WebDAV filesystem implementation for the absfs ecosystem.

webdavfs provides bidirectional WebDAV support for the absfs ecosystem:

1. Client Mode - Access remote WebDAV servers through the absfs.FileSystem interface
2. Server Mode - Expose any absfs.FileSystem as a WebDAV server

This enables seamless integration with any WebDAV-compliant server (Nextcloud, ownCloud, Apache mod_dav, nginx, etc.) and allows serving any absfs filesystem (memfs, osfs, s3fs, unionfs, etc.) over WebDAV.

import "github.com/absfs/webdavfs"

// Connect to a WebDAV server
fs, err := webdavfs.New(&webdavfs.Config{
    URL:      "https://webdav.example.com/remote.php/dav/files/user/",
    Username: "user",
    Password: "password",
})
if err != nil {
    log.Fatal(err)
}
defer fs.Close()

// Use standard absfs operations
file, _ := fs.Open("/documents/report.txt")

import (
    "github.com/absfs/memfs"
    "github.com/absfs/webdavfs"
)

// Create any absfs.FileSystem
fs, _ := memfs.NewFS()

// Serve it via WebDAV
server := webdavfs.NewServer(fs, &webdavfs.ServerConfig{
    Prefix: "/webdav",
    Auth: &webdavfs.BasicAuth{
        Realm: "My Server",
        Validator: func(user, pass string) bool {
            return user == "admin" && pass == "secret"
        },
    },
})

http.ListenAndServe(":8080", server)

webdavfs follows the Direct Backend Integration pattern used by other absfs network filesystem implementations like sftpfs and s3fs. The implementation consists of:

1. FileSystem struct - Holds WebDAV client connection and configuration
2. File wrapper - Adapts WebDAV file operations to the absfs.File interface
3. Protocol mapping - Translates absfs operations to WebDAV HTTP methods

┌─────────────────────┐
│  absfs Application  │
│  (uses absfs API)   │
└──────────┬──────────┘
           │ absfs.FileSystem interface
           ▼
┌─────────────────────┐
│    webdavfs         │
│  FileSystem struct  │
└──────────┬──────────┘
           │ WebDAV HTTP protocol
           ▼
┌─────────────────────┐
│  WebDAV Server      │
│  (remote storage)   │
└─────────────────────┘

The package implements the complete absfs.FileSystem interface hierarchy:

• OpenFile(name string, flag int, perm os.FileMode) (File, error) → WebDAV GET/PUT/MKCOL
• Mkdir(name string, perm os.FileMode) error → WebDAV MKCOL
• Remove(name string) error → WebDAV DELETE
• Rename(oldpath, newpath string) error → WebDAV MOVE
• Stat(name string) (os.FileInfo, error) → WebDAV PROPFIND
• Chmod(name string, mode os.FileMode) error → WebDAV PROPPATCH (limited support)
• Chtimes(name string, atime, mtime time.Time) error → WebDAV PROPPATCH
• Chown(name string, uid, gid int) error → WebDAV PROPPATCH (limited support)

• Separator() → Returns '/'
• ListSeparator() → Returns ':'
• Chdir(dir string) error → Local state tracking
• Getwd() (string, error) → Local state tracking
• TempDir() string → Returns server-specific temp path
• Open(name string) (File, error) → Convenience wrapper for OpenFile
• Create(name string) (File, error) → Convenience wrapper for OpenFile
• MkdirAll(name string, perm os.FileMode) error → Recursive MKCOL
• RemoveAll(path string) error → Recursive DELETE
• Truncate(name string, size int64) error → WebDAV partial PUT

The File wrapper implements absfs.File (which extends io.Reader, io.Writer, io.Seeker, io.Closer):

• Read(b []byte) (int, error) → HTTP GET with range
• Write(b []byte) (int, error) → HTTP PUT with buffering
• Close() error → Flush writes, close connection
• Seek(offset int64, whence int) (int64, error) → Update position tracking
• Stat() (os.FileInfo, error) → WebDAV PROPFIND

• ReadAt(b []byte, off int64) (int, error) → HTTP GET with Range header
• WriteAt(b []byte, off int64) (int, error) → HTTP PUT with Content-Range
• Readdir(n int) ([]os.FileInfo, error) → WebDAV PROPFIND with depth=1
• Readdirnames(n int) ([]string, error) → Wrapper around Readdir
• Truncate(size int64) error → WebDAV partial PUT
• Sync() error → Flush buffered writes

Standard DAV properties accessed via PROPFIND:

• displayname → File name
• getcontentlength → File size
• getlastmodified → Modification time
• resourcetype → File vs directory detection
• getetag → Cache validation
• getcontenttype → MIME type

