Decoding the Secrets of Binary Data (Droidcon NYC 2016)

Video: https://www.youtube.com/watch?v=T_p22jMZSrk
Code: https://github.com/swankjesse/encoding

Opaque blobs of data have hexed Android programmers for too long. It’s time to byte the bullet and learn how data is transmitted and persisted.

In this talk we’ll:

💾 Learn a bit about base64, little-endian, and EOF.
💾 See how inefficient encodings nibble away resources.
💾 Hash out the differences between ASCII, UTF-8, and other charsets.
💾 Zip through examples of compression, crypto, and protocol buffers.
💾 Load up on APIs and discover what Square’s Okio has in store.

This talk offers a short introduction to an array of topics. You’ll learn enough to be encode & decode whatever data you select!

Transcript

1. @jessewilson Decoding the Secrets of Binary Data https://github.com/swankjesse/encoding
2. Encoding @jessewilson https://github.com/swankjesse/encoding
3. 0 1
6. Goals • Get comfortable with bytes • Write simpler, more efficient programs
7. Plan • Bottom up • History • Math • Code
8. 1095 AD
9. Date: Aprilis 11, 1095 From: Emperor Alexios Komnenos To: Robert II, Count of Flanders Bob, Looks like we’re gonna war with the Turks. Could you see if the Pope could help us crusade against ’em? Thanks! Alex Letters! • Human readable • Signed
10. Date: Aprilis 11, 1095 From: Emperor Alexios Komnenos To: Robert II, Count of Flanders Bob, Looks like we’re gonna war with the Turks. Could you see if the Pope could help us crusade against ’em? Thanks! Alex Letters! • Slow, dangerous to transmit • Awkward to store • Requires Literacy!
12. Telegraphs NYC SF
13. Telegraphs NYC SF
14. Morse Code A • ▬ G ▬ ▬ • M ▬ ▬ S • • • Y ▬ • ▬ ▬ 4 • • • • ▬ B ▬ • • • H • • • • N ▬ • T ▬ Z ▬ ▬ • • 5 • • • • • C ▬ • ▬ • I • • O ▬ ▬ ▬ U • • ▬ 0 ▬ ▬ ▬ ▬ ▬ 6 ▬ • • • • D ▬ • • J • ▬ ▬ ▬ P • ▬ ▬ • V • • • ▬ 1 • ▬ ▬ ▬ ▬ 7 ▬ ▬ • • • E • K ▬ • ▬ Q ▬ ▬ • ▬ W • ▬ ▬ 2 • • ▬ ▬ ▬ 8 ▬ ▬ ▬ • • F • • ▬ • L • ▬ • • R • ▬ • X ▬ • • ▬ 3 • • • ▬ ▬ 9 ▬ ▬ ▬ ▬ •
15. A • ▬ G ▬ ▬ • M ▬ ▬ S • • • Y ▬ • ▬ ▬ 4 • • • • ▬ B ▬ • • • H • • • • N ▬ • T ▬ Z ▬ ▬ • • 5 • • • • • C ▬ • ▬ • I • • O ▬ ▬ ▬ U • • ▬ 0 ▬ ▬ ▬ ▬ ▬ 6 ▬ • • • • D ▬ • • J • ▬ ▬ ▬ P • ▬ ▬ • V • • • ▬ 1 • ▬ ▬ ▬ ▬ 7 ▬ ▬ • • • E • K ▬ • ▬ Q ▬ ▬ • ▬ W • ▬ ▬ 2 • • ▬ ▬ ▬ 8 ▬ ▬ ▬ • • F • • ▬ • L • ▬ • • R • ▬ • X ▬ • • ▬ 3 • • • ▬ ▬ 9 ▬ ▬ ▬ ▬ • ▬ • •
16. A • ▬ G ▬ ▬ • M ▬ ▬ S • • • Y ▬ • ▬ ▬ 4 • • • • ▬ B ▬ • • • H • • • • N ▬ • T ▬ Z ▬ ▬ • • 5 • • • • • C ▬ • ▬ • I • • O ▬ ▬ ▬ U • • ▬ 0 ▬ ▬ ▬ ▬ ▬ 6 ▬ • • • • D ▬ • • J • ▬ ▬ ▬ P • ▬ ▬ • V • • • ▬ 1 • ▬ ▬ ▬ ▬ 7 ▬ ▬ • • • E • K ▬ • ▬ Q ▬ ▬ • ▬ W • ▬ ▬ 2 • • ▬ ▬ ▬ 8 ▬ ▬ ▬ • • F • • ▬ • L • ▬ • • R • ▬ • X ▬ • • ▬ 3 • • • ▬ ▬ 9 ▬ ▬ ▬ ▬ • ▬ • • ▬ ▬ ▬
17. A • ▬ G ▬ ▬ • M ▬ ▬ S • • • Y ▬ • ▬ ▬ 4 • • • • ▬ B ▬ • • • H • • • • N ▬ • T ▬ Z ▬ ▬ • • 5 • • • • • C ▬ • ▬ • I • • O ▬ ▬ ▬ U • • ▬ 0 ▬ ▬ ▬ ▬ ▬ 6 ▬ • • • • D ▬ • • J • ▬ ▬ ▬ P • ▬ ▬ • V • • • ▬ 1 • ▬ ▬ ▬ ▬ 7 ▬ ▬ • • • E • K ▬ • ▬ Q ▬ ▬ • ▬ W • ▬ ▬ 2 • • ▬ ▬ ▬ 8 ▬ ▬ ▬ • • F • • ▬ • L • ▬ • • R • ▬ • X ▬ • • ▬ 3 • • • ▬ ▬ 9 ▬ ▬ ▬ ▬ • ▬ • • ▬ ▬ ▬ ▬ •
18. A • ▬ G ▬ ▬ • M ▬ ▬ S • • • Y ▬ • ▬ ▬ 4 • • • • ▬ B ▬ • • • H • • • • N ▬ • T ▬ Z ▬ ▬ • • 5 • • • • • C ▬ • ▬ • I • • O ▬ ▬ ▬ U • • ▬ 0 ▬ ▬ ▬ ▬ ▬ 6 ▬ • • • • D ▬ • • J • ▬ ▬ ▬ P • ▬ ▬ • V • • • ▬ 1 • ▬ ▬ ▬ ▬ 7 ▬ ▬ • • • E • K ▬ • ▬ Q ▬ ▬ • ▬ W • ▬ ▬ 2 • • ▬ ▬ ▬ 8 ▬ ▬ ▬ • • F • • ▬ • L • ▬ • • R • ▬ • X ▬ • • ▬ 3 • • • ▬ ▬ 9 ▬ ▬ ▬ ▬ • ▬ • • ▬ ▬ ▬ ▬ • • • ▬
