth_failed_count = %d\n", auth_failed_count);
+      }
+      // Printer is stopped or not accepting jobs
+      else
+      {
+        if (!printer_count)
+          fprintf(stderr, "INFO: Primary Printer, %s, not available.  "
+                  "Attempting Failovers...\n",
+                  tmp_device_uri);
+        else
+          fprintf(stderr, "INFO: Failover Printer, %s, not available.  "
+                  "Attempting Failovers..\n",
+                  tmp_device_uri);
+        printer_count++;
+        tmp_device_uri = (char *)cupsArrayNext(printer_array);
+      }
+    } while (tmp_device_uri != NULL);
+
+    if (selected_uri && !printer_count)
+      fprintf(stderr, "STATE: -primary-printer-failed\n");
+    else
+      fprintf(stderr, "STATE: +primary-printer-failed\n");
+
+    if (job_canceled)
+    {
+      fprintf(stderr, "DEBUG: Job Canceled\n");
+      goto cleanup;
+    }
+
+    if (!selected_uri && auth_failed_count == printer_count)
+    {
+      fprintf(stderr, "ERROR:  All failover printers failed with "
+              "authorization issues.\n");
+      rc = CUPS_BACKEND_AUTH_REQUIRED;
+      fprintf(stderr, "ATTR: auth-info-required=%s\n", auth_info_required);
+      goto cleanup;
+    }
+    else if (!selected_uri && retry_count + 1 < retry_max)
+    {
+      fprintf(stderr, "INFO: No suitable printer found...retrying...\n");
+      sleep(2);
+      continue;
+    }
+    else if (selected_uri)
+    {
+      fprintf(stderr, "DEBUG: Using printer, %s.\n", selected_uri);
+      break;
+    }
+  }
+
+  if (!selected_uri)
+  {
+    fprintf(stderr, "ERROR: No suitable printer found.  Aborting print\n");
+    rc = CUPS_BACKEND_FAILED;
+    goto cleanup;
+  }
+
+  rc = move_job(atoi(argv[1]), selected_uri);
+
+  if (job_canceled)
+    rc = CUPS_BACKEND_OK;
+
+cleanup :
+  if (job_canceled)
+    rc = CUPS_BACKEND_OK;
+
+  tmp_device_uri = (char *)cupsArrayFirst(printer_array);
+  do
+  {
+    free((void *)tmp_device_uri);
+  } while ((tmp_device_uri = (char *)cupsArrayNext(printer_array)) != NULL);
+
+  cupsArrayDelete(printer_array);
+  sleep(2);
+  return (rc);
+}
+
+/*
+ * 'check_printer()' - Checks the status of a remote printer and returns
+ *                     back a good/bad/busy status.
+ */
+int
+check_printer(const char *device_uri)
+{
+  ipp_t           *attributes = NULL;     /* attributes for device_uri */
+  ipp_attribute_t *tmp_attribute;         /* for examining attribs     */
+  int              rc = FO_PRINTER_GOOD;  /* return code               */
+  char            *reason;                /* printer state reason */
+  int              i;
+
+  fprintf(stderr, "DEBUG: Checking printer %s\n",device_uri);
+
+  rc = get_printer_attributes(device_uri, &attributes);
+  if ( rc != CUPS_BACKEND_OK )
+  {
+    fprintf(stderr, "DEBUG: Failed to get attributes from printer: %s\n",
+            device_uri);
+    if ( rc == CUPS_BACKEND_AUTH_REQUIRED )
+      return (FO_AUTH_REQUIRED);
+    else
+      return (FO_PRINTER_BAD);
+  }
+
+ /*
+  * Check if printer is accepting jobs
+  */
+  if ((tmp_attribute = ippFindAttribute(attributes,
+                                        "printer-is-accepting-jobs",
