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[feat] add a simple conflict resolution mecanism.

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The server tries to merge conflicting saves of
the same layer.

What it does:

- use the `If-Unmodified-Since` header to check
  if changes happened to the stored data ;
- Compare the incoming version with its reference version
  to get a diff.
- Reapply the diff on top of the latest version.
- If the merge is not possible, return a
  "422 Conflict" HTTP response.
- If the merge worked, return the merged document,
  to be updated by the client.
This commit is contained in:
Alexis Métaireau 2020-03-25 08:56:43 +01:00
parent 34e0461ca8
commit f37ed700f6
5 changed files with 336 additions and 24 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
umap/static/umap/js/umap.layer.js
View file

@ -1535,6 +1535,12 @@ L.U.DataLayer = L.Evented.extend({
this.map.post(this.getSaveUrl(), {
data: formData,
callback: function (data, response) {
// Response contains geojson only if save has conflicted and conflicts have
// been resolved. So we need to reload to get extra data (saved from someone else)
if (data.geojson) {
this.clear()
this.fromGeoJSON(data.geojson)
}
this._geojson = geojson
this._last_modified = response.getResponseHeader('Last-Modified')
this.setUmapId(data.id)

164
umap/tests/test_datalayer_views.py
View file

@ -1,8 +1,11 @@
import json
import time
from copy import deepcopy
from pathlib import Path
import pytest
from django.core.files.base import ContentFile
from django.core.files.uploadedfile import SimpleUploadedFile
from django.urls import reverse
from umap.models import DataLayer, Map
@ -19,7 +22,10 @@ def post_data():
"display_on_load": True,
"settings": '{"displayOnLoad": true, "browsable": true, "name": "name"}',
"rank": 0,
"geojson": '{"type":"FeatureCollection","features":[{"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[-3.1640625,53.014783245859235],[-3.1640625,51.86292391360244],[-0.50537109375,51.385495069223204],[1.16455078125,52.38901106223456],[-0.41748046875,53.91728101547621],[-2.109375,53.85252660044951],[-3.1640625,53.014783245859235]]]},"properties":{"_umap_options":{},"name":"Ho god, sounds like a polygouine"}},{"type":"Feature","geometry":{"type":"LineString","coordinates":[[1.8017578124999998,51.16556659836182],[-0.48339843749999994,49.710272582105695],[-3.1640625,50.0923932109388],[-5.60302734375,51.998410382390325]]},"properties":{"_umap_options":{},"name":"Light line"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[0.63720703125,51.15178610143037]},"properties":{"_umap_options":{},"name":"marker he"}}],"_umap_options":{"displayOnLoad":true,"name":"new name","id":1668,"remoteData":{},"color":"LightSeaGreen","description":"test"}}',
"geojson": SimpleUploadedFile(
"name.json",
b'{"type":"FeatureCollection","features":[{"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[-3.1640625,53.014783245859235],[-3.1640625,51.86292391360244],[-0.50537109375,51.385495069223204],[1.16455078125,52.38901106223456],[-0.41748046875,53.91728101547621],[-2.109375,53.85252660044951],[-3.1640625,53.014783245859235]]]},"properties":{"_umap_options":{},"name":"Ho god, sounds like a polygouine"}},{"type":"Feature","geometry":{"type":"LineString","coordinates":[[1.8017578124999998,51.16556659836182],[-0.48339843749999994,49.710272582105695],[-3.1640625,50.0923932109388],[-5.60302734375,51.998410382390325]]},"properties":{"_umap_options":{},"name":"Light line"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[0.63720703125,51.15178610143037]},"properties":{"_umap_options":{},"name":"marker he"}}],"_umap_options":{"displayOnLoad":true,"name":"new name","id":1668,"remoteData":{},"color":"LightSeaGreen","description":"test"}}',
),
}
@ -385,3 +391,159 @@ def test_anonymous_user_can_edit_if_inherit_and_map_in_public_mode(
assert response.status_code == 200
modified_datalayer = DataLayer.objects.get(pk=datalayer.pk)
assert modified_datalayer.name == name
@pytest.fixture
def reference_data():
return {
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"geometry": {"type": "Point", "coordinates": [-1, 2]},
"properties": {"_umap_options": {}, "name": "foo"},
},
{
"type": "Feature",
"geometry": {"type": "LineString", "coordinates": [2, 3]},
