[go-while]

A news server that sends more than its reply put NewsCache's connection to it out of step. Examples are a block after a status that announces none (215 and a list in reply to GROUP, 430 and text) or the rest of an overlong line. The next command read those lines as its reply, and every later reply was shifted, so the client got 430 for an article the server has, or 403.

Fix (NServer-0.9.1/NServer.cc, RServer::issue, new RServer::stale_reply): NewsCache sends one command at a time and reads each reply to its end, so the stream buffer is empty before the next command. issue() now checks rdbuf()->in_avail() first. That counts bytes already read from the socket, from TLS or after inflating, so a compressed connection's trailing flush bytes don't count, and the check doesn't depend on timing. When anything is left, NewsCache closes the connection and connects again, and connect() selects the current group again. Inside connect() the set-up fails instead, and the caller retries as for a lost connection.

Test (tests/e2e/replycorpus_test.go, TestUpstreamReplyCorpus): runs the 82 cases of nntp-testkit v0.14.0's reply corpus whose command NewsCache sends upstream: the greeting, MODE READER, AUTHINFO, COMPRESS, GROUP, LISTGROUP, OVER, ARTICLE, LIST, STAT, POST and QUIT. Each case replaces the first reply on a connection. After the client steps, a command that has to go to the server must get the right reply (an article, or the overview for the ARTICLE cases). DATE must still answer 111, and QUIT must end the session with exit 0. For a reply to a set-up command, which comes again on every connection, a clean 403 is allowed, but wrong data isn't.

• Without the fix (main ed82e37): 10 cases fail, all with a wrong or missing follow-up reply: group-215-block, group-100-block, listgroup-215-block, list-231-block, list-282-block, over-225-block, article-222-block, article-430-block, stat-220-block, authinfo-user-215-block.
• With the fix: 82/82 pass. Full e2e suite green (353 s, local build) and unit checks 22/22.

NEWS: changes/fix-upstream-stale-reply.md.

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