add some notes and basic code

.vscode/settings.json

@@ -1,3 +1,4 @@
 {
-    "clangd.path": "/usr/bin/clangd"
+    "clangd.path": "/usr/bin/clangd",
+    "clangd.arguments": [ "--header-insertion=never" ]
 }

README.md

@@ -1,5 +1,5 @@
 # cws
-A Web Server written in C (educational purposes)
+A simple Web Server written in C (learning purposes)
 
 ## Requirements
 - [meson](https://mesonbuild.com/index.html)
@@ -26,3 +26,5 @@ And then run `cws`!
 
 ## Resources
 - [Beej's Guide to Network Programming](https://beej.us/guide/bgnet/)
+
+You can find my journey inside the `notes` directory!

include/colors.h

@@ -0,0 +1,11 @@
+#ifndef __COLORS_H__
+#define __COLORS_H__
+
+#define RED "\033[31m"
+#define GREEN "\033[32m"
+#define YELLOW "\033[33m"
+#define BLUE "\033[34m"
+#define BOLD "\033[1m"
+#define RESET "\033[0m"
+
+#endif

include/main.h

@@ -1,7 +1,6 @@
 #ifndef __MAIN_H__
 #define __MAIN_H__
 
-#define GREEN_COLOR "\033[32m"
-#define RESET_COLOR "\033[0m"
+#include <stdio.h>
 
 #endif

include/server.h

@@ -1,13 +1,20 @@
 #ifndef __SERVER_H__
 #define __SERVER_H__
 
-#include <string.h>
-#include <sys/types.h>
-#include <sys/socket.h>
+#include <arpa/inet.h>
 #include <netdb.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 
 #define PORT 3030
 // how many pending connections the queue will hold
 #define BACKLOG 10
 
+int start_server(void);
+
 #endif

include/utils.h

@@ -0,0 +1,17 @@
+#ifndef __UTILS_H__
+#define __UTILS_H__
+
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// Print every IPs of a hostname
+void print_ips(const char *hostname, const char *port);
+
+#endif

notes/basic-concepts.md

@@ -0,0 +1,118 @@
+# Basic concepts
+Before reading, this document could contain errors, please check everything you read.
+
+- [Basic concepts](#basic-concepts)
+    - [Socket](#socket)
+    - [Internet sockets](#internet-sockets)
+    - [Byte Order](#byte-order)
+    - [Structs](#structs)
+      - [struct addrinfo](#struct-addrinfo)
+      - [struct sockaddr](#struct-sockaddr)
+      - [struct sockaddr\_in](#struct-sockaddr_in)
+      - [struct sockaddr\_storage](#struct-sockaddr_storage)
+    - [IP Addresses](#ip-addresses)
+    - [getaddrinfo()](#getaddrinfo)
+
+
+### Socket
+When Unix programs do some I/O they do it reading/writing to a **file descriptor**. A file descriptor is an integer associated with an open file, it can be anything. To communicate over the internet using a file descriptor we'll make a call to the `socket()` system routine.
+
+### Internet sockets
+There are two types of Internet sockets:
+1. Stream Sockets (SOCK_STREAM) - error-free and a realiable two-way communication (TCP)
+2. Datagram Sockets (SOCK_DGRAM) - connectionless (UDP)
+
+### Byte Order
+- Big-Endian (also called **Network Byte Order**)
+- Little-Endian
+
+Before making any transmission we have to convert the byte order to a Network Byte Order, we can do this with simple functions:
+
+| Function | Description           |
+| -------- | --------------------- |
+| htons()  | Host to Network Short |
+| htonl()  | Host to Network Long  |
+| ntohs()  | Network to Host Short |
+| ntohl()  | Network to Host Long  |
+
+And convert the answer to the host byte order.
+
+### Structs
+#### struct addrinfo
+This struct prepares the socket address strcutures for subsequent use.
+
+```c
+struct addrinfo {
+    int              ai_flags;     // AI_PASSIVE, AI_CANONNAME, etc.
+    int              ai_family;    // AF_INET, AF_INET6, AF_UNSPEC
+    int              ai_socktype;  // SOCK_STREAM, SOCK_DGRAM
+    int              ai_protocol;  // use 0 for "any"
+    size_t           ai_addrlen;   // size of ai_addr in bytes
+    struct sockaddr *ai_addr;      // struct sockaddr_in or _in6
+    char            *ai_canonname; // full canonical hostname
+
+    struct addrinfo *ai_next;      // linked list, next node
+};
+```
+
+#### struct sockaddr
+Inside the struct we can see there is a pointer to the `struct sockaddr`, that is defined as follows:
+
+```c
+struct sockaddr {
+    unsigned short    sa_family;    // address family, AF_xxx
+    char              sa_data[14];  // 14 bytes of protocol address
+};
+```
+
+#### struct sockaddr_in
+But, we can avoid to pack manually the stuff inside this struct and use the `struct sockaddr_in` (or `struct sockaddr_in6` for IPv6) with a fast cast that is made for the Internet:
+
+```c
+struct sockaddr_in {
+    short int          sin_family;  // Address family, AF_INET
+    unsigned short int sin_port;    // Port number
+    struct in_addr     sin_addr;    // Internet address
+    unsigned char      sin_zero[8]; // Same size as struct sockaddr
+};
+```
+
+`sin_zero` is used to pad the struct to the length of a sockaddr and it should be set to all zeros (`memset()`).
+
+#### struct sockaddr_storage
+This struct is designed to storage both IPv4 and IPv6 structures. Example, when a client is going to connect to your server you don't know if it is a IPv4 or IPv6 so you use this struct and then cast to what you need (check the `ss_family` first).
+
+```c
+struct sockaddr_storage {
+    sa_family_t  ss_family;     // address family
+
+    // all this is padding, implementation specific, ignore it:
+    char      __ss_pad1[_SS_PAD1SIZE];
+    int64_t   __ss_align;
+    char      __ss_pad2[_SS_PAD2SIZE];
+};
+```
+
+### IP Addresses
+Here's a way to convert an IP address string into a struct.
+
+```c
+struct sockaddr_in sa;
+struct sockaddr_in6 sa6;
+
+inet_pton(AF_INET, "192.168.0.1", &(sa.sin_addr));
+inet_pton(AF_INET6, "2001:db8:63b3:1::3490", &(sa6.sin6_addr));
+```
+
+There is a very easy function called `inet_pton()`, *pton* stands for **Presentation to network**. If you want to do the same but from binary to string you have `inet_ntop()`.
+
+### getaddrinfo()
+```c
+int getaddrinfo(const char *node,     // e.g. "www.example.com" or IP
+                const char *service,  // e.g. "http" or port number
+                const struct addrinfo *hints,
+                struct addrinfo **res);
+```
+
+The `node` could be a host name or IP address. `service` could be a port number or a service found in `/etc/services` (e.g. "http" or "ftp" or "telnet").
+`hints` points to a struct you already filled and `res` contains a linked list of results.