"properties": {"_umap_options": {}, "name": "bar"},
},
{
"type": "Feature",
"geometry": {"type": "Point", "coordinates": [3, 4]},
"properties": {"_umap_options": {}, "name": "marker"},
},
],
"_umap_options": {
"displayOnLoad": True,
"name": "new name",
"id": 1668,
"remoteData": {},
"color": "LightSeaGreen",
"description": "test",
},
}
def test_optimistic_merge_both_added(client, datalayer, map, reference_data):
url = reverse("datalayer_update", args=(map.pk, datalayer.pk))
client.login(username=map.owner.username, password="123123")
# Reference data is:
# Point (-1, 2); Linestring (2, 3); Point (3, 4).
post_data = {
"name": "name",
"display_on_load": True,
"rank": 0,
"geojson": SimpleUploadedFile(
"foo.json", json.dumps(reference_data).encode("utf-8")
),
}
response = client.post(url, post_data, follow=True)
assert response.status_code == 200
response = client.get(reverse("datalayer_view", args=(map.pk, datalayer.pk)))
reference_timestamp = response["Last-Modified"]
# Client 1 adds "Point 5, 6" to the existing data
client1_feature = {
"type": "Feature",
"geometry": {"type": "Point", "coordinates": [5, 6]},
"properties": {"_umap_options": {}, "name": "marker"},
}
client1_data = deepcopy(reference_data)
client1_data["features"].append(client1_feature)
# Sleep to change the current timestamp (used in the If-Unmodified-Since header)
time.sleep(1)
post_data["geojson"] = SimpleUploadedFile(
"foo.json",
json.dumps(client1_data).encode("utf-8"),
)
response = client.post(
url, post_data, follow=True, HTTP_IF_UNMODIFIED_SINCE=reference_timestamp
)
assert response.status_code == 200
# Client 2 adds "Point 7, 8" instead, on the same reference.
client2_feature = {
"type": "Feature",
"geometry": {"type": "Point", "coordinates": [7, 8]},
"properties": {"_umap_options": {}, "name": "marker"},
}
client2_data = deepcopy(reference_data)
client2_data["features"].append(client2_feature)
post_data["geojson"] = SimpleUploadedFile(
"foo.json",
json.dumps(client2_data).encode("utf-8"),
)
response = client.post(
url, post_data, follow=True, HTTP_IF_UNMODIFIED_SINCE=reference_timestamp
)
assert response.status_code == 200
modified_datalayer = DataLayer.objects.get(pk=datalayer.pk)
merged_features = json.load(modified_datalayer.geojson)["features"]
for reference_feature in reference_data["features"]:
assert reference_feature in merged_features
assert client1_feature in merged_features
assert client2_feature in merged_features
def test_optimistic_merge_conflicting_change_raises(
client, datalayer, map, reference_data
):
url = reverse("datalayer_update", args=(map.pk, datalayer.pk))
client.login(username=map.owner.username, password="123123")
# Reference data is:
# Point (-1, 2); Linestring (2, 3); Point (3, 4).
post_data = {
"name": "name",
"display_on_load": True,
"rank": 0,
"geojson": SimpleUploadedFile(
"foo.json", json.dumps(reference_data).encode("utf-8")
),
}
response = client.post(url, post_data, follow=True)
assert response.status_code == 200
response = client.get(reverse("datalayer_view", args=(map.pk, datalayer.pk)))
reference_timestamp = response["Last-Modified"]
# First client changes the first feature.
client1_data = deepcopy(reference_data)
client1_data["features"][0]["geometry"] = {"type": "Point", "coordinates": [5, 6]}
# Sleep to change the current timestamp (used in the If-Unmodified-Since header)
time.sleep(1)
post_data["geojson"] = SimpleUploadedFile(
"foo.json",
json.dumps(client1_data).encode("utf-8"),
)
response = client.post(
url, post_data, follow=True, HTTP_IF_UNMODIFIED_SINCE=reference_timestamp
)
assert response.status_code == 200
# Second client changes the first feature as well.
client2_data = deepcopy(reference_data)
client2_data["features"][0]["geometry"] = {"type": "Point", "coordinates": [7, 8]}
post_data["geojson"] = SimpleUploadedFile(
"foo.json",
json.dumps(client2_data).encode("utf-8"),
)
response = client.post(
url, post_data, follow=True, HTTP_IF_UNMODIFIED_SINCE=reference_timestamp
)
assert response.status_code == 412
# Check that the server rejected conflicting changes.
modified_datalayer = DataLayer.objects.get(pk=datalayer.pk)
merged_features = json.load(modified_datalayer.geojson)["features"]
assert merged_features == client1_data["features"]

