C-Web-Server: Kat Johnson-Fries

NOTES.MD

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+# Web Server
+
+Software that: 
+- accepts HTTP requests (e.g. GET requests for HTML pages), and 
+- returns responses (e.g. HTML pages). 
+Examples: 
+- GET requests for getting data from RESTful API endpoints, images within web pages, and 
+- POST requests to upload data to the server (e.g. a form submission or file upload).
+- PUT
+- DELETE
+- HEAD same as GET, but does not return anything in the message body. The returned metadata should be identical to info returned in a GET request.
+- ping 1.1.1.1 (Internet's fastest DNS (Domain Name System) address )
+- datatrace -n 1.1.1.1  traceroute 1.1.1.1
+
+## Networking Protocols
+Protocol: established code of procedures between client and servers handling requests and responses.
+
+Data packets are encapulated from the ground up (starting with the HTTP header and ending with the Ethernet Header)
+
+### Network Stack / Data Encapulation Hierarchy 
+|-----------------------|
+|    Ethernet Header    | Routing on the LAN        Physical/Data ling
+|  Network Access Layer |                           Access physical media
+|-----------------------|
+|  IP (Address) Header  | Routing on the Internet   How Data Is Transferred
+| Network/Internet Layer|                           Defines datagram/               
+|-----------------------|
+|   TCP Header / UDP    | Data integrity            Reliability
+|    Transport Layer    |                           End-to-end deliver
+|-----------------------|
+|      HTTP Header      | Deals with web data       Formats req & resp
+|   Application Layer   |                           
+|-----------------------|
+| <h1>Hello World!</h1> | Actual data
+|_______________________|
+
+### Ethernet
+Sends data and listens at the same time to make sure it is identical. If it isn't it means someone else is sending at the same time and the data will become corrupt. So, it wait 7.6 + random seconds and resends. If too many try sending at the same time the ethernet fails/overload (packet storm).
+
+### TCP Protocol (Transmission Control Protocol)
+- Reliable
+- Uses Three-Way Handshake
+- Breaks packet into smaller packets
+
+Client/Initiator                                    Server / Listener
+----------------------------------                  -----------------------------------------
+connect()                                           listen()
+                                   -----SYN----->   TCB initialized to SYN-RECEIVED STATE
+
+Success code returned by connect() <---SYN-ACK---
+
+                                   -----ACK----->   TCB transitions to Established State^^^
+
+                        Completion: Data packets exchanged
+
+^^^ If the ACK was never recieved the server has another set for losts packets.
+
+### UDP (User Datagram Protocol) Protocol (vs TCP)
+- Not as reliable
+- Less protocols and more lost packets
+- Ability to send significantly more packets than TCP
+- No handshake or acknowledgement
+
+
+
+## Unix Sockets
+- Higher level example of a socket is socket.io API
+- Low level sockets API is what this project will implement
+    - supports both TCP & UDP and IPv4 and IPv6
+
+### Files in Unix: "Everything in Unix is a file."
+File Descriptors (fd): Integer value associated with an open file.
+FILE *fp = fopen("text.txt", "w");
+printf("%d, fp);    // this would print an integer value
+
+File Descriptor       Global File Table             Inode Table
+---------------    -----------------------      -------------------
+0                  read-only, offset: 0
+1                  write-only, offset: 0        /dev/pts22
+2
+3                  read-write, offset: 12       /path/myfile.txt
+4                  read-write, offset: 8        /path/myfile3.txt
+
+Caveat: File can refer to:
+- network connection  (shared file)
+- pipe
+- terminal
+- actual file
+
+### Unix-Style Sockets API System Calls
+
+Client
+---------
+socket()
+connect()
+write()
+read()
+
+Server
+---------
+socket()
+bind()              net.c 79
+listen()            net.c 100
+accept()
+read()
+write()
+
+- socket() creates a new socket (the fd is stored to an int)
+- bind() bind IP address (associated with a network card)
+- send() write data
+- recv() read data
+
+
+#### Initializing a Socket
+
+```c
+#include <sys/socket.h>
+int sockfd = socket (...)   // initialize a socket (file descriptor)
+send(sockfd, response, responseLength, 0);    // 0 is a flag
+recv(sockfd, request, requestBufferSize - 1, 0); // 0 is a flag
+```
+
+P1                          P2
+   _____             ______
+fd _____ shared file ______ fd
+
+
+
+Services by Port Number
+- 7:    echo
+- 21:   ftp (File Transfer Protocol)
+- 23:   telnet (TCP connection with a server & issue raw HTTP requests)
+        telnet www.example.com 80
+- 25:   smtp (Simple Mail Transfer)
+- 80:   http / www
+- 6000: x11 (X Window System -- a unix based gui)
+
+
+
+
+## HTTP Protocol
+- HTTP responsible for formatting requests and responses between client and servers
+- HTTP does *not* handle how data is transfered.
+- HTTP does *not* hand reliability
+
+### How to Format HTTP Packets
+
+#### Format of a GET Request
+Syntax:
+HTTP Method /URL  Protocol/Version          ** /URL w/o .com
+Host: Host of target URL
+Blank line indicating the end of the Request use \n (even if there is no body a blank line is required)
+
+Example:
+GET /example HTTP/1.1
+Host: lambdaschool.com
+Connection: close
+X-Header: whatever
+
+
+GET /pub/WWW/TheProject.html HTTP/1.1
+Host: www.w3.org
+
+
+#### Format of a POST Request
+Syntax:
+POST request-URI HTTP-version
+Content-Type: mime-type
+Content-Length: number-of-bytes
+(other optional request headers)
+
+(URL-encoded query string)
+
+Example:
+POST /magazines HTTP/1.1
+Host: example.gov.au
+Accept: application/json, text/javascript
+
+#### Format of a DELETE Request
+DELETE /magazines HTTP/1.1
+Host: example.gov.au
+Accept: application/json, text/javascript
+
+#### Format of a HEAD Request
+HEAD /magazines HTTP/1.1
+Host: example.gov.au
+Accept: application/json, text/javascript
+
+### Format of a Response
+Syntax:
+Protocol/Version Status Code
+Date: Timestamp when response was created
+Connection: close     (set to open if more info will be sent)
+Content-Length: number of bytes in the body (w/o blank line)
+Content-Type: MIME (Multipurpose Internet Mail Extensions) type of the content of the body to be rendered  (text/html, text/plain, text/css, image/jpg, image/gif, image/png, application/json, application/javascript, multipart/form-data)
+
+<html><head><title>Data being sent back</title></head></html>
+
+#### Example: 200 Response
+HTTP/1.1 200 OK
+Date: Wed Dec 20 13:05:11 PST 2017
+Connection: close
+Content-Length: 12345
+Content-Type: text/html
+
+<html><head><title>Lambda</title></head></html>
+
+#### Example: 404 Response
+HTTP/1.1 404 Not Found
+Date: Wed Dec 20 13:05:11 PST 2017
+Connection: close
+Content-Length: 13
+Content-Type: text/plain
+
+404 Not Found
+
+send_response() response_length send() sprintf() strlen()  sprintf()  time() localtime() time.h
+
+
+## MISC
+
+### sscanf & spacing
+- useful for parsing incoming request from a web browser
+- sscanf is scanf for strings
+- Request and responses have specific spacing
+    - e.g.: GET /example HTTP/1.1
+            HTTP/1.1 404 Not Found
+- %20 is the ASCII Hex code for space. Used for space in URL (no additional spaces allowed)
+- JS equivalent to .split(" ")
+- C compiler will concatenate char * that are next to each other, e.g., char *s = "my" "string"
+
+```c
+#include <stdio.h>
+
+/*
+GET /foobar HTTP/1.1
+Host: www.example.com
+Connection: closecon
+X-Header: whatever
+*/
+
+int main(void)
+{
+    // s holds the HTTP request
+    char *s = "GET /foobar HTTP/1.1\nHost: www.example.com\nConnection: close\nX-Header: whatever";
+
+    char method[200];
+    char path[8192];
+
+    sscanf(s, "%s %s", method, path);
+
+    printf("method: \"%s\"\n", method);
+    printf("path: \"%s\"\n", path);
+}
+```
+
+### sprintf & Content Length
+- useful for building outgoing response to the server
+- use char *body to save body.
+- int length = strlen(body);
+- use %s
+
+```c
+#include <stdio.h>
+#include <string.h>
+​
+int main(void)
+{
+    char response[500000];
+​
+    char *body = "<h1>Hello, world!</h1>";
+    int length = strlen(body);
+​
+    sprintf(response, "HTTP/1.1 200 OK\n"
+            "Content-Type: text/html\n"
+            "Content-Length: %d\n"
+            "Connection: close\n"
+            "\n"
+            "%s",
+            length, body
+        );
+​
+    printf("%s", response); // send()
+}
+```
+
+## Cache
+
+Get Requests
+GET /index.html
+GET /index.html
+GET /style.css
+GET /foo.gif
+GET /style.css
+GET /index.html
+
+Cache(3)        Disk
+
+
+
+head               tail
+
+bar -> foo -> style
+style -> bar -> foo
+
+|||||||HASHTABLE|||||||
+index <-> style <-> bar
+
+Add a cache miss to head of list O(1)
+Remove LRU from end of list O(1)
+Remove LRU from hashtable O(1)
+
+Item in cache? O(1)

