NNTP ( Network News Transfer Protocol )

• Server-to-server exchanges
  In the server-to-server exchange, one server either requests the latest articles from another server (pull) or allows the other server to push new articles to it. In either case, both servers engage in a conversation in which specific newsgroup information is requested and then delivered. A primary goal is to prevent the sending system from sending articles that the receiver already has. Select newsgroups and articles can be blocked.



• User-to-server connections
  Users run news readers, which are now included with most Web browsers. The user first connects with a newsgroup server (usually located at an ISP (Internet service provider), then downloads a list of available newsgroups. The user can then subscribe to a newsgroup and begin reading articles available in that group or post new articles.
  Before NNCP, USENET servers used UUCP (UNIX-to-UNIX Copy Program) to exchange information. UUCP is a "flood broadcast" mechanism. Hosts send new news articles they receive to other hosts, which in turn forward the news on to other hosts that they feed. Usually, a host receives duplicates of articles and must discard those duplicates-a time-consuming process and waste of bandwidth.

NNTP commands


Command	Description
ARTICLE	There are two forms to the ARTICLE command (and the related BODY, HEAD, and STAT commands), each using a different method of specifying which article is to be retrieved.
AUTHINFO	AUTHINFO is used to inform a server about the identity of a user of the server.
CHECK	CHECK is used by a peer to discover if the article with the specified message-id should be sent to the server using the TAKETHIS command.
DATE	The first NNTP working group discussed and proposed a syntax for this command to help clients find out the current time from the servers perspective.
GROUP	The successful selection response will return the article numbers of the first and last articles in the group, and an estimate of the number of articles on file in the group.
HELP	Provides a short summary of commands that are understood by this implementation of the server.
IHAVE	The IHAVE command informs the server that the client has an article whose id is .
LIST	Returns a list of valid newsgroups and associated information.
LISTGROUP	The LISTGROUP command is used to get a listing of all the article numbers in a particular news group.
MODE READER	MODE READER is used by the client to indicate to the server that it is a news reading client.
MODE STREAM	MODE STREAM is used by a peer to indicate to the server that it would like to suspend the lock step conversational nature of NNTP and send commands in streams.
NEWGROUPS	A list of newsgroups created since will be listed in the same format as the LIST command.
NEWNEWS	A list of message-ids of articles posted or received to the specified newsgroup since "date" will be listed.
NEXT	The internally maintained "current article pointer" is advanced to the next article in the current newsgroup.
POST	After the articles header and body have been completely sent by the client to the server, a further response code will be returned to indicate success or failure of the posting attempt.
QUIT	The server process acknowledges the QUIT command and then closes the connection to the client.
SLAVE	Indicates to the server that this client connection is to a slave server, rather than a user.
TAKETHIS	TAKETHIS is used to send articles to a server when in streaming mode.
XGTITLE	The XGTITLE command is used to retrieve news group descriptions for specific news groups.
XHDR	The XHDR command is used to retrieve specific headers from specific articles.
XINDEX	The XINDEX command is used to retrieve an index file in the format of originally created for use by the TIN [6] news reader.
XOVER	The XOVER command returns information from the overview database for the article(s) specified.
XPAT	The XPAT command is used to retrieve specific headers from specific articles, based on pattern matching on the contents of the header.
XPATH	The XPATH command is used to determine the filenames in which an article is filed. It first appeared in INN.
XREPLIC	The XREPLIC command makes is possible to exactly duplicate the news spool structure of one server in another server.
XROVER	The XROVER command returns reference information from the overview database for the article(s) specified.
XTHREAD	The XTHREAD command is used to retrieve threading information in format of originally created for use by the TRN news reader.

• Text Responses
  Text is sent only after a numeric status response line has been sent that indicates that text will follow. Text is sent as a series of successive lines of textual matter, each terminated with CR-LF pair. A single line containing only a period (.) is sent to indicate the end of the text (i.e., the server will send a CR-LF pair at the end of the last line of text, a period, and another CR-LF pair).



• Status Responses
  These are status reports from the server and indicate the response to the last command received from the client.
  Status response lines begin with a 3 digit numeric code which is sufficient to distinguish all responses. Some of these may herald the subsequent transmission of text.
  
