feat(kzip tool): use vfs to allow for changing filesystem impl (#3971)

kythe/go/platform/tools/kzip/infocmd/BUILD

@@ -9,6 +9,7 @@ go_library(
     ],
     deps = [
         "//kythe/go/platform/kzip",
+        "//kythe/go/platform/vfs",
         "//kythe/go/util/cmdutil",
         "@com_github_google_subcommands//:go_default_library",
         "@org_bitbucket_creachadair_stringset//:go_default_library",

kythe/go/platform/tools/kzip/infocmd/infocmd.go

@@ -22,9 +22,9 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
-	"os"
 
 	"kythe.io/kythe/go/platform/kzip"
+	"kythe.io/kythe/go/platform/vfs"
 	"kythe.io/kythe/go/util/cmdutil"
 
 	"bitbucket.org/creachadair/stringset"
@@ -55,7 +55,7 @@ func (c *infoCommand) Execute(ctx context.Context, fs *flag.FlagSet, _ ...interf
 	if c.input == "" {
 		return c.Fail("required --input path missing")
 	}
-	f, err := os.Open(c.input)
+	f, err := vfs.Open(ctx, c.input)
 	if err != nil {
 		return c.Fail("error opening archive: %v", err)
 	}

kythe/go/platform/tools/kzip/mergecmd/mergecmd.go

@@ -23,15 +23,14 @@ import (
 	"fmt"
 	"io"
 	"log"
-	"os"
 	"path/filepath"
 
-	"bitbucket.org/creachadair/stringset"
 	"kythe.io/kythe/go/platform/kzip"
 	"kythe.io/kythe/go/platform/tools/kzip/flags"
 	"kythe.io/kythe/go/platform/vfs"
 	"kythe.io/kythe/go/util/cmdutil"
 
+	"bitbucket.org/creachadair/stringset"
 	"github.com/google/subcommands"
 )
 
@@ -108,7 +107,7 @@ func mergeArchives(ctx context.Context, out io.WriteCloser, archives []string, o
 
 	filesAdded := stringset.New()
 	for _, path := range archives {
-		if err := mergeInto(wr, path, filesAdded); err != nil {
+		if err := mergeInto(ctx, wr, path, filesAdded); err != nil {
 			wr.Close()
 			return err
 		}
@@ -120,14 +119,14 @@ func mergeArchives(ctx context.Context, out io.WriteCloser, archives []string, o
 	return nil
 }
 
-func mergeInto(wr *kzip.Writer, path string, filesAdded stringset.Set) error {
-	f, err := os.Open(path)
+func mergeInto(ctx context.Context, wr *kzip.Writer, path string, filesAdded stringset.Set) error {
+	f, err := vfs.Open(ctx, path)
 	if err != nil {
 		return fmt.Errorf("error opening archive: %v", err)
 	}
 	defer f.Close()
 
-	stat, err := f.Stat()
+	stat, err := vfs.Stat(ctx, path)
 	if err != nil {
 		return err
 	}

kythe/go/platform/tools/kzip/viewcmd/BUILD

@@ -10,6 +10,7 @@ go_library(
     ],
     deps = [
         "//kythe/go/platform/kzip",
+        "//kythe/go/platform/vfs",
         "//kythe/go/util/cmdutil",
         "//kythe/proto:buildinfo_go_proto",
         "//kythe/proto:cxx_go_proto",

kythe/go/platform/tools/kzip/viewcmd/viewcmd.go

@@ -29,6 +29,7 @@ import (
 	"time"
 
 	"kythe.io/kythe/go/platform/kzip"
+	"kythe.io/kythe/go/platform/vfs"
 	"kythe.io/kythe/go/util/cmdutil"
 
 	"github.com/golang/protobuf/jsonpb"
@@ -71,7 +72,7 @@ func (c *cmd) Execute(ctx context.Context, fs *flag.FlagSet, args ...interface{}
 		ext := filepath.Ext(path)
 		base := filepath.Base(strings.TrimSuffix(path, ext))
 
-		f, err := os.Open(path)
+		f, err := vfs.Open(ctx, path)
 		if err != nil {
 			log.Printf("Error opening .kzip file: %v", err)
 			hasErrors = true

kythe/go/platform/vfs/vfs.go

@@ -54,7 +54,7 @@ type Reader interface {
 	Stat(ctx context.Context, path string) (os.FileInfo, error)
 
