OLM-2753: Semver veneer pipe support

staging/operator-registry/alpha/veneer/semver/README.md

@@ -56,9 +56,10 @@ In this example, `Candidate` has the entire version range of bundles,  `Fast` ha
 ```
 % ./bin/opm alpha render-veneer semver -h
 Generate a file-based catalog from a single 'semver veneer' file
+When FILE is '-' or not provided, the veneer is read from standard input
 
 Usage:
-  opm alpha render-veneer semver <filename> [flags]
+  opm alpha render-veneer semver [FILE] [flags]
 
 Flags:
   -h, --help            help for semver
@@ -68,6 +69,22 @@ Global Flags:
       --skip-tls-verify   skip TLS certificate verification for container image registries while pulling bundles
       --use-http          use plain HTTP for container image registries while pulling bundles
 ```
+
+Example command usage:
+```
+# Example with file argument passed in
+opm alpha render-veneer semver infile.semver.veneer.yaml
+
+# Example with no file argument passed in
+opm alpha render-veneer semver -o yaml < infile.semver.veneer.yaml > outfile.yaml
+
+# Example with "-" as the file argument passed in
+cat infile.semver.veneer.yaml | opm alpha render-veneer semver -o mermaid -
+```
+Note that if the command is called without a file argument and nothing passed in on standard input,
+the command will hang indefinitely. Either a file argument or file information passed 
+in on standard input is required by the command.
+
 With the veneer attribute `GenerateMajorChannels: true` resulting major channels from the command are (skipping the rendered bundle image output):
 ```yaml
 ---

staging/operator-registry/alpha/veneer/semver/semver.go

@@ -3,7 +3,7 @@ package semver
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"sort"
 
 	"github.com/blang/semver/v4"
@@ -18,8 +18,8 @@ import (
 
 // data passed into this module externally
 type Veneer struct {
-	Ref string
-	Reg image.Registry
+	Data     io.Reader
+	Registry image.Registry
 }
 
 // IO structs -- BEGIN
@@ -78,7 +78,7 @@ type semverRenderedChannelVersions map[string]map[string]semver.Version // e.g.
 func (v Veneer) Render(ctx context.Context) (*declcfg.DeclarativeConfig, error) {
 	var out declcfg.DeclarativeConfig
 
-	sv, err := readFile(v.Ref)
+	sv, err := readFile(v.Data)
 	if err != nil {
 		return nil, fmt.Errorf("semver-render: unable to read file: %v", err)
 	}
@@ -88,7 +88,7 @@ func (v Veneer) Render(ctx context.Context) (*declcfg.DeclarativeConfig, error)
 		r := action.Render{
 			AllowedRefMask: action.RefBundleImage,
 			Refs:           []string{b.Image},
-			Registry:       v.Reg,
+			Registry:       v.Registry,
 		}
 		c, err := r.Run(ctx)
 		if err != nil {
@@ -114,8 +114,8 @@ func (v Veneer) Render(ctx context.Context) (*declcfg.DeclarativeConfig, error)
 	return &out, nil
 }
 
-func readFile(ref string) (*semverVeneer, error) {
-	data, err := ioutil.ReadFile(ref)
+func readFile(data io.Reader) (*semverVeneer, error) {
+	fileData, err := io.ReadAll(data)
 	if err != nil {
 		return nil, err
 	}
@@ -126,7 +126,7 @@ func readFile(ref string) (*semverVeneer, error) {
 		GenerateMinorChannels: true,
 		AvoidSkipPatch:        false,
 	}
-	if err := yaml.Unmarshal(data, &sv); err != nil {
+	if err := yaml.Unmarshal(fileData, &sv); err != nil {
 		return nil, err
 	}
 	return &sv, nil

staging/operator-registry/cmd/opm/alpha/veneer/semver.go

@@ -18,16 +18,19 @@ import (
 func newSemverCmd() *cobra.Command {
 	output := ""
 	cmd := &cobra.Command{
-		Use:   "semver <filename>",
-		Short: "Generate a file-based catalog from a single 'semver veneer' file",
-		Long:  `Generate a file-based catalog from a single 'semver veneer' file`,
-		Args:  cobra.MinimumNArgs(1),
+		Use:   "semver [FILE]",
+		Short: "Generate a file-based catalog from a single 'semver veneer' file \nWhen FILE is '-' or not provided, the veneer is read from standard input",
+		Long:  "Generate a file-based catalog from a single 'semver veneer' file \nWhen FILE is '-' or not provided, the veneer is read from standard input",
+		Args:  cobra.MaximumNArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
-			ref := args[0]
-
-			var (
-				err error
-			)
+			// Handle different input argument types
+			// When no arguments or "-" is passed to the command,
+			// assume input is coming from stdin
+			// Otherwise open the file passed to the command
+			data, err := openFileOrReadStdin(cmd, args)
+			if err != nil {
+				return err
+			}
 
 			var write func(declcfg.DeclarativeConfig, io.Writer) error
 			switch output {
@@ -53,12 +56,12 @@ func newSemverCmd() *cobra.Command {
 			defer reg.Destroy()
 
 			veneer := semver.Veneer{
-				Ref: ref,
-				Reg: reg,
+				Data:     data,
+				Registry: reg,
 			}
 			out, err := veneer.Render(cmd.Context())
 			if err != nil {
-				log.Fatalf("semver %q: %v", ref, err)
+				log.Fatalf("semver %q: %v", data, err)
 			}
 
 			if out != nil {
@@ -74,3 +77,10 @@ func newSemverCmd() *cobra.Command {
 	cmd.Flags().StringVarP(&output, "output", "o", "json", "Output format (json|yaml|mermaid)")
 	return cmd
 }
+
+func openFileOrReadStdin(cmd *cobra.Command, args []string) (io.Reader, error) {
+	if len(args) == 0 || args[0] == "-" {
+		return cmd.InOrStdin(), nil
+	}
+	return os.Open(args[0])
+}