serve and publish commands now take a --metadata option

If provided, the --metadata option is the path to a JSON file containing
metadata that should be displayed alongside the dataset.

    datasette /tmp/fivethirtyeight.db --metadata /tmp/metadata.json

Currently that metadata format looks like this:

    {
        "title": "Five Thirty Eight",
        "license": "CC Attribution 4.0 License",
        "license_url": "http://creativecommons.org/licenses/by/4.0/",
        "source": "fivethirtyeight/data on GitHub",
        "source_url": "https://github.com/fivethirtyeight/data"
    }

If provided, this will be used by the index template and to populate the
common footer.

The publish command also accepts this argument, and will package any provided
metadata up and include it with the resulting Docker container.

    datasette publish --metadata /tmp/metadata.json /tmp/fivethirtyeight.db

Closes #68

datasette/app.py

@@ -73,7 +73,7 @@ class BaseView(HTTPMethodView):
         return [str(r[1]) for r in rows]
 
     def resolve_db_name(self, db_name, **kwargs):
-        databases = self.ds.metadata()
+        databases = self.ds.inspect()
         hash = None
         name = None
         if '-' in db_name:
@@ -110,7 +110,7 @@ class BaseView(HTTPMethodView):
         def sql_operation_in_thread():
             conn = getattr(connections, db_name, None)
             if not conn:
-                info = self.ds.metadata()[db_name]
+                info = self.ds.inspect()[db_name]
                 conn = sqlite3.connect(
                     'file:{}?immutable=1'.format(info['file']),
                     uri=True,
@@ -192,6 +192,7 @@ class BaseView(HTTPMethodView):
             ), **{
                 'url_json': path_with_ext(request, '.json'),
                 'url_jsono': path_with_ext(request, '.jsono'),
+                'metadata': self.ds.metadata,
             }}
             r = self.jinja.render(
                 template,
@@ -216,7 +217,7 @@ class IndexView(HTTPMethodView):
 
     async def get(self, request, as_json):
         databases = []
-        for key, info in sorted(self.ds.metadata().items()):
+        for key, info in sorted(self.ds.inspect().items()):
             database = {
                 'name': key,
                 'hash': info['hash'],
@@ -247,6 +248,7 @@ class IndexView(HTTPMethodView):
                 'index.html',
                 request,
                 databases=databases,
+                metadata=self.ds.metadata,
             )
 
 
@@ -261,8 +263,8 @@ class DatabaseView(BaseView):
         if request.args.get('sql'):
             return await self.custom_sql(request, name, hash)
         tables = []
-        table_metadata = self.ds.metadata()[name]['tables']
-        for table_name, table_rows in table_metadata.items():
+        table_inspect = self.ds.inspect()[name]['tables']
+        for table_name, table_rows in table_inspect.items():
             rows = await self.execute(
                 name,
                 'PRAGMA table_info([{}]);'.format(table_name)
@@ -304,7 +306,7 @@ class DatabaseView(BaseView):
 
 class DatabaseDownload(BaseView):
     async def view_get(self, request, name, hash, **kwargs):
-        filepath = self.ds.metadata()[name]['file']
+        filepath = self.ds.inspect()[name]['file']
         return await response.file_stream(
             filepath, headers={
                 'Content-Disposition': 'attachment; filename="{}"'.format(filepath)
@@ -399,7 +401,7 @@ class TableView(BaseView):
         if use_rowid:
             display_columns = display_columns[1:]
         rows = list(rows)
-        info = self.ds.metadata()
+        info = self.ds.inspect()
         table_rows = info[name]['tables'].get(table)
         after = None
         after_link = None
@@ -471,7 +473,7 @@ class RowView(BaseView):
 
 
 class Datasette:
-    def __init__(self, files, num_threads=3, cache_headers=True, page_size=50, metadata=None):
+    def __init__(self, files, num_threads=3, cache_headers=True, page_size=50, inspect_data=None, metadata=None):
         self.files = files
         self.num_threads = num_threads
         self.executor = futures.ThreadPoolExecutor(
@@ -479,43 +481,42 @@ class Datasette:
         )
         self.cache_headers = cache_headers
         self.page_size = page_size
-        self._metadata = metadata
+        self._inspect = inspect_data
+        self.metadata = metadata
 
-    def metadata(self):
-        if self._metadata:
-            return self._metadata
-        metadata = {}
-        for filename in self.files:
-            path = Path(filename)
-            name = path.stem
-            if name in metadata:
-                raise Exception('Multiple files with same stem %s' % name)
-            # Calculate hash, efficiently
-            m = hashlib.sha256()
-            with path.open('rb') as fp:
-                while True:
-                    data = fp.read(HASH_BLOCK_SIZE)
-                    if not data:
-                        break
-                    m.update(data)
-            # List tables and their row counts
-            tables = {}
-            with sqlite3.connect('file:{}?immutable=1'.format(path), uri=True) as conn:
-                conn.row_factory = sqlite3.Row
-                table_names = [
-                    r['name']
-                    for r in conn.execute('select * from sqlite_master where type="table"')
-                ]
-                for table in table_names:
-                    tables[table] = conn.execute('select count(*) from "{}"'.format(table)).fetchone()[0]
+    def inspect(self):
+        if not self._inspect:
+            self._inspect = {}
+            for filename in self.files:
+                path = Path(filename)
+                name = path.stem
+                if name in self._inspect:
+                    raise Exception('Multiple files with same stem %s' % name)
+                # Calculate hash, efficiently
+                m = hashlib.sha256()
+                with path.open('rb') as fp:
+                    while True:
+                        data = fp.read(HASH_BLOCK_SIZE)
+                        if not data:
+                            break
+                        m.update(data)
+                # List tables and their row counts
+                tables = {}
+                with sqlite3.connect('file:{}?immutable=1'.format(path), uri=True) as conn:
+                    conn.row_factory = sqlite3.Row
+                    table_names = [
+                        r['name']
+                        for r in conn.execute('select * from sqlite_master where type="table"')
+                    