Add JSON patch helper

Adds helper function for building JsonPatch operation lists,
which allows modifying a resource without having to manually
refresh the object and retry the change on conflict.

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>

pkg/util/patch.go

@@ -0,0 +1,109 @@
+package util
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/types"
+)
+
+// controllerPatcher matches the Patch function exposed by rancher/wrangler Controllers
+type controllerPatcher[T runtime.Object] interface {
+	Patch(name string, pt types.PatchType, data []byte, subresources ...string) (T, error)
+}
+
+// clientPatcher matches the Patch function exposed by k8s.io/client-go Clients
+type clientPatcher[T runtime.Object] interface {
+	Patch(ctx context.Context, name string, pt types.PatchType, data []byte, opts metav1.PatchOptions, subresources ...string) (T, error)
+}
+
+// patchWrapper wraps the Patch functions provided by either wrangler or client-go
+type patchWrapper[T runtime.Object] struct {
+	patcher any
+}
+
+// NewPatcher wraps the provided controller or client for use as a generic patcher
+// note that the patcher is not validated for use until `Patch` is called
+func NewPatcher[T runtime.Object](patcher any) *patchWrapper[T] {
+	return &patchWrapper[T]{
+		patcher: patcher,
+	}
+}
+
+// Patch applies the provided PatchList to the specified resource
+func (p *patchWrapper[T]) Patch(ctx context.Context, pl *PatchList, name string, subresources ...string) (T, error) {
+	var t T
+	if pl == nil {
+		pl = NewPatchList()
+	}
+	b, err := json.Marshal(pl.ops)
+	if err != nil {
+		return t, err
+	}
+	if patch, ok := p.patcher.(clientPatcher[T]); ok {
+		return patch.Patch(ctx, name, types.JSONPatchType, b, metav1.PatchOptions{}, subresources...)
+	}
+	if patch, ok := p.patcher.(controllerPatcher[T]); ok {
+		return patch.Patch(name, types.JSONPatchType, b, subresources...)
+	}
+	return t, fmt.Errorf("unable to patch %T with %T", t, p.patcher)
+}
+
+// PatchList is a generic list of JSONPatch operations to apply to a resource
+type PatchList struct {
+	ops []map[string]any
+}
+
+// NewPatchList creates a new empty patch list
+func NewPatchList() *PatchList {
+	return &PatchList{ops: []map[string]any{}}
+}
+
+// Add appends an `add` operation to the patch list
+func (pl *PatchList) Add(value any, path ...string) *PatchList {
+	if pl == nil {
+		pl = NewPatchList()
+	}
+	if len(path) > 0 {
+		for i := range path {
+			path[i] = strings.ReplaceAll(path[i], "/", "~1")
+		}
+		pl.ops = append(pl.ops, map[string]any{
+			"op":    "add",
+			"value": value,
+			"path":  "/" + strings.Join(path, "/"),
+		})
+	}
+	return pl
+}
+
+// Remove appends a `remove` operation to the patch list
+func (pl *PatchList) Remove(path ...string) *PatchList {
+	if pl == nil {
+		pl = NewPatchList()
+	}
+	if len(path) > 0 {
+		for i := range path {
+			path[i] = strings.ReplaceAll(path[i], "/", "~1")
+		}
+		pl.ops = append(pl.ops, map[string]any{
+			"op":   "remove",
+			"path": "/" + strings.Join(path, "/"),
+		})
+	}
+	return pl
+}
+
+// ToJSON returns a JSON string containing the patch operations
+// This is just a thin wrapper around `json.Marshal`
+func (pl *PatchList) ToJSON() (string, error) {
+	if pl == nil {
+		pl = NewPatchList()
+	}
+	b, err := json.Marshal(pl.ops)
+	return string(b), err
+}