19. A • ▬ G ▬ ▬ • M ▬ ▬ S • • • Y ▬ • ▬ ▬ 4 • • • • ▬ B ▬ • • • H • • • • N ▬ • T ▬ Z ▬ ▬ • • 5 • • • • • C ▬ • ▬ • I • • O ▬ ▬ ▬ U • • ▬ 0 ▬ ▬ ▬ ▬ ▬ 6 ▬ • • • • D ▬ • • J • ▬ ▬ ▬ P • ▬ ▬ • V • • • ▬ 1 • ▬ ▬ ▬ ▬ 7 ▬ ▬ • • • E • K ▬ • ▬ Q ▬ ▬ • ▬ W • ▬ ▬ 2 • • ▬ ▬ ▬ 8 ▬ ▬ ▬ • • F • • ▬ • L • ▬ • • R • ▬ • X ▬ • • ▬ 3 • • • ▬ ▬ 9 ▬ ▬ ▬ ▬ • ▬ • • ▬ ▬ ▬ ▬ • • • ▬ ▬
20. A • ▬ G ▬ ▬ • M ▬ ▬ S • • • Y ▬ • ▬ ▬ 4 • • • • ▬ B ▬ • • • H • • • • N ▬ • T ▬ Z ▬ ▬ • • 5 • • • • • C ▬ • ▬ • I • • O ▬ ▬ ▬ U • • ▬ 0 ▬ ▬ ▬ ▬ ▬ 6 ▬ • • • • D ▬ • • J • ▬ ▬ ▬ P • ▬ ▬ • V • • • ▬ 1 • ▬ ▬ ▬ ▬ 7 ▬ ▬ • • • E • K ▬ • ▬ Q ▬ ▬ • ▬ W • ▬ ▬ 2 • • ▬ ▬ ▬ 8 ▬ ▬ ▬ • • F • • ▬ • L • ▬ • • R • ▬ • X ▬ • • ▬ 3 • • • ▬ ▬ 9 ▬ ▬ ▬ ▬ • ▬ • • ▬ ▬ ▬ ▬ • • • ▬ ▬
21. Morse Code NYC SF
22. Morse Code • Telegraphs! • 15 words per minute • Wireless in 1898
23. Morse Code • Very limited characters • No lowercase • Limited punctuation* • Average message: 12 words * For example, morse code doesn’t have an asterisk symbol.
24. Binary Refresher!
26. 200 205 = + 5
27. 2×100 205 = + 5×1
28. 2×100 205 = + + 0×10 5×1
29. 2×102 205 = + + 0×101 5×10
32. 128 8 + 205 = 64 4 + + + 1
33. 1×128 1×8 + 205 = 1×64 1×4 + + + 1×1
34. 1×128 1×8 + 205 1×64 + 1×4 + 0×32 0×16 + + 0×2 + 1×1 + =
35. 1×27 1×23 + 205 1×26 + 1×22 + 0×25 0×24 + + 0×21 + 1×20 + =
36. 205 1×27 1×23 1×26 1×22 0×25 0×24 0×21 1×20 =
37. 205 1×27 1×23 1×26 1×22 0×25 0×240×21 1×20 0b =
38. Binary Refresher! • Decimal lets you represent any integer with a sequence of digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 • Binary lets you represent any integer with a sequence of bits: 0, 1
39. Binary Refresher! • Typically prefixed with “0b”, like 0b11001101
40. Binary Refresher! • N bits can represent 2N values • 8 bits: 0..255 • 16 bits: 0..65,535 • 32 bits: 0..4,294,967,295 • 64 bits: 0..18,446,744,073,709,551,615
41. Binary Refresher! NYC SF
42. Layering • Given a wire that transmits a single bit, we can use binary to encode any integer! • This works because the sender and recipient agree on how to interpret the sequence • That interpretation is called an encoding
43. Bytes • Though binary supports any number of bits, we like 8-bit integers • An 8-bit integer is called a byte • 256 values from 0 to 255
45. ASCII • American Standard Code for Information Interchange • A table of characters • Interpret a sequence of bytes as a string of characters!
46. ASCII • Work started in 1960 • Only uses 7 bits: in 1967 bits were very expensive! • That means there’s 27 = 128 characters
47. ASCII 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL
48. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 68
49. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 68 111
50. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 68 111 110
51. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 68 111 110 117
52. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 68 111 110 117 116
53. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 68 111 110 117 116
54. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 68 111 110 117 116
55. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 111 110 117 116 0 1 0 0 0 1 0 0
56. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 110 117 116 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1
57. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 117 116 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0
58. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 116 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 1 1 1 0 1 0 1
59. 0 NULL 16 DLE 32 SP 48 0 64 @ 80 P 96 ` 112 p 1 SOH 17 DC1 33 ! 49 1 65 A 81 Q 97 a 113 q 2 STX 18 DC2 34 " 50 2 66 B 82 R 98 b 114 r 3 ETX 19 DC3 35 # 51 3 67 C 83 S 99 c 115 s 4 EOT 20 DC4 36 $ 52 4 68 D 84 T 100 d 116 t 5 ENQ 21 NAK 37 % 53 5 69 E 85 U 101 e 117 u 6 ACK 22 SYN 38 & 54 6 70 F 86 V 102 f 118 v 7 BEL 23 ETB 39 ' 55 7 71 G 87 W 103 g 119 w 8 BS 24 CAN 40 ( 56 8 72 H 88 X 104 h 120 x 9 HT 25 EM 41 ) 57 9 73 I 89 Y 105 i 121 y 10 LF 26 SUB 42 * 58 : 74 J 90 Z 106 j 122 z 11 VT 27 ESC 43 + 59 ; 75 K 91 [ 107 k 123 { 12 FF 28 FS 44 , 60 < 76 L 92 \ 108 l 124 | 13 CR 29 GS 45 - 61 = 77 M 93 ] 109 m 125 } 14 SO 30 RS 46 . 62 > 78 N 94 ^ 110 n 126 ~ 15 SI 31 US 47 / 63 ? 79 O 95 _ 111 o 127 DEL 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 1 1 1 0 1 0 1 0 1 1 1 0 1 0 0
60. 1980’s
61. boss, what should I be working on?
62. boss, what should I be working on? resume polishing
63. boss, what should I be working on?
64. boss, what should I be working on? résumé polishing
65. Charset Hell • ASCII is English only • But non-English people also use computers!
66. Charset Hell • Operating systems were installed for a specific character set and wouldn’t work with any others • Documents couldn’t mix Greek, French, and Russian characters • If you see ISO-8859-1, run away!
68. Unicode • Support all languages in a single system • A code point is a universal ID for a character
69. UTF-16 • 16-bit Unicode Transformation Format • 2 bytes per code point • This is Java’s char type
70. ASCII UTF-16
71. ASCII 0 1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 D UTF-16
72. ASCII 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D UTF-16 o
73. ASCII 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D UTF-16 on
74. ASCII 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 1 1 1 0 1 0 1 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 1 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D UTF-16 onu
75. ASCII 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 1 1 1 0 1 0 1 0 1 1 1 0 1 0 0 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 1 1 1 0 1 0 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D UTF-16 onut
76. ASCII 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 1 1 1 0 1 0 1 0 1 1 1 0 1 0 0 0 1 0 0 0 1 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 0 1 1 1 0 1 0 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D UTF-16 onut
77. UTF-16 characters • Max code point is 65,535 • Code point for is 127,849 • 127,849 > 65,535
78. Java’s char is broken! • There’s a system called “surrogate pairs” which is like multidex for code points • It splits a single code point across 2 chars • It’s an incredible pain
79. 
 char[] s = "Café ".toCharArray(); C a f é 0 1 2 3 4 5 6
80. String s = “Café ";
 
