Windows Sockets Network Programming

by Bob Quinn and Dave Shute, with foreword by Martin Hall
Addison-Wesley, Reading, MA, ISBN: 0-201-63372-8
Now shipping (late November, 1995)

1: Introduction to Windows Sockets

What is Windows Sockets?


What are its Benefits?


• An Open Standard
  
• Provides Source Code Portability
  
• Supports Dynamic Linking
  
• Benefits Summary
  

What is its History?


What is its Future?


Conclusion

2: Windows Sockets Concepts

The OSI Network Model


• Services & Interfaces
  

The WinSock Network Model


• Information and Data
  
• Application Protocols
  

OSI layers and WinSock


• Application Layer
  
• Presentation Layer
  
• Session Layer
  
• Transport Layer
  
• Network Layer
  
• Data Link Layer
  
• Physical Layer
  

Modular Boxes


Services & Protocols


Protocols & APIs

3: TCP/IP Protocol Services

What is TCP/IP?


Transport Services


• Connection-less Services: UDP
  
• Connection-oriented Services: TCP
  
• Deciding on a Transport: UDP versus TCP
  

Network services


• IP Services
  
• ICMP Services
  

Support Protocols & Services


• Domain Name Service (DNS)
  
• Address Resolution Protocol (ARP)
  
• Other Support Protocols
  

What's its History?


What's its Future?

4: Network Program Mechanics

Client-Server Model


• Client & Server Association
  

Network Program Sketch


Open a Socket


• socket()
  

Name the Socket


• sockaddr Structure
  
• sockaddr_in Structure
  
• Port Numbers
  
• Local IP Address
  
• What's in a Socket Name?
  
  • bind()
    
• Client Socket Name is Optional
  

Associate with Another Socket


• How a Server Prepares for an Association
  
  • listen()
    
• How a Client Initiates an Association
  
  • connect()
    
• How a Server Completes an Association
  
  • accept()
    

Send and Receive Between Sockets


• Sending Data on a "connected" Socket
  
  • send()
    
• Sending Data on an "unconnected" Socket
  
  • sendto()
    
• Receiving Data
  
  • recv()
    
  • recvfrom()
    
• Association as Socket Demultiplexer
  

Close the Socket


• closesocket()
  
• shutdown()
  

Client & Server Sketches


• Connection-oriented (TCP) Network Applications
  
• Connection-less (UDP) Network Applications
  
  • Set the Remote Socket Name Once
    
  • Set the Remote Socket Name Each Datagram
    

5: Operation Modes

What are Operation Modes?


• Wait on Hold: Blocking
  
• Call Again Later: Non-blocking
  
• Request a Call Back: Asynchronous
  

Blocking


• Blocking Sockets
  
• Blocking Functions
  
• Blocking is Fake
  
• Blocking Hook Functions
  
• The Blocking Context
  
  • React to WSAEINPROGRESS Gracefully
    
  • Detect with WSAIsBlocking()
    
  • Canceling Blocking Operations
    
  • Maintain Application State
    
• Canceling Blocking Operations
  
  • Cancellation occurs later
    
  • Further Socket Use is Limited
    
  • Cancellation Occurs Later
    
  • Further Socket Use is Limited
    
  • Cancellation May Fail
    
  • Code Example
    
• Timeouts on Blocking Operations
  
  • Automatic Timeouts
    
  • User Settable Timeouts
    
  • TCP Keepalive Timeouts
    
• No Receive Minimum
  
• Code Example
  

Non-Blocking


• How Do You Make a Socket Non-blocking?
  
• Success and failure are not absolutes!
  
  • WSAEWOULDBLOCK Error
    
  • Partial success
    
• Polling Instead of Blocking
  
• Explicit Yielding
  
• Code Example
  

Asynchronous


• What Are the Asynchronous Functions?
  
  • WSAAsyncGetXByY()
    
  • Code Example
    
  • AU_Time Application
    

Performance Differences


Platform Differences


• Blocking is Real
  
• Threaded Applications
  
• Other Things Hold True
  

6: Socket States

What are the Socket States?


• Datagram Socket States
  
• Stream Socket States
  

What are the Methods of Detection?


