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+/*
+ * Copyright 2011 Daniel Drown
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * translate.h - translate from one version of ip to another
+ */
+#ifndef __TRANSLATE_H__
+#define __TRANSLATE_H__
+
+#include <linux/if_tun.h>
+
+#define MAX_TCP_HDR (15 * 4)   // Data offset field is 4 bits and counts in 32-bit words.
+
+// A clat_packet is an array of iovec structures representing a packet that we are translating.
+// The CLAT_POS_XXX constants represent the array indices within the clat_packet that contain
+// specific parts of the packet. The packet_* functions operate on all the packet segments past a
+// given position.
+enum clat_packet_index { CLAT_POS_TUNHDR, CLAT_POS_IPHDR, CLAT_POS_TRANSPORTHDR,
+                         CLAT_POS_ICMPERR_IPHDR, CLAT_POS_ICMPERR_TRANSPORTHDR,
+                         CLAT_POS_PAYLOAD, CLAT_POS_MAX };
+typedef struct iovec clat_packet[CLAT_POS_MAX];
+
+// Calculates the checksum over all the packet components starting from pos.
+uint16_t packet_checksum(uint32_t checksum, clat_packet packet, int pos);
+
+// Returns the total length of the packet components after pos.
+uint16_t packet_length(clat_packet packet, int pos);
+
+// Returns true iff the given IPv6 address is in the plat subnet.
+int is_in_plat_subnet(const struct in6_addr *addr6);
+
+// Functions to create tun, IPv4, and IPv6 headers.
+void fill_tun_header(struct tun_pi *tun_header, uint16_t proto);
+void fill_ip_header(struct iphdr *ip_targ, uint16_t payload_len, uint8_t protocol,
+                    const struct ip6_hdr *old_header);
+void fill_ip6_header(struct ip6_hdr *ip6, uint16_t payload_len, uint8_t protocol,
+                     const struct iphdr *old_header);
+
+// Translate ICMP packets.
+int icmp_to_icmp6(clat_packet out, int pos, const struct icmphdr *icmp, uint32_t checksum,
+                  const char *payload, size_t payload_size);
+int icmp6_to_icmp(clat_packet out, int pos, const struct icmp6_hdr *icmp6, uint32_t checksum,
+                  const char *payload, size_t payload_size);
+
+// Translate TCP and UDP packets.
+int tcp_packet(clat_packet out, int pos, const struct tcphdr *tcp, uint32_t checksum, size_t len);
+int udp_packet(clat_packet out, int pos, const struct udphdr *udp, uint32_t checksum, size_t len);
+
+int tcp_translate(clat_packet out, int pos, const struct tcphdr *tcp, size_t header_size,
+                  uint32_t checksum, const char *payload, size_t payload_size);
+int udp_translate(clat_packet out, int pos, const struct udphdr *udp, uint32_t checksum,
+                  const char *payload, size_t payload_size);
+
+#endif /* __TRANSLATE_H__ */