Streaming mode for downloading all rows as a CSV (#315)

* table.csv?_stream=1 to download all rows - refs #266

This option causes Datasette to serve ALL rows in the table, by internally
following the _next= pagination links and serving everything out as a stream.

Also added new config option, allow_csv_stream, which can be used to disable
this feature.

* New config option max_csv_mb limiting size of CSV export

.travis.yml

@@ -13,6 +13,7 @@ script:
 jobs:
   include:
     - stage: deploy latest.datasette.io
+      if: branch = master AND type = push
       script:
         - pip install .
         - npm install -g now
@@ -23,7 +24,6 @@ jobs:
         - now alias --token=$NOW_TOKEN
         - echo "{\"name\":\"datasette-latest-$ALIAS\",\"alias\":\"$ALIAS.datasette.io\"}" > now.json
         - now alias --token=$NOW_TOKEN
-      on: master
     - stage: release tagged version
       if: tag IS present
       python: 3.6

datasette/app.py

@@ -94,6 +94,12 @@ CONFIG_OPTIONS = (
     ConfigOption("cache_size_kb", 0, """
         SQLite cache size in KB (0 == use SQLite default)
     """.strip()),
+    ConfigOption("allow_csv_stream", True, """
+        Allow .csv?_stream=1 to download all rows (ignoring max_returned_rows)
+    """.strip()),
+    ConfigOption("max_csv_mb", 100, """
+        Maximum size allowed for CSV export in MB. Set 0 to disable this limit.
+    """.strip()),
 )
 DEFAULT_CONFIG = {
     option.name: option.default

datasette/utils.py

@@ -832,3 +832,22 @@ def value_as_boolean(value):
 
 class ValueAsBooleanError(ValueError):
     pass
+
+
+class WriteLimitExceeded(Exception):
+    pass
+
+
+class LimitedWriter:
+    def __init__(self, writer, limit_mb):
+        self.writer = writer
+        self.limit_bytes = limit_mb * 1024 * 1024
+        self.bytes_count = 0
+
+    def write(self, bytes):
+        self.bytes_count += len(bytes)
+        if self.limit_bytes and (self.bytes_count > self.limit_bytes):
+            raise WriteLimitExceeded("CSV contains more than {} bytes".format(
+                self.limit_bytes
+            ))
+        self.writer.write(bytes)

datasette/views/base.py

@@ -16,6 +16,7 @@ from datasette.utils import (
     CustomJSONEncoder,
     InterruptedError,
     InvalidSql,
+    LimitedWriter,
     path_from_row_pks,
     path_with_added_args,
     path_with_format,
@@ -150,13 +151,23 @@ class BaseView(RenderMixin):
         return await self.view_get(request, name, hash, **kwargs)
 
     async def as_csv(self, request, name, hash, **kwargs):
+        stream = request.args.get("_stream")
+        if stream:
+            # Some quick sanity checks
+            if not self.ds.config["allow_csv_stream"]:
+                raise DatasetteError("CSV streaming is disabled", status=400)
+            if request.args.get("_next"):
+                raise DatasetteError(
+                    "_next not allowed for CSV streaming", status=400
+                )
+            kwargs["_size"] = "max"
+        # Fetch the first page
         try:
             response_or_template_contexts = await self.data(
                 request, name, hash, **kwargs
             )
             if isinstance(response_or_template_contexts, response.HTTPResponse):
                 return response_or_template_contexts
-
             else:
                 data, extra_template_data, templates = response_or_template_contexts
         except (sqlite3.OperationalError, InvalidSql) as e:
@@ -167,6 +178,7 @@ class BaseView(RenderMixin):
 
         except DatasetteError:
             raise
+
         # Convert rows and columns to CSV
         headings = data["columns"]
         # if there are expanded_columns we need to add additional headings
@@ -179,8 +191,22 @@ class BaseView(RenderMixin):
                     headings.append("{}_label".format(column))
 
         async def stream_fn(r):
-            writer = csv.writer(r)
+            nonlocal data
+            writer = csv.writer(LimitedWriter(r, self.ds.config["max_csv_mb"]))
+            first = True
+            next = None
+            while first or (next and stream):
+                try:
+                    if next:
+                        kwargs["_next"] = next
+                    if not first:
+                        data, extra_template_data, templates = await self.data(
+                            request, name, hash, **kwargs
+                        )
+                    if first:
                         writer.writerow(headings)
+                        first = False
+                    next = data.get("next")
                     for row in data["rows"]:
                         if not expanded_columns:
                             # Simple path
@@ -195,6 +221,10 @@ class BaseView(RenderMixin):
                                 else:
                                     new_row.append(cell)
                             writer.writerow(new_row)
+                except Exception as e:
+                    print('caught this', e)
+                    r.write(str(e))
+                    return
 
         content_type = "text/plain; charset=utf-8"
         headers = {}
@@ -393,7 +423,8 @@ class BaseView(RenderMixin):
         return r
 
     async def custom_sql(
-        self, request, name, hash, sql, editable=True, canned_query=None
+        self, request, name, hash, sql, editable=True, canned_query=None,
+        _size=None
     ):
         params = request.raw_args
         if "sql" in params:
@@ -415,6 +446,8 @@ class BaseView(RenderMixin):
         extra_args = {}
         if params.get("_timelimit"):
             extra_args["custom_time_limit"] = int(params["_timelimit"])
+        if _size:
+            extra_args["page_size"] = _size
         results = await self.ds.execute(
             name, sql, params, truncate=True, **extra_args
         )

datasette/views/database.py

@@ -9,13 +9,13 @@ from .base import BaseView, DatasetteError
 
 class DatabaseView(BaseView):
 
