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//! S-TAG (Service VLAN Tag) Information Element
//!
//! The S-TAG IE contains service provider VLAN tagging information for Ethernet packet filtering.
//! Per 3GPP TS 29.244 Section 8.2.95, this IE is used in Ethernet packet filtering scenarios.
//!
//! S-TAG is used in provider bridging (IEEE 802.1ad) for service provider VLAN tagging.
use crate::error::PfcpError;
use crate::ie::{Ie, IeType};
/// S-TAG (Service VLAN Tag)
///
/// Represents service provider VLAN tagging information per IEEE 802.1ad.
///
/// # 3GPP Reference
/// 3GPP TS 29.244 Section 8.2.95
///
/// # Structure
/// - Octet 5: Flags (PCP Priority, DEI)
/// - Octet 5-6: VID (VLAN ID) - 12 bits
///
/// ```text
/// Bits 8-6: PCP (Priority Code Point) - 3 bits
/// Bit 5: DEI (Drop Eligible Indicator) - 1 bit
/// Bits 4-1 (and next 8 bits): VID (VLAN ID) - 12 bits
/// ```
///
/// # Examples
///
/// ```
/// use rs_pfcp::ie::s_tag::STag;
///
/// // Create S-TAG with priority 3, no DEI, VLAN ID 100
/// let stag = STag::new(3, false, 100).unwrap();
/// assert_eq!(stag.priority(), 3);
/// assert_eq!(stag.dei(), false);
/// assert_eq!(stag.vid(), 100);
///
/// // Marshal and unmarshal
/// let bytes = stag.marshal();
/// let parsed = STag::unmarshal(&bytes).unwrap();
/// assert_eq!(stag, parsed);
/// ```
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct STag {
/// Priority Code Point (0-7, 3 bits)
pcp: u8,
/// Drop Eligible Indicator (boolean)
dei: bool,
/// VLAN ID (0-4095, 12 bits)
vid: u16,
}
impl STag {
/// Maximum valid priority (3 bits = 0-7)
pub const MAX_PRIORITY: u8 = 7;
/// Maximum valid VID (12 bits = 0-4095)
pub const MAX_VID: u16 = 4095;
/// Create a new S-TAG
///
/// # Arguments
/// * `pcp` - Priority Code Point (0-7)
/// * `dei` - Drop Eligible Indicator
/// * `vid` - VLAN ID (0-4095)
///
/// # Errors
/// Returns error if PCP > 7 or VID > 4095
///
/// # Example
/// ```
/// use rs_pfcp::ie::s_tag::STag;
///
/// let stag = STag::new(5, true, 1000).unwrap();
/// assert_eq!(stag.priority(), 5);
/// assert_eq!(stag.dei(), true);
/// assert_eq!(stag.vid(), 1000);
/// ```
pub fn new(pcp: u8, dei: bool, vid: u16) -> Result<Self, PfcpError> {
if pcp > Self::MAX_PRIORITY {
return Err(PfcpError::invalid_value(
"S-TAG PCP",
pcp.to_string(),
format!("exceeds maximum {}", Self::MAX_PRIORITY),
));
}
if vid > Self::MAX_VID {
return Err(PfcpError::invalid_value(
"S-TAG VID",
vid.to_string(),
format!("exceeds maximum {}", Self::MAX_VID),
));
}
Ok(STag { pcp, dei, vid })
}
/// Get the Priority Code Point
pub fn priority(&self) -> u8 {
self.pcp
}
/// Get the Drop Eligible Indicator
pub fn dei(&self) -> bool {
self.dei
}
/// Get the VLAN ID
pub fn vid(&self) -> u16 {
self.vid
}
/// Marshal S-TAG to bytes
///
/// # Returns
/// 3-byte array with S-TAG encoded
pub fn marshal(&self) -> [u8; 3] {
let mut bytes = [0u8; 3];
// Byte 0: PCP (3 bits) | DEI (1 bit) | VID[11:8] (4 bits)
bytes[0] = (self.pcp << 5) | ((self.dei as u8) << 4) | ((self.vid >> 8) as u8 & 0x0F);
// Byte 1: VID[7:0]
bytes[1] = (self.vid & 0xFF) as u8;
// Byte 2: Spare (0)
bytes[2] = 0;
bytes
}
/// Unmarshal S-TAG from bytes
///
/// # Arguments
/// * `data` - Byte slice containing S-TAG data (must be at least 3 bytes)
///
/// # Errors
/// Returns error if data is too short
///
/// # Example
/// ```
/// use rs_pfcp::ie::s_tag::STag;
///
/// let stag = STag::new(7, false, 4095).unwrap();
/// let bytes = stag.marshal();
/// let parsed = STag::unmarshal(&bytes).unwrap();
/// assert_eq!(stag, parsed);
/// ```
pub fn unmarshal(data: &[u8]) -> Result<Self, PfcpError> {
if data.len() < 3 {
return Err(PfcpError::invalid_length(
"S-TAG",
IeType::STag,
3,
data.len(),
));
}
// Extract PCP (bits 7-5 of byte 0)
let pcp = (data[0] >> 5) & 0x07;
// Extract DEI (bit 4 of byte 0)
let dei = (data[0] & 0x10) != 0;
