Computer Networks and Telecommunications Programming Assignments 2 and 3

A simple chat application that consists of client and server components, which communicate via the MsgP protocol and a REST API. Both are specified below.

Test using Postman with this collection!

The basic functionality of the server is as follows:

• It maintains a non-persistent list of chat groups (groups are created on demand and are not persistent across server executions.
• It allows clients to join any of the existing groups, or create a new one implicitly by requesting to join a group that does not exist.
• Upon request, it provides to clients a list of the available groups, the current membership of the group, and the history of message sent to a particular group.
• It allows clients to send messages to individual users, a specific group, or multiple groups.

Client: java csci4311.chat.CLIUserAgent <user> <server> [<port>]

Server: java csci4311.chat.ChatServer [<port>] [<rest_port>]

The default ports (if not specified) are 4311 and 8311 (REST API).

The agent shows a prompt of the form @[user]>>, e.g., @alice >>.

Messages received are displayed in the form [<sender>] <message>.

The user agent reads all user input from the standard input stream and supports the following single-line commands:

Joins the specified group and reports current number of members.

Example:

join 4311
Joined #4311 with 3 current members.

Leaves the specified group, no output on success. Returns error if trying leave a group of which the user is not a member.

Example:

leave 4311
[bob] sorry I am late
[3/5]
leave 4311
Not a member of #4311.

List the currently available groups and the number of members. No output if no groups.

Example:

groups
#4311 has 12 members
#5311 has 3 members
#test has 0 members

Lists group membership. Error if no such group, no output if no members.

Example:

users 4311
@alice @bob

Lists the log of messages for a particular group.

Example:

history 4311
[alice] hello
[bob] sorry I am late
[charlie] let’s get started

Sends a message to users & groups on the list.

• Error if any of the recipients do not exist.
• Individual users are prefaced by @ and groups by #.
• Messages sent to a group(s) become part of the history of all those group(s).

Example:

send @bob #4311 #5311 when is the assignment due?

All commands are in plaintext ASCII format, and they all start with the string msgp. Users and groups are alphanumeric strings of up to 32 characters.

Adds a user to a chat group.

• If the group does not yet exist, it is created (reply code 200).
• If the user is already a member, no action is required (reply 201).

Format:

msgp join <user> <group>

Example:

msgp join alice 4311

Removes a user from a chat group (200).

• If user is not a member (but the group exists) return 201.
• If the group does not exist, return 400.

Format:

msgp leave <user> <group>

Example:

msgp leave alice 4311

Enumerated the current list of groups, including empty ones (200).

• Group names are returned one per line, with a blank line marking the end of the list.
• 201 if empty result.

Format:

 msgp groups

Example response:

msgp 200 ok
csci
4311
5311
<cr><lf>

Enumerates the current list of users for a given groups (200).

• User names are returned one per line, with a blank line marking the end of the list.
• 201 if empty result, 400 if no such group exists.

Format:

msgp users <group>

Example:

msgp users 4311

Example response:

msgp 200 ok
alice
bob
<cr><lf>

Sends a message to the given list of recipients.

• Group messages becomes part of the history for that group.
• The sender is given by a from: header clause, the recipients by one, or more, to: headers.
• User names are prefaced with the @ character, whereas groups by the # character.
• Returns 200 upon success, 400 if any of the recipients does not exist.

Format:

msgp send
from: <user>
to: @<user>|#<group>
to: ...
<cr><lf>
<single line message>
<cr><lf>

Example:

msgp send
from: alice
to: @bob
to: #4311
<cr><lf>
hi bob!
<cr><lf>

Provides a chronological list of messages for a given group (200).

• 201 if empty result, 400 if no such group.

Format:

msgp history <group>

The format of the messages is exactly the same as in the case of send.

For example, the request:

msgp history 4311

Would yield something like:

msgp 200 OK
msgp send
from: alice
to: #4311
<cr><lf>
hello everyone!
<cr><lf>
msgp send
from: bob
to: #4311
<cr><lf>
sorry for being late!
<cr><lf>

Server always precedes its answer (if any) with one of three reply code, single-line messages:

msgp 200 OK
msgp 201 No result
msgp 400 Error

Enumerate the users currently logged in.

Reply codes:

• 200 success

Returns an array users, empty JSON object {} if none.

Example (CLI) invocation:

curl "http://<server>:<port>/users"

Response body:

{
  "users": [
    "alice",
    "bob",
    "charlie"
  ]
}

Enumerate the currently available groups.

Reply codes:

• 200 success

Returns a list (array) of available groups, empty JSON object {} if none.

Example invocation:

curl "http://<server>:<port>/groups"

Response body:

{
  "groups": [
    "4311",
    "5311"
  ]
}

Enumerate the membership of the given group.

Reply codes:

• 200 success
• 400 no such group

Returns a list (array) of users in the group, empty JSON object {} if none.

Example invocation:

curl "http://<server>:<port>/group/4311"

Response body:

{
  "users": [
    "alice",
    "bob"
  ]
}

Add a user to a group (join). If the groups does not exist, it gets created.

Reply codes:

• 200 success, user added to existing group
• 201 success, user added to a newly created group

Returns the list of current users in the group.

Example invocation:

curl –d "user=alice" "http://<server>:<port>/4311

Response body:

{
  "users": [
    "alice"
  ]
}

Remove a user from a group (leave).

Reply codes:

• 200 success;
• 400 no such group; o 401no such user.

Returns the remaining group membership.

Example invocation:

curl –X DELETE "http://<server>:<port>/group/4311/alice"

Enumerate the messages sent to the given group, or user.

Reply codes:

• 200 success;
• 400 no such group
• 401 no such user

Returns a list (array) of messages sent to the given group, or user; each returned message is an MsgP-encoded string.

Example invocations:

"http://<server>:<port>/messages/4311" —> curl "http://<server>:<port>/messages/@alice"

Response body:

{
  "messages": [
    "from: alice<cr><lf>to: #4311<cr><lf>hello everyone!<cr><lf>",
    "from: bob<cr><lf>to: #4311<cr><lf>sorry for being late!<cr><lf>"
  ]
}

Posts a new message with the given MsgP-encoded content. The server should parse the text for users and group designated by the @ and # signs, respectively.

Reply codes:

• 200 success
• 400 no such group
• 401 no such user

Returns an empty JSON object.

Example invocation:

curl --data @<message_filename> "http://<server>:<port>/message

<message_filename> contains the msgp message.