 for (int i = 0, size = s.length(); i < size; i++) {
 char c = s.charAt(i);
 System.out.printf("The character at %d is '%c'%n", i, c);
 }
81. String s = “Café ";
 
 for (int i = 0, size = s.length(); i < size; i++) {
 char c = s.charAt(i);
 System.out.printf("The character at %d is '%c'%n", i, c);
 } The character at 0 is 'C' The character at 1 is 'a' The character at 2 is 'f' The character at 3 is 'é' The character at 4 is ' ' The character at 5 is ' ' The character at 6 is ' '
82. String s = “Café ";
 
 for (int i = 0, size = s.length(); i < size; ) {
 int c = s.codePointAt(i);
 System.out.printf("The code point at %d is '%c'%n", i, c); i += Character.charCount(c);
 }
83. String s = “Café ";
 
 for (int i = 0, size = s.length(); i < size; ) {
 int c = s.codePointAt(i);
 System.out.printf("The code point at %d is '%c'%n", i, c); i += Character.charCount(c);
 } The code point at 0 is 'C' The code point at 1 is 'a' The code point at 2 is 'f' The code point at 3 is 'é' The code point at 4 is ' ' The code point at 5 is ' '
85. UTF-8 • 8-bit Unicode Transformation Format • Variable number of bytes per code point • This is how modern apps transmit & store text
86. Image copyright Chris55, https://commons.wikimedia.org/wiki/File:Utf8webgrowth.svg
87. UTF-8 • Many common characters are 1-byte • Some are 2 and 3 bytes. ‘ ’ is 4 bytes. • Self-delimiting • Self-aligning
88. 0 1 1 0 1 0 1 1 1 0 1 1 1 1 0 1 0 1 0 1 0 1 0 1 0 ≤7 ≤11 ≤16 ≤21 “How many bits do you need?”
89. C “How many bits do you need?” a f é sp
90. C “How many bits do you need?” a f é sp 67
91. 1 0 0 0 0 1 1 C “How many bits do you need?” a f é sp
92. 1 0 0 0 0 1 1 C “How many bits do you need?” a f é sp 97
93. 1 0 0 0 0 1 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a f é sp
94. 1 0 0 0 0 1 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a f é sp 102
95. 1 0 0 0 0 1 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a 1 1 0 0 1 1 0 f é sp
96. 233 1 0 0 0 0 1 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a 1 1 0 0 1 1 0 f é sp
97. 1 1 1 0 1 0 0 1 1 0 0 0 0 1 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a 1 1 0 0 1 1 0 f é sp
98. 1 1 1 0 1 0 0 1 1 0 0 0 0 1 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a 1 1 0 0 1 1 0 f é sp 32
99. 1 0 0 0 0 0 1 1 1 0 1 0 0 1 1 0 0 0 0 1 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a 1 1 0 0 1 1 0 f é sp
100. 1 0 0 0 0 0 1 1 1 0 1 0 0 1 1 0 0 0 0 1 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a 1 1 0 0 1 1 0 f é sp 127,849
101. 1 0 1 0 0 1 0 0 1 1 0 1 1 1 1 1 1 1 1 0 0 0 0 0 1 1 1 0 1 0 0 1 1 0 0 0 0 1 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a 1 1 0 0 1 1 0 f é sp
102. 0 1 1 0 1 1 1 1 0 1 0 0 1 0 0 0 1 0 1 0 1 0 1 0 0 1 0 0 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 0 1 0 0 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a 1 1 0 0 1 1 0 f é sp 1 1 1 0 0 0 0 1 1
103. 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 0 0 0 1 0 0 0 1 0 1 0 1 0 1 0 0 1 0 0 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 0 1 0 0 1 C “How many bits do you need?” 1 1 0 0 0 0 1 a 1 1 0 0 1 1 0 f é sp 1 1 1 0 0 0 0 1 1
104. 0 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 0 1 0 1 0 0 1 1 1 1 1 0 0 0 0 1 0 0 1 1 1 1 1 1 0 0 0 1 1 0 1 1 0 1 0 1 0 0 1 0 1 1 0 0 0 0 1 0 1 1 0 0 1 1 0 0 0 1 0 0 0 0 0
105. UTF-8 • Basically the best thing ever • Superset of ASCII • Great for JSON and HTML because delimiter characters <, > and " are 1-byte
106. Colors
107. R G B
111. R 255 0 G 255 0 B 255 0 255 255 255
112. R 255 0 G 255 0 B 255 0 255 0 255
113. R 255 0 G 255 0 B 255 0 20 206 210
114. Hexadecimal Refresher!
115. Hexadecimal Refresher! • Decimal digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 • Binary bits: 0, 1 • Hexadecimal digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f
117. 205 192 = + 13
118. 205 12×16 = + 13×1
119. 205 12×161 = + 13×160
120. 205 c×161 = + d×160
121. 205 c = d 0x
122. Hexadecimal Refresher! • Prefixed with “0x”, like 0xcd • Hex bytes are always two digits: 00, 01, 02 … ff • Sequences of bytes are okay: 0bb634
123. Hexadecimal Refresher! • Colors: #ffffff • URL escaping: http://example.com/?q=hello%20world • Unicode code points U+2020 • IPv6 addresses: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
124. R 255 0 G 255 0 B 255 0 ced214
125. Pictures
126. Pictures • Just a 2D array of colors • Given 3 bytes per pixel: • 64 × 64 icon is 12,288 bytes • 1080 × 1920 picture is 5.9 MiB • Compression is important!
127. Pictures • Android can use fewer bits per pixel • ARGB_8888: alpha, red, green, and blue get 8 bits each • RGB_565: red gets 5 bits, geen gets 6, blue gets 5 bits
128. RGB_565 ARGB_8888
129. RGB_454 ARGB_8888
130. RGB_232 ARGB_8888
131. /** https://en.wikipedia.org/wiki/BMP_file_format */
 public void encode(BufferedSink sink) throws IOException {
 int height = pixels.length;
 int width = pixels[0].length;
 
