Add README

Author: sawsa307

pkg/i2gw/providers/gce/README.md

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+# GCE Provider
+
+The project supports translating ingress-gce specific annotations.
+
+Currently supported annotations:
+`kubernetes.io/ingress.class`: Though it is a deprecated annotation for most providers, GCE still uses this annotation to specify the specific type of load balancers created by GKE Ingress.
+
+## Implementation-specific features
+
+The following implementation-specific features are supported:
+
+- Ingress path with type `ImplementationSpecific` will:
+  - Translate to equivalent Gateway Prefix path but dropping `/*`, if `/*` exists
+  - Translate to equivalent Exact path otherwise.
+
+Examples:
+| Ingress `ImplementationSpecific` Path | map to Gateway Path                    |
+| ------------------------------------- | -------------------------------------- |
+| /*                                    | / Prefix                               |
+| /v1/*                                 | /v1 Prefix                             |
+| /v1                                   | /v1 Exact                              |
+| /v1/                                  | /v1/ Exact                             |
+
+Note: For Ingress `ImplementationSpecific` path with `/v1/*`, it will map to
+`/v1/` or `/v1/v2` but not `/v1`. If you want to avoid such "overmapping",
+please consider switching to `Prefix`, `Exact`, or an `ImplementationSpecific`
+path without `*` before converting Ingress to Gateway.
+
+## Feature list
+Currently supported:
+- [Basic Internal Ingress](https://github.com/GoogleCloudPlatform/gke-networking-recipes/tree/main/ingress/single-cluster/ingress-internal-basic)
+- [Basic external Ingress](https://github.com/GoogleCloudPlatform/gke-networking-recipes/tree/main/ingress/single-cluster/ingress-external-basic)
+- [Ingress with custom default backend](https://github.com/GoogleCloudPlatform/gke-networking-recipes/tree/main/ingress/single-cluster/ingress-custom-default-backend)
+
+To be supported:
+ - [Ingress with custom HTTP health check](https://github.com/GoogleCloudPlatform/gke-networking-recipes/tree/main/ingress/single-cluster/ingress-custom-http-health-check)
+ - [IAP enabled ingress](https://github.com/GoogleCloudPlatform/gke-networking-recipes/tree/main/ingress/single-cluster/ingress-iap)
+ - [Google Cloud Armor enabled ingress](https://github.com/GoogleCloudPlatform/gke-networking-recipes/blob/main/ingress/single-cluster/ingress-cloudarmor/README.md)
+ - [Ingress with HTTPS redirect](https://github.com/GoogleCloudPlatform/gke-networking-recipes/tree/main/ingress/single-cluster/ingress-https)
+
+## Summary of GKE Ingress annotation
+External Ingress:
+https://cloud.google.com/kubernetes-engine/docs/how-to/load-balance-ingress#summary_of_external_ingress_annotations
+
+Internal Ingress:
+https://cloud.google.com/kubernetes-engine/docs/how-to/internal-load-balance-ingress#summary_of_internal_ingress_annotations

pkg/i2gw/providers/gce/implementation_specific.go

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+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package gce
+
+import (
+	"strings"
+
+	"github.com/kubernetes-sigs/ingress2gateway/pkg/i2gw/providers/common"
+	"k8s.io/klog/v2"
+	gatewayv1 "sigs.k8s.io/gateway-api/apis/v1"
+)
+
+// implementationSpecificHTTPPathTypeMatch maps the Implementation Specific
+// HTTP path and type to the corresponding Gateway HTTP ones.
+func implementationSpecificHTTPPathTypeMatch(path *gatewayv1.HTTPPathMatch) {
+	pmExact := gatewayv1.PathMatchExact
+	pmPrefix := gatewayv1.PathMatchPathPrefix
+
+	if *path.Value == "/*" {
+		path.Type = &pmPrefix
+		path.Value = common.PtrTo("/")
+		return
+	}
+	if !strings.HasSuffix(*path.Value, "/*") {
+		path.Type = &pmExact
+		return
+	}
+
+	currentValue := *path.Value
+	path.Type = &pmPrefix
+	path.Value = common.PtrTo(strings.TrimSuffix(*path.Value, "/*"))
+	klog.Warningf("After conversion, ImplementationSpecific Path %s will additionally map to %s. See README.md for details.", currentValue, *path.Value)
+}