+.new
+Historical note: We have &%condition%& on ACLs and on Routers. Routers
+are far older, and use one set of semantics. ACLs are newer and when
+they were created, the ACL &%condition%& process was given far stricter
+parse semantics. The &%bool{}&% expansion condition uses the same rules as
+ACLs. The &%bool_lax{}%& expansion condition uses the same rules as
+Routers. More pointedly, the &%bool_lax{}%& was written to match the existing
+Router rules processing behavior.
+
+This is best illustrated in an example:
+.code
+# If used in an ACL condition will fail with a syntax error, but
+# in a router condition any extra characters are treated as a string
+
+$ exim -be '${if eq {${lc:GOOGLE.com}} {google.com}} {yes} {no}}'
+true {yes} {no}}
+
+$ exim -be '${if eq {${lc:WHOIS.com}} {google.com}} {yes} {no}}'
+ {yes} {no}}
+.endd
+In each example above, the &%if%& statement actually ends after
+&"{google.com}}"&. Since no true or false braces were defined, the
+default &%if%& behavior is to return a boolean true or a null answer
+(which evaluates to false). The rest of the line is then treated as a
+string. So the first example resulted in the boolean answer &"true"&
+with the string &" {yes} {no}}"& appended to it. The second example
+resulted in the null output (indicating false) with the string
+&" {yes} {no}}"& appended to it.
+
+In fact you can put excess forward braces in too. In the router
+&%condition%&, Exim's parser only looks for &"{"& symbols when they
+mean something, like after a &"$"& or when required as part of a
+conditional. But otherwise &"{"& and &"}"& are treated as ordinary
+string characters.
+
+Thus, in a Router, the above expansion strings will both always evaluate
+true, as the result of expansion is a non-empty string which doesn't
+match an explicit false value. This can be tricky to debug. By
+contrast, in an ACL either of those strings will always result in an
+expansion error because the result doesn't look sufficiently boolean.
+.wen
+
git://git.exim.org / exim.git / blobdiff