2 # DiffReader reads OSM diffs and applies them to the database.
4 # Uses the streaming LibXML "Reader" interface to cut down on memory
5 # usage, so hopefully we can process fairly large diffs.
7 include ConsistencyValidations
9 # maps each element type to the model class which handles it
13 "relation" => Relation
17 # Construct a diff reader by giving it a bunch of XML +data+ to parse
18 # in OsmChange format. All diffs must be limited to a single changeset
19 # given in +changeset+.
20 def initialize(data, changeset)
21 @reader = XML::Reader.string(data)
22 @changeset = changeset
23 # document that's (re-)used to handle elements expanded out of the
24 # diff processing stream.
25 @doc = XML::Document.new
26 @doc.root = XML::Node.new("osm")
30 # Reads the next element from the XML document. Checks the return value
31 # and throws an exception if an error occurred.
33 # NOTE: XML::Reader#read returns false for EOF and raises an
34 # exception if an error occurs.
37 rescue LibXML::XML::Error => ex
38 raise OSM::APIBadXMLError.new("changeset", xml, ex.message)
43 # An element-block mapping for using the LibXML reader interface.
45 # Since a lot of LibXML reader usage is boilerplate iteration through
46 # elements, it would be better to DRY and do this in a block. This
47 # could also help with error handling...?
49 # if the start element is empty then don't do any processing, as
50 # there won't be any child elements to process!
51 unless @reader.empty_element?
52 # read the first element
55 while @reader.node_type != 15 do # end element
56 # because we read elements in DOM-style to reuse their DOM
57 # parsing code, we don't always read an element on each pass
58 # as the call to @reader.next in the innermost loop will take
59 # care of that for us.
60 if @reader.node_type == 1 # element
64 if @reader.has_attributes?
65 while @reader.move_to_next_attribute == 1
66 attributes[@reader.name] = @reader.value
69 @reader.move_to_element
72 yield name, attributes
82 # An element-block mapping for using the LibXML reader interface.
84 # Since a lot of LibXML reader usage is boilerplate iteration through
85 # elements, it would be better to DRY and do this in a block. This
86 # could also help with error handling...?
88 with_element do |model_name,model_attributes|
89 model = MODELS[model_name]
90 raise OSM::APIBadUserInput.new("Unexpected element type #{model_name}, " +
91 "expected node, way or relation.") if model.nil?
92 # new in libxml-ruby >= 2, expand returns an element not associated
93 # with a document. this means that there's no encoding parameter,
94 # which means basically nothing works.
95 expanded = @reader.expand
97 # create a new, empty document to hold this expanded node
98 new_node = @doc.import(expanded)
101 yield model, new_node
104 # remove element from doc - it will be garbage collected and the
105 # rest of the document is re-used in the next iteration.
106 @doc.root.child.remove!
111 # Checks a few invariants. Others are checked in the model methods
112 # such as save_ and delete_with_history.
113 def check(model, xml, new)
114 raise OSM::APIBadXMLError.new(model, xml) if new.nil?
115 unless new.changeset_id == @changeset.id
116 raise OSM::APIChangesetMismatchError.new(new.changeset_id, @changeset.id)
121 # Consume the XML diff and try to commit it to the database. This code
122 # is *not* transactional, so code which calls it should ensure that the
123 # appropriate transaction block is in place.
125 # On a failure to meet preconditions (e.g: optimistic locking fails)
126 # an exception subclassing OSM::APIError will be thrown.
129 # data structure used for mapping placeholder IDs to real IDs
130 node_ids, way_ids, rel_ids = {}, {}, {}
131 ids = { :node => node_ids, :way => way_ids, :relation => rel_ids}
133 # take the first element and check that it is an osmChange element
135 raise OSM::APIBadUserInput.new("Document element should be 'osmChange'.") if @reader.name != 'osmChange'
137 result = OSM::API.new.get_xml_doc
138 result.root.name = "diffResult"
140 # loop at the top level, within the <osmChange> element
141 with_element do |action_name,action_attributes|
142 if action_name == 'create'
143 # create a new element. this code is agnostic of the element type
144 # because all the elements support the methods that we're using.