// Extract VID (bits 3-0 of byte 0 + byte 1)
let vid = (((data[0] & 0x0F) as u16) << 8) | (data[1] as u16);
Ok(STag { pcp, dei, vid })
}
/// Convert to generic IE
///
/// # Example
/// ```
/// use rs_pfcp::ie::s_tag::STag;
/// use rs_pfcp::ie::IeType;
///
/// let stag = STag::new(2, false, 500).unwrap();
/// let ie = stag.to_ie();
/// assert_eq!(ie.ie_type, IeType::STag);
/// ```
pub fn to_ie(&self) -> Ie {
Ie::new(IeType::STag, self.marshal().to_vec())
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_stag_new_valid() {
let stag = STag::new(0, false, 0).unwrap();
assert_eq!(stag.priority(), 0);
assert!(!stag.dei());
assert_eq!(stag.vid(), 0);
let stag2 = STag::new(7, true, 4095).unwrap();
assert_eq!(stag2.priority(), 7);
assert!(stag2.dei());
assert_eq!(stag2.vid(), 4095);
}
#[test]
fn test_stag_new_invalid_pcp() {
let result = STag::new(8, false, 100);
assert!(result.is_err());
let err = result.unwrap_err();
assert!(matches!(err, PfcpError::InvalidValue { .. }));
}
#[test]
fn test_stag_new_invalid_vid() {
let result = STag::new(3, false, 4096);
assert!(result.is_err());
let err = result.unwrap_err();
assert!(matches!(err, PfcpError::InvalidValue { .. }));
}
#[test]
fn test_stag_marshal() {
let stag = STag::new(5, true, 1000).unwrap();
let bytes = stag.marshal();
assert_eq!(bytes.len(), 3);
// Expected byte 0: 101 1 0011 = 0xB3
assert_eq!(bytes[0], 0xB3);
// Verify VID low byte = 0xE8
assert_eq!(bytes[1], 0xE8);
// Spare byte
assert_eq!(bytes[2], 0x00);
}
#[test]
fn test_stag_unmarshal_valid() {
let data = [0xB3, 0xE8, 0x00]; // PCP=5, DEI=1, VID=1000
let stag = STag::unmarshal(&data).unwrap();
assert_eq!(stag.priority(), 5);
assert!(stag.dei());
assert_eq!(stag.vid(), 1000);
}
#[test]
fn test_stag_unmarshal_short() {
let data = [0xB3, 0xE8];
let result = STag::unmarshal(&data);
assert!(result.is_err());
}
#[test]
fn test_stag_unmarshal_empty() {
let result = STag::unmarshal(&[]);
assert!(result.is_err());
let err = result.unwrap_err();
assert!(matches!(err, PfcpError::InvalidLength { .. }));
}
#[test]
fn test_stag_round_trip() {
let test_cases = vec![
(0, false, 0),
(7, true, 4095),
(3, false, 100),
(5, true, 1000),
(1, false, 1),
];
for (pcp, dei, vid) in test_cases {
let original = STag::new(pcp, dei, vid).unwrap();
let marshaled = original.marshal();
let unmarshaled = STag::unmarshal(&marshaled).unwrap();
assert_eq!(
original, unmarshaled,
"Failed for PCP={}, DEI={}, VID={}",
pcp, dei, vid
);
}
}
#[test]
fn test_stag_to_ie() {
let stag = STag::new(4, false, 200).unwrap();
let ie = stag.to_ie();
assert_eq!(ie.ie_type, IeType::STag);
assert_eq!(ie.payload.len(), 3);
// Verify IE can be unmarshaled
let parsed = STag::unmarshal(&ie.payload).unwrap();
assert_eq!(stag, parsed);
}
#[test]
fn test_stag_scenarios() {
// Scenario 1: Service provider backbone VLAN
let backbone = STag::new(7, false, 100).unwrap();
assert_eq!(backbone.vid(), 100);
assert_eq!(backbone.priority(), 7);
// Scenario 2: Customer service VLAN with DEI
let customer_service = STag::new(5, true, 500).unwrap();
assert_eq!(customer_service.priority(), 5);
assert!(customer_service.dei());
// Scenario 3: Provider Edge VLAN
let pe_vlan = STag::new(6, false, 1000).unwrap();
assert_eq!(pe_vlan.vid(), 1000);
// Scenario 4: QinQ double tagging scenario
let outer_tag = STag::new(4, false, 2000).unwrap();
assert_eq!(outer_tag.vid(), 2000);
// Scenario 5: Maximum values for provider network
let max_stag = STag::new(7, true, 4095).unwrap();
assert_eq!(max_stag.priority(), 7);
assert!(max_stag.dei());
assert_eq!(max_stag.vid(), 4095);
}
#[test]
fn test_stag_boundary_values() {
// Minimum values
assert!(STag::new(0, false, 0).is_ok());
// Maximum values
assert!(STag::new(7, true, 4095).is_ok());
// Out of range
assert!(STag::new(8, false, 0).is_err());
assert!(STag::new(0, false, 4096).is_err());
}
}