1 files changed, 61 insertions, 0 deletions
diff --git a/hst/grp_pwd.go b/hst/grp_pwd.go
new file mode 100644
index 00000000..1a5c962e
--- /dev/null
+++ b/hst/grp_pwd.go
@@ -0,0 +1,61 @@
+package hst
+
+import (
+	"fmt"
+	"strconv"
+)
+
+const (
+	// UserOffset is the offset for UID and GID ranges for each user.
+	UserOffset = 100000
+	// RangeSize is the size of each UID and GID range.
+	RangeSize = UserOffset / 10
+
+	// IdentityStart is the first [Config.Identity] value. This is enforced in cmd/hsu.
+	IdentityStart = 0
+	// IdentityEnd is the last [Config.Identity] value. This is enforced in cmd/hsu.
+	IdentityEnd = AppEnd - AppStart
+
+	// AppStart is the first app user UID and GID.
+	AppStart = RangeSize * 1
+	// AppEnd is the last app user UID and GID.
+	AppEnd = AppStart + RangeSize - 1
+
+	/* these are for Rosa OS: use the ranges below to determine whether a process is isolated */
+
+	// IsolatedStart is the start of UID and GID for fully isolated sandboxed processes.
+	IsolatedStart = RangeSize * 9
+	// IsolatedEnd is the end of UID and GID for fully isolated sandboxed processes.
+	IsolatedEnd = IsolatedStart + RangeSize - 1
+)
+
+// A UID represents a kernel uid in the init namespace.
+type UID uint32
+
+// String returns the username corresponding to this uid.
+//
+// Not safe against untrusted input.
+func (uid UID) String() string {
+	appid := uid % UserOffset
+	userid := uid / UserOffset
+	if appid >= IsolatedStart && appid <= IsolatedEnd {
+		return fmt.Sprintf("u%d_i%d", userid, appid-IsolatedStart)
+	} else if appid >= AppStart && appid <= AppEnd {
+		return fmt.Sprintf("u%d_a%d", userid, appid-AppStart)
+	} else {
+		return strconv.Itoa(int(uid))
+	}
+}
+
+// A GID represents a kernel gid in the init namespace.
+type GID uint32
+
+// String returns the group name corresponding to this gid.
+//
+// Not safe against untrusted input.
+func (gid GID) String() string { return UID(gid).String() }
+
+// ToUser returns a [hst.UID] value from userid and appid.
+//
+// Not safe against untrusted input.
+func ToUser[U int | uint32](userid, appid U) U { return userid*UserOffset + AppStart + appid }