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805 | - | 1 | // /////////////////////////////////////////////////////////////////////////////// |
2 | // Copyright (C) 2010, Frank Blumenberg |
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3 | // |
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4 | // See License.txt for complete licensing and attribution information. |
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5 | // Permission is hereby granted, free of charge, to any person obtaining a copy |
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6 | // of this software and associated documentation files (the "Software"), to deal |
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7 | // in the Software without restriction, including without limitation the rights |
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8 | // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell |
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9 | // copies of the Software, and to permit persons to whom the Software is |
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10 | // furnished to do so, subject to the following conditions: |
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11 | // |
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12 | // The above copyright notice and this permission notice shall be included in all |
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13 | // copies or substantial portions of the Software. |
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14 | // |
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15 | // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
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16 | // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
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17 | // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE |
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18 | // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
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19 | // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, |
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20 | // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN |
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21 | // THE SOFTWARE. |
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22 | // |
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23 | // /////////////////////////////////////////////////////////////////////////////// |
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24 | |||
25 | #import "NSData+MKCommandDecode.h" |
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26 | |||
27 | #define kInvalidMKCommand @"Invalid MK command" |
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28 | |||
29 | // /////////////////////////////////////////////////////////////////////////////// |
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30 | #pragma mark Helper funktions |
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31 | |||
32 | static NSData * decode64(const char * inBuffer, int length) |
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33 | { |
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34 | unsigned char a, b, c, d; |
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35 | unsigned char x, y, z; |
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36 | |||
37 | int srcIdx = 0; |
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38 | int dstIdx = 0; |
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39 | |||
40 | NSMutableData * outData = [NSMutableData dataWithLength:length]; |
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41 | unsigned char * outBuffer = [outData mutableBytes]; |
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42 | |||
43 | if (inBuffer[srcIdx] != 0) |
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44 | { |
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45 | while (length != 0) |
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46 | { |
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47 | a = inBuffer[srcIdx++] - '='; |
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48 | b = inBuffer[srcIdx++] - '='; |
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49 | c = inBuffer[srcIdx++] - '='; |
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50 | d = inBuffer[srcIdx++] - '='; |
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51 | |||
52 | x = (a << 2) | (b >> 4); |
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53 | y = ((b & 0x0f) << 4) | (c >> 2); |
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54 | z = ((c & 0x03) << 6) | d; |
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55 | |||
56 | if (length--) outBuffer[dstIdx++] = x; else break; |
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57 | if (length--) outBuffer[dstIdx++] = y; else break; |
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58 | if (length--) outBuffer[dstIdx++] = z; else break; |
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59 | } |
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60 | } |
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61 | |||
62 | [outData setLength:dstIdx]; |
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63 | return outData; |
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64 | } |
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65 | |||
66 | // /////////////////////////////////////////////////////////////////////////////// |
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67 | @implementation NSData (MKCommandDecode) |
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68 | |||
69 | - (NSUInteger) frameLength; |
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70 | { |
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71 | NSUInteger frameLength = [self length]; |
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72 | const char * frameBytes = [self bytes]; |
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73 | |||
74 | if (frameLength > 0 && frameBytes[frameLength - 1] == '\r') |
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75 | frameLength--; |
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76 | |||
77 | return frameLength; |
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78 | } |
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79 | |||
80 | |||
81 | - (BOOL) isMkData |
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82 | { |
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83 | NSUInteger frameLength = [self frameLength]; |
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84 | const char * frameBytes = [self bytes]; |
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85 | |||
86 | if ( frameLength < 5) |
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87 | { |
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88 | NSLog(@"The frame length is to short %d. Frame is invalid", frameLength); |
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89 | return NO; |
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90 | } |
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91 | |||
92 | if (frameBytes[0] != '#') |
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93 | { |
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94 | NSLog(@"The frame is no MK frame"); |
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95 | return NO; |
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96 | } |
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97 | |||
98 | return YES; |
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99 | } |
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100 | |||
101 | |||
102 | - (BOOL) isCrcOk |
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103 | { |
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104 | |||
105 | if (![self isMkData]) |
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106 | return NO; |
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107 | |||
108 | NSUInteger frameLength = [self frameLength]; |
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109 | const uint8_t * frameBytes = [self bytes]; |
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110 | |||
111 | uint8_t crc2 = frameBytes[frameLength - 1]; |
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112 | uint8_t crc1 = frameBytes[frameLength - 2]; |
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113 | |||
114 | int crc = 0; |
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115 | for (int i = 0; i < frameLength - 2; i++) |
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116 | { |
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117 | crc += frameBytes[i]; |
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118 | } |
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119 | |||
120 | crc %= 4096; |
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121 | |||
122 | if (crc1 == ('=' + (crc / 64)) && crc2 == ('=' + crc % 64)) |
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123 | return YES; |
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124 | |||
125 | return NO; |
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126 | } |
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127 | |||
128 | - (MKAddress) address |
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129 | { |
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130 | if (![self isCrcOk]) |
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131 | [NSException raise:kInvalidMKCommand format:@"cannot get the address from a invalid MK frame"]; |
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132 | |||
133 | const char * frameBytes = [self bytes]; |
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134 | |||
135 | return (MKAddress)(frameBytes[1] - 'a'); |
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136 | } |
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137 | |||
138 | - (MKCommandId) command |
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139 | { |
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140 | if (![self isCrcOk]) |
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141 | [NSException raise:kInvalidMKCommand format:@"cannot get the address from a invalid MK frame"]; |
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142 | |||
143 | const char * frameBytes = [self bytes]; |
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144 | return frameBytes[2]; |
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145 | } |
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146 | |||
147 | |||
148 | - (NSData *) payload; |
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149 | { |
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150 | NSUInteger frameLength = [self frameLength]; |
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151 | const char * frameBytes = [self bytes]; |
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152 | |||
153 | int startIndex = 3; |
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154 | int frameDataLength = frameLength - startIndex - 2; |
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155 | |||
156 | return decode64(frameBytes + startIndex, frameDataLength); |
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157 | } |
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158 | |||
159 | |||
160 | @end |