Refacture structure proposal. (#1793)

command/cat-main.go

@@ -0,0 +1,152 @@
+/*
+ * Minio Client, (C) 2015 Minio, Inc.
+ *
+ * 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 command
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"syscall"
+
+	"github.com/minio/cli"
+	"github.com/minio/minio/pkg/probe"
+)
+
+var (
+	catFlags = []cli.Flag{
+		cli.BoolFlag{
+			Name:  "help, h",
+			Usage: "Help of cat",
+		},
+	}
+)
+
+// Display contents of a file.
+var catCmd = cli.Command{
+	Name:   "cat",
+	Usage:  "Display contents of a file.",
+	Action: mainCat,
+	Flags:  append(catFlags, globalFlags...),
+	CustomHelpTemplate: `NAME:
+   mc {{.Name}} - {{.Usage}}
+
+USAGE:
+   mc {{.Name}} [FLAGS] SOURCE [SOURCE...]
+
+FLAGS:
+  {{range .Flags}}{{.}}
+  {{end}}
+EXAMPLES:
+   1. Stream an object from Amazon S3 cloud storage to mplayer standard input.
+      $ mc {{.Name}} s3/ferenginar/klingon_opera_aktuh_maylotah.ogg | mplayer -
+
+   2. Concantenate contents of file1.txt and stdin to standard output.
+      $ mc {{.Name}} file1.txt - > file.txt
+
+   3. Concantenate multiple files to one.
+      $ mc {{.Name}} part.* > complete.img
+
+`,
+}
+
+// checkCatSyntax performs command-line input validation for cat command.
+func checkCatSyntax(ctx *cli.Context) {
+	args := ctx.Args()
+	if !args.Present() {
+		args = []string{"-"}
+	}
+	for _, arg := range args {
+		if strings.HasPrefix(arg, "-") && len(arg) > 1 {
+			fatalIf(probe.NewError(errors.New("")), fmt.Sprintf("Unknown flag ‘%s’ passed.", arg))
+		}
+	}
+}
+
+// catURL displays contents of a URL to stdout.
+func catURL(sourceURL string) *probe.Error {
+	var reader io.Reader
+	switch sourceURL {
+	case "-":
+		reader = os.Stdin
+	default:
+		// Ignore size, since os.Stat() would not return proper size all the
+		// time for local filesystem for example /proc files.
+		var err *probe.Error
+		if reader, err = getSourceStream(sourceURL); err != nil {
+			return err.Trace(sourceURL)
+		}
+	}
+	return catOut(reader).Trace(sourceURL)
+}
+
+// catOut reads from reader stream and writes to stdout.
+func catOut(r io.Reader) *probe.Error {
+	// Read till EOF.
+	if _, e := io.Copy(os.Stdout, r); e != nil {
+		switch e := e.(type) {
+		case *os.PathError:
+			if e.Err == syscall.EPIPE {
+				// stdout closed by the user. Gracefully exit.
+				return nil
+			}
+			return probe.NewError(e)
+		default:
+			return probe.NewError(e)
+		}
+	}
+	return nil
+}
+
+// mainCat is the main entry point for cat command.
+func mainCat(ctx *cli.Context) {
+	// Set global flags from context.
+	setGlobalsFromContext(ctx)
+
+	// check 'cat' cli arguments.
+	checkCatSyntax(ctx)
+
+	// Set command flags from context.
+	stdinMode := false
+	if !ctx.Args().Present() {
+		stdinMode = true
+	}
+
+	// handle std input data.
+	if stdinMode {
+		fatalIf(catOut(os.Stdin).Trace(), "Unable to read from standard input.")
+		return
+	}
+
+	// if Args contain ‘-’, we need to preserve its order specially.
+	args := []string(ctx.Args())
+	if ctx.Args().First() == "-" {
+		for i, arg := range os.Args {
+			if arg == "cat" {
+				// Overwrite ctx.Args with os.Args.
+				args = os.Args[i+1:]
+				break
+			}
+		}
+	}
+
+	// Convert arguments to URLs: expand alias, fix format.
+	for _, url := range args {
+		fatalIf(catURL(url).Trace(url), "Unable to read from ‘"+url+"’.")
+	}
+}