Ignore incompatible YAML data.

README.md

@@ -111,19 +111,24 @@ equivalent using `HTTP::Cookie`:
         # after
         jar.save(file)
 
-`HTTP::Cookie` and `CookieJar` raises runtime errors to help
-migration, so try running your test code once to find out how to fix
-your code base.
+`HTTP::Cookie`/`CookieJar` raise runtime errors to help migration, so
+after replacing the class names, try running your test code once to
+find out how to fix your code base.
 
-The YAML serialization format has changed.  Loading YAML files
-generated by `Mechanize::CookieJar#save_as` will not raise an
-exception, but the content is simply ignored.  Note that there is
-(obviously) no forward compatibillity in the YAML serialization.
+### File formats
+
+The YAML serialization format has changed, and `HTTP::CookieJar#load`
+cannot import what is written in a YAML file saved by
+`Mechanize::CookieJar#save_as`.  `HTTP::CookieJar#load` will not raise
+an exception if an incompatible YAML file is given, but the content is
+silently ignored.
+
+Note that there is (obviously) no forward compatibillity with this.
 Trying to load a YAML file saved by `HTTP::CookieJar` with
-`Mechanize::CookieJar` will fail in `ArgumentError`.
+`Mechanize::CookieJar` will fail in runtime error.
 
 On the other hand, there has been (and will ever be) no change in the
-cookies.txt format.
+cookies.txt format, so use it instead if compatibility is required.
 
 ## Contributing
 

lib/http/cookie_jar/yaml_saver.rb

@@ -13,11 +13,18 @@ class HTTP::CookieJar::YAMLSaver < HTTP::CookieJar::AbstractSaver
 
   def load(io, jar)
     begin
-      YAML.load(io)
+      data = YAML.load(io)
     rescue ArgumentError
+      @logger.warn "unloadable YAML cookie data discarded" if @logger
+      return
+    end
+
+    unless data.instance_of?(Array)
       @logger.warn "incompatible YAML cookie data discarded" if @logger
       return
-    end.each { |cookie|
+    end
+
+    data.each { |cookie|
       jar.add(cookie)
     }
   end