4 files changed, 291 insertions, 0 deletions
diff --git a/back/auth/auth.go b/back/auth/auth.go
new file mode 100644
index 0000000..5685001
--- /dev/null
+++ b/back/auth/auth.go
@@ -0,0 +1,17 @@
+package auth
+
+import "fmt"
+
+const (
+	// Maximum number of bytes in a Username.
+	MaxUsernameSize = 64
+)
+
+type Username string
+
+func ValidiateUsername(s string) (Username, error) {
+	if len(s) > MaxUsernameSize {
+		return "", fmt.Errorf("username longer than %d bytes: %q", MaxUsernameSize, s)
+	}
+	return Username(s), nil
+}
diff --git a/back/cmd/authfs/main.go b/back/cmd/authfs/main.go
new file mode 100644
index 0000000..f8618df
--- /dev/null
+++ b/back/cmd/authfs/main.go
@@ -0,0 +1,66 @@
+/*
+This is the authfs daemon. It stores the user database and client
+sessions, and it serves a 9P filesystem for managing them.
+
+User data (usernames and password hashes) are stored on disk. Sessions
+are stored in memory.
+*/
+package main
+
+import (
+	"context"
+	"flag"
+	"log"
+	"net"
+	"os"
+
+	"github.com/docker-archive/go-p9p"
+)
+
+const (
+	defaultNetwork = "unix"
+	defaultAddress = "authfs.sock"
+)
+
+var (
+	network, address string
+
+	outlog = log.New(os.Stdout, "authfs [info]: ", log.LstdFlags)
+	errlog = log.New(os.Stderr, "authfs [error]: ", log.LstdFlags|log.Llongfile)
+)
+
+func main() {
+	flag.StringVar(&network, "net", defaultNetwork, "network transport protocol: {tcp, unix}")
+	flag.StringVar(&address, "addr", defaultAddress, "IP address or Unix socket path to listen on")
+	flag.Parse()
+
+	ln, err := net.Listen(network, address)
+	if err != nil {
+		errlog.Fatal(err)
+	}
+	defer logErr(ln.Close())
+
+	for {
+		if conn, err := ln.Accept(); err == nil {
+			outlog.Println("connected", conn.RemoteAddr())
+			go handle(conn)
+		} else {
+			errlog.Println(err)
+		}
+	}
+}
+
+func handle(conn net.Conn) {
+	defer logErr(conn.Close())
+	ctx := context.Background()
+	handler := p9p.Dispatch(NewSession())
+	if err := p9p.ServeConn(ctx, conn, handler); err != nil {
+		errlog.Printf("%v: %v\n", conn.RemoteAddr(), err)
+	}
+}
+
+func logErr(err error) {
+	if err != nil {
+		errlog.Println(err)
+	}
+}
diff --git a/back/cmd/authfs/root.go b/back/cmd/authfs/root.go
new file mode 100644
index 0000000..70ca643
--- /dev/null
+++ b/back/cmd/authfs/root.go
@@ -0,0 +1,21 @@
+package main
+
+const rootQid = p9p.Qid{
+	Type: QTDIR,
+	Version: 0x0,
+	Path: 0x1,
+}
+
+// Root is the root Dir which contains /users and /sessions.
+type Root struct {
+	path string
+}
+
+func (r Root) Qid() p9p.Qid { return rootQid }
+
+func (r Root) Stat() (p9p.Dir, error) {
+	return p9p.Dir{
+		Qid: rootQid,
+		Mode: DMDIR | DMREAD,
+		
+}
diff --git a/back/cmd/authfs/session.go b/back/cmd/authfs/session.go
new file mode 100644
index 0000000..2d4eb98
--- /dev/null
+++ b/back/cmd/authfs/session.go
@@ -0,0 +1,187 @@
+package main
+
+import (
+	"context"
+	"sync"
+
+	"github.com/docker-archive/go-p9p"
+)
+
+// Session implements the p9p.Session interface.
