1 files changed, 140 insertions, 0 deletions
diff --git a/server.go b/server.go
new file mode 100644
index 0000000..e34e3f2
--- /dev/null
+++ b/server.go
@@ -0,0 +1,140 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"os"
+	"os/user"
+	"strings"
+)
+
+const TableName = "membership"
+
+type Server struct {
+	HostName   string
+	Groups     []string
+	GroupsFile string
+}
+
+func ServeUnixSocket(listenner net.Listener, srv *Server) error {
+	for {
+		// Accept an incoming connection.
+		conn, err := listenner.Accept()
+		if errors.Is(err, net.ErrClosed) {
+			break
+		} else if err != nil {
+			fmt.Fprintln(os.Stderr, err.Error())
+
+			continue
+		}
+
+		go func(conn net.Conn) {
+			defer conn.Close()
+
+			err = srv.HandleConn(conn, conn)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, err.Error())
+			}
+		}(conn)
+
+	}
+
+	return nil
+}
+
+func (s *Server) readGroupList() ([]string, error) {
+	f, err := os.Open(s.GroupsFile)
+	if err != nil {
+		return nil, err
+	}
+
+	buf, err := io.ReadAll(f)
+	if err != nil {
+		return nil, err
+	}
+
+	groups := strings.Split(string(buf), "\n")
+
+	return groups, nil
+}
+
+func (s *Server) HandleConn(w io.Writer, r io.Reader) error {
+	for {
+		var req Request
+
+		_, err := readNetString(r, &req)
+		if errors.Is(err, io.EOF) {
+			break
+		}
+
+		if req.Name != TableName {
+			if _, err = writeNetString(w, &ReplyPerm{Reason: "unexpected name"}); err != nil {
+				return err
+			}
+
+			return nil
+		}
+
+		strs := strings.SplitN(req.Key, "@", 2)
+		if len(strs) != 2 {
+			return fmt.Errorf("unexpected email address format")
+		}
+		userName := strs[0]
+		hostName := strs[1]
+
+		if hostName != s.HostName {
+			if _, err := writeNetString(w, &ReplyNotFound{}); err != nil {
+				return err
+			}
+
+			return nil
+		}
+
+		u, err := user.Lookup(userName)
+		if _, ok := err.(user.UnknownUserError); ok {
+			_, err := writeNetString(w, &ReplyNotFound{})
+			return err
+		} else if err != nil {
+			return err
+		}
+
+		groups, err := lookupGroupNames(u)
+		if err != nil {
+			return err
+		}
+
+		isListed := make(map[string]bool)
+
+		for _, v := range s.Groups {
+			isListed[v] = true
+		}
+
+		groupsFile, err := s.readGroupList()
+		if err != nil {
+			return fmt.Errorf("reading white list: %w", err)
+		}
+
+		for _, v := range groupsFile {
+			isListed[v] = true
+		}
+
+		found := false
+
+		for _, name := range groups {
+			found = isListed[name]
+			if found {
+				_, err = writeNetString(w, &ReplyOK{Data: "OK"})
+				return err
+			}
+		}
+
+		_, err = writeNetString(w, &ReplyNotFound{})
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}