 int bytesPerPixel = 3;
 int rowByteCountWithoutPadding = (bytesPerPixel * width);
 int rowByteCount = ((rowByteCountWithoutPadding + 3) / 4) * 4;
 int pixelDataSize = rowByteCount * height;
 int bmpHeaderSize = 14;
 int dibHeaderSize = 40;
 
 // BMP Header
 sink.writeUtf8("BM"); // ID.
 sink.writeIntLe(bmpHeaderSize + dibHeaderSize + pixelDataSize); // File size.
 sink.writeShortLe(0); // Unused.
 sink.writeShortLe(0); // Unused.
 sink.writeIntLe(bmpHeaderSize + dibHeaderSize); // Offset of pixel data.
 
 // DIB Header
 sink.writeIntLe(dibHeaderSize);

132. int dibHeaderSize = 40;
 
 // BMP Header
 sink.writeUtf8("BM"); // ID.
 sink.writeIntLe(bmpHeaderSize + dibHeaderSize + pixelDataSize); // File size.
 sink.writeShortLe(0); // Unused.
 sink.writeShortLe(0); // Unused.
 sink.writeIntLe(bmpHeaderSize + dibHeaderSize); // Offset of pixel data.
 
 // DIB Header
 sink.writeIntLe(dibHeaderSize);
 sink.writeIntLe(width);
 sink.writeIntLe(height);
 sink.writeShortLe(1); // Color plane count.
 sink.writeShortLe(bytesPerPixel * Byte.SIZE);
 sink.writeIntLe(0); // No compression.
 sink.writeIntLe(16); // Size of bitmap data including padding.
 sink.writeIntLe(2835); // Horizontal print resolution in pixels/meter. (72 dpi).
 sink.writeIntLe(2835); // Vertical print resolution in pixels/meter. (72 dpi).
 sink.writeIntLe(0); // Palette color count.
 sink.writeIntLe(0); // 0 important colors.
 
 // Pixel data.

133. sink.writeIntLe(0); // Palette color count.
 sink.writeIntLe(0); // 0 important colors.
 
 // Pixel data.
 for (int y = height - 1; y >= 0; y--) {
 int[] row = pixels[y];
 for (int x = 0; x < width; x++) {
 int pixel = row[x];
 sink.writeByte((pixel & 0x0000ff)); // Blue.
 sink.writeByte((pixel & 0x00ff00) >>> 8); // Green.
 sink.writeByte((pixel & 0xff0000) >>> 16); // Red.
 }
 
 // Padding for 4-byte alignment.
 for (int p = rowByteCountWithoutPadding; p < rowByteCount; p++) {
 sink.writeByte(0);
 }
 }
 }

134. Pictures on Bytes • This bitmap writer is 50 lines of code • Decoders are more difficult! • Good specs make it easy
135. sink.writeIntLe(0); // Palette color count.
 sink.writeIntLe(0); // 0 important colors.
 
 // Pixel data.
 for (int y = height - 1; y >= 0; y--) {
 int[] row = pixels[y];
 for (int x = 0; x < width; x++) {
 int pixel = row[x];
 sink.writeByte((pixel & 0x0000ff)); // Blue.
 sink.writeByte((pixel & 0x00ff00) >>> 8); // Green.
 sink.writeByte((pixel & 0xff0000) >>> 16); // Red.
 }
 
 // Padding for 4-byte alignment.
 for (int p = rowByteCountWithoutPadding; p < rowByteCount; p++) {
 sink.writeByte(0);
 }
 }
 }

136. sink.writeIntLe(0); // Palette color count.
 sink.writeIntLe(0); // 0 important colors.
 
