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filesystem.go
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filesystem.go
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// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You 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 filesystem contains an extensible file system abstraction. It allows
// various kinds of storage systems to be used uniformly, notably through textio.
//
// Registered file systems at minimum implement the Interface abstraction, and
// can then optionally implement Remover, Renamer, and Copier to support
// rename operations. Filesystems are only expected to handle their own IO, and
// not cross file system IO. Should cross file system IO be required, additional
// utility methods should be added to this package to support them.
package filesystem
import (
"context"
"fmt"
"io"
"strings"
"time"
"github.com/apache/beam/sdks/v2/go/pkg/beam/internal/errors"
)
var registry = make(map[string]func(context.Context) Interface)
// wellKnownSchemeImportPaths is used for delivering useful error messages when a
// scheme is not found.
var wellKnownSchemeImportPaths = map[string]string{
"memfs": "github.com/apache/beam/sdks/v2/go/pkg/beam/io/filesystem/memfs",
"default": "github.com/apache/beam/sdks/v2/go/pkg/beam/io/filesystem/local",
"gs": "github.com/apache/beam/sdks/v2/go/pkg/beam/io/filesystem/gcs",
"s3": "github.com/apache/beam/sdks/v2/go/pkg/beam/io/filesystem/s3",
}
// Register registers a file system backend under the given scheme. For
// example, "hdfs" would be registered a HFDS file system and HDFS paths used
// transparently.
func Register(scheme string, fs func(context.Context) Interface) {
if _, ok := registry[scheme]; ok {
panic(fmt.Sprintf("scheme %v already registered", scheme))
}
registry[scheme] = fs
}
// New returns a new Interface for the given file path's scheme.
func New(ctx context.Context, path string) (Interface, error) {
scheme := getScheme(path)
mkfs, ok := registry[scheme]
if !ok {
return nil, errorForMissingScheme(scheme, path)
}
return mkfs(ctx), nil
}
func errorForMissingScheme(scheme, path string) error {
messageSuffix := ""
if suggestedImportPath, ok := wellKnownSchemeImportPaths[scheme]; ok {
messageSuffix = fmt.Sprintf(": Consider adding the following import to your program to register an implementation for %q:\n import _ %q", scheme, suggestedImportPath)
}
return errors.Errorf("file system scheme %q not registered for %q%s", scheme, path, messageSuffix)
}
// Interface is a filesystem abstraction that allows beam io sources and sinks
// to use various underlying storage systems transparently.
type Interface interface {
io.Closer
// List expands a pattern to a list of filenames.
// Returns nil if there are no matching files.
List(ctx context.Context, glob string) ([]string, error)
// OpenRead opens a file for reading.
OpenRead(ctx context.Context, filename string) (io.ReadCloser, error)
// OpenWrite opens a file for writing. If the file already exist, it will be
// overwritten. The returned io.WriteCloser should be closed to commit the write.
OpenWrite(ctx context.Context, filename string) (io.WriteCloser, error)
// Size returns the size of a file in bytes.
Size(ctx context.Context, filename string) (int64, error)
}
// The following interfaces are optional for the filesystems, but
// to support more efficient or composite operations when possible.
// LastModifiedGetter is an interface for getting the last modified time
// of a file.
type LastModifiedGetter interface {
LastModified(ctx context.Context, filename string) (time.Time, error)
}
// Remover is an interface for removing files from the filesystem.
// To be considered for promotion to Interface.
type Remover interface {
Remove(ctx context.Context, filename string) error
}
// Copier is an interface for copying files in the filesystem.
type Copier interface {
Copy(ctx context.Context, oldpath, newpath string) error
}
// Renamer is an interface for renaming or moving files in the filesystem.
type Renamer interface {
Rename(ctx context.Context, oldpath, newpath string) error
}
func getScheme(path string) string {
if index := strings.Index(path, "://"); index > 0 {
return path[:index]
}
return "default"
}
// ValidateScheme panics if the given path's scheme does not have a
// corresponding file system registered.
func ValidateScheme(path string) {
if strings.TrimSpace(path) == "" {
panic("empty file glob provided")
}
scheme := getScheme(path)
if _, ok := registry[scheme]; !ok {
panic(errorForMissingScheme(scheme, path))
}
}