WebDAV is a loosely defined standard with varying server implementations:

1. Permissions - Not all servers support Unix permissions via PROPPATCH

   • Chmod may be a no-op on some servers
   • Chown typically unsupported in most WebDAV servers

2. Atomic Operations - Limited atomicity guarantees

   • No native locking in basic WebDAV (requires WebDAV Locking extension)
   • Concurrent writes may result in race conditions

3. Performance - Network latency considerations

   • Each operation is an HTTP request
   • Directory listings can be expensive (recursive PROPFIND)
   • Consider using caching wrappers like corfs for read-heavy workloads

4. Partial Updates - Server-dependent support

   • WriteAt and Truncate require Content-Range support
   • Some servers may require full file replacement

1. Authentication - Support for HTTP Basic, Digest, and Bearer tokens
2. TLS/HTTPS - Strongly recommended for production use
3. Credentials - Stored in memory, consider using credential helpers
4. Path Traversal - All paths sanitized before HTTP requests

import "github.com/absfs/webdavfs"

// Connect to WebDAV server
fs, err := webdavfs.New(&webdavfs.Config{
    URL:      "https://webdav.example.com/remote.php/dav/files/user/",
    Username: "user",
    Password: "password",
})
if err != nil {
    log.Fatal(err)
}
defer fs.Close()

// Use standard absfs operations
file, err := fs.Create("documents/report.txt")
if err != nil {
    log.Fatal(err)
}
defer file.Close()

_, err = file.Write([]byte("Hello WebDAV!"))

import (
    "github.com/absfs/webdavfs"
    "github.com/absfs/corfs"
    "github.com/absfs/memfs"
)

// Remote WebDAV as primary
remote, _ := webdavfs.New(&webdavfs.Config{...})

// Local memory cache
cache := memfs.NewFS()

// Wrap with cache-on-read
fs := corfs.New(remote, cache)

// First read hits remote, subsequent reads use cache
data, _ := fs.ReadFile("large-file.bin")

import (
    "github.com/absfs/webdavfs"
    "github.com/absfs/cowfs"
)

// WebDAV base layer (read-only in practice)
base, _ := webdavfs.New(&webdavfs.Config{...})

// Local overlay for writes
overlay := os.DirFS("/tmp/overlay")

// Writes go to overlay, reads fall through to WebDAV
fs := cowfs.New(overlay, base)

// Modify without affecting remote until explicit sync
fs.WriteFile("config.yml", data, 0644)

import (
    "github.com/absfs/webdavfs"
    "github.com/absfs/sftpfs"
    "github.com/absfs/s3fs"
)

// Access same logical filesystem via different protocols
webdav, _ := webdavfs.New(&webdavfs.Config{URL: "https://..."})
sftp, _ := sftpfs.New(&sftpfs.Config{Host: "..."})
s3, _ := s3fs.New(&s3fs.Config{Bucket: "..."})

// Application code uses absfs.FileSystem interface
// Can switch between protocols transparently
var fs absfs.FileSystem = webdav

Expected package structure:

webdavfs/
├── README.md           # This file
├── FUZZING.md          # Fuzz testing documentation
├── go.mod              # Module definition
├── webdavfs.go         # FileSystem implementation
├── file.go             # File wrapper implementation
├── client.go           # WebDAV HTTP client
├── properties.go       # WebDAV property parsing
├── config.go           # Configuration structs
├── errors.go           # Error handling
├── webdavfs_test.go    # Integration tests
└── fuzz_test.go        # Fuzz tests

type FileSystem struct {
    client *webdavClient
    root   string
    cwd    string
}

func New(config *Config) (*FileSystem, error)
func (fs *FileSystem) OpenFile(...) (absfs.File, error)
func (fs *FileSystem) Mkdir(...) error
// ... other Filer methods

type File struct {
    fs       *FileSystem
    path     string
    mode     int
    offset   int64
    info     os.FileInfo
    buffer   *bytes.Buffer  // For write buffering
    modified bool
}

func (f *File) Read(b []byte) (int, error)
func (f *File) Write(b []byte) (int, error)
// ... other File methods

type webdavClient struct {
    httpClient *http.Client
    baseURL    *url.URL
    auth       authProvider
}

func (c *webdavClient) propfind(...) (*multistatus, error)
func (c *webdavClient) get(...) (io.ReadCloser, error)
func (c *webdavClient) put(...) error
func (c *webdavClient) mkcol(...) error
func (c *webdavClient) delete(...) error
func (c *webdavClient) move(...) error

• Mock HTTP server using httptest
• Test each absfs method with various WebDAV responses
• Error handling for malformed XML, network errors
• Path sanitization and encoding