+                                        IPP_TAG_BOOLEAN)) != NULL &&
+      !tmp_attribute->values[0].boolean)
+  {
+    fprintf(stderr,
+            "DEBUG: Printer, %s, is not accepting jobs.\n",
+            device_uri);
+
+    rc = FO_PRINTER_BAD;
+  }
+
+ /*
+  * Check if printer is stopped or busy processing
+  */
+  if ((tmp_attribute = ippFindAttribute(attributes,
+                                        "printer-state",
+                                        IPP_TAG_ENUM)) != NULL)
+  {
+    // Printer Stopped
+    if ( tmp_attribute->values[0].integer == IPP_PRINTER_STOPPED )
+    {
+      fprintf(stderr, "DEBUG: Printer, %s, stopped.\n", device_uri);
+      rc = FO_PRINTER_BAD;
+    }
+    // Printer Busy
+    else if ( tmp_attribute->values[0].integer == IPP_PRINTER_PROCESSING )
+    {
+      fprintf(stderr, "DEBUG: Printer %s is busy.\n", device_uri);
+      rc = FO_PRINTER_BUSY;
+    }
+  }
+
+  /*
+   * Parse through the printer-state-reasons
+   */
+  if ((tmp_attribute = ippFindAttribute(attributes, "printer-state-reasons",
+                                        IPP_TAG_KEYWORD)) != NULL)
+  {
+    for (i = 0; i < tmp_attribute->num_values; i++)
+    {
+      reason = tmp_attribute->values[i].string.text;
+      int len = strlen(reason);
+
+      if (len > 8 && !strcmp(reason + len - 8, "-warning"))
+      {
+        fprintf(stderr, "DEBUG: Printer Supply Warning, %s\n", reason);
+        rc = FO_PRINTER_BAD;
+      }
+      else if (len > 6 && !strcmp(reason + len - 6, "-error"))
+      {
+        fprintf(stderr, "DEBUG: Printer Supply Error, %s\n", reason);
+        rc = FO_PRINTER_BAD;
+      }
+    }
+  }
+
+  return (rc);
+}
+
+/*
+ * 'read_config()' - Parses the failover and failover-retries options
+ *
+ */
+static int
+read_config(cups_array_t *printer_array, int *retries, const char *options)
+{
+
+  const char    *tmp;                   /* temporary ptr                     */
+  char          *tok_tmp;               /* temporary ptr for option  parsing */
+  int            jobopts_count = 0;     /* number of options                 */
+  cups_option_t *jobopts = NULL;        /* job options                       */
+
+
+  fprintf(stderr, "DEBUG: Reading Configuration.\n");
+  jobopts_count = cupsParseOptions(options, 0, &jobopts);
+
+  if (!jobopts_count)
+  {
+    fprintf(stderr,
+            "ERROR: No job options!  Cannot find failover options!\n");
+    return (CUPS_BACKEND_STOP);
+  }
+
+ /*
+  * Get attributes from the primary printer
+  */
+  fprintf(stderr, "DEBUG: Searching for failover option.\n");
+
+  if ((tmp = cupsGetOption("failover", jobopts_count, jobopts)) != NULL)
+  {
+    fprintf(stderr, "DEBUG: Failover option contents: %s.\n", tmp);
+
+    tok_tmp = strdup(tmp);
+
+    tmp = strtok(tok_tmp, ",");
+    do
+    {
+      cupsArrayAdd(printer_array, strdup(tmp));
+    } while ((tmp = strtok(NULL,",")) != NULL);
+
+    free(tok_tmp);
+  }
+  else
+  {
+   /*
+    * The queue is misconfigured, so return back CUPS_BACKEND_STOP
+    */
+    fprintf(stderr, "ERROR: failover option not specified!\n");
+    return (CUPS_BACKEND_STOP);
+  }
+
+ /*
+  * Get the failover-retries value, if it exists.
