This document discusses building a cross-platform cryptocurrency application. It covers using a monorepo architecture for code reuse across mobile, desktop, and npm library applications. It also discusses developing cryptocurrency wallet features like generating transactions and signatures, smart contracts, and blockchain basics.

1. Building a cross-platform
cryptocurrency app
Oliver Hager
& Dylan Butler

2. Oliver Hager
Software Craftsman @ Dextra
Developer @ Burst
Brazil since 2008
Capoeira since 2001
Coding since 1992
oliverhager
ohager
@ohager5

3. Dylan Butler
Manager, Cloud Front End
Engineering @ PlayStation
Developer @ Burst
Developer for 15 years
Licensed attorney
dylanbutler
blankey1337
@blankey1337

4. Building a cross-platform cryptocurrency
application

5. Cross-Platform Monorepo App Architecture

6. Library Development & Maintenance

7. Cryptocurrency App Development

8. Smart Contracts

9. Blockchain Basics

10. A block contains transactions.
TX1
...
TXn

11. Transactions carry arbitrary data of limited length.
TX1
...
TXn
4022e1a87
23171628e
484750a..
.

12. 0x98F…
TX1
...
TXn
Each validated block is identified by a hash.
4022e1a87
23171628e
484750a..
.

13. 0x98F…
TX1
...
TXn
Validation is done by the P2P network.
4022e1a87
23171628e
484750a..
.
0x98F...

14. This hash is combined with the content of the prior block.
0x1337…
TX1
...
TXn
0xBA75…
TX1
...
TXn
0xF0CA…
TX1
...
TXn

15. Blockchain is useful as a ledger, or transaction record.

16. Most famous use case: Cryptocurrency

17. BURSTCOIN and BITCOIN

18. The difference?

19. Proof of Capacity

20. Energy Efficient

22. Faster transactions

23. Smart Contracts

24. And even more features

25. Community
August 2014
Genesis Block
Dev Unknown
August 2017
PoC
Consortium
January 2019
BAT and BMF
founded
January 2016
Community
Takeover

28. How I got started

29. June 2017

30. BTC Price: $2.500 USD

31. BTC is gaining traction.

32. What would I do if I could go back in time?

33. I’d jump into 2010 and start mining Bitcoin!

34. But I was too late.

35. Then I heard about hard-drive mining.

36. I was immediately interested.

37. I tested out mining.

38. It could be more user-friendly.

39. My first contribution: Autoplotter

40. I started working on other tools.

41. Still mining this whole time.

42. How I got started

43. I wanted to understand.

44. I wanted to help.

45. I saw opportunity.

46. I built a few small Burst tools.

47. But something was preventing mass adoption.

48. Getting a local wallet setup and running was painful.

49. The Burst wallet was also not available on iOS devices.

50. If I couldn’t use it, my friends & family couldn’t either.

51. It was clear what needed to be done.

52. Burst needed an
easy-to-use wallet.

53. I started working on a new wallet.

54. It was a popular idea.

55. Then I got a message.

58. Let’s get started

59. Project Goals

60. 1. It needs to be easy to use

61. 2. It needs to be secure

62. 3. It needs to be cross-platform:

63. A. Web

64. B. Desktop

65. C. Mobile

66. What should we call this project?

67. Project Phoenix

68. A cross-platform cryptocurrency wallet

70. Is this real life?

71. We both have full-time jobs.

72. Time is precious.

73. We started thinking.

74. Code reuse is going to be important.

75. How are we going to manage these apps and libs?

76. Enter the monorepo

77. Monorepo, not monolith

79. Mobile, desktop, and npm libs are published separately.

84. npm library (@burstjs)

85. NPM Library Do’s and Don’ts

86. Do: Follow Semver
Credits: jontejada.com

87. Don’t: Import from src

88. Do: Import from dist or out

89. Do: Use Lerna for scoped packages

90. Do: Document the reusable things

91. We settled on jsdoc2md and typedoc

92. npm scoped packages

93. Minified bundle

94. Hammer Demo Time

95. Modern software requires modern
tooling.

96. Code Quality

97. Drafting a releaseTravis CI

98. Codacy

99. Codecov

100. Snyk

101. Drafting a release

102. One line does everything

103. It builds and tests the Angular app

104. It builds each of the desktop targets

105. It creates a draft release on GitHub

106. And uploads the artifacts to the release

107. Docs are auto-published to Github Pages

108. We’ve got our stack. Now what?

109. Let’s build a crypto app

110. Logging into a crypto app is different.

111. A client/server architectures require trust.

112. Trust in the server.

113. Cryptocurrencies are different.

114. Decentralized = trustless

115. No username-password pair

116. No username-password pair

117. Just a single passphrase

118. Your passphrase is your account

119. Your passphrase is your account

120. You never actually login.

121. Prove that public key derives from passphrase.

122. No server calls

123. Making a transaction
Sending money

124. What do we need to make a transaction?

125. Sufficient balance

126. A correct passphrase

127. Sender

128. Recipient

129. Amount

130. Fee

131. If we have those ingredients, we can make a transaction.

132. sendAmount

133. How to send transactions
over the blockchain?

134. Send, sign and broadcast

135. Sign and broadcast

136. generateSignature

137. Broadcast it to peers

138. Those peers will tell their peers

139. Miners put transactions into a block

140. Then seal a block with a hash

141. Nodes validate the block

142. And the cycle repeats

143. Smart Contracts

144. 0x98F…
TX1
...
TXn
Remember?
4022e1a87
23171628e
484750a..
.

145. 0x98F…
TX1
...
TXn
Executable Code is Data
12070300003033040308000000350
001090000001e090000000c129b02
00002835070308000000123100000
01a06000000331001090000003506
030a000000100a000000110700000
033100109000000320a033504010a
000000100a0000001106000000020
a00000007000000060a0000000400
0000100a

146. Code is Law

147. Blockchain is Single Source of Truth

148. Smart Contracts are the reactive parts

149. Automated and Trustless Execution

150. Use case: Gaming

151. Use case: Ownership

152. Use case: Supply Chain

153. In BURST Smart Contracts are written in Java

154. Compiled to machine code

155. Published to the blockchain

156. Triggered on each transaction

157. And eventually executes

158. Execution costs!

159. Limited Space for Code!

160. Blocktime

161. Hammer Demo Time