events: add support for label filter with key only

Fixes: #26702

Signed-off-by: TusharMohapatra07 <tusharmohapatra.gig@gmail.com>

docs/source/markdown/podman-events.1.md

@@ -99,7 +99,7 @@ filters are supported:
 | container  | [Name or ID] Container's name or ID |
 | event      | event_status (described above)      |
 | image      | [Name or ID] Image name or ID       |
-| label      | [key=value] label                   |
+| label      | [key] or [key=value] label          |
 | pod        | [Name or ID] Pod name or ID         |
 | volume     | [Name or ID] Volume name or ID      |
 | type       | Event_type (described above)        |

libpod/events/filters.go

@@ -67,14 +67,20 @@ func generateEventFilter(filter, filterValue string) (func(e *Event) bool, error
 			var found bool
 			// iterate labels and see if we match a key and value
 			for eventKey, eventValue := range e.Attributes {
-				filterValueSplit := strings.SplitN(filterValue, "=", 2)
-				// if the filter isn't right, just return false
-				if len(filterValueSplit) < 2 {
-					return false
-				}
-				if eventKey == filterValueSplit[0] && eventValue == filterValueSplit[1] {
-					found = true
-					break
+				filterKey, filterVal, hasValue := strings.Cut(filterValue, "=")
+				// match "key=value" or "key"
+				if !hasValue {
+					// match by key only
+					if eventKey == filterKey {
+						found = true
+						break
+					}
+				} else {
+					// match by key and value
+					if eventKey == filterKey && eventValue == filterVal {
+						found = true
+						break
+					}
 				}
 			}
 			return found

test/system/090-events.bats

@@ -28,6 +28,10 @@ load helpers.network
     run_podman events --since "$before" --filter type=container --filter container=$cname --filter event=start --stream=false
     is "$output" "$expect" "filtering just by container"
 
+    # Filter just by label key (without value)
+    run_podman events --since "$before" --filter type=container --filter label=${labelname} --filter event=start --stream=false
+    is "$output" "$expect" "filtering by label key only"
+
     # check --no-trunc=false
     truncID=${id:0:12}
     run_podman events --since "$before" --filter container=$cname --filter event=start --stream=false --no-trunc=false