+type Session struct {
+	mu   sync.Mutex
+	fids map[p9p.Fid]Fid
+	*Root
+}
+
+type Fid struct {
+	File
+	uname string
+}
+
+type File interface {
+	Qid() p9p.Qid
+	Stat() (p9p.Dir, error)
+	Open(mode p9p.Flag) error
+	Remove() error
+	Read(ctx context.Context, p []byte, offset int64) (n int, err error)
+	Write(ctx context.Context, p []byte, offset int64) (n int, err error)
+}
+
+type Dir interface {
+	File
+	Create(ctx context.Context, name string, perm uint32, mode p9p.Flag) (File, error)
+	Walk(ctx context.Context, name string) (File, error)
+}
+
+func NewSession(root *Root) p9p.Session {
+	return &Session{
+		fids: make(map[p9p.Fid]Fid),
+		Root: root,
+	}
+}
+
+func (s *Session) Auth(ctx context.Context, afid p9p.Fid, uname, aname string) (p9p.Qid, error) {
+	return p9p.Qid{}, p9p.MessageRerror{"authfs: no authentication required"}
+}
+
+func (s *Session) Attach(ctx context.Context, fid, afid p9p.Fid, uname, aname string) (p9p.Qid, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if _, exists := s.fids[fid]; exists {
+		return p9p.Qid{}, p9p.ErrDupfid
+	}
+	f := Fid{s.root, uname}
+	s.fids[fid] = f
+	return f.Qid(), nil
+}
+
+func (s *Session) Clunk(ctx context.Context, fid p9p.Fid) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if _, ok := s.fids[fid]; ok {
+		delete(s.fids, fid)
+		return nil
+	} else {
+		return p9p.ErrUnknownfid
+	}
+}
+
+func (s *Session) Remove(ctx context.Context, fid p9p.Fid) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	f, ok := s.fids[fid]
+	if !ok {
+		return p9p.ErrUnknownfid
+	}
+	delete(s.fids, fid) // clunk
+	return f.Remove()
+}
+
+func (s *Session) Walk(ctx context.Context, fid, newfid p9p.Fid, names ...string) ([]p9p.Qid, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	f, ok := s.fids[fid]
+	if !ok {
+		return nil, p9p.ErrUnknownfid
+	}
+
+	if _, exists := s.fids[newfid]; exists {
+		return nil, p9p.ErrDupfid
+	}
+
+	var (
+		qids []p9p.Qid
+		err  error
+		dot  = f
+	)
+	defer func() { s.fids[newfid] = dot }()
+	for _, name := range names {
+		dir, ok := dot.File.(Dir)
+		if !ok {
+			return qids, p9p.ErrWalknodir
+		}
+		dot.File, err = dir.Walk(ctx, name)
+		if err != nil {
+			return qids, err
+		}
+		qids = append(qids, dot.File.Qid())
+	}
+	return qids, nil
+}
+
+func (s *Session) Read(ctx context.Context, fid p9p.Fid, p []byte, offset int64) (n int, err error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if f, ok := s.fids[fid]; ok {
+		return f.File.Read(ctx, p, offset)
+	} else {
+		return 0, p9p.ErrUnknownfid
+	}
+}
+
+func (s *Session) Write(ctx context.Context, fid p9p.Fid, p []byte, offset int64) (n int, err error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if f, ok := s.fids[fid]; ok {
+		return f.File.Write(ctx, p, offset)
+	} else {
+		return 0, p9p.ErrUnknownfid
+	}
+}
+
+func (s *Session) Open(ctx context.Context, fid p9p.Fid, mode p9p.Flag) (p9p.Qid, uint32, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	f, ok := s.fids[fid]
+	if !ok {
+		return p9p.Qid{}, 0, p9p.ErrUnknownfid
+	}
+	if err := f.Open(mode); err != nil {
+		return p9p.Qid{}, 0, err
+	}
+	return f.File.Qid(), 0, nil
+}
+
+func (s *Session) Create(ctx context.Context, parent p9p.Fid, name string, perm uint32, mode p9p.Flag) (p9p.Qid, uint32, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	f, ok := s.fids[parent]
+	if !ok {
+		return p9p.Qid{}, 0, p9p.ErrUnknownfid
+	}
+	dir, ok := f.File.(Dir)
+	if !ok {
+		return p9p.Qid{}, 0, p9p.ErrCreatenondir
+	}
+
+	child, err := dir.Create(ctx, name, perm, mode)
+	return child.Qid(), 0, err
+}
+
+func (s *Session) Stat(ctx context.Context, fid p9p.Fid) (p9p.Dir, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if f, ok := s.fids[fid]; ok {
+		return f.File.Stat()
+	} else {
+		return p9p.Dir{}, p9p.ErrUnknownfid
+	}
+}
+
+func (s *Session) WStat(ctx context.Context, fid p9p.Fid, dir p9p.Dir) error {
+	return p9p.ErrPerm
+}
+
+func (s *Session) Version() (msize int, version string) {
+	return p9p.DefaultMSize, p9p.DefaultVersion
+}