usefor-article-04 April 2001
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8.8. Duties of a Gateway
A Gateway transforms an article into the native message format of
another medium, or translates the messages of another medium into
news articles. Encapsulation of a news article into a message of MIME
type application/news-transmission, or the subsequent undoing of that
encapsulation, is not gatewaying, since it involves no transformation
of the article.
There are two basic types of gateway, the Outgoing Gateway that
transforms a news article into a different type of message, and the
Incoming Gateway that transforms a message from another medium into a
news article and injects it into a Netnews system. These are handled
separately below.
The primary dictat for a gateway is:
Above all, prevent loops.
Transformation of an article into another medium stands a very high
chance of discarding or interfering with the protection inherent in
the news system against duplicate articles. The most common problem
caused by gateways is "spews," gateway loops that cause previously
posted articles to be reinjected repeatedly into Usenet. To prevent
this, a gateway MUST take precautions against loops, as detailed
below.
If bidirectional gatewaying (both an incoming and an outgoing
gateway) is being set up between Netnews and some other medium, the
incoming and outgoing gateways SHOULD be coordinated to avoid
reinjection of gated articles. Circular gatewaying (gatewaying a
message into another medium and then back into Netnews) SHOULD NOT be
done; encapsulation of the article SHOULD be used instead where this
is necessary.
A second general principal of gatewaying is that the transformations
applied to the message SHOULD be as minimal as possible while still
accomplishing the gatewaying. Every change made by a gateway
potentially breaks a property of one of the media or loses
information, and therefore only those transformations made necessary
by the differences between the media should be applied.
It is worth noting that safe bidirectional gatewaying between a
mailing list and a newsgroup is far easier if the newsgroup is
moderated. Posts to the moderated group and submissions to the
mailing list can then go through a single point that does the
necessary gatewaying and then sends the message out to both the
newsgroup and the mailing list at the same time, eliminating most of
the possibility of loops. Bidirectional gatewaying between a mailing
list and an unmoderated newsgroup, in contrast, is difficult to do
correctly and is far more fragile.
Newsgroups intended to be bidirectionally gated to a mailing list
SHOULD therefore be moderated where possible, even if the moderator
is a simple gateway and injecting agent that correctly handles
crossposting to other moderated groups and otherwise passes all
traffic.
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#Diff to first older
--- ../usefor-article-03/Duties_of_a_Gateway.out February 2000
+++ ../usefor-article-04/Duties_of_a_Gateway.out April 2001
@@ -1,6 +1,57 @@
-8.7. Duties of a Gateway
+8.8. Duties of a Gateway
- NOT DONE
-[Volunteers to write it? There is lots of useful material in [Son-of-
-1036].]
+ A Gateway transforms an article into the native message format of
+ another medium, or translates the messages of another medium into
+ news articles. Encapsulation of a news article into a message of MIME
+ type application/news-transmission, or the subsequent undoing of that
+ encapsulation, is not gatewaying, since it involves no transformation
+ of the article.
+ There are two basic types of gateway, the Outgoing Gateway that
+ transforms a news article into a different type of message, and the
+ Incoming Gateway that transforms a message from another medium into a
+ news article and injects it into a Netnews system. These are handled
+ separately below.
+
+ The primary dictat for a gateway is:
+
+ Above all, prevent loops.
+
+ Transformation of an article into another medium stands a very high
+ chance of discarding or interfering with the protection inherent in
+ the news system against duplicate articles. The most common problem
+ caused by gateways is "spews," gateway loops that cause previously
+ posted articles to be reinjected repeatedly into Usenet. To prevent
+ this, a gateway MUST take precautions against loops, as detailed
+ below.
+
+ If bidirectional gatewaying (both an incoming and an outgoing
+ gateway) is being set up between Netnews and some other medium, the
+ incoming and outgoing gateways SHOULD be coordinated to avoid
+ reinjection of gated articles. Circular gatewaying (gatewaying a
+ message into another medium and then back into Netnews) SHOULD NOT be
+ done; encapsulation of the article SHOULD be used instead where this
+ is necessary.
+
+ A second general principal of gatewaying is that the transformations
+ applied to the message SHOULD be as minimal as possible while still
+ accomplishing the gatewaying. Every change made by a gateway
+ potentially breaks a property of one of the media or loses
+ information, and therefore only those transformations made necessary
+ by the differences between the media should be applied.
+
+ It is worth noting that safe bidirectional gatewaying between a
+ mailing list and a newsgroup is far easier if the newsgroup is
+ moderated. Posts to the moderated group and submissions to the
+ mailing list can then go through a single point that does the
+ necessary gatewaying and then sends the message out to both the
+ newsgroup and the mailing list at the same time, eliminating most of
+ the possibility of loops. Bidirectional gatewaying between a mailing
+ list and an unmoderated newsgroup, in contrast, is difficult to do
+ correctly and is far more fragile.
+
+ Newsgroups intended to be bidirectionally gated to a mailing list
+ SHOULD therefore be moderated where possible, even if the moderator
+ is a simple gateway and injecting agent that correctly handles
+ crossposting to other moderated groups and otherwise passes all
+ traffic.