+  */
+  fprintf(stderr, "DEBUG: Searching for failover-retries option.\n");
+
+  if ((tmp = cupsGetOption("failover-retries",
+                           jobopts_count, jobopts)) != NULL)
+  {
+    fprintf(stderr, "DEBUG: failover-retries option contents: %s.\n", tmp);
+    *retries = atoi(tmp);
+  }
+  else
+  {
+    *retries = FAILOVER_DEFAULT_RETRIES;
+    fprintf(stderr, "DEBUG: Failed to get failover-retries option\n");
+    fprintf(stderr, "DEBUG: Defaulted to %d retries\n", *retries);
+  }
+
+  return (CUPS_BACKEND_OK);
+}
+
+/*
+ * 'get_printer_attributes()' - Sends an IPP Get-Attributes request to
+ *                              a URI
+ */
+int
+get_printer_attributes(const char *device_uri, ipp_t **attributes)
+{
+  char               uri[HTTP_MAX_URI];         /* Updated URI without login */
+  int                version;                   /* IPP version */
+  char               scheme[256];               /* Scheme in URI */
+  ipp_status_t       ipp_status;                /* Status of IPP request */
+  char               hostname[1024];            /* Hostname */
+  char               resource[1024];            /* Resource infoo */
+  char               addrname[256];             /* Address name */
+  int                port;                      /* IPP Port number */
+  char               portname[255];             /* Port as string */
+  http_t            *http;                      /* HTTP connection */
+  ipp_t             *request;                   /* IPP request */
+  int                rc = CUPS_BACKEND_OK;      /* Return Code */
+  char               username[256];             /* Username for device URI */
+  char              *option_ptr;                /* for parsing resource opts */
+  const char * const pattrs[] =                 /* Printer attributes wanted */
+    {
+      "printer-is-accepting-jobs",
+      "printer-state",
+      "printer-state-reasons"
+    };
+
+  if (job_canceled)
+    return (CUPS_BACKEND_OK);
+
+  fprintf(stderr, "DEBUG: Getting Printer Attributes.\n");
+  fprintf(stderr, "DEBUG: Device URL %s.\n", device_uri);
+
+ /*
+  * Parse device_uri
+  */
+  if (httpSeparateURI(HTTP_URI_CODING_ALL, device_uri, scheme, sizeof(scheme),
+                     username, sizeof(username), hostname, sizeof(hostname),
+                     &port, resource, sizeof(resource)) != HTTP_URI_OK)
+  {
+    fprintf(stderr, "ERROR: Problem parsing device_uri, %s\n", device_uri);
+    return (CUPS_BACKEND_STOP);
+  }
+
+  if (!port)
+    port = IPP_PORT;
+
+  sprintf(portname, "%d", port);
+
+  fprintf(stderr, "DEBUG: Getting Printer Attributes.\n");
+
+ /*
+  * Configure password
+  */
+  cupsSetPasswordCB(password_cb);
+
+ /*
+  * reset, in case a previous attempt for
+  * another printer left residue
+  */
+  cupsSetUser(NULL);
+  password = NULL;
+  password_retries = 0;
+
+  if (*username)
+  {
+    if ((password = strchr(username, ':')) != NULL)
+    {
+      *password = '\0';
+      password++;
+    }
+
+    cupsSetUser(username);
+  }
+  else if (!getuid())
+  {
+    const char *username_env;
+
+    if ((username_env = getenv("AUTH_USERNAME")) != NULL)
+    {
+      cupsSetUser(username_env);
+      password = getenv("AUTH_PASSWORD");
+    }
+  }
+
+ /*
+  * Try connecting to the remote server...
+  */
+  fprintf(stderr, "DEBUG: Connecting to %s:%d\n", hostname, port);
+  _cupsLangPuts(stderr, _("INFO: Connecting to printer...\n"));
+
+  http = httpConnectEncrypt(hostname, port, cupsEncryption());
+
+ /*
+  * Deal the socket not being open.
+  */
+  if (!http)
+  {
+    int error = errno;          /* Connection error */
+
+    switch (error)
+    {
+    case EHOSTDOWN :
+      _cupsLangPuts(stderr, _("WARNING: "
+                              "The printer may not exist or "
+                              "is unavailable at this time.\n"));
+      break;
+    case EHOSTUNREACH :
+      _cupsLangPuts(stderr, _("WARNING: "
+                              "The printer is unreachable at this "
+                              "time.\n"));
+      break;
+    case ECONNREFUSED :
+      _cupsLangPuts(stderr, _("WARNING: "
+                              "Connection Refused.\n"));
+      break;
+    default :
+      fprintf(stderr, "DEBUG: Connection error: %s\n", strerror(errno));
+      break;
+    }
+
+    rc = CUPS_BACKEND_FAILED;
+    sleep(5);
+    goto prt_available_cleanup;
+  }
+
+
+#ifdef AF_INET6
+  if (http->hostaddr->addr.sa_family == AF_INET6)
+    fprintf(stderr, "DEBUG: Connected to [%s]:%d (IPv6)...\n",
+            httpAddrString(http->hostaddr, addrname, sizeof(addrname)),
+            ntohs(http->hostaddr->ipv6.sin6_port));
+  else
+#endif /* AF_INET6 */
+  if (http->hostaddr->addr.sa_family == AF_INET)
+    fprintf(stderr, "DEBUG: Connected to %s:%d (IPv4)...\n",
+            httpAddrString(http->hostaddr, addrname, sizeof(addrname)),
+            ntohs(http->hostaddr->ipv4.sin_port));
+
+ /*
+  * Search the resource string for options.
