# Uses the streaming LibXML "Reader" interface to cut down on memory
# usage, so hopefully we can process fairly large diffs.
class DiffReader
- include ConsistencyValidations
-
# maps each element type to the model class which handles it
- MODELS = {
- "node" => Node,
- "way" => Way,
+ MODELS = {
+ "node" => Node,
+ "way" => Way,
"relation" => Relation
- }
+ }.freeze
##
# Construct a diff reader by giving it a bunch of XML +data+ to parse
# in OsmChange format. All diffs must be limited to a single changeset
# given in +changeset+.
def initialize(data, changeset)
- @reader = XML::Reader.new data
+ @reader = XML::Reader.string(data)
@changeset = changeset
+ # document that's (re-)used to handle elements expanded out of the
+ # diff processing stream.
+ @doc = XML::Document.new
+ @doc.root = XML::Node.new("osm")
+ end
+
+ ##
+ # Reads the next element from the XML document. Checks the return value
+ # and throws an exception if an error occurred.
+ def read_or_die
+ # NOTE: XML::Reader#read returns false for EOF and raises an
+ # exception if an error occurs.
+ @reader.read
+ rescue LibXML::XML::Error => e
+ raise OSM::APIBadXMLError.new("changeset", xml, e.message)
end
##
- # An element-block mapping for using the LibXML reader interface.
+ # An element-block mapping for using the LibXML reader interface.
#
# Since a lot of LibXML reader usage is boilerplate iteration through
# elements, it would be better to DRY and do this in a block. This
# could also help with error handling...?
def with_element
- # skip the first element, which is our opening element of the block
- @reader.read
- # loop over all elements.
- # NOTE: XML::Reader#read returns 0 for EOF and -1 for error.
- while @reader.read == 1
- break if @reader.node_type == 15 # end element
- next unless @reader.node_type == 1 # element
- yield @reader.name
+ # if the start element is empty then don't do any processing, as
+ # there won't be any child elements to process!
+ unless @reader.empty_element?
+ # read the first element
+ read_or_die
+
+ while @reader.node_type != 15 # end element
+ # because we read elements in DOM-style to reuse their DOM
+ # parsing code, we don't always read an element on each pass
+ # as the call to @reader.next in the innermost loop will take
+ # care of that for us.
+ if @reader.node_type == 1 # element
+ name = @reader.name
+ attributes = {}
+
+ if @reader.has_attributes?
+ attributes[@reader.name] = @reader.value while @reader.move_to_next_attribute == 1
+
+ @reader.move_to_element
+ end
+
+ yield name, attributes
+ else
+ read_or_die
+ end
+ end
end
+ read_or_die
end
##
- # An element-block mapping for using the LibXML reader interface.
+ # An element-block mapping for using the LibXML reader interface.
#
# Since a lot of LibXML reader usage is boilerplate iteration through
# elements, it would be better to DRY and do this in a block. This
# could also help with error handling...?
def with_model
- with_element do |model_name|
+ with_element do |model_name, _model_attributes|
model = MODELS[model_name]
- raise "Unexpected element type #{model_name}, " +
- "expected node, way, relation." if model.nil?
- yield model, @reader.expand
+ if model.nil?
+ raise OSM::APIBadUserInput, "Unexpected element type #{model_name}, " \
+ "expected node, way or relation."
+ end
+ # new in libxml-ruby >= 2, expand returns an element not associated
+ # with a document. this means that there's no encoding parameter,
+ # which means basically nothing works.
+ expanded = @reader.expand
+
+ # create a new, empty document to hold this expanded node
+ new_node = @doc.import(expanded)
+ @doc.root << new_node
+
+ yield model, new_node
@reader.next
+
+ # remove element from doc - it will be garbage collected and the
+ # rest of the document is re-used in the next iteration.
+ @doc.root.child.remove!
end
end
# such as save_ and delete_with_history.
def check(model, xml, new)
raise OSM::APIBadXMLError.new(model, xml) if new.nil?
- unless new.changeset_id == @changeset.id
- raise OSM::APIChangesetMismatchError.new(new.changeset_id, @changeset.id)
- end
+ raise OSM::APIChangesetMismatchError.new(new.changeset_id, @changeset.id) unless new.changeset_id == @changeset.id
end
##
# is *not* transactional, so code which calls it should ensure that the
# appropriate transaction block is in place.
#
- # On a failure to meet preconditions (e.g: optimistic locking fails)
+ # On a failure to meet preconditions (e.g: optimistic locking fails)
# an exception subclassing OSM::APIError will be thrown.
def commit
+ # data structure used for mapping placeholder IDs to real IDs
+ ids = { :node => {}, :way => {}, :relation => {} }
- node_ids, way_ids, rel_ids = {}, {}, {}
- ids = { :node => node_ids, :way => way_ids, :relation => rel_ids}
+ # take the first element and check that it is an osmChange element
+ @reader.read
+ raise OSM::APIBadUserInput, "Document element should be 'osmChange'." if @reader.name != "osmChange"
- result = OSM::API.new.get_xml_doc
+ result = OSM::API.new.xml_doc
result.root.name = "diffResult"
- # loop at the top level, within the <osmChange> element (although we
- # don't actually check this...)