  The first digit of the response broadly indicates the success, failure, or progress of the previous command.



NNTP Reply Code


Code	Description
1yz	Informative message.
2yz	Command ok.
3yz	Command ok so far, send the rest of it.
4yz	Command was correct, but couldn't be performed for some reason.
5yz	Command unimplemented, or incorrect, or a serious program error occurred.
x0z	Connection, setup, and miscellaneous messages.
x1z	Newsgroup selection.
x2z	Article selection.
x3z	Distribution functions.
x4z	Posting.
x8z	Nonstandard (private implementation) extensions.
x9z	Debugging output.




• General Responses
  The following is a list of general response codes that may be sent by the NNTP server. These are not specific to any one command, but may be returned as the result of a connection, a failure, or some unusual condition.
  
  In general, 1xx codes may be ignored or displayed as desired; code 200 or 201 is sent upon initial connection to the NNTP server depending upon posting permission; code 400 will be sent when the NNTP server discontinues service (by operator request, for example); and 5xx codes indicate that the command could not be performed for some unusual reason.



NNTP Reply Codes


Code	Description
100	Help text follows.
199	Debug output.
200	Server ready - posting allowed.
201	Server ready - no posting allowed.
202	Slave status noted.
205	Closing connection - goodbye!
211	n f l s group selected.
215	List of newsgroups follows.
220	n article retrieved - head and body follow 221 n article retrieved - head follows.
222	n article retrieved - body follows.
223	n article retrieved - request text separately 230 list of new articles by message-id follows.
231	List of new newsgroups follows.
235	Article transferred ok.
240	Article posted ok.
335	Send article to be transferred. End with ..
340	Send article to be posted. End with ..
400	Service discontinued.
411	No such news group.
412	No newsgroup has been selected.
420	No current article has been selected.
421	No next article in this group.
422	No previous article in this group.
423	No such article number in this group.
430	No such article found.
435	Article not wanted - do not send it.
436	Transfer failed - try again later.
437	Article rejected - do not try again.
440	Posting not allowed.
441	Posting failed.
500	Command not recognized.
501	Command syntax error.
502	Access restriction or permission denied.
503	Program fault - command not performed.

Example 1: relative access with NEXT



          S:      (listens at TCP port 119)



          C:      (requests connection on TCP port 119)

          S:      200 wombatvax news server ready - posting ok



          (client asks for a current newsgroup list)

          C:      LIST

          S:      215 list of newsgroups follows

          S:      net.wombats 00543 00501 y

          S:      net.unix-wizards 10125 10011 y

                  (more information here)

          S:      net.idiots 00100 00001 n

          S:      .



          (client selects a newsgroup)

          C:      GROUP net.unix-wizards

          S:      211 104 10011 10125 net.unix-wizards group selected

                  (there are 104 articles on file, from 10011 to 10125)



          (client selects an article to read)

          C:      STAT 10110

          S:      223 10110 <23445@sdcsvax.ARPA> article retrieved - statistics

                  only (article 10110 selected, its message-id is

                  <23445@sdcsvax.ARPA>)



          (client examines the header)

          C:      HEAD

          S:      221 10110 <23445@sdcsvax.ARPA> article retrieved - head

                  follows (text of the header appears here)

          S:      .



          (client wants to see the text body of the article)

          C:      BODY

          S:      222 10110 <23445@sdcsvax.ARPA> article retrieved - body

                  follows (body text here)

          S:      .



          (client selects next article in group)

          C:      NEXT

          S:      223 10113 <21495@nudebch.uucp> article retrieved - statistics

                  only (article 10113 was next in group)



          (client finishes session)

          C:      QUIT

          S:      205 goodbye.

Example 2: absolute article access with ARTICLE



          S:      (listens at TCP port 119)



          C:      (requests connection on TCP port 119)

          S:      201 UCB-VAX netnews server ready -- no posting allowed



          C:      GROUP msgs

          S:      211 103 402 504 msgs Your new group is msgs

                  (there are 103 articles, from 402 to 504)



          C:      ARTICLE 401

          S:      423 No such article in this newsgroup



          C:      ARTICLE 402

          S:      220 402 <4105@ucbvax.ARPA> Article retrieved, text follows

          S:      (article header and body follow)

          S:      .