+  * We only care about version, for the moment.
+  */
+  version = 11;
+
+  if ((option_ptr = strchr(resource, '?')) != NULL)
+  {
+    *option_ptr++ = '\0';
+
+    if ((option_ptr = strstr(option_ptr, "version="))!=NULL)
+    {
+      int   minor;       /* minor version from URI */
+      int   major;       /* major version from URI */
+      char *version_str; /* ipp version */
+
+      option_ptr += 8;
+      version_str = option_ptr;
+
+      while (*option_ptr && *option_ptr != '&' && *option_ptr != '+')
+        option_ptr++;
+
+      if (*option_ptr)
+        *option_ptr = '\0';
+
+      sscanf(version_str, "%d.%d", &major, &minor);
+
+      version = (major * 10) + minor;
+
+      switch(version)
+      {
+      case 10 :
+      case 11 :
+      case 20 :
+      case 21 :
+        fprintf(stderr,
+                "DEBUG: Set version to %d from URI\n",
+                version);
+        break;
+      default :
+        _cupsLangPrintf(stderr,
+                        _("DEBUG: Invalid version, %d, from URI.  "
+                          "Using default of 1.1 \n"),
+                        version);
+        version = 11;
+      }
+    }
+  }
+
+
+ /*
+  * Build a URI for the printer.  We can't use the URI in argv[0]
+  * because it might contain username:password information...
+  */
+  if (httpAssembleURI(HTTP_URI_CODING_ALL, uri, sizeof(uri), scheme, NULL,
+                      hostname, port, resource) != HTTP_URI_OK)
+  {
+    fprintf(stderr, "ERROR: Problem assembling printer URI from host %s, "
+            "port %d, resource %s\n", hostname, port, resource);
+    return (CUPS_BACKEND_STOP);
+  }
+
+ /*
+  * Build the IPP request...
+  */
+  request = ippNewRequest(IPP_GET_PRINTER_ATTRIBUTES);
+  request->request.op.version[0] = version / 10;
+  request->request.op.version[1] = version % 10;
+
+  ippAddString(request, IPP_TAG_OPERATION, IPP_TAG_URI, "printer-uri",
+               NULL, uri);
+
+  ippAddStrings(request, IPP_TAG_OPERATION, IPP_TAG_KEYWORD,
+                "requested-attributes", sizeof(pattrs) / sizeof(pattrs[0]),
+                NULL, pattrs);
+
+ /*
+  * Do the request...
+  */
+  fputs("DEBUG: Getting supported attributes...\n", stderr);
+
+  fprintf(stderr, "DEBUG: IPP Request Structure Built.\n");
+
+  *attributes = cupsDoRequest(http, request, resource);
+  ipp_status = cupsLastError();
+
+  fprintf(stderr, "DEBUG: Get-Printer-Attributes: %s (%s)\n",
+          ippErrorString(ipp_status), cupsLastErrorString());
+
+  if (ipp_status > IPP_OK_CONFLICT)
+  {
+    fprintf(stderr, "DEBUG: Get-Printer-Attributes returned %s.\n",
+            ippErrorString(ipp_status));
+    switch(ipp_status)
+    {
+    case IPP_FORBIDDEN :
+    case IPP_NOT_AUTHORIZED :
+      _cupsLangPuts(stderr, _("ERROR: Not Authorized.\n"));
+      rc = CUPS_BACKEND_AUTH_REQUIRED;
+      break;
+    case IPP_PRINTER_BUSY :
+    case IPP_SERVICE_UNAVAILABLE :
+      _cupsLangPuts(stderr, _("ERROR: "
+                              "The printer is not responding.\n"));
+      rc = CUPS_BACKEND_FAILED;
+      break;
+    case IPP_BAD_REQUEST :
+    case IPP_VERSION_NOT_SUPPORTED :
+      fprintf(stderr, "ERROR: Destination does not support IPP version %d\n",
+              version);
+    case IPP_NOT_FOUND :
+      _cupsLangPuts(stderr, _("ERROR: "
