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/* SPDX-License-Identifier: GPL-3.0-or-later */
#pragma once
#include "heap.h"
#include <netinet/in.h>
#include <stddef.h>
#include <stdint.h>
#include <sys/types.h>
//
// A two-path UDP tunnel implementation.
//
// The tunnel uses two physical paths to transmit packets to the same destination.
//
// Sent packets are assigned a sequence number and transmitted through one of the
// two paths according to a weighted round-robin scheduler.
//
// On the receiving end, packets are buffered in a reorder buffer and a best effort is made
// to deliver packets in order.
//
#define MPU_MTU (1500U - 20 - 8) //!< Maximum payload size for traditional IP/UDP headers
typedef struct {
int sockfd;
float weight;
} mpu_path_t; //!< Physical path for packet transmission
typedef struct {
uint64_t seq_num;
} mpu_hdr_t; //!< Tunnel packet header
typedef struct {
uint64_t timestamp; // in milliseconds
uint16_t packet_len;
union {
uint8_t buf[MPU_MTU];
mpu_hdr_t hdr;
} packet;
} mpu_slot_t; //!< Packet slot for reorder buffer
typedef struct {
mpu_path_t paths[2];
// Weighted round-robin scheduler state
float credits[2];
uint64_t send_seq_num;
// Reorder buffer
uint64_t recv_seq_num;
int reorder_window; // in milliseconds
heap_t reorder_heap;
} mpu_ctx_t;
/// Initialize MPU context with two physical paths
/// Returns 0 on success, -1 on failure (errno is set).
int mpu_init(mpu_ctx_t* ctx,
int sock0, float weight0,
int sock1, float weight1,
int reorder_window, // in milliseconds
size_t reorder_slots);
/// Send a packet through the tunnel. Packet must not exceed MPU_MTU - sizeof(mpu_hdr_t).
/// Returns 0 on success, -1 on failure (errno is set).
int mpu_send(mpu_ctx_t* ctx, const uint8_t* data, size_t len);
/// Receive a packet from the tunnel, blocking until one is available.
/// Returns the length of the received data, or -1 on failure (errno is set).
ssize_t mpu_recv(mpu_ctx_t* ctx, uint8_t* data, size_t len);
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