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@S_Shimotori - try! Swift Tokyo 2024
Parallel Socket Communication
in Swift
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S_Shimotori
iOS Engineer @ LY Corporation
Eventer
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3 at try! Swift Tokyo Meetup 2023/01/21 Sat.
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From Application to Hardware
Kernel
Application
Hardware
Standard Libraries
iOS application, macOS application, …
URL, URLSession
Socket
Network interface
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Lower
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From Application to Hardware
Kernel
Hardware
Standard Libraries
iOS application, macOS application, …
URL, URLSession
Socket
Network interface
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Application
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Parallel Socket Communication in Swift
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Inter-Process Communication
Process A Process B
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Socket Communication
Process B
Socket
Process A
Socket
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Host A Host B
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Sample: Ping
$ ping -c 2 example.com
PING example.com (93.184.216.34): 56 data bytes
64 bytes from 93.184.216.34: icmp_seq=0 ttl=52 time=165.910 ms
64 bytes from 93.184.216.34: icmp_seq=1 ttl=52 time=108.211 ms
--- example.com ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 108.211/137.060/165.910/28.850 ms
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Sample: Ping
$ ping -c 2 example.com
PING example.com (93.184.216.34): 56 data bytes
64 bytes from 93.184.216.34: icmp_seq=0 ttl=52 time=165.910 ms
64 bytes from 93.184.216.34: icmp_seq=1 ttl=52 time=108.211 ms
--- example.com ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 108.211/137.060/165.910/28.850 ms
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byte count IP address sequence No. TTL elapsed time
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Communication with Ping
64 bytes from 93.184.216.34: icmp_seq=0 ttl=52 time=165.910 ms
56 bytes message
icmp_seq=0
64 bytes message
icmp_seq=0 93.184.216.34
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Interface of Serial Ping in Swift
func ping(
identifier: UInt16,
sequenceNumber: UInt16,
to address: String
) async throws -> Result data including elapsed time
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Let’s dive into
socket communication!
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Break Down Goals into Tasks
• Create a datagram socket
• Encode/Decode a message
• Execute system calls for messaging
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Break Down Goals into Tasks
• Create a datagram socket
• Encode/Decode a message
• Execute system calls for messaging
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Datagram Socket
Process
Datagram
Socket
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Your computer
Destination host
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Socket on Swift
let fileDescriptor: Int32 = Foundation.socket(…)
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Socket on Swift
let fileDescriptor: Int32 = Foundation.socket(…)
sendto(fileDescriptor, …)
recvfrom(fileDescriptor, …)
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Socket on Swift
let fileDescriptor: Int32 = Foundation.socket(…)
sendto(fileDescriptor, …)
recvfrom(fileDescriptor, …)
close(fileDescriptor)
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Socket on Swift
let fileDescriptor: Int32 = Foundation.socket(…)
sendto(fileDescriptor, …)
recvfrom(fileDescriptor, …)
close(fileDescriptor)
sendto(fileDescriptor, …) // runtime error
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Socket on Swift
‘
fi
leDescriptor' used after consume
let fileDescriptor = FileDescriptor(fd: socket(…))
fileDescriptor.send(…)
fileDescriptor.receive(…)
fileDescriptor.close() // consuming func
fileDescriptor.send(…)
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struct FileDescriptor: ~Copyable
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Break Down Goals into Tasks
• Create a datagram socket ✅
• Encode/Decode a message
• Execute system calls for messaging
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00001000 00000000 11110111 11110110
00000000 00000100 00000000 00000101
……
Binary Message Data for Ping
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Binary Message Data for Ping
type code checksum
identi
fi
er sequence number
00001000 00000000 11110111 11110110
00000000 00000100 00000000 00000101
……
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Using Structure to Encode Message
struct ICMPEchoRequest {
let type: UInt8
let code: UInt8
let checksum: UInt16
let identifier: UInt16
let sequenceNumber: UInt16
……
}
00001000
00000000
11110111 11110110
00000000 00000100
00000000 00000101
……
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Byte Order
• Big endian, in network
00000000 00000101 = 5
• Little endian, in Swift
00000101 00000000 = 0b101 = UInt16(5)
00000000 00000101 = 0b101_00000000 = UInt16(1280)
00000000 00000101 = UInt16(5).bigEndian = UInt16(1280)
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Using Structure to Decode Received Message
struct IPv4Header {
……
let timeToLive: UInt8
……
let sourceIPAddress: in_addr
……
}
……
01000000
……
01111111 00000000
00000000 00000001
……
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Break Down Goals into Tasks
• Create a datagram socket ✅
• Encode/Decode a message ✅
• Execute system calls for messaging
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System Calls for Datagram Socket
• sendto(…, UnsafeRawPointer, …) -> length of message
• poll(…, Int32) -> result
• recvfrom(…, UnsafeMutableRawPointer, …) -> length of message
pointer to Data
pointer to Data for storing
timeout
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System Call with Unsafe Types
message.withUnsafeBytes { pointerToMessage in
withUnsafePointer(to: address) { pointerToAddress in
sendto(…, UnsafeRawPointer, …, UnsafePointer, …)
}
}
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Poll before Receive
// These functions block until receiving
_ = poll(…, Int32)
_ = recvfrom(…, UnsafeMutableRawPointer, …)
timeout
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mutable Data
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Break Down Goals into Tasks
• Create a datagram socket ✅
• Encode/Decode a message ✅
• Execute system calls for messaging ✅
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Datagram
Socket
Data Flow of “Serial” Ping
Timer
UI
Data Binding
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Your computer
Destination host
every sec.