 // Pixel data.
 for (int y = height - 1; y >= 0; y--) {
 int[] row = pixels[y];
 for (int x = 0; x < width; x++) {
 int pixel = row[x];
 sink.writeByte((pixel & 0x0000ff)); // Blue.
 sink.writeByte((pixel & 0x00ff00) >>> 8); // Green.
 sink.writeByte((pixel & 0xff0000) >>> 16); // Red.
 }
 
 // Padding for 4-byte alignment.
 for (int p = rowByteCountWithoutPadding; p < rowByteCount; p++) {
 sink.writeByte(0);
 }
 }
 }

137. (pixel & 0xff0000) >>> 16 • Shifting and masking lets you access the bits within an integer • & and | operators treat each int like a 32-element boolean array! • <<, >> and >>> operators slide bits left and right
138. 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0000ab00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 00ffab40 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 00ffab40 0000ff00 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0x00ffab40 & 0x0000ff00
139. 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0000ab00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 00ffab40 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 00ffab40 0000ff00 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0x00ffab40 & 0x0000ff00
140. 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0000ab00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 00ffab40 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 00ffab40 0000ff00 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0x00ffab40 & 0x0000ff00 & =
141. 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00000ab00 0x0000ab00 >> 8
142. 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00000ab00 0x0000ab00 >> 8 { 8
143. 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 000000ab 0x0000ab00 >> 8
144. 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 000000ab 0x0000ab00 >> 8 = 0x000000ab
145. sink.writeIntLe(0); // Palette color count.
 sink.writeIntLe(0); // 0 important colors.
 
 // Pixel data.
 for (int y = height - 1; y >= 0; y--) {
 int[] row = pixels[y];
 for (int x = 0; x < width; x++) {
 int pixel = row[x];
 sink.writeByte((pixel & 0x0000ff)); // Blue.
 sink.writeByte((pixel & 0x00ff00) >>> 8); // Green.
 sink.writeByte((pixel & 0xff0000) >>> 16); // Red.
 }
 
 // Padding for 4-byte alignment.
 for (int p = rowByteCountWithoutPadding; p < rowByteCount; p++) {
 sink.writeByte(0);
 }
 }
 }

146. This space intentionally left blank
147. int dibHeaderSize = 40;
 
 // BMP Header
 sink.writeUtf8("BM"); // ID.
 sink.writeIntLe(bmpHeaderSize + dibHeaderSize + pixelDataSize); // File size.
 sink.writeShortLe(0); // Unused.
 sink.writeShortLe(0); // Unused.
 sink.writeIntLe(bmpHeaderSize + dibHeaderSize); // Offset of pixel data.
 
 // DIB Header
 sink.writeIntLe(dibHeaderSize);
 sink.writeIntLe(width);
 sink.writeIntLe(height);
 sink.writeShortLe(1); // Color plane count.
 sink.writeShortLe(bytesPerPixel * Byte.SIZE);
 sink.writeIntLe(0); // No compression.
 sink.writeIntLe(16); // Size of bitmap data including padding.
 sink.writeIntLe(2835); // Horizontal print resolution in pixels/meter. (72 dpi).
 sink.writeIntLe(2835); // Vertical print resolution in pixels/meter. (72 dpi).
 sink.writeIntLe(0); // Palette color count.
 sink.writeIntLe(0); // 0 important colors.
 
 // Pixel data.