• Function Call Success or Failure
  
• Synchronous Detection
  
• Asynchronous Detection
  

WSAAsyncSelect()


• How Does WSAAsyncSelect() Work?
  
• What are the Asynchronous Events?
  
• Avoid Windows of Misopportunity
  
• What are the Re-enabling Functions?
  
• What's in a Notification Message?
  
• Be Prepared for Failure
  
• Looping in Response
  
• Canceling Asynchronous Notification
  
• Event Descriptions
  
  • FD_ACCEPT Event
    
  • FD_CLOSE Event
    
  • FD_CONNECT Event
    
  • FD_OOB Event
    
  • FD_READ Event
    
  • FD_WRITE Event
    
• AS_ECHO Application
  

select()


• How Do You Use select()?
  
  • FD_CLR (socket, *fd_set)
    
  • FD_ISSET (socket, *fd_set)
    
  • FD_SET (socket, *fd_set)
    
  • FD_ZERO (*fd_set)
    
• select() Input Parameters
  
  • readfds
    
  • writefds
    
  • exceptfds
    
  • timeval Structure
    
• Don't Use select() as a Timer
  
• Beware Timeout of Zero
  
• Code Example
  

Peeking at Data


• ioctlsocket() FIONREAD Command
  
• recv() with MSG_PEEK Flag
  

Out-of-band Data


• TCP Limitations
  
• ioctlsocket() SIOCATMARK Command
  
  • Code Example
    

The Listening State

7: Sample Application and Library

Sample FTP Client


• File Transfer Protocol Overview
  
  • Control Connection
    
  • Data Connection
    
  • FTP Commands
    
  • FTP Replies
    
• FTP Finite State Machine
  
• AC_FTP Application
  
• AC_FTP in Operation
  

Sample Library


• CenterWnd()
  
• CloseConn()
  
• CreateLclFile()
  
• Dlg_About()
  
• GetAddr()
  
• GetBuf()
  
• GetHostID()
  
• GetLclDir()
  
• GetPort()
  
• WSAErrStr()
  
• WSAperror()
  

WinSockx.h


Globals.c


WSA_Xtra.h

8: Host Names & Addresses

Host Name and Address Resolution


• hostent Structure
  
• Host Name Resolution
  
  • gethostbyname()
    
    • Code Example
      
  • WSAAsyncGetHostByName()
    
    • Upon Completion
      
    • Sketch of Function Operation
      
    • Code Example
      
• Address Resolution
  
  • gethostbyaddr()
    
    • Code Example
      
  • WSAAsyncGetHostByAddr()
    
    • Code Example
      

Host Table, DNS & NIS


• Host Table
  
• Domain Name System (DNS)
  
• Network Information Service (NIS)
  

Local Host Information


• gethostname()
  

Addresses and Formatting


• in_addr structure
  
  • Address References
    
  • Address Class
    
  • Common Addresses
    
• inet_addr()
  
  • Code Example
    
• inet_ntoa()
  
  • Code Example
    

Protocol and Address Families

9: Socket Information & Control

Socket Control


• FIONBIO
  
  • Code Example
    
• FIONREAD
  
  • Code Example
    
• SIOCATMARK
  
  • Code Example
    
• Other Control Commands
  

Socket Options


• getsockopt() and setsockopt()
  
• Code Examples
  
  • setsockopt() with Boolean Option
    
  • getsockopt() with Integer Option
    
  • setsockopt() with struct linger Option
    
• SO_ACCEPTCONN
  
• SO_BROADCAST
  
  • What's a Broadcast Address?
    
  • Multicast Addresses
    
  • Proper use of Broadcasts
    
• SO_DEBUG
  
• SO_DONTLINGER
  
• SO_DONTROUTE
  
• SO_ERROR
  
• SO_KEEPALIVE
  
  • How Do Keepalives Work?
    
  • How Often are Keepalives Sent?
    
  • Implement Your Own Keepalive
    
• SO_LINGER
  
  • Avoiding Ambiguities
    
  • Do You Need SO_LINGER?
    
  • linger Structure
    
  • Code Example
    
• SO_OOBINLINE
  
• SO_RCVBUF and SO_SNDBUF
  
• SO_REUSEADDR
  
• SO_TYPE
  
• TCP_NODELAY
  
  • What's the Nagle Algorithm?
    
