Make the role in relations optional, with a test to make sure it is. Also start moving the errors reading the xml to exceptions, thus making it possible to give meaningful error messages, when bad xml is sent (More work is required on this including doing the same for nodes and ways). With the latest gems update it seems that the lib xml handling was broken, using the newer method. Adding the content type for the exceptions.

lib/osm.rb

@@ -11,35 +11,39 @@ module OSM
   # The base class for API Errors.
   class APIError < RuntimeError
     def render_opts
-      { :text => "", :status => :internal_server_error }
+      { :text => "Generic API Error", :status => :internal_server_error, :content_type => "text/plain" }
     end
   end
 
   # Raised when an API object is not found.
   class APINotFoundError < APIError
     def render_opts
-      { :nothing => true, :status => :not_found }
+      { :text => "The API wasn't found", :status => :not_found, :content_type => "text/plain" }
     end
   end
 
   # Raised when a precondition to an API action fails sanity check.
   class APIPreconditionFailedError < APIError
+    def initialize(message = "")
+      @message = message
+    end
+    
     def render_opts
-      { :text => "", :status => :precondition_failed }
+      { :text => "Precondition failed: #{@message}", :status => :precondition_failed, :content_type => "text/plain" }
     end
   end
 
   # Raised when to delete an already-deleted object.
   class APIAlreadyDeletedError < APIError
     def render_opts
-      { :text => "", :status => :gone }
+      { :text => "The object has already been deleted", :status => :gone, :content_type => "text/plain" }
     end
   end
 
   # Raised when the user logged in isn't the same as the changeset
   class APIUserChangesetMismatchError < APIError
     def render_opts
-      { :text => "The user doesn't own that changeset", :status => :conflict }
+      { :text => "The user doesn't own that changeset", :status => :conflict, :content_type => "text/plain" }
     end
   end
 
@@ -52,14 +56,14 @@ module OSM
     attr_reader :changeset
     
     def render_opts
-      { :text => "The changeset #{@changeset.id} was closed at #{@changeset.closed_at}.", :status => :conflict }
+      { :text => "The changeset #{@changeset.id} was closed at #{@changeset.closed_at}.", :status => :conflict, :content_type => "text/plain" }
     end
   end
   
   # Raised when a change is expecting a changeset, but the changeset doesn't exist
   class APIChangesetMissingError < APIError
     def render_opts
-      { :text => "You need to supply a changeset to be able to make a change", :status => :conflict }
+      { :text => "You need to supply a changeset to be able to make a change", :status => :conflict, :content_type => "text/plain" }
     end
   end
 
@@ -72,7 +76,7 @@ module OSM
     
     def render_opts
       { :text => "Changeset mismatch: Provided #{@provided} but only " +
-        "#{@allowed} is allowed.", :status => :conflict }
+      "#{@allowed} is allowed.", :status => :conflict, :content_type => "text/plain" }
     end
   end
   
@@ -85,20 +89,20 @@ module OSM
     
     def render_opts
       { :text => "Unknown action #{@provided}, choices are create, modify, delete.",
-      :status => :bad_request }
+      :status => :bad_request, :content_type => "text/plain" }
     end
   end
 
   # Raised when bad XML is encountered which stops things parsing as
   # they should.
   class APIBadXMLError < APIError
-    def initialize(model, xml)
-      @model, @xml = model, xml
+    def initialize(model, xml, message="")
+      @model, @xml, @message = model, xml, message
     end
 
     def render_opts
-      { :text => "Cannot parse valid #{@model} from xml string #{@xml}",
-        :status => :bad_request }
+      { :text => "Cannot parse valid #{@model} from xml string #{@xml}. #{@message}",
+      :status => :bad_request, :content_type => "text/plain" }
     end
   end
 
@@ -113,7 +117,7 @@ module OSM
     def render_opts
       { :text => "Version mismatch: Provided " + provided.to_s +
         ", server had: " + latest.to_s + " of " + type + " " + id.to_s, 
-        :status => :conflict }
+        :status => :conflict, :content_type => "text/plain" }
     end
   end
 
@@ -128,7 +132,7 @@ module OSM
 
     def render_opts
       { :text => "Element #{@type}/#{@id} has duplicate tags with key #{@tag_key}.",
-        :status => :bad_request }
+        :status => :bad_request, :content_type => "text/plain" }
     end
   end
   
@@ -143,7 +147,7 @@ module OSM
     
     def render_opts
       { :text => "You tried to add #{provided} nodes to the way, however only #{max} are allowed",
-      :status => :bad_request }
+        :status => :bad_request, :content_type => "text/plain" }
     end
   end
 
@@ -155,7 +159,7 @@ module OSM
     end
 
     def render_opts
-      { :text => message, :mime_type => "text/plain", :status => :bad_request }
+      { :text => @message, :content_type => "text/plain", :status => :bad_request }
     end
   end