148. 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 Big Endian
149. 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Big Endian
150. 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 Big Endian
151. 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 1 0 1 0 1 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 Big Endian
152. 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 1 0 1 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 Big Endian
153. 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 1 0 1 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 Big Endian
154. 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 Little Endian
155. 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 Little Endian
156. 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 Little Endian
157. 1 0 1 0 1 0 1 1 1 1 1 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 Little Endian
158. 1 0 1 0 1 0 1 1 1 1 1 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 Little Endian
159. 1 0 1 0 1 0 1 1 1 1 1 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0 0 0 0 Little Endian
160. Data Models
161. Conference App! • Each talk has an ID, date, room, title, and speaker
162. JSON is Good Stuff {
 "id": 72017,
 "date": "2016-09-30T18:30:00Z",
 "room": "RIGHT",
 "title": "Decoding the Secrets of Binary Data",
 "speaker": "Jesse Wilson"
 }
163. JSON is Good Stuff {
 "id": 72017,
 "date": "2016-09-30T18:30:00Z",
 "room": "RIGHT",
 "title": "Decoding the Secrets of Binary Data",
 "speaker": "Jesse Wilson"
 } • A nice format that builds on UTF-8 • Easy to read & write
164. JSON is Self-Delimiting {
 "id": 72017,
 "date": "2016-09-30T18:30:00Z",
 "room": "RIGHT",
 "title": "Decoding the Secrets of Binary Data",
 "speaker": "Jesse Wilson"
 } • A JSON document has both structure and data • Uses escape sequences like \" to be completely unambiguous
165. "2016-09-30T18:30:00Z" • System.currentTimeMillis() returns milliseconds since January 1, 1970 at 00:00:00 UTC • A date that’s 8 bytes in memory is 22 bytes in JSON!
166. • Space: a simple message like this one is ~128 bytes • Time: bigger sequences take longer to decode JSON Space & Time
167. • Google’s “small, fast, simple” structured data format • Upon closer inspection, it’s not that different from JSON! • But it has a schema Protocol Buffers
168. { message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } "id": 72017, "date": "2016-09-30T18:30:00Z", "room": "RIGHT", "title": "Decoding the Secrets of Binary Data", "speaker": "Jesse Wilson" } "id" "date" "room" "title" "speaker" 72017 "2016-09-30T18:30:00Z", "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson",
169. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 }
170. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 000 enum, int32, int64... 001 fixed64 010 string, message 101 fixed32 Length Mode
171. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 000 enum, int32, int64... 001 fixed64 010 string, message 101 fixed32 Length Mode 1 0 1
172. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 000 enum, int32, int64... 001 fixed64 010 string, message 101 fixed32 Length Mode 1 0 1 0 0 1
173. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 000 enum, int32, int64... 001 fixed64 010 string, message 101 fixed32 Length Mode 0 0 0 1 0 1 0 0 1
174. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 000 enum, int32, int64... 001 fixed64 010 string, message 101 fixed32 Length Mode 0 0 0 1 0 1 0 1 0 0 0 1
175. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 000 enum, int32, int64... 001 fixed64 010 string, message 101 fixed32 Length Mode 0 0 0 1 0 1 0 1 0 0 1 0 0 0 1
176. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 0 0 0 1 0 1 0 1 0 0 1 0 0 0 1
177. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 0 0 0 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1
178. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 0 0 0 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 0 1 0 0 0 1
179. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 0 0 0 1 1 0 0 0 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 0 1 0 0 0 1
180. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 0 0 0 1 1 0 0 0 0 0 0 0 1 1 0 1 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 1
181. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 0 0 0 1 1 0 0 0 0 0 0 0 1 1 0 1 0 0 1 0 1 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 1
182. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 0 0 0 1 1 0 0 0 0 0 0 0 1 1 0 1 0 0 1 0 1 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 1
183. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }
 } 0d 11 18 22 2a
184. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a { "id": 72017, "date": "2016-09-30T18:30:00Z", "room": "RIGHT", "title": "Decoding the Secrets of Binary Data", "speaker": "Jesse Wilson" } "id" "date" "room" "title" "speaker" 72017 "2016-09-30T18:30:00Z", "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson",
185. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a 72017 "2016-09-30T18:30:00Z", "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson",
186. message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a 72017 "2016-09-30T18:30:00Z", "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson",
187. 51 19 01 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a "2016-09-30T18:30:00Z", "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson", 00
188. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a "2016-09-30T18:30:00Z", "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson", 00
189. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a "2016-09-30T18:30:00Z", "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson", 00
190. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson", 00 000001577D37EE40
191. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson", 00 00 00 01 57 7D 37 EE 40
192. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a "RIGHT", "Decoding the Secrets of Binary Data", "Jesse Wilson", 00 00 00 01 57 7D 37 EE 40
193. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a "Decoding the Secrets of Binary Data", "Jesse Wilson", 00 00 00 01 57 7D 37 EE 40 02
194. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a "Decoding the Secrets of Binary Data" "Jesse Wilson", 00 00 01 57 7D 37 EE 40 02 00
195. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a 4465636f64696e67207468652053656372657473206f662042696e6172792044617461 "Jesse Wilson", 00 00 00 01 57 7D 37 EE 40 02
196. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a 4465636f64696e67207468652053656372657473206f662042696e6172792044617461 "Jesse Wilson", 00 00 00 01 57 7D 37 EE 40 02 23
197. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a 4465636f64696e67207468652053656372657473206f662042696e6172792044617461 "Jesse Wilson" 00 00 00 01 57 7D 37 EE 40 02 23
198. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a 4465636f64696e67207468652053656372657473206f662042696e6172792044617461 4a657373652057696c736f6e 00 00 00 01 57 7D 37 EE 40 02 23
199. 511901 message Talk {
 optional fixed32 id = 1;
 optional fixed64 date = 2;
 optional Room room = 3;
 optional string title = 4;
 optional string speaker = 5;
 
