Doc note re 9999 days & 32bit time (SSL certs)

[exim.git] / doc / doc-docbook / spec.xfpt

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index d86f767ad9a2e3b328da8c6bc4c3708b50fd15f7..140d8f993b83bfab94e29093aed65ee85c4175a6 100644 (file)
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -16333,7 +16333,7 @@ router is skipped, and the address is offered to the next one.
 If the result is any other value, the router is run (as this is the last
 precondition to be evaluated, all the other preconditions must be true).
 
-This option is unique in that multiple &%condition%& options may be present.
+This option is unusual in that multiple &%condition%& options may be present.
 All &%condition%& options must succeed.
 
 The &%condition%& option provides a means of applying custom conditions to the
@@ -16532,6 +16532,9 @@ The &%headers_add%& option is expanded after &%errors_to%&, but before
 the expansion is forced to fail, the option has no effect. Other expansion
 failures are treated as configuration errors.
 
+Unlike most options, &%headers_add%& can be specified multiple times
+for a router; all listed headers are added.
+
 &*Warning 1*&: The &%headers_add%& option cannot be used for a &(redirect)&
 router that has the &%one_time%& option set.
 
@@ -16565,6 +16568,9 @@ The &%headers_remove%& option is expanded after &%errors_to%& and
 the option has no effect. Other expansion failures are treated as configuration
 errors.
 
+Unlike most options, &%headers_remove%& can be specified multiple times
+for a router; all listed headers are removed.
+
 &*Warning 1*&: The &%headers_remove%& option cannot be used for a &(redirect)&
 router that has the &%one_time%& option set.
 
@@ -19568,6 +19574,9 @@ routers. If the result of the expansion is an empty string, or if the expansion
 is forced to fail, no action is taken. Other expansion failures are treated as
 errors and cause the delivery to be deferred.
 
+Unlike most options, &%headers_add%& can be specified multiple times
+for a transport; all listed headers are added.
+
 
 
 .option headers_only transports boolean false
@@ -19590,6 +19599,9 @@ routers. If the result of the expansion is an empty string, or if the expansion
 is forced to fail, no action is taken. Other expansion failures are treated as
 errors and cause the delivery to be deferred.
 
+Unlike most options, &%headers_remove%& can be specified multiple times
+for a router; all listed headers are added.
+
 
 
 .option headers_rewrite transports string unset
@@ -25854,6 +25866,8 @@ install if the receiving end is a client MUA that can interact with a user.
 .cindex "certificate" "self-signed"
 You can create a self-signed certificate using the &'req'& command provided
 with OpenSSL, like this:
+. ==== Do not shorten the duration here without reading and considering
+. ==== the text below.  Please leave it at 9999 days.
 .code
 openssl req -x509 -newkey rsa:1024 -keyout file1 -out file2 \
             -days 9999 -nodes
@@ -25866,6 +25880,22 @@ that you are prompted for, and any use that is made of the key causes more
 prompting for the passphrase. This is not helpful if you are going to use
 this certificate and key in an MTA, where prompting is not possible.
 
+. ==== I expect to still be working 26 years from now.  The less technical
+. ==== debt I create, in terms of storing up trouble for my later years, the
+. ==== happier I will be then.  We really have reached the point where we
+. ==== should start, at the very least, provoking thought and making folks
+. ==== pause before proceeding, instead of leaving all the fixes until two
+. ==== years before 2^31 seconds after the 1970 Unix epoch.
+. ==== -pdp, 2012
+NB: we are now past the point where 9999 days takes us past the 32-bit Unix
+epoch.  If your system uses unsigned time_t (most do) and is 32-bit, then
+the above command might produce a date in the past.  Think carefully about
+the lifetime of the systems you're deploying, and either reduce the duration
+of the certificate or reconsider your platform deployment.  (At time of
+writing, reducing the duration is the most likely choice, but the inexorable
+progression of time takes us steadily towards an era where this will not
+be a sensible resolution).
+
 A self-signed certificate made in this way is sufficient for testing, and
 may be adequate for all your requirements if you are mainly interested in
 encrypting transfers, and not in secure identification.
@@ -31481,6 +31511,10 @@ headers_add = X-added-header: added by $primary_hostname\n\
 .endd
 Exim does not check the syntax of these added header lines.
 
+Multiple &%headers_add%& options for a single router or transport can be
+specified; the values will be concatenated (with a separating newline
+added) before expansion.
+
 The result of expanding &%headers_remove%& must consist of a colon-separated
 list of header names. This is confusing, because header names themselves are
 often terminated by colons. In this case, the colons are the list separators,
@@ -31488,6 +31522,11 @@ not part of the names. For example:
 .code
 headers_remove = return-receipt-to:acknowledge-to
 .endd
+
+Multiple &%headers_remove%& options for a single router or transport can be
+specified; the values will be concatenated (with a separating colon
+added) before expansion.
+
 When &%headers_add%& or &%headers_remove%& is specified on a router, its value
 is expanded at routing time, and then associated with all addresses that are
 accepted by that router, and also with any new addresses that it generates. If