          C:      HEAD 403

          S:      221 403 <3108@mcvax.UUCP> Article retrieved, header follows

          S:      (article header follows)

          S:      .



          C:      QUIT

          S:      205 UCB-VAX news server closing connection.  Goodbye.

Example 3: NEWGROUPS command



          S:      (listens at TCP port 119)



          C:      (requests connection on TCP port 119)

          S:      200 Imaginary Institute News Server ready (posting ok)



          (client asks for new newsgroups since April 3, 1985)

          C:      NEWGROUPS 850403 020000



          S:      231 New newsgroups since 03/04/85 02:00:00 follow

          S:      net.music.gdead

          S:      net.games.sources

          S:      .



          C:      GROUP net.music.gdead

          S:      211 0 1 1 net.music.gdead Newsgroup selected

                  (there are no articles in that newsgroup, and

                  the first and last article numbers should be ignored)



          C:      QUIT

          S:      205 Imaginary Institute news server ceasing service.  Bye!

Example 4: posting a news article



          S:      (listens at TCP port 119)



          C:      (requests connection on TCP port 119)

          S:      200 BANZAIVAX news server ready, posting allowed.



          C:      POST

          S:      340 Continue posting; Period on a line by itself to end

          C:      (transmits news article in RFC850 format)

          C:      .

          S:      240 Article posted successfully.



          C:      QUIT

          S:      205 BANZAIVAX closing connection.  Goodbye.

Example 5: interruption due to operator request



          S:      (listens at TCP port 119)



          C:      (requests connection on TCP port 119)

          S:      201 genericvax news server ready, no posting allowed.



                  (assume normal conversation for some time, and

                  that a newsgroup has been selected)



          C:      NEXT

          S:      223 1013 <5734@mcvax.UUCP> Article retrieved; text separate.



          C:      HEAD

          C:      221 1013 <5734@mcvax.UUCP> Article retrieved; head follows.



          S:      (sends head of article, but halfway through is

                  interrupted by an operator request.  The following

                  then occurs, without client intervention.)

          S:      (ends current line with a CR-LF pair)

          S:      .

          S:      400 Connection closed by operator.  Goodbye.

          S:      (closes connection)

Example 6: Using the news server to distribute news between systems.



          S:      (listens at TCP port 119)



          C:      (requests connection on TCP port 119)

          S:      201 Foobar NNTP server ready (no posting)



          (client asks for new newsgroups since 2 am, May 15, 1985)

          C:      NEWGROUPS 850515 020000

          S:      235 New newsgroups since 850515 follow

          S:      net.fluff

          S:      net.lint

          S:      .



          (client asks for new news articles since 2 am, May 15, 1985)

          C:      NEWNEWS * 850515 020000

          S:      230 New news since 850515 020000 follows

          S:      <1772@foo.UUCP>

          S:      <87623@baz.UUCP>

          S:      <17872@GOLD.CSNET>

          S:      .



          (client asks for article <1772@foo.UUCP>)

          C:      ARTICLE <1772@foo.UUCP>

          S:      220 <1772@foo.UUCP> All of article follows

          S:      (sends entire message)

          S:      .



          (client asks for article <87623@baz.UUCP>

          C:      ARTICLE <87623@baz.UUCP>

          S:      220 <87623@baz.UUCP> All of article follows

          S:      (sends entire message)

          S:      .



          (client asks for article <17872@GOLD.CSNET>

          C:      ARTICLE <17872@GOLD.CSNET>

          S:      220 <17872@GOLD.CSNET> All of article follows

          S:      (sends entire message)

          S:      .

          (client offers an article it has received recently)

          C:      IHAVE <4105@ucbvax.ARPA>

          S:      435 Already seen that one, where you been?



          (client offers another article)

          C:      IHAVE <4106@ucbvax.ARPA>

          S:      335 News to me!   to end.

          C:      (sends article)

          C:      .

          S:      235 Article transferred successfully.  Thanks.



          (or)



          S:      436 Transfer failed.



          (client is all through with the session)

          C:      QUIT

          S:      205 Foobar NNTP server bids you farewell.

■ Parent layer
■ Child layer

TCP

NNTP