  • What Applications Need TCP_NODELAY?
    
• Unsupported Options
  
• Future Options
  

Blocking Hooks


• WSASetBlockingHook()
  
• WSAUnhookBlockingHook()
  
• Blocking Hook Functions
  

Socket Names


• getsockname()
  
  • Code Example
    
• getpeername()
  
  • Code Example
    

Blocking Status


• WSAIsBlocking()
  

10: Support Routines

Startup and Cleanup


• WSAStartup()
  
  • When and Where?
    
  • WSAStartup() Error Messages
    
  • WSAData structure
    
  • Version Negotiation
    
  • Code Example
    
• WSACleanup()
  

Byte Ordering


• Byte Ordering Functions
  
  • htons()
    
  • ntohs()
    
  • ntohl()
    
  • htonl()
    
  • Code Example
    

Service Names and Ports


• servent Structure
  
• Service Resolution
  
  • getservbyname()
    
    • Code Example
      
  • WSAAsyncGetServByName()
    
    • Upon Completion
      
    • Code Example
      
• Port Resolution
  
  • getservbyport()
    
  • WSAAsyncGetServByPort()
    
• Services Database
  

Protocol Names and Numbers


• protoent Structure
  
• Protocol Name Resolution
  
  • getprotobyname()
    
    • Code Example
      
  • WSAAsyncGetProtoByName()
    
    • Code Example
      
• Protocol Number Resolution
  
  • getprotobynumber()
    
  • WSAAsyncGetProtoByNumber()
    
• Protocols Database
  

Error Reporting


• WSAGetLastError()
  
• WSASetLastError()
  
  • Code Example
    
• Error Text Display
  

11: DLLs over WinSock

Creating a New API


• Emulated API
  
• Application Protocol API
  
• Encapsulated WinSock API
  

DLL Issues


• Reentrancy
  
• Setting a Blocking Hook
  
• Task Management
  
  • Registering the Application Process
    
  • Registering a Helper Process
    
• Loading the WinSock DLL Explicitly
  

Sample DLL


• WSASimpl Application
  
• WSASimpl DLL
  

12: Porting from BSD Sockets

Differences to Consider


• Sockets are not File Handles
  
• Cannot dup() a Socket
  
• close() and ioctl() Functions are Renamed
  
• read(), write() or fcntl() Functions Unavailable
  
• Some ioctlsocket() FIO Command Unavailable
  
• select()'s fd_sets are Opaque
  
• select() Doesn't Act as a Timer
  
• signal() Unavailable
  
• Domain Name Unavailable
  
• Address Info and Manipulation Unavailable
  
• syslog() Unavailable
  
• errno Variable Unavailable
  
• perror() and strerror() Unavailable
  
• Database File Manipulation Unavailable
  
• bcmp(), bcopy() and bzero() Unavailable
  
• Local IPC Unavailable
  
• OOB API Differs
  
• setsockopt() SO_DEBUG optional
  

16-bit Windows Considerations


• 16-bit Windows Doesn't Clean House
  
• 16-bit Windows is Non-preemptive
  
• 16-bit Windows File System isn't Secure
  
• 16-bit Windows Uses Segmented Addressing
  
• fork() Unavailable
  

Incidentals


• Include Files
  
• Socket Domains
  
• Socket Types
  
• Socket Handles
  
• Error Values
  

Functions List

13: Debugging

Problem Types


• Installation Problem
  
• Network Problem
  
• Application Problem
  
• WinSock DLL Problem
  

What failed, and how?