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Advanced: Parallel Requests
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Monitoring Multiple Hosts
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Monitoring Multiple Hosts
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deadman
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Multiple Request Messages
Datagram
Socket
Host A
Host B
Host C
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ping
Your computer
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Multiple Reply Messages
Datagram
Socket
Host A
Host B
Host C
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reply
Your computer
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Multiple Reply Messages
Datagram
Socket
Host A
Host B
Host C
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reply
Your computer
Timers
UI
Data Binding
while true {
poll(…)
}
timeout
cancel
Timer
every sec.
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Logic that We Should Code in Swift
• Sorting received messages
• Handling timeout
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Supplement: About ncurses
• Thread-unsafe
• Managing screens using OpaquePointer
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Summary
• You can experience socket communication using Swift.
• Swift ensures safety and helps parallel communication.
• Have fun learning socket communication with Swift!
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@S_Shimotori_pub
@S-Shimotori
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References
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Official Pages
• API Reference: iOS Manual Pages
• https://developer.apple.com/library/archive/documentation/System/Conceptual/
ManPages_iPhoneOS/index.html
• Unsafe Swift - WWDC20 - Videos - Apple Developer
• https://developer.apple.com/videos/play/wwdc2020/10648
• Safely manage pointers in Swift - WWDC20 - Videos - Apple Developer
• https://developer.apple.com/videos/play/wwdc2020/10167/
• swift-evolution/proposals/0390-noncopyable-structs-and-enums.md at main · apple/swift-
evolution
• https://github.com/apple/swift-evolution/blob/main/proposals/0390-noncopyable-structs-and-
enums.md
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apple/swift - Int.bigEndian
• swift/stdlib/public/core/Integers.swift at d7b3d3e319d99ee3956dd1af899b73112d7517fd · apple/swift
• https://github.com/apple/swift/blob/d7b3d3e319d99ee3956dd1af899b73112d7517fd/stdlib/public/core/
Integers.swift#L2296-L2321
• swift/stdlib/public/core/IntegerTypes.swift.gyb at 633d5bc45a7c0a7b0e481701cf3f8fc2025f8f51 · apple/swift
• https://github.com/apple/swift/blob/633d5bc45a7c0a7b0e481701cf3f8fc2025f8f51/stdlib/public/core/
IntegerTypes.swift.gyb#L1646-L1654
• llvm-project/llvm/include/llvm/IR/Intrinsics.td at 11fcae69dbea4860e20ab799ecca9b0432d7f19d · llvm/llvm-
project
• https://github.com/llvm/llvm-project/blob/11fcae69dbea4860e20ab799ecca9b0432d7f19d/llvm/include/
llvm/IR/Intrinsics.td#L638-L641
• LLVM Language Reference Manual — LLVM 19.0.0git documentation
• https://llvm.org/docs/LangRef.html#id664
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System Programming
• Kerrisk, Michael. The Linux Programming Interface. No Starch Press.
• ઍॅ࣏ ༁. LinuxϓϩάϥϛϯάΠϯλϑΣʔε. ΦϥΠϦʔɾδϟύϯ
• UNIXωοτϫʔΫϓϩάϥϛϯάʹొ͢Δߏମͷհͱਖ਼͍͍͠ํ
• “Introduction and proper use of structures in UNIX network programming”
• http://cms.phys.s.u-tokyo.ac.jp/~naoki/CIPINTRO/NETWORK/struct.html
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Ping
• upa/deadman: deadman is a curses-based host status checking application using ping
• https://github.com/upa/deadman
• Ping͕OKͱͳΔ݅ʢҟͳΔΞυϨε͔ΒԠ͕ฦ͖ͬͯͨ߹ʣ
• “Conditions under which a ping is fine (when a response is returned from a different
address)”
• https://infrastructure-engineer.com/tcpip-basic-0005/
• ICMPͷNAPTӽ͑-ϙʔτ൪߸͕ͳ͍ͷʹͳͥʁ | izuminͷඋ
• “ICMP through NAT traversal-Why it can pass without a port number”
• https://izuminmin.com/network/icmpping-napt/
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Resources
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Image Resources
• ͔Θ͍͍ϑϦʔૉࡐू ͍Β͢ͱ
• https://www.irasutoya.com/
• About X | Our logo, brand guidelines, and tools
• https://about.x.com/en/who-we-are/brand-toolkit
• GitHub Logos and Usage
• https://github.com/logos
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