feat(prepa): add pseudo-code for v1-v4

TP-AIPS-2024-ALNET-Paul-preparation-v1-v4.md

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+Use `shift + K` in vim/nvim to open the man page of function undor cursor.
+
+# tsock_v1 pseudo-code : UDP only
+
+```
+parse and validate arguments.
+fail if requests TCP
+
+if source:
+  build local socket -> socket()
+  build and resolve destination address -> gethostbyname()
+  for loop:
+      construire_message()
+      send datagrams -> sendto()
+  exit()
+else:    # puit
+  build local socket -> socket()
+  build address -> INADDR_ANY
+  bind socket to address -> bind()
+  while True:   # receive unlimited messages
+    receive datagram -> recvfrom()
+    afficher_message()
+```
+  
+# tsock_v2 pseudo-code : UDP/TCP
+
+```
+parse and validate arguments.
+
+if source:
+  build local socket -> socket()
+  build and resolve destination address -> gethostbyname()
+  if TCP:
+    open connection to receiver -> connect()
+    for loop:
+      construire_message()
+      send message -> send()
+    close connection -> close()
+  else:  # UDP
+    same as in v1
+  exit()
+else:    # puit
+  build local socket -> socket()
+  build address -> INADDR_ANY
+  bind socket to address -> bind()
+  if TCP :
+    set incoming connection queue size -> listen()
+    while True:   # receive unlimited connections (one at a time)
+      accept an incoming connection -> accept()
+      while connection open and new message:
+        read incoming stream -> read()
+        afficher_message()
+      # connection closed by emitter
+  else :
+    same as in v1
+```
+
+**EDIT** : Turns out v3/v4 pseudocode isn't required. For your viewing pleasure.
+
+# tsock_v3 pseudo-code : UDP/TCP with custom length & number of messages
+
+Pretty much the same as tsock_v2 but buffer sizes are dynamically allocated (implies changes
+in parameters to read/write functions). Also changes the number of iterations in the for loops.
+
+# tsock_v4 pseudo-code : Standalone server
+
+UDP implies on the client listener side sending a hello packet to server to request data. how to know last packet ?
+
+TODO
+
+```
+parse and validate arguments.
+
+void send_messages():
+  for loop:
+    construire_message()
+    send message -> send()
+
+if client:
+  build local socket -> socket()
+  build and resolve destination address -> gethostbyname()
+  if TCP:
+    open connection to server -> connect()
+    if emitter:
+      send_messages()
+      close()
+    else:  # receiver
+      while connection open:
+        read()
+        afficher_message()
+  if UDP:
+    if emitter:
+      send_messages()
+    else:
+      send datagram to request data -> send()
+      while True: # exit condition ??
+        read()
+        afficher_message()
+
+else:  # server
+  build local socket -> socket()
+  build address -> INADDR_ANY
+  bind socket to address -> bind()
+  if TCP:
+    while True:
+      accept() produces new connection socket
+      fork() 
+      close(listening socket) on child
+      close(new connection socket) on parent
+      # within child process
+      if emitter:
+        send_messages()
+        close()
+      else:  # receiver
+        while connection open:
+          read()
+          afficher_message()
+      exit() on child
+  else:  # UDP
+    if emitter:
+      while read():  # receive request datagram
+        fork()
+        # on child
+        build socket if required
+        send_messages()
+    else:  # receiver
+      while True:
+        read()
+        afficher_message()
+```
+
+When as a TCP server, we may want to reap the dead children processes using waitpid() and errno.