67
umap/tests/test_merge_features.py Normal file
View file

@ -0,0 +1,67 @@
import pytest
from umap.utils import merge_features
def test_adding_one_element():
assert merge_features(["A", "B"], ["A", "B", "C"], ["A", "B", "D"]) == [
"A",
"B",
"C",
"D",
]
def test_adding_elements():
assert merge_features(["A", "B"], ["A", "B", "C", "D"], ["A", "B", "E", "F"]) == [
"A",
"B",
"C",
"D",
"E",
"F",
]
# Order does not count
assert merge_features(["A", "B"], ["B", "C", "D", "A"], ["A", "B", "E", "F"]) == [
"B",
"C",
"D",
"A",
"E",
"F",
]
def test_adding_one_removing_one():
assert merge_features(["A", "B"], ["A", "C"], ["A", "B", "D"]) == [
"A",
"C",
"D",
]
def test_removing_same_element():
# No added element (otherwise we cannot know if "new" elements are old modified
# or old removed and new added).
assert merge_features(["A", "B", "C"], ["A", "B"], ["A", "B"]) == [
"A",
"B",
]
def test_removing_changed_element():
with pytest.raises(ValueError):
merge_features(["A", "B"], ["A", "C"], ["A"])
def test_changing_removed_element():
with pytest.raises(ValueError):
merge_features(["A", "B"], ["A"], ["A", "C"])
def test_changing_same_element():
with pytest.raises(ValueError):
merge_features(["A", "B"], ["A", "D"], ["A", "C"])
# Order does not count
with pytest.raises(ValueError):
merge_features(["A", "B", "C"], ["B", "D", "A"], ["A", "E", "B"])

29
umap/utils.py
View file

@ -116,3 +116,32 @@ def gzip_file(from_path, to_path):
def is_ajax(request):
return request.headers.get("x-requested-with") == "XMLHttpRequest"
class ConflictError(ValueError):
pass
def merge_features(reference: list, latest: list, incoming: list):
"""Finds the changes between reference and incoming, and reapplies them on top of latest."""
if latest == incoming:
return latest
removed = [item for item in reference if item not in incoming]
added = [item for item in incoming if item not in reference]
# Ensure that items changed in the reference weren't also changed in the latest.
for item in removed:
if item not in latest:
raise ConflictError()
merged = latest[:]
# Reapply the changes on top of the latest.
for item in removed:
merged.delete(item)
for item in added:
merged.append(item)
return merged

92
umap/views.py
View file

@ -5,6 +5,7 @@ import re
import socket
from datetime import datetime, timedelta
from http.client import InvalidURL
from io import BytesIO
from pathlib import Path
from urllib.error import HTTPError, URLError
from urllib.parse import quote, urlparse
@ -61,7 +62,7 @@ from .forms import (
UserProfileForm,
)
from .models import DataLayer, Licence, Map, Pictogram, Star, TileLayer
from .utils import get_uri_template, gzip_file, is_ajax
from .utils import ConflictError, get_uri_template, gzip_file, is_ajax, merge_features
User = get_user_model()
@ -851,6 +852,10 @@ class GZipMixin(object):
def gzip_path(self):
return Path(f"{self.path}{self.EXT}")
def compute_last_modified(self, path):
stat = os.stat(path)
return http_date(stat.st_mtime)
@property
def last_modified(self):
# Prior to 1.3.0 we did not set gzip mtime as geojson mtime,
@ -864,8 +869,7 @@ class GZipMixin(object):
if self.accepts_gzip and self.gzip_path.exists()
else self.path
)
stat = os.stat(path)
return http_date(stat.st_mtime)
return self.compute_last_modified(path)
@property
def accepts_gzip(self):
@ -929,34 +933,78 @@ class DataLayerUpdate(FormLessEditMixin, GZipMixin, UpdateView):
model = DataLayer
form_class = DataLayerForm
def form_valid(self, form):
self.object = form.save()
# Simple response with only metadatas (client should not reload all data
# on save)
response = simple_json_response(
**self.object.metadata(self.request.user, self.request)
)
response["Last-Modified"] = self.last_modified
return response
def has_been_modified_since(self, if_unmodified_since):
return if_unmodified_since and self.last_modified != if_unmodified_since
def is_unmodified(self):
"""Optimistic concurrency control."""
modified = True
if_unmodified = self.request.META.get("HTTP_IF_UNMODIFIED_SINCE")
if if_unmodified:
if self.last_modified != if_unmodified:
modified = False
return modified
def merge(self, if_unmodified_since):
"""
Attempt to apply the incoming changes to the document the client was using, and
then merge it with the last document we have on storage.
Returns either None (if the merge failed) or the merged python GeoJSON object.
"""
# Use If-Modified-Since to find the correct version in our storage.
for name in self.object.get_versions():
path = os.path.join(settings.MEDIA_ROOT, self.object.get_version_path(name))
if if_unmodified_since == self.compute_last_modified(path):
with open(path) as f:
reference = json.loads(f.read())
break
else:
# If the document is not found, we can't merge.
return None
# New data received in the request.
entrant = json.loads(self.request.FILES["geojson"].read())
# Latest known version of the data.
with open(self.path) as f:
latest = json.loads(f.read())
try:
merged_features = merge_features(
reference["features"], latest["features"], entrant["features"]
)
latest["features"] = merged_features
return latest
except ConflictError:
return None
def post(self, request, *args, **kwargs):
self.object = self.get_object()
if self.object.map.pk != int(self.kwargs["map_id"]):
return HttpResponseForbidden()
if not self.object.can_edit(user=self.request.user, request=self.request):
return HttpResponseForbidden()
if not self.is_unmodified():
ius_header = self.request.META.get("HTTP_IF_UNMODIFIED_SINCE")
if self.has_been_modified_since(ius_header):
merged = self.merge(ius_header)
if not merged:
return HttpResponse(status=412)
return super(DataLayerUpdate, self).post(request, *args, **kwargs)
# Replace the uploaded file by the merged version.
self.request.FILES["geojson"].file = BytesIO(
json.dumps(merged).encode("utf-8")
)
# Mark the data to be reloaded by form_valid
self.request.session["needs_reload"] = True
return super().post(request, *args, **kwargs)
def form_valid(self, form):
self.object = form.save()
data = {**self.object.metadata(self.request.user, self.request)}
if self.request.session.get("needs_reload"):
data["geojson"] = json.loads(self.object.geojson.read().decode())
self.request.session["needs_reload"] = False
response = simple_json_response(**data)
response["Last-Modified"] = self.last_modified
return response
class DataLayerDelete(DeleteView):