Allow the receiver to request a preferred resolution

The sender tries to find a resolution that is close to the preferred one
of the receiver.

Fixes: QubesOS/qubes-issues#8424

qubes-rpc/services/qvc.Webcam

@@ -4,4 +4,4 @@
 # Copyright (C) 2021 Demi Marie Obenour <[email protected]>
 # Licensed under the MIT License. See LICENSE file for details.
 export DISPLAY=:0
-exec python3 -- /usr/share/qubes-video-companion/sender/webcam.py
+exec python3 -- /usr/share/qubes-video-companion/sender/webcam.py ${1:+"$1"}

receiver/qubes-video-companion

@@ -4,18 +4,39 @@
 # Licensed under the MIT License. See LICENSE file for details.
 
 [ "$DEBUG" == 1 ] && set -x
+set -u -e
 
 set -E # Enable function inheritance of traps
 trap exit ERR
+unset GETOPT_COMPATIBLE
+name=${0##*/}
 
 usage() {
-    echo "Usage: qubes-video-companion webcam|screenshare [destination qube]"
-} >&2
+    printf '%s: Usage: qubes-video-companion [--resolution=WIDTHxHEIGHTxFPS] [--] webcam|screenshare [destination qube]\n' "$name"
+    exit "$1"
+}
 
-if [ "$#" -gt 2 ] && [ "$#" -lt 1 ]; then
-    usage
-    exit 1
-fi
+resolution=
+opts=$(getopt "--name=$name" --longoptions=resolution:,help -- r: "$@") || exit
+eval "set -- $opts"
+while :; do
+    case $1 in
+        -r|--resolution)
+            if [[ -z "$2" ]]; then
+                printf '%s: Empty resolution argument\n' "$name"
+                usage 0
+            fi >&2
+            resolution=${2//@/+}
+            resolution=${resolution//x/+}
+            shift 2
+            ;;
+        --help) usage 0;;
+        --) shift; break;;
+        *) exit 1;; # cannot happen
+    esac
+done
+
+if [ "$#" -gt 2 ] || [ "$#" -lt 1 ]; then usage 1 >&2; fi
 
 video_source="$1" qube=${2-'@default'}
 
@@ -27,18 +48,17 @@ case "$video_source" in
         qvc_service="qvc.ScreenShare"
         ;;
     *)
-        usage
-        exit 1
+        usage 1
         ;;
 esac
 
-exit_clean() {
+exit_clean () {
     exit_code="$?"
 
     /usr/share/qubes-video-companion/receiver/destroy.sh
     sudo rm -f "$qvc_lock_file"
 
-    if [ "$video_source" == "webcam" ] && [ "$exit_code" == "141" ]; then
+    if [ "$video_source" = "webcam" ] && [ "$exit_code" = "141" ]; then
         echo "The webcam device is in use! Please stop any instance of Qubes Video Companion running on another qube." >&2
         exit 1
     fi
@@ -57,4 +77,4 @@ fi
 
 /usr/share/qubes-video-companion/receiver/setup.sh
 # Filter standard error escape characters for safe printing to the terminal from the video sender
-qrexec-client-vm --filter-escape-chars-stderr -- "$qube" "$qvc_service" /usr/share/qubes-video-companion/receiver/receiver.py
+qrexec-client-vm --filter-escape-chars-stderr -- "$qube" "$qvc_service+$resolution" /usr/share/qubes-video-companion/receiver/receiver.py

sender/service.py

@@ -137,11 +137,8 @@ def start_transmission(self) -> None:
     def main(cls, self) -> NoReturn:
         """Program entry point"""
 
-        import argparse
         import qubesdb  # pylint: disable=import-error
 
-        argparse.ArgumentParser().parse_args()
-
         target_domain = qubesdb.QubesDB().read("/name")
         if target_domain is None:
             # dom0 doesn't have a /name value in its QubesDB

sender/webcam.py

@@ -15,8 +15,43 @@
 class Webcam(Service):
     """Webcam video source class"""
 
-    def __init__(self):
-        self.main(self)
+    untrusted_requested_width: int
+    untrusted_requested_height: int
+    untrusted_requested_fps: int
+
+    def __init__(self, *, untrusted_arg: str):
+        if untrusted_arg:
+            untrusted_arg_bytes = untrusted_arg.encode('ascii', 'strict')
+            def parse_int(untrusted_decimal: bytes) -> int:
+                if not ((1 <= len(untrusted_decimal) <= 4) and
+                        untrusted_decimal.isdigit() and
+                        untrusted_decimal[0] != b"0"):
+                    print("Invalid argument " + untrusted_arg + ": bad number",
+                          file=sys.stderr)
+                    sys.exit(1)
+                return int(untrusted_decimal, 10)
+            if len(untrusted_arg_bytes) > 14:
+                # qrexec has already sanitized the argument to some degree,
+                # so this is safe
+                print("Invalid argument " + untrusted_arg +
+                      ": too long (limit 14 bytes)", file=sys.stderr)
+                sys.exit(1)
+            arg_list = untrusted_arg_bytes.split(b"+", 4)
+            if len(arg_list) != 3:
+                print("Invalid argument " + untrusted_arg +
+                      ": wrong number of integers (expected 3)",
+                      file=sys.stderr)
+                sys.exit(1)
+            ( self.untrusted_requested_width
+            , self.untrusted_requested_height
+            , self.untrusted_requested_fps
+            ) = map(parse_int, arg_list)
+        else:
+            self.untrusted_requested_width = 0
+            self.untrusted_requested_height = 0
+            self.untrusted_requested_fps = 0
+
+        Service.main(self)
 
     def video_source(self) -> str:
         return "webcam"
@@ -60,6 +95,11 @@ def parameters(self):
             else:
                 print("Cannot parse output %r of v4l2ctl" % i, file=sys.stderr)
         formats.sort(key=lambda x: x[0] * x[1] * x[2], reverse=True)
+        if self.untrusted_requested_fps:
+            formats.sort(key=lambda x:
+                         (x[0] - self.untrusted_requested_width) ** 2 +
+                         (x[1] - self.untrusted_requested_height) ** 2 +
+                         (x[2] - self.untrusted_requested_fps) ** 2)
         return formats[0]
 
     def pipeline(self, width: int, height: int, fps: int, **kwargs):
@@ -108,4 +148,11 @@ def pipeline(self, width: int, height: int, fps: int, **kwargs):
 
 
 if __name__ == "__main__":
-    webcam = Webcam()
+    _untrusted_arg = ""
+    if len(sys.argv) == 2:
+        _untrusted_arg = sys.argv[1]
+    elif len(sys.argv) != 1:
+        print("Must have 0 or 1 argument, not " + str(len(sys.argv)),
+              file=sys.stderr)
+        sys.exit(1)
+    webcam = Webcam(untrusted_arg=_untrusted_arg)