1 /**
2 @file packet.c
3 @brief ENet packet management functions
4 */
5 #include <string.h>
6 #define ENET_BUILDING_LIB 1
7 #include "enet/enet.h"
8
9 /** @defgroup Packet ENet packet functions
10 @{
11 */
12
13 /** Creates a packet that may be sent to a peer.
14 @param dataContents initial contents of the packet's data; the packet's data will remain uninitialized if dataContents is NULL.
15 @param dataLength size of the data allocated for this packet
16 @param flags flags for this packet as described for the ENetPacket structure.
17 @returns the packet on success, NULL on failure
18 */
19 ENetPacket *
enet_packet_create(const void * data,size_t dataLength,enet_uint32 flags)20 enet_packet_create(const void *data, size_t dataLength, enet_uint32 flags)
21 {
22 ENetPacket *packet = (ENetPacket *)enet_malloc(sizeof(ENetPacket));
23 if (packet == NULL)
24 return NULL;
25
26 if (flags & ENET_PACKET_FLAG_NO_ALLOCATE)
27 packet->data = (enet_uint8 *)data;
28 else if (dataLength <= 0)
29 packet->data = NULL;
30 else
31 {
32 packet->data = (enet_uint8 *)enet_malloc(dataLength);
33 if (packet->data == NULL)
34 {
35 enet_free(packet);
36 return NULL;
37 }
38
39 if (data != NULL)
40 memcpy(packet->data, data, dataLength);
41 }
42
43 packet->referenceCount = 0;
44 packet->flags = flags;
45 packet->dataLength = dataLength;
46 packet->freeCallback = NULL;
47 packet->userData = NULL;
48
49 return packet;
50 }
51
52 /** Destroys the packet and deallocates its data.
53 @param packet packet to be destroyed
54 */
enet_packet_destroy(ENetPacket * packet)55 void enet_packet_destroy(ENetPacket *packet)
56 {
57 if (packet == NULL)
58 return;
59
60 if (packet->freeCallback != NULL)
61 (*packet->freeCallback)(packet);
62 if (!(packet->flags & ENET_PACKET_FLAG_NO_ALLOCATE) &&
63 packet->data != NULL)
64 enet_free(packet->data);
65 enet_free(packet);
66 }
67
68 /** Attempts to resize the data in the packet to length specified in the
69 dataLength parameter
70 @param packet packet to resize
71 @param dataLength new size for the packet data
72 @returns 0 on success, < 0 on failure
73 */
enet_packet_resize(ENetPacket * packet,size_t dataLength)74 int enet_packet_resize(ENetPacket *packet, size_t dataLength)
75 {
76 enet_uint8 *newData;
77
78 if (dataLength <= packet->dataLength || (packet->flags & ENET_PACKET_FLAG_NO_ALLOCATE))
79 {
80 packet->dataLength = dataLength;
81
82 return 0;
83 }
84
85 newData = (enet_uint8 *)enet_malloc(dataLength);
86 if (newData == NULL)
87 return -1;
88
89 memcpy(newData, packet->data, packet->dataLength);
90 enet_free(packet->data);
91
92 packet->data = newData;
93 packet->dataLength = dataLength;
94
95 return 0;
96 }
97
98 static int initializedCRC32 = 0;
99 static enet_uint32 crcTable[256];
100
101 static enet_uint32
reflect_crc(int val,int bits)102 reflect_crc(int val, int bits)
103 {
104 int result = 0, bit;
105
106 for (bit = 0; bit < bits; bit++)
107 {
108 if (val & 1) result |= 1 << (bits - 1 - bit);
109 val >>= 1;
110 }
111
112 return result;
113 }
114
115 static void
initialize_crc32(void)116 initialize_crc32(void)
117 {
118 int byte;
119
120 for (byte = 0; byte < 256; ++byte)
121 {
122 enet_uint32 crc = reflect_crc(byte, 8) << 24;
123 int offset;
124
125 for (offset = 0; offset < 8; ++offset)
126 {
127 if (crc & 0x80000000)
128 crc = (crc << 1) ^ 0x04c11db7;
129 else
130 crc <<= 1;
131 }
132
133 crcTable[byte] = reflect_crc(crc, 32);
134 }
135
136 initializedCRC32 = 1;
137 }
138
139 enet_uint32
enet_crc32(const ENetBuffer * buffers,size_t bufferCount)140 enet_crc32(const ENetBuffer *buffers, size_t bufferCount)
141 {
142 enet_uint32 crc = 0xFFFFFFFF;
143
144 if (!initializedCRC32) initialize_crc32();
145
146 while (bufferCount-- > 0)
147 {
148 const enet_uint8 *data = (const enet_uint8 *)buffers->data,
149 *dataEnd = &data[buffers->dataLength];
150
151 while (data < dataEnd)
152 {
153 crc = (crc >> 8) ^ crcTable[(crc & 0xFF) ^ *data++];
154 }
155
156 ++buffers;
157 }
158
159 return ENET_HOST_TO_NET_32(~crc);
160 }
161
162 /** @} */
163