• Comprehensive fuzz testing for security and robustness
• Tests XML parsing, path encoding, HTTP response handling, authentication headers, and property values
• Helps discover edge cases and potential security vulnerabilities
• See FUZZING.md for detailed documentation

• Real WebDAV server (docker container)
• Full absfs compliance test suite
• Concurrent access patterns
• Large file handling

Against common WebDAV servers:

• Apache mod_dav
• nginx with ngx_http_dav_module
• Nextcloud
• ownCloud
• SabreDAV

The server functionality allows exposing any absfs.FileSystem as a WebDAV server. This is useful for:

• Serving in-memory filesystems for testing
• Creating WebDAV gateways to S3, SFTP, or other storage backends
• Implementing virtual filesystems with WebDAV access

┌─────────────────────┐
│   WebDAV Client     │
│  (any HTTP client)  │
└──────────┬──────────┘
           │ WebDAV HTTP protocol
           ▼
┌─────────────────────┐
│  webdavfs.Server    │
│  (HTTP handler)     │
└──────────┬──────────┘
           │ webdav.FileSystem interface
           ▼
┌─────────────────────┐
│ ServerFileSystem    │
│ (adapter)           │
└──────────┬──────────┘
           │ absfs.FileSystem interface
           ▼
┌─────────────────────┐
│  Any absfs FS       │
│  (memfs, osfs, etc) │
└─────────────────────┘

type ServerConfig struct {
    // Prefix is the URL path prefix (e.g., "/webdav")
    Prefix string

    // Auth is an optional authentication provider
    Auth AuthProvider

    // Logger logs each request
    Logger func(r *http.Request, err error)

    // LockSystem for WebDAV locking (default: in-memory)
    LockSystem webdav.LockSystem
}

server := webdavfs.NewServer(fs, &webdavfs.ServerConfig{
    Auth: &webdavfs.BasicAuth{
        Realm: "My WebDAV Server",
        Validator: func(username, password string) bool {
            return username == "admin" && password == "secret"
        },
    },
})

server := webdavfs.NewServer(fs, &webdavfs.ServerConfig{
    Auth: &webdavfs.BearerAuth{
        Realm: "API",
        Validator: func(token string) bool {
            return token == "valid-api-token"
        },
    },
})

Implement the AuthProvider interface:

type AuthProvider interface {
    Authenticate(w http.ResponseWriter, r *http.Request) bool
}

import (
    "github.com/absfs/memfs"
    "github.com/absfs/osfs"
    "github.com/absfs/unionfs"
    "github.com/absfs/webdavfs"
)

// Create layers
base, _ := osfs.NewFS()
overlay, _ := memfs.NewFS()

// Create union
ufs, _ := unionfs.New(overlay, base)

// Serve via WebDAV
server := webdavfs.NewServer(ufs, nil)
http.ListenAndServe(":8080", server)

import (
    "github.com/absfs/s3fs"
    "github.com/absfs/webdavfs"
)

// Connect to S3
s3, _ := s3fs.New(&s3fs.Config{
    Bucket: "my-bucket",
    Region: "us-east-1",
})

// Serve S3 bucket via WebDAV
server := webdavfs.NewServer(s3, &webdavfs.ServerConfig{
    Prefix: "/s3",
})
http.ListenAndServe(":8080", server)

server := webdavfs.NewServer(fs, &webdavfs.ServerConfig{
    Logger: func(r *http.Request, err error) {
        if err != nil {
            log.Printf("WebDAV ERROR %s %s: %v", r.Method, r.URL.Path, err)
        } else {
            log.Printf("WebDAV %s %s", r.Method, r.URL.Path)
        }
    },
})

• absfs - Core filesystem abstraction
• memfs - In-memory filesystem
• osfs - OS filesystem wrapper
• sftpfs - SFTP protocol access
• s3fs - S3-compatible object storage
• corfs - Cache-on-read wrapper
• cowfs - Copy-on-write layers
• unionfs - Union/overlay filesystem

• golang.org/x/net/webdav - WebDAV server implementation (used by Server mode)
• github.com/studio-b12/gowebdav - WebDAV client library

This implementation follows absfs ecosystem principles:

1. Interface Compliance - Full implementation of absfs.FileSystem
2. Composition-Friendly - Works seamlessly with other absfs wrappers
3. Minimal Dependencies - Only essential WebDAV protocol libraries
4. Error Transparency - WebDAV errors wrapped in absfs error types
5. Zero Configuration - Sensible defaults, minimal required config
6. Test Coverage - Comprehensive tests against real servers

MIT License - see LICENSE file for details.

Contributions welcome! Please ensure:

• All absfs.FileSystem methods implemented
• Tests pass against multiple WebDAV servers
• Documentation updated for new features
• Error handling follows absfs patterns