PROJECT.MD

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+Todo:
+
+* HTTP request parser
+* HTTP response builder
+* LRU cache
+  * Doubly linked list (some functionality provided)
+  * Use existing hashtable functionality (below)
+
+Already done:
+
+* `net.h` and `net.c` contain low-level networking code
+* `mime.h` and `mime.c` contains functionality for determining the MIME type of a file
+* `file.h` and `file.c` contains handy file-reading code that you may want to utilize, namely the `file_load()` and `file_free()` functions for reading file data and deallocating file data, respectively (or you could just perform these operations manually as well)
+* `hashtable.h` and `hashtable.c` contain an implementation of a hashtable (this one is a bit more complicated than what you built in the Hashtables sprint)
+* `llist.h` and `llist.c` contain an implementation of a doubly-linked list (used solely by the hashable--you don't need it)
+* `cache.h` and `cache.c` are where you will implement the LRU cache functionality for days 3 and 4
+
+
+## Start at main (in server.c)
+- Start listening for connections
+- When a connection arrives, receive the request data.
+- Parse the reqest data.
+- Build response data.
+- Send response data.
+- Close the connection and wait for the next one.
+
+handle_http_request() (in server.c)
+implement
+
+/d20() implement
+
+
+send_response() implement
+
+
+get_file() implement
+
+

src/mime.c

@@ -27,7 +27,7 @@ char *mime_type_get(char *filename)
         return DEFAULT_MIME_TYPE;
     }
 
-    ext++;
+    ext++; // move to character after . in ext names (.html)
 
     strlower(ext);