src/main.c

@@ -1,6 +1,17 @@
 #include "main.h"
-#include <stdio.h>
+#include "colors.h"
+#include "server.h"
+#include "utils.h"
 
-int main(void) {
-    puts(GREEN_COLOR "Running cws..." RESET_COLOR);
+int main(int argc, char **argv) {
+	fprintf(stdout, BOLD GREEN "Running cws...\n" RESET);
+
+	int ret = start_server();
+	if (ret < 0) {
+		fprintf(stderr, BOLD RED "Unable to start web server\n");
+	}
+
+	print_ips("google.com", "80");
+
+	return 0;
 }

src/meson.build

@@ -1 +1 @@
-sources = files('main.c', 'server.c')
+sources = files('main.c', 'server.c', 'utils.c')

src/server.c

@@ -1,5 +1,34 @@
 #include "server.h"
+#include "colors.h"
 
 int start_server(void) {
+	char ipv4[INET_ADDRSTRLEN];
+	struct sockaddr_in sa;
+
+	inet_pton(AF_INET, "192.168.0.1", &(sa.sin_addr));
+	inet_ntop(AF_INET, &(sa.sin_addr), ipv4, INET_ADDRSTRLEN);
+
+	fprintf(stdout, BLUE "IPv4: %s\n" RESET, ipv4);
+
 	return 0;
 }
+
+void get_local_ip(void) {
+	char service[] = "3030";
+	struct addrinfo hints;
+	struct addrinfo *res;
+
+	memset(&hints, 0, sizeof hints);
+	hints.ai_family = AF_UNSPEC;	 // IPv4 or IPv6
+	hints.ai_socktype = SOCK_STREAM; // TCP
+	hints.ai_flags = AI_PASSIVE;	 // fill in IP for me
+
+	int status = getaddrinfo(NULL, service, &hints, &res);
+	if (status != 0) {
+		fprintf(stderr, RED "getaddrinfo() error: %s\n" RESET,
+			gai_strerror(status));
+		exit(1);
+	}
+
+	freeaddrinfo(res);
+}

src/utils.c

@@ -0,0 +1,40 @@
+#include "utils.h"
+#include "colors.h"
+
+void print_ips(const char *hostname, const char *port) {
+	struct addrinfo ai;
+	struct addrinfo *res;
+
+	memset(&ai, 0, sizeof ai);
+
+	ai.ai_family = AF_UNSPEC;
+	ai.ai_socktype = SOCK_STREAM;
+
+	int status = getaddrinfo(hostname, port, &ai, &res);
+	if (status < 0) {
+		fprintf(stderr, RED "getaddrinfo(): %s\n" RESET,
+			gai_strerror(status));
+		exit(1);
+	}
+
+	char ipv4[INET_ADDRSTRLEN];
+	char ipv6[INET6_ADDRSTRLEN];
+
+	for (struct addrinfo *p = res; p != NULL; p = p->ai_next) {
+		if (p->ai_family == AF_INET) {
+			struct sockaddr_in *sin =
+			    (struct sockaddr_in *)p->ai_addr;
+			inet_ntop(AF_INET, &sin->sin_addr, ipv4,
+				  INET_ADDRSTRLEN);
+			fprintf(stdout, BLUE "%s\n" RESET, ipv4);
+		} else if (p->ai_family == AF_INET6) {
+			struct sockaddr_in6 *sin6 =
+			    (struct sockaddr_in6 *)p->ai_addr;
+			inet_ntop(AF_INET6, &sin6->sin6_addr, ipv6,
+				  INET6_ADDRSTRLEN);
+			fprintf(stdout, BLUE "%s\n" RESET, ipv6);
+		}
+	}
+
+	freeaddrinfo(res);
+}