- with_element do |action_name|
- if action_name == 'create'
+ # loop at the top level, within the <osmChange> element
+ with_element do |action_name, action_attributes|
+ case action_name
+ when "create"
# create a new element. this code is agnostic of the element type
# because all the elements support the methods that we're using.
with_model do |model, xml|
- new = model.from_xml_node(xml, true)
+ new = model.from_xml_node(xml, :create => true)
check(model, xml, new)
# when this element is saved it will get a new ID, so we save it
# to produce the mapping which is sent to other elements.
- placeholder_id = xml['id'].to_i
+ placeholder_id = xml["id"].to_i
raise OSM::APIBadXMLError.new(model, xml) if placeholder_id.nil?
+ # check if the placeholder ID has been given before and throw
+ # an exception if it has - we can't create the same element twice.
+ model_sym = model.to_s.downcase.to_sym
+ raise OSM::APIBadUserInput, "Placeholder IDs must be unique for created elements." if ids[model_sym].include? placeholder_id
+
# some elements may have placeholders for other elements in the
# diff, so we must fix these before saving the element.
- new.fix_placeholders!(ids)
+ new.fix_placeholders!(ids, placeholder_id)
# create element given user
new.create_with_history(@changeset.user)
-
+
# save placeholder => allocated ID map
- ids[model.to_s.downcase.to_sym][placeholder_id] = new.id
+ ids[model_sym][placeholder_id] = new.id
# add the result to the document we're building for return.
xml_result = XML::Node.new model.to_s.downcase
xml_result["new_version"] = new.version.to_s
result.root << xml_result
end
-
- elsif action_name == 'modify'
+
+ when "modify"
# modify an existing element. again, this code doesn't directly deal
# with types, but uses duck typing to handle them transparently.
with_model do |model, xml|
# get the new element from the XML payload
- new = model.from_xml_node(xml, false)
+ new = model.from_xml_node(xml, :create => false)
check(model, xml, new)
+ # if the ID is a placeholder then map it to the real ID
+ model_sym = model.to_s.downcase.to_sym
+ client_id = new.id
+ is_placeholder = ids[model_sym].include? client_id
+ id = is_placeholder ? ids[model_sym][client_id] : client_id
+
# and the old one from the database
- old = model.find(new.id)
+ old = model.find(id)
+ # translate any placeholder IDs to their true IDs.
new.fix_placeholders!(ids)
+ new.id = id
+
old.update_from(new, @changeset.user)
xml_result = XML::Node.new model.to_s.downcase
- xml_result["old_id"] = old.id.to_s
- xml_result["new_id"] = new.id.to_s
+ xml_result["old_id"] = client_id.to_s
+ xml_result["new_id"] = id.to_s
# version is updated in "old" through the update, so we must not
# return new.version here but old.version!
xml_result["new_version"] = old.version.to_s
result.root << xml_result
end
- elsif action_name == 'delete'
+ when "delete"
# delete action. this takes a payload in API 0.6, so we need to do
# most of the same checks that are done for the modify.
with_model do |model, xml|
- new = model.from_xml_node(xml, false)
+ # delete doesn't have to contain a full payload, according to
+ # the wiki docs, so we just extract the things we need.
+ new_id = xml["id"].to_i
+ raise OSM::APIBadXMLError.new(model, xml, "ID attribute is required") if new_id.nil?
+
+ # if the ID is a placeholder then map it to the real ID
+ model_sym = model.to_s.downcase.to_sym
+ is_placeholder = ids[model_sym].include? new_id
+ id = is_placeholder ? ids[model_sym][new_id] : new_id
+
+ # build the "new" element by modifying the existing one
+ new = model.find(id)
+ new.changeset_id = xml["changeset"].to_i
+ new.version = xml["version"].to_i
check(model, xml, new)
- old = model.find(new.id)
+ # fetch the matching old element from the DB
+ old = model.find(id)
# can a delete have placeholders under any circumstances?
# if a way is modified, then deleted is that a valid diff?
new.fix_placeholders!(ids)
- old.delete_with_history!(new, @changeset.user)
xml_result = XML::Node.new model.to_s.downcase
- xml_result["old_id"] = old.id.to_s
+ # oh, the irony... the "new" element actually contains the "old" ID
+ # a better name would have been client/server, but anyway...
+ xml_result["old_id"] = new_id.to_s
+
+ if action_attributes["if-unused"]
+ begin
+ old.delete_with_history!(new, @changeset.user)
+ rescue OSM::APIAlreadyDeletedError, OSM::APIPreconditionFailedError
+ xml_result["new_id"] = old.id.to_s
+ xml_result["new_version"] = old.version.to_s
+ end
+ else
+ old.delete_with_history!(new, @changeset.user)
+ end
+
result.root << xml_result
end
else
# no other actions to choose from, so it must be the users fault!
- raise OSM::APIChangesetActionInvalid.new(action_name)
+ raise OSM::APIChangesetActionInvalid, action_name
end
end
# return the XML document to be rendered back to the client
- return result
+ result
end
-
end
projects / rails.git / blobdiff