In the Snap patch PAPPL to allow normal-user clients access the Snap'…

…s server

The server run by the Snap runs as root, as a Snap is installed into
the system, not into the user's home directory and so a process
started by the Snap installation must be a system process and that is
why Snaps run daemons as root.

Running the Printer Application as a client (from the command line) it
runs as the calling user and PAPPL does not associate it with the
system-wide server which the Snap has started as root. PAPPL always
creates the socket file with the user ID in the file name, so the call
as client uses its own socket file name, does not find the Snap's
server and fires up its own server.

See michaelrsweet/pappl#148

When building the Snap we are patching PAPPL now in a way that if a
client does not find a server uder the user's socket name, it tries
root's socket name (the system-wide server of the Snap in our case),
and only if this also fails it fires up its own server.

patches/pappl-system-wide-server-socket-support.patch

@@ -0,0 +1,71 @@
+diff --git a/pappl/mainloop-private.h b/pappl/mainloop-private.h
+index 5af4695..9bde73a 100644
+--- a/pappl/mainloop-private.h
++++ b/pappl/mainloop-private.h
+@@ -59,7 +59,7 @@ extern void	_papplMainloopAddPrinterURI(ipp_t *request, const char *printer_name
+ extern http_t	*_papplMainloopConnect(const char *base_name, bool auto_start) _PAPPL_PRIVATE;
+ extern http_t	*_papplMainloopConnectURI(const char *base_name, const char *printer_uri, char  *resource, size_t rsize) _PAPPL_PRIVATE;
+ extern char	*_papplMainloopGetDefaultPrinter(http_t *http, char *buffer, size_t bufsize) _PAPPL_PRIVATE;
+-extern char	*_papplMainloopGetServerPath(const char *base_name, char *buffer, size_t bufsize) _PAPPL_PRIVATE;
++  extern char	*_papplMainloopGetServerPath(const char *base_name, bool system_wide, char *buffer, size_t bufsize) _PAPPL_PRIVATE;
+
+
+ //
+diff --git a/pappl/mainloop-subcommands.c b/pappl/mainloop-subcommands.c
+index a572d6e..a79ac03 100644
+--- a/pappl/mainloop-subcommands.c
++++ b/pappl/mainloop-subcommands.c
+@@ -605,7 +605,7 @@ _papplMainloopRunServer(
+     papplSystemSetPrinterDrivers(system, num_drivers, drivers, autoadd_cb, /* create_cb */NULL, driver_cb, data);
+
+   // Listen for connections...
+-  papplSystemAddListeners(system, _papplMainloopGetServerPath(base_name, sockname, sizeof(sockname)));
++  papplSystemAddListeners(system, _papplMainloopGetServerPath(base_name, false, sockname, sizeof(sockname)));
+
+   // Finish initialization...
+   if (!system->save_cb)
+diff --git a/pappl/mainloop-support.c b/pappl/mainloop-support.c
+index e54f438..deb5d94 100644
+--- a/pappl/mainloop-support.c
++++ b/pappl/mainloop-support.c
+@@ -316,8 +316,12 @@ _papplMainloopConnect(
+   char		sockname[1024];		// Socket filename
+
+
+-  // See if the server is running...
+-  http = httpConnect2(_papplMainloopGetServerPath(base_name, sockname, sizeof(sockname)), 0, NULL, AF_UNSPEC, HTTP_ENCRYPTION_IF_REQUESTED, 1, 30000, NULL);
++  // See if a user server is running...
++  http = httpConnect2(_papplMainloopGetServerPath(base_name, false, sockname, sizeof(sockname)), 0, NULL, AF_UNSPEC, HTTP_ENCRYPTION_IF_REQUESTED, 1, 30000, NULL);
++
++  // See if there is a system-wide server
++  if (!http)
++    http = httpConnect2(_papplMainloopGetServerPath(base_name, true, sockname, sizeof(sockname)), 0, NULL, AF_UNSPEC, HTTP_ENCRYPTION_IF_REQUESTED, 1, 30000, NULL);
+
+   if (!http && auto_start)
+   {
+@@ -333,6 +337,8 @@ _papplMainloopConnect(
+       NULL
+     };
+
++    _papplMainloopGetServerPath(base_name, false, sockname, sizeof(sockname));
++
+     posix_spawnattr_init(&server_attrs);
+     posix_spawnattr_setpgroup(&server_attrs, 0);
+
+@@ -449,6 +455,7 @@ _papplMainloopGetDefaultPrinter(
+ char *					// O - Socket filename
+ _papplMainloopGetServerPath(
+     const char *base_name,		// I - Base name
++    bool       system_wide,		// I - System-wide server
+     char       *buffer,			// I - Buffer for filename
+     size_t     bufsize)			// I - Size of buffer
+ {
+@@ -463,7 +470,7 @@ _papplMainloopGetServerPath(
+     tmpdir = "/tmp";
+ #endif // __APPLE__
+
+-  snprintf(buffer, bufsize, "%s/%s%d.sock", tmpdir, base_name, (int)getuid());
++  snprintf(buffer, bufsize, "%s/%s%d.sock", tmpdir, base_name, (system_wide ? 0 : (int)getuid()));
+   _PAPPL_DEBUG("Creating domain socket as '%s'.\n", buffer);
+
+   return (buffer);

snap/snapcraft.yaml

@@ -22,6 +22,13 @@ apps:
     plugs: [avahi-control, home, network, network-bind, raw-usb]
 
 parts:
+  patches:
+    plugin: dump
+    source: patches
+    organize:
+      '*' : patches/
+    override-prime: ""
+
   jpeglib:
     plugin: autotools
     source: https://www.ijg.org/files/jpegsrc.v9d.tar.gz
@@ -45,6 +52,10 @@ parts:
     source: https://github.com/michaelrsweet/pappl
     source-type: git
     plugin: autotools
+    override-build: |
+        set -eux
+        patch -p1 < $SNAPCRAFT_STAGE/patches/pappl-system-wide-server-socket-support.patch
+        snapcraftctl build
     configflags: [--prefix=/usr, --enable-libjpeg,--enable-libpng,--enable-libusb,--with-dnssd=avahi]
     build-packages: [libavahi-client-dev, libgnutls28-dev, libjpeg-dev, libpam-dev, libpng-dev, libusb-1.0-0-dev, zlib1g-dev]
     stage-packages: [libavahi-client3, libpng16-16, libusb-1.0-0]
@@ -62,7 +73,7 @@ parts:
         - lib
         - usr/lib
         - usr/lib/libpappl.so.1
-    after: [jpeglib]
+    after: [patches, jpeglib]
 
   qpdf:
     source: https://github.com/qpdf/qpdf/releases/download/release-qpdf-10.0.1/qpdf-10.0.1.tar.gz