kyaml: initial support for yaml and resource manipulation

kyaml/kio/kio.go

@@ -0,0 +1,106 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package kio contains low-level libraries for reading, modifying and writing
+// Resource Configuration and packages.
+package kio
+
+import (
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+)
+
+// Reader reads ResourceNodes. Analogous to io.Reader.
+type Reader interface {
+	Read() ([]*yaml.RNode, error)
+}
+
+// ResourceNodeSlice is a collection of ResourceNodes.
+// While ResourceNodeSlice has no inherent constraints on ordering or uniqueness, specific
+// Readers, Filters or Writers may have constraints.
+type ResourceNodeSlice []*yaml.RNode
+
+var _ Reader = ResourceNodeSlice{}
+
+func (o ResourceNodeSlice) Read() ([]*yaml.RNode, error) {
+	return o, nil
+}
+
+// Writer writes ResourceNodes. Analogous to io.Writer.
+type Writer interface {
+	Write([]*yaml.RNode) error
+}
+
+type WriterFunc func([]*yaml.RNode) error
+
+func (fn WriterFunc) Write(o []*yaml.RNode) error {
+	return fn(o)
+}
+
+// GrepFilter modifies a collection of Resource Configuration by returning the modified slice.
+// When possible, Filters should be serializable to yaml so that they can be described
+// declaratively as data.
+//
+// Analogous to http://www.linfo.org/filters.html
+type Filter interface {
+	Filter([]*yaml.RNode) ([]*yaml.RNode, error)
+}
+
+// FilterFunc can be used to implement GrepFilter by defining a function.
+type FilterFunc func([]*yaml.RNode) ([]*yaml.RNode, error)
+
+func (fn FilterFunc) Filter(o []*yaml.RNode) ([]*yaml.RNode, error) {
+	return fn(o)
+}
+
+// Pipeline reads Resource Configuration from a set of Inputs, applies some
+// transformations, and writes the results to a set of Outputs.
+//
+// Analogous to http://www.linfo.org/pipes.html
+type Pipeline struct {
+	// Inputs provide sources for Resource Configuration to be read.
+	Inputs []Reader `yaml:"inputs,omitempty"`
+
+	// Filters are transformations applied to the Resource Configuration.
+	// They are applied in the order they are specified.
+	// Analogous to http://www.linfo.org/filters.html
+	Filters []Filter `yaml:"filters,omitempty"`
+
+	// Outputs are where the transformed Resource Configuration is written.
+	Outputs []Writer `yaml:"outputs,omitempty"`
+}
+
+// Execute implements the Pipeline pipeline.
+func (p Pipeline) Execute() error {
+	var result []*yaml.RNode
+
+	// read from the inputs
+	for _, i := range p.Inputs {
+		nodes, err := i.Read()
+		if err != nil {
+			return err
+		}
+		result = append(result, nodes...)
+	}
+	if len(result) == 0 {
+		// no inputs to operate on
+		return nil
+	}
+
+	// apply operations
+	var err error
+	for i := range p.Filters {
+		op := p.Filters[i]
+		result, err = op.Filter(result)
+		if len(result) == 0 || err != nil {
+			return err
+		}
+	}
+
+	// write to the outputs
+	for _, o := range p.Outputs {
+		if err := o.Write(result); err != nil {
+			return err
+		}
+	}
+	return nil
+}