From 2abf6dc82fb4df2249cbd920cbf82d7d68ff4467 Mon Sep 17 00:00:00 2001
From: Fabio Scotto di Santolo <fabio.scottodisantolo@gmail.com>
Date: Fri, 22 Aug 2025 16:33:15 +0200
Subject: [PATCH] Added README for extra arguments

---
 16_NetworkIPCSockets/README.md | 99 ++++++++++++++++++++++++++++++++++
 README.md                      |  5 ++
 2 files changed, 104 insertions(+)
 create mode 100644 16_NetworkIPCSockets/README.md

diff --git a/16_NetworkIPCSockets/README.md b/16_NetworkIPCSockets/README.md
new file mode 100644
index 0000000..f1e8e34
--- /dev/null
+++ b/16_NetworkIPCSockets/README.md
@@ -0,0 +1,99 @@
+# 📘 APUE – Chapter 16: Sockets Summary
+
+### **1. Introduction to Sockets**
+
+- Sockets are an abstraction for network communication.
+- Enable communication between processes over the network.
+- Support multiple protocols: TCP, UDP (IPv4, IPv6).
+
+### **2. Socket Types**
+
+- `SOCK_STREAM` – TCP (reliable, connection-oriented).
+- `SOCK_DGRAM` – UDP (connectionless, unreliable).
+- `SOCK_SEQPACKET` – sequenced, reliable datagrams (less common).
+- `SOCK_RAW` – raw access to IP packets (used in advanced networking).
+
+### **3. Socket System Calls**
+
+1. `int socket(int domain, int type, int protocol);`
+   - Create a new socket descriptor.
+2. `int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen);`
+   - Assign an address/port to a socket (server side).
+3. `int listen(int sockfd, int backlog);`
+   - Mark socket as passive (ready to accept connections).
+4. `int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);`
+   - Accept a new incoming connection (blocking call).
+5. `int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);`
+   - Establish connection to a server (client side).
+6. `ssize_t read(int sockfd, void *buf, size_t count);`
+7. `ssize_t write(int sockfd, const void *buf, size_t count);`
+8. `ssize_t recv(int sockfd, void *buf, size_t len, int flags);`
+9. `ssize_t send(int sockfd, const void *buf, size_t len, int flags);`
+10. `int close(int sockfd);`
+    - Close the socket and free resources.
+
+### **4. Socket Address Structures**
+
+- IPv4: `struct sockaddr_in`
+
+  ```c
+  struct sockaddr_in {
+      sa_family_t sin_family;  // AF_INET
+      in_port_t sin_port;      // port number (network byte order)
+      struct in_addr sin_addr; // IP address
+  };
+  ```
+
+- IPv6: `struct sockaddr_in6`
+- Generic: `struct sockaddr` for compatibility.
+
+### **5. Data Conversion Utilities**
+
+- `htons()`, `htonl()`: host to network byte order (short/long)
+- `ntohs()`, `ntohl()`: network to host byte order
+- `inet_pton()`: convert string IP to `struct in_addr` or `struct in6_addr`
+- `inet_ntop()`: convert address structure to string
+
+### **6. TCP Client-Server Model**
+
+**Server:**
+
+1. `socket()`
+2. `bind()`
+3. `listen()`
+4. `accept()` → handle client
+5. `read()/write()` → communicate
+6. `close()`
+
+**Client:**
+
+1. `socket()`
+2. `connect()`
+3. `read()/write()` → communicate
+4. `close()`
+
+### **7. UDP Model**
+
+- Connectionless: no `listen()`/`accept()`.
+- Use `sendto()` and `recvfrom()` for communication.
+- No guarantee of delivery; suitable for lightweight or real-time protocols.
+
+### **8. Concurrency in Servers**
+
+- **Process-based**: `fork()` for each client
+- **Thread-based**: `pthread_create()` for each client
+- **I/O multiplexing**: `select()`, `poll()`, `epoll()`
+
+### **9. Error Handling**
+
+- Check return values of all socket calls.
+- Use `perror()` or `strerror()` for diagnostics.
+- Handle `EINTR` for interruptible syscalls.
+
+### **10. Key Takeaways**
+
+- Sockets abstract network communication using familiar file descriptor semantics.
+- TCP ensures reliable, ordered delivery; UDP is fast but unreliable.
+- Address conversions (`inet_pton`, `inet_ntop`) are essential for portability.
+- Concurrency requires careful design: processes, threads, or event loops.
+- Practice writing small client-server programs to solidify concepts.
diff --git a/README.md b/README.md
index 6ebb013..c2a25ae 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,7 @@
 # 📚 Linux System Programming – Chapter Index
 
 Welcome! This is a collection of chapter summaries from the book **Linux System Programming** by Robert Love. Each chapter is organized in its own folder.
+In the section extra there are other arguments take by ***Advanced Programming in the UNIX Enviroment*** by W. Richard Stevens.
 
 ## Available Chapters
 
@@ -15,6 +16,10 @@ Welcome! This is a collection of chapter summaries from the book **Linux System
 - [Chapter 10 - Signals](10_Signals/README.md)
 - [Exercises](exercises/README.md)
 
+## Extra (APUE)
+
+- [Chapter 16 - Network IPC: Sockets](16_NetworkIPCSockets/README.md)
+
 > Each file contains an English summary of the chapter's key concepts.
 
 ## License