 	// Open opens an existing file for reading, as os.Open.
-	Open(ctx context.Context, path string) (io.ReadCloser, error)
+	Open(ctx context.Context, path string) (FileReader, error)
 
 	// Glob returns all the paths matching the specified glob pattern, as
 	// filepath.Glob.
@@ -87,6 +87,14 @@ type Writer interface {
 	Remove(ctx context.Context, path string) error
 }
 
+// FileReader composes interfaces from io that readable files from the vfs must
+// implement.
+type FileReader interface {
+	io.ReadCloser
+	io.ReaderAt
+	io.Seeker
+}
+
 // Default is the global default VFS used by Kythe libraries that wish to access
 // the file system.  This is usually the LocalFS and should only be changed in
 // very specialized cases (i.e. don't change it).
@@ -112,7 +120,7 @@ func MkdirAll(ctx context.Context, path string, mode os.FileMode) error {
 }
 
 // Open opens an existing file for reading, using the Default VFS.
-func Open(ctx context.Context, path string) (io.ReadCloser, error) { return Default.Open(ctx, path) }
+func Open(ctx context.Context, path string) (FileReader, error) { return Default.Open(ctx, path) }
 
 // Create creates a new file for writing, using the Default VFS.
 func Create(ctx context.Context, path string) (io.WriteCloser, error) {
@@ -151,9 +159,9 @@ func (LocalFS) MkdirAll(_ context.Context, path string, mode os.FileMode) error
 }
 
 // Open implements part of the VFS interface.
-func (LocalFS) Open(_ context.Context, path string) (io.ReadCloser, error) {
+func (LocalFS) Open(_ context.Context, path string) (FileReader, error) {
 	if path == "-" {
-		return ioutil.NopCloser(os.Stdin), nil
+		return stdinWrapper{os.Stdin}, nil
 	}
 	return os.Open(path)
 }
@@ -207,3 +215,30 @@ func (UnsupportedWriter) Rename(_ context.Context, _, _ string) error { return E
 
 // Remove implements part of Writer interface.  It is not supported.
 func (UnsupportedWriter) Remove(_ context.Context, _ string) error { return ErrNotSupported }
+
+// UnseekableFileReader implements the io.Seeker and io.ReaderAt at portion of
+// FileReader with stubs that always return ErrNotSupported.
+type UnseekableFileReader struct {
+	io.ReadCloser
+}
+
+// ReadAt implements io.ReaderAt interface. It is not supported.
+func (UnseekableFileReader) ReadAt([]byte, int64) (int, error) {
+	return 0, ErrNotSupported
+}
+
+// Seek implements io.Seeker interface. It is not supported.
+func (UnseekableFileReader) Seek(int64, int) (int64, error) {
+	return 0, ErrNotSupported
+}
+
+// stdinWrapper is similar in purpose to ioutil.NopCloser, but allows access to
+// other os.File methods that implement FileReader rather than restricting to
+// just ioutil.ReadCloser.
+type stdinWrapper struct {
+	*os.File
+}
+
+func (stdinWrapper) Close() error {
+	return nil
+}

kythe/go/platform/vfs/zip/fs.go

@@ -70,15 +70,19 @@ func (z FS) Stat(_ context.Context, path string) (os.FileInfo, error) {
 	return f.FileInfo(), nil
 }
 
-// Open implements part of vfs.Reader, returning a io.ReadCloser owned by
+// Open implements part of vfs.Reader, returning a vfs.FileReader owned by
 // the underlying zip archive. It is safe to open multiple files concurrently,
 // as documented by the zip package.
-func (z FS) Open(_ context.Context, path string) (io.ReadCloser, error) {
+func (z FS) Open(_ context.Context, path string) (vfs.FileReader, error) {
 	f := z.find(path)
 	if f == nil {
 		return nil, os.ErrNotExist
 	}
-	return f.Open()
+	fo, err := f.Open()
+	if err != nil {
+		return nil, err
+	}
+	return vfs.UnseekableFileReader{fo}, nil
 }
 
 // Glob implements part of vfs.Reader using filepath.Match to compare the