+                              "The printer configuration is incorrect or the "
+                              "printer no longer exists.\n"));
+      rc = CUPS_BACKEND_STOP;
+      break;
+    default :
+      rc = CUPS_BACKEND_FAILED;
+    }
+    goto prt_available_cleanup;
+  }
+
+prt_available_cleanup :
+  httpClose(http);
+  return (rc);
+}
+
+static int
+move_job(int        jobid,              /* Job ID */
+         const char *dest)              /* Destination ipp address */
+{
+  ipp_t *request;                       /* IPP Request */
+  char  job_uri[HTTP_MAX_URI];          /* job-uri */
+
+  http_t* http = httpConnectEncrypt(cupsServer(), ippPort(), cupsEncryption());
+
+  if (!http)
+  {
+    _cupsLangPrintf(stderr,
+                    _("failover: Unable to connect to server: %s\n"),
+                    strerror(errno));
+    return (CUPS_BACKEND_FAILED);
+  }
+
+ /*
+  * Build a CUPS_MOVE_JOB request, which requires the following
+  * attributes:
+  *
+  *    job-uri/printer-uri
+  *    job-printer-uri
+  *    requesting-user-name
+  */
+
+  request = ippNewRequest(CUPS_MOVE_JOB);
+
+  snprintf(job_uri, sizeof(job_uri), "ipp://localhost/jobs/%d", jobid);
+  ippAddString(request, IPP_TAG_OPERATION, IPP_TAG_URI, "job-uri", NULL,
+               job_uri);
+
+  ippAddString(request, IPP_TAG_OPERATION, IPP_TAG_NAME,
+               "requesting-user-name",
+               NULL, cupsUser());
+
+  ippAddString(request, IPP_TAG_JOB, IPP_TAG_URI, "job-printer-uri",
+               NULL, dest);
+
+ /*
+  * Do the request and get back a response...
+  */
+
+  ippDelete(cupsDoRequest(http, request, "/jobs"));
+
+  httpClose(http);
+
+  if (cupsLastError() > IPP_OK_CONFLICT)
+  {
+    _cupsLangPrintf(stderr, "failover: %s\n", cupsLastErrorString());
+    return (CUPS_BACKEND_FAILED);
+  }
+  else
+    return (CUPS_BACKEND_OK);
+}
+
+/*
+ * 'sigterm_handler()' - handles a sigterm, i.e. job canceled
+ */
+static void
+sigterm_handler(int sig)
+{
+  if (!job_canceled)
+  {
+    write(2, "DEBUG: Got SIGTERM.\n", 20);
+    job_canceled = 1;
+  }
+  else
+  {
+   /*
+    * Job has already been canceled, so just exit
+    */
+    exit(1);
+  }
+}
+
+/*
+ * 'password_cb()' - Disable the password prompt for cupsDoFileRequest().
+ */
+static const char *                     /* O - Password  */
+password_cb(const char *prompt)         /* I - Prompt (not used) */
+{
+  auth_info_required = "username,password";
+  password_retries++;
+
+  if(password_retries < FAILOVER_PASSWORD_RETRIES_MAX)
+    return (password);
+  else
+    return (NULL);
+}
diff -up cups-2.4.0/backend/Makefile.failover cups-2.4.0/backend/Makefile
--- cups-2.4.0/backend/Makefile.failover	2021-11-29 15:27:31.000000000 +0100
+++ cups-2.4.0/backend/Makefile	2021-12-15 11:08:27.433009704 +0100
@@ -25,6 +25,7 @@ RBACKENDS =	\
 		ipp \
 		lpd \
 		usb \
+		failover \
 		$(DNSSD_BACKEND)
 UBACKENDS =	\
 		snmp \
@@ -45,6 +46,7 @@ LIBOBJS	=	\
 OBJS	=	\
 		ipp.o \
 		lpd.o \
+		failover.o \
 		dnssd.o \
 		snmp.o \
 		socket.o \
@@ -264,6 +266,15 @@ lpd:	lpd.o ../cups/$(LIBCUPS) libbackend
 
 
 #
+# failover
+#
+
+failover:	failover.o ../cups/$(LIBCUPS) libbackend.a
+	echo Linking $@...
+	$(LD_CC) $(ALL_LDFLAGS) -o failover failover.o libbackend.a $(LINKCUPS)
+
+
+#
 # snmp
 #