145 with_model do |model, xml|
146 new = model.from_xml_node(xml, true)
147 check(model, xml, new)
149 # when this element is saved it will get a new ID, so we save it
150 # to produce the mapping which is sent to other elements.
151 placeholder_id = xml['id'].to_i
152 raise OSM::APIBadXMLError.new(model, xml) if placeholder_id.nil?
154 # check if the placeholder ID has been given before and throw
155 # an exception if it has - we can't create the same element twice.
156 model_sym = model.to_s.downcase.to_sym
157 raise OSM::APIBadUserInput.new("Placeholder IDs must be unique for created elements.") if ids[model_sym].include? placeholder_id
159 # some elements may have placeholders for other elements in the
160 # diff, so we must fix these before saving the element.
161 new.fix_placeholders!(ids, placeholder_id)
163 # create element given user
164 new.create_with_history(@changeset.user)
166 # save placeholder => allocated ID map
167 ids[model_sym][placeholder_id] = new.id
169 # add the result to the document we're building for return.
170 xml_result = XML::Node.new model.to_s.downcase
171 xml_result["old_id"] = placeholder_id.to_s
172 xml_result["new_id"] = new.id.to_s
173 xml_result["new_version"] = new.version.to_s
174 result.root << xml_result
177 elsif action_name == 'modify'
178 # modify an existing element. again, this code doesn't directly deal
179 # with types, but uses duck typing to handle them transparently.
180 with_model do |model, xml|
181 # get the new element from the XML payload
182 new = model.from_xml_node(xml, false)
183 check(model, xml, new)
185 # if the ID is a placeholder then map it to the real ID
186 model_sym = model.to_s.downcase.to_sym
188 is_placeholder = ids[model_sym].include? client_id
189 id = is_placeholder ? ids[model_sym][client_id] : client_id
191 # and the old one from the database
194 # translate any placeholder IDs to their true IDs.
195 new.fix_placeholders!(ids)
198 old.update_from(new, @changeset.user)
200 xml_result = XML::Node.new model.to_s.downcase
201 xml_result["old_id"] = client_id.to_s
202 xml_result["new_id"] = id.to_s
203 # version is updated in "old" through the update, so we must not
204 # return new.version here but old.version!
205 xml_result["new_version"] = old.version.to_s
206 result.root << xml_result
209 elsif action_name == 'delete'
210 # delete action. this takes a payload in API 0.6, so we need to do
211 # most of the same checks that are done for the modify.
212 with_model do |model, xml|
213 # delete doesn't have to contain a full payload, according to
214 # the wiki docs, so we just extract the things we need.
215 new_id = xml['id'].to_i
216 raise OSM::APIBadXMLError.new(model, xml, "ID attribute is required") if new_id.nil?
218 # if the ID is a placeholder then map it to the real ID
219 model_sym = model.to_s.downcase.to_sym
220 is_placeholder = ids[model_sym].include? new_id
221 id = is_placeholder ? ids[model_sym][new_id] : new_id
223 # build the "new" element by modifying the existing one
225 new.changeset_id = xml['changeset'].to_i
226 new.version = xml['version'].to_i
227 check(model, xml, new)
229 # fetch the matching old element from the DB
232 # can a delete have placeholders under any circumstances?
233 # if a way is modified, then deleted is that a valid diff?
234 new.fix_placeholders!(ids)
236 xml_result = XML::Node.new model.to_s.downcase
237 # oh, the irony... the "new" element actually contains the "old" ID
238 # a better name would have been client/server, but anyway...
239 xml_result["old_id"] = new_id.to_s
241 if action_attributes["if-unused"]
243 old.delete_with_history!(new, @changeset.user)
244 rescue OSM::APIPreconditionFailedError => ex
245 xml_result["new_id"] = old.id.to_s
246 xml_result["new_version"] = old.version.to_s
249 old.delete_with_history!(new, @changeset.user)
252 result.root << xml_result
256 # no other actions to choose from, so it must be the users fault!
257 raise OSM::APIChangesetActionInvalid.new(action_name)
261 # return the XML document to be rendered back to the client