1 files changed, 131 insertions, 0 deletions
diff --git a/server/user/user.go b/server/user/user.go
new file mode 100644
index 0000000..405dc55
--- /dev/null
+++ b/server/user/user.go
@@ -0,0 +1,131 @@
+package user
+
+import (
+	"dtail/config"
+	"dtail/fs/permissions"
+	"dtail/logger"
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+)
+
+const maxLinkDepth int = 100
+
+// User represents an end-user which connected to the server via the DTail client.
+type User struct {
+	// The user name.
+	Name string
+	// The remote address connected from.
+	remoteAddress string
+	// The permissions the user has.
+	permissions []string
+}
+
+// New returns a new user.
+func New(name, remoteAddress string) *User {
+	return &User{
+		Name:          name,
+		remoteAddress: remoteAddress,
+	}
+}
+
+// String representation of the user.
+func (u *User) String() string {
+	return fmt.Sprintf("%s@%s", u.Name, u.remoteAddress)
+}
+
+// HasFilePermission is used to determine whether user is alowed to read a file.
+func (u *User) HasFilePermission(filePath string) (hasPermission bool) {
+	cleanPath, err := filepath.EvalSymlinks(filePath)
+	if err != nil {
+		logger.Error(u, filePath, "Unable to evaluate symlinks", err)
+		hasPermission = false
+		return
+	}
+
+	cleanPath, err = filepath.Abs(cleanPath)
+	if err != nil {
+		logger.Error(u, cleanPath, "Unable to make file path absolute", err)
+		hasPermission = false
+		return
+	}
+
+	if cleanPath != filePath {
+		logger.Info(u, filePath, cleanPath, "Calculated new clean path from original file path (possibly symlink)")
+	}
+
+	hasPermission, err = u.hasFilePermission(cleanPath)
+	if err != nil {
+		logger.Warn(u, cleanPath, err)
+	}
+
+	return
+}
+
+func (u *User) hasFilePermission(cleanPath string) (bool, error) {
+	// First check file system Linux/UNIX permission.
+	if _, err := permissions.ToRead(u.Name, cleanPath); err != nil {
+		return false, fmt.Errorf("User without OS file system permissions to read file: '%v'", err)
+	}
+	logger.Info(u, cleanPath, "User has OS file system permissions to read file")
+
+	// If file system permission is given, also check permissions
+	// as configured in DTail config file.
+	if len(u.permissions) == 0 {
+		p, err := config.ServerUserPermissions(u.Name)
+		if err != nil {
+			return false, err
+		}
+		u.permissions = p
+	}
+
+	var hasPermission bool
+	var err error
+
+	if hasPermission, err = u.iteratePaths(cleanPath); err != nil {
+		return false, err
+	}
+
+	// Only allow to follow regular files or symlinks.
+	info, err := os.Lstat(cleanPath)
+	if err != nil {
+		return false, fmt.Errorf("Unable to determine file type: '%v'", err)
+	}
+
+	if !info.Mode().IsRegular() {
+		return false, fmt.Errorf("Can only open regular files or follow symlinks")
+	}
+
+	return hasPermission, nil
+}
+
+func (u *User) iteratePaths(cleanPath string) (bool, error) {
+	for _, permission := range u.permissions {
+		var regexStr string
+		var negate bool
+
+		if strings.HasPrefix(permission, "!") {
+			regexStr = permission[1:]
+			negate = true
+		}
+		regexStr = permission
+		negate = false
+
+		re, err := regexp.Compile(regexStr)
+		if err != nil {
+			return false, fmt.Errorf("Permission test failed, can't compile regex '%s': '%v'", regexStr, err)
+		}
+
+		if negate && re.MatchString(cleanPath) {
+			return false, fmt.Errorf("Permission test failed, matching negative pattern '%s'", permission)
+		}
+
+		if !negate && re.MatchString(cleanPath) {
+			logger.Info(u, cleanPath, "Permission test passed partially, matching positive pattern", permission)
+		}
+	}
+
+	return true, nil
+}