 enum Room {
 UP = 1; RIGHT = 2; DOWN = 3; LEFT = 4;
 }a
 }a 0d 11 18 22 2a 4465636f64696e67207468652053656372657473206f662042696e6172792044617461 4a657373652057696c736f6e 00 00 00 01 57 7D 37 EE 40 02 23 0c
200. 511901 0d 11 18 22 2a 4a657373652057696c736f6e 00 00 00 01 57 7D 37 EE 40 02 23 0c 4465636f64696e67207468652053656372657473206f662042696e6172792044617461
201. 511901 0d 11 18 22 2a 4465636f64696e6720746865205365637265747 4a657373652057696c736f6e 00 00 00 01 57 7D 37 EE 40 02 23 0c 3206f662042696e6172792044617461
202. 511901 0d 11 18 22 2a 4465636f64696e6720746865205365637265747 4a657373652057696c736f6e 00 00 00 01 57 7D 37 EE 40 02 23 0c 3206f662042696e6172792044617461
203. 511901 0d 11 18 22 2a 4465636f64696e6720746865205365637265747 4a657373652057696c736f6e 00 00 00 01 57 7D 37 EE 40 02 23 0c 3206f662042696e6172792044617461 • Protocol Buffers are small and fast • ~1 byte for each field name • Compact encoding for numbers and enums • Strings stay the same length! • This message is 67 bytes in protocol buffers, vs. 128 for JSON
204. Java I/O
205. • Mutable! • equals() doesn’t work like it should: can’t be a map key! • Doesn’t implement Comparable byte[] is bad
206. • Range is -128..127 but you usually want 0..255 • But unsigned when you call InputStream.read() byte is signed
207. • Range is -128..127 but you usually want 0..255 • But unsigned when you call InputStream.read() byte is signed
208. Okio
209. Okio • Square’s library for efficient I/O • Used by OkHttp, Retrofit, Wire, Moshi
210. • Immutable! • equals() works like it should • Implements Comparable ByteString is good
211. ByteString makes data easy ByteString byteString = ByteString.decodeHex("436166c3a920f09f8da9");
 assertThat(byteString.size()).isEqualTo(10);
 assertThat(byteString.getByte(0)).isEqualTo((byte) 0x43);
 assertThat(byteString.getByte(0)).isEqualTo((byte) 67);
 
 String cafeDonuts = byteString.utf8();
 assertThat(cafeDonuts).isEqualTo("Café ");
 
 ByteString cafe = ByteString.encodeUtf8("Café");
 assertThat(byteString.startsWith(cafe)).isTrue();
212. ByteString and Parcelable
213. class Talk implements Parcelable {
 public static final Parcelable.Creator<Talk> CREATOR = new Parcelable.Creator<Talk>() {
 @Override public Talk createFromParcel(Parcel in) {
 int id = in.readInt();
 long date = in.readLong();
 Room room = Room.values()[in.readInt()];
 String title = in.readString();
 String speaker = in.readString();
 return new Talk(id, date, room, title, speaker);
 }
 };
 …
 
 @Override public void writeToParcel(Parcel out, int flags) {
 out.writeInt(id);
 out.writeLong(date);
 out.writeInt(room.ordinal());
 out.writeString(title);
 out.writeString(speaker);
 }
 }
214. @Test public void decodeGolden() {
 Talk talk = new Talk(72017, 1475260200000L, Room.RIGHT,
 "Decoding the Secrets of Binary Data", "Jesse Wilson");
 ByteString goldenData = ByteString.decodeHex("01000000511901004034…");
 assertThat(parcelDecode(goldenData, Talk.CREATOR)).isEqualTo(talk);
 }a
 
 private <T extends Parcelable> T parcelDecode(
 ByteString byteString, Parcelable.Creator<T> creator) {
 Parcel parcel = Parcel.obtain();
 try {
 parcel.unmarshall(byteString.toByteArray(), 0, byteString.size());
 parcel.setDataPosition(0);
 return parcel.readTypedObject(creator);
 } finally {
 parcel.recycle();
 }a
 }a
215. @Test public void decodeGolden() {
 Talk talk = new Talk(72017, 1475260200000L, Room.RIGHT,
 "Decoding the Secrets of Binary Data", "Jesse Wilson");
 ByteString goldenData = ByteString.decodeHex("01000000511901004034…");
 assertThat(parcelDecode(goldenData, Talk.CREATOR)).isEqualTo(talk);
 }a
 
 private <T extends Parcelable> T parcelDecode(
 ByteString byteString, Parcelable.Creator<T> creator) {
 Parcel parcel = Parcel.obtain();
 try {
 parcel.unmarshall(byteString.toByteArray(), 0, byteString.size());
 parcel.setDataPosition(0);
 return parcel.readTypedObject(creator);
 } finally {
 parcel.recycle();
 }a
 }a
216. Next Steps
217. • Everything is bytes • Java Strings are UTF-16. Encoded text is usually UTF-8 • Hex is handy • Don’t be afraid of shifting and masking • Integers are big or little-endian • Java’s I/O APIs are trouble 6 tips
218. • You can encode almost anything • Okio makes it easy No Black Boxes
219. @jessewilson https://github.com/swankjesse/encoding Thanks!