V7

2026-08-16 03:48:57 -03:00
parent 5621de243a
commit c02b36c83d
48 changed files with 5398 additions and 2221 deletions
@@ -0,0 +1,122 @@
+package tech.xvanturing.freeproxy.vpn.net
+
+const val PROTO_ICMP = 1
+const val PROTO_TCP = 6
+const val PROTO_UDP = 17
+
+/** IPv4 首部。选项字段不解析，但 [headerLength] 已把它算在内。 */
+class Ipv4Header(
+    val headerLength: Int,
+    val totalLength: Int,
+    val protocol: Int,
+    val sourceIp: Int,
+    val destIp: Int,
+) {
+    val payloadLength: Int get() = totalLength - headerLength
+
+    companion object {
+        const val MIN_SIZE = 20
+
+        /** 解析失败返回 null（畸形包直接丢弃，不抛异常 —— 转发热路径上异常代价太高）。 */
+        fun parse(buffer: ByteArray, length: Int): Ipv4Header? {
+            if (length < MIN_SIZE) return null
+            val versionAndIhl = buffer.u8(0)
+            if ((versionAndIhl ushr 4) != 4) return null
+
+            val headerLength = (versionAndIhl and 0x0F) * 4
+            if (headerLength < MIN_SIZE || headerLength > length) return null
+
+            val totalLength = buffer.u16(2)
+            if (totalLength < headerLength || totalLength > length) return null
+
+            // 本栈不做分片重组：MF 置位或分片偏移非零的包一律丢弃。
+            // TUN 的 MTU 由我们自己设定，正常流量不会走到这里。
+            val fragmentField = buffer.u16(6)
+            val moreFragments = (fragmentField and 0x2000) != 0
+            val fragmentOffset = fragmentField and 0x1FFF
+            if (moreFragments || fragmentOffset != 0) return null
+
+            return Ipv4Header(
+                headerLength = headerLength,
+                totalLength = totalLength,
+                protocol = buffer.u8(9),
+                sourceIp = buffer.ipv4(12),
+                destIp = buffer.ipv4(16),
+            )
+        }
+    }
+}
+
+/** TCP 首部。 */
+class TcpHeader(
+    val sourcePort: Int,
+    val destPort: Int,
+    val sequence: Long,
+    val acknowledgment: Long,
+    val dataOffset: Int,
+    val flags: Int,
+    val window: Int,
+) {
+    val isFin: Boolean get() = (flags and FIN) != 0
+    val isSyn: Boolean get() = (flags and SYN) != 0
+    val isRst: Boolean get() = (flags and RST) != 0
+    val isAck: Boolean get() = (flags and ACK) != 0
+
+    override fun toString(): String = buildString {
+        if (isSyn) append("SYN ")
+        if (isAck) append("ACK ")
+        if (isFin) append("FIN ")
+        if (isRst) append("RST ")
+        append("seq=").append(sequence).append(" ack=").append(acknowledgment)
+    }
+
+    companion object {
+        const val MIN_SIZE = 20
+
+        const val FIN = 0x01
+        const val SYN = 0x02
+        const val RST = 0x04
+        const val PSH = 0x08
+        const val ACK = 0x10
+        const val URG = 0x20
+
+        fun parse(buffer: ByteArray, offset: Int, length: Int): TcpHeader? {
+            if (length < MIN_SIZE) return null
+            val dataOffset = ((buffer.u8(offset + 12) ushr 4) and 0x0F) * 4
+            if (dataOffset < MIN_SIZE || dataOffset > length) return null
+            return TcpHeader(
+                sourcePort = buffer.u16(offset),
+                destPort = buffer.u16(offset + 2),
+                sequence = buffer.u32(offset + 4),
+                acknowledgment = buffer.u32(offset + 8),
+                dataOffset = dataOffset,
+                flags = buffer.u8(offset + 13),
+                window = buffer.u16(offset + 14),
+            )
+        }
+    }
+}
+
+/** UDP 首部。 */
+class UdpHeader(
+    val sourcePort: Int,
+    val destPort: Int,
+    val length: Int,
+) {
+    val payloadLength: Int get() = length - SIZE
+
+    companion object {
+        const val SIZE = 8
+
+        fun parse(buffer: ByteArray, offset: Int, available: Int): UdpHeader? {
+            if (available < SIZE) return null
+            val length = buffer.u16(offset + 4)
+            if (length < SIZE || length > available) return null
+            return UdpHeader(
+                sourcePort = buffer.u16(offset),
+                destPort = buffer.u16(offset + 2),
+                length = length,
+            )
+        }
+    }
+}