• Protection Faults
  

Problem Qualification


Installation Debugging


Network Debugging


• Generic Network Debugging
  
• Host Resolution Debugging
  

Application Debugging


Debugging Tools


• Network Debugging Utilities
  
  • ping
    
  • traceroute
    
  • nslookup
    
  • Standard UNIX Tools
    
  • SNMP Tools
    
  • Ad hoc Tools
    
  • Network Analyzers
    
• Application Debugging Utilities
  
  • WinScope
    
  • X-Ray Winsock
    
  • Create Your Own WinSock Watcher
    

WinSock Compliance & Performance Utilities


• wsatest
  
• Windows Sockets API Tester (WSAT)
  
• Socket Wrencher
  

Other Application Debugging Tools

14: Do's and Don'ts

Characterizing Your Application


Application Data Flow


• Use Big Buffers
  
• Think MTU
  
• Consider the Maxim
  
  • Send Moderate Amounts
    
  • Receive Large Amounts
    
• Don't Peek
  
• Receive Before You Send
  

Stream Algorithms


• Sending Structured Data
  
  • Code Example
    
• Sending Interactive Data
  
• Detecting a Dead Connection
  
• Verifying Data Delivery
  

Datagram Algorithms


• Implementing a Timeout
  
• Sequencing Datagrams
  
• Throttling Sends
  
• Synchronizing Sender and Receiver
  

Good News Code


• Check Returns
  
• Check for Partial Success
  
• Expect Any Error at Any Time
  
• Check for Non-Fatal Errors
  
• Handle Errors Gracefully
  
• Leave an Out
  
• Don't Ignore Warnings
  

Common Traps and Pitfalls


• Opening and Naming a Socket
  
• Connecting
  
• Listening and Receiving
  
• Closing a Socket
  
• Using Host Names and Addresses
  
• Using WSAAsyncSelect()
  
• Using Blocking Sockets
  
• Exiting an Application
  
• Miscellaneous
  

15: Platforms

The WOSA Network Model


32-bit WinSock


• Windows 95
  
• Cross-Execution
  
• 32-bit WinSock Features
  
  • New Socket Options
    
    • SO_OPENTYPE
      
    • SO_RCVTIMEO and SO_SNDTIMEO
      
  • Service Features
    
  • Other Protocol Suites
    
• 32-bit operating system advantages
  
  • Blocking is Real!
    
  • Threading
    
  • Sockets are File Handles
    
  • Console Interface
    

Other platforms

16: Optional Features

Optional Standard is an Oxymoron


Should You use Optional Features?


SOCK_RAW


• ICMP Ping Application
  
• Traceroute
  
• Code Example
  

Multicast


• Why Use Multicast?
  
• Multicast API
  
  • IP_ADD_MEMBERSHIP
    
  • IP_DROP_MEMBERSHIP
    
  • IP_MULTICAST_IF
    
  • IP_MULTICAST_LOOP
    
  • IP_MULTICAST_TTL
    
• Multicast Mechanics
  
• Code Example
  

Loopback


Sharing Sockets


• Is Socket Sharing Possible?
  

Optional Options


Sockets as File Handles


Expect Any Error Anywhere


Other Optional Features

17: WinSock 2

Do You Need WinSock 2?


Overview of Features


Multiple Protocol Support


• WinSock 2 Architecture
  
• Protocol independence
  
• Namespace Independence
  
  • Globally Unique Identifiers
    
  • Generic Address Formatting
    
  • Parametric Service Searches
    
  • Service Installation and Registration
    

Overlapped I/O


Scatter and Gather


Quality of Service


Socket Groups


Multipoint and Multicast


Conditional Acceptance


Connect and Disconnect Data


Socket Sharing


Protocol-Specific Additions


• WSAIoctl()
  
• get/setsockopt()
  

Appendix A: TCP/IP Protocol Headers

Layering within TCP/IP Packets


ARP Header


IP Header


ICMP Header


IGMP Header


UDP Header


TCP Header


Sample Dialogs


• Server on Same Subnet
  
• Server on Different Subnet
  

Appendix B: Quick Reference

Structures


Functions


Macros

Appendix C: Error Reference

Where to Get Error Values


Where Errors Came From


What Errors to Expect


User-Fixable Errors


Detailed Error Descriptions


• Error-less Functions
  
• Function-less Errors
  
• Error Description List
  

Errors in Numerical Order

Appendix D: What You Need

Essential Files


• Where to Get Them
  

Compile & Link Mechanics


Using Different WinSocks


Using Different Languages

Appendix E: Information Sources

Internet Sources


• URLs and URIs
  
• FTP sites
  
• List Servers
  
• Mail lists
  
• Newsgroups
  
• Web Pages
  

Bibliography


• RFCs
  
• FAQs
  
• Articles
  
• Texts