-    async def data(self, request, name, hash, default_labels=False):
+    async def data(self, request, name, hash, default_labels=False, _size=None):
         if request.args.get("sql"):
             if not self.ds.config["allow_sql"]:
                 raise DatasetteError("sql= is not allowed", status=400)
             sql = request.raw_args.pop("sql")
             validate_sql_select(sql)
-            return await self.custom_sql(request, name, hash, sql)
+            return await self.custom_sql(request, name, hash, sql, _size=_size)
 
         info = self.ds.inspect()[name]
         metadata = self.ds.metadata.get("databases", {}).get(name, {})

datasette/views/table.py

@@ -220,7 +220,7 @@ class RowTableShared(BaseView):
 
 class TableView(RowTableShared):
 
-    async def data(self, request, name, hash, table, default_labels=False):
+    async def data(self, request, name, hash, table, default_labels=False,  _next=None, _size=None):
         canned_query = self.ds.get_canned_query(name, table)
         if canned_query is not None:
             return await self.custom_sql(
@@ -375,7 +375,7 @@ class TableView(RowTableShared):
 
         count_sql = "select count(*) {}".format(from_sql)
 
-        _next = special_args.get("_next")
+        _next = _next or special_args.get("_next")
         offset = ""
         if _next:
             if is_view:
@@ -462,7 +462,7 @@ class TableView(RowTableShared):
 
         extra_args = {}
         # Handle ?_size=500
-        page_size = request.raw_args.get("_size")
+        page_size = _size or request.raw_args.get("_size")
         if page_size:
             if page_size == "max":
                 page_size = self.max_returned_rows
@@ -512,6 +512,8 @@ class TableView(RowTableShared):
         facet_results = {}
         facets_timed_out = []
         for column in facets:
+            if _next:
+                continue
             facet_sql = """
                 select {col} as value, count(*) as count
                 {from_sql} {and_or_where} {col} is not null
@@ -665,6 +667,8 @@ class TableView(RowTableShared):
                 for facet_column in columns:
                     if facet_column in facets:
                         continue
+                    if _next:
+                        continue
                     if not self.ds.config["suggest_facets"]:
                         continue
                     suggested_facet_sql = '''

docs/config.rst

@@ -125,3 +125,24 @@ Sets the amount of memory SQLite uses for its `per-connection cache <https://www
 ::
 
     datasette mydatabase.db --config cache_size_kb:5000
+
+
+allow_csv_stream
+----------------
+
+Enables the feature where an entire table (potentially hundreds of thousands of
+rows) can be exported as a single CSV file. This is turned on by default - you
+can turn it off like this::
+
+::
+
+    datasette mydatabase.db --config allow_csv_stream:off
+
+
+max_csv_mb
+----------
+
+The maximum size of CSV that can be exported, in megabytes. Defaults to 100MB.
+You can disable the limit entirely by settings this to 0::
+
+    datasette mydatabase.db --config max_csv_mb:0

docs/metadata.rst

@@ -122,6 +122,7 @@ This will restrict sorting of ``example_table`` to just the ``height`` and
 You can also disable sorting entirely by setting ``"sortable_columns": []``
 
 .. _label_columns:
+
 Specifying the label column for a table
 ---------------------------------------
 

tests/fixtures.py

@@ -71,6 +71,13 @@ def app_client_larger_cache_size():
     })
 
 
+@pytest.fixture(scope='session')
+def app_client_csv_max_mb_one():
+    yield from app_client(config={
+        'max_csv_mb': 1,
+    })
+
+
 def generate_compound_rows(num):
     for a, b, c in itertools.islice(
         itertools.product(string.ascii_lowercase, repeat=3), num

tests/test_api.py

@@ -901,6 +901,8 @@ def test_config_json(app_client):
         "default_cache_ttl": 365 * 24 * 60 * 60,
         "num_sql_threads": 3,
         "cache_size_kb": 0,
+        "allow_csv_stream": True,
+        "max_csv_mb": 100,
     } == response.json
 
 

tests/test_csv.py

@@ -1,4 +1,4 @@
-from .fixtures import app_client # noqa
+from .fixtures import app_client, app_client_csv_max_mb_one # noqa
 
 EXPECTED_TABLE_CSV = '''id,content
 1,hello
@@ -59,3 +59,28 @@ def test_table_csv_download(app_client):
     assert 'text/csv; charset=utf-8' == response.headers['Content-Type']
     expected_disposition = 'attachment; filename="simple_primary_key.csv"'
     assert expected_disposition == response.headers['Content-Disposition']
+
+
+def test_max_csv_mb(app_client_csv_max_mb_one):
+    response = app_client_csv_max_mb_one.get(
+        "/fixtures.csv?sql=select+randomblob(10000)+"
+        "from+compound_three_primary_keys&_stream=1&_size=max"
+    )
+    # It's a 200 because we started streaming before we knew the error
+    assert response.status == 200
+    # Last line should be an error message
+    last_line = [line for line in response.body.split(b"\r\n") if line][-1]
+    assert last_line.startswith(b"CSV contains more than")
+
+
+def test_table_csv_stream(app_client):
+    # Without _stream should return header + 100 rows:
+    response = app_client.get(
+        "/fixtures/compound_three_primary_keys.csv?_size=max"
+    )
+    assert 101 == len([b for b in response.body.split(b"\r\n") if b])
+    # With _stream=1 should return header + 1001 rows
+    response = app_client.get(
+        "/fixtures/compound_three_primary_keys.csv?_stream=1"
+    )
+    assert 1002 == len([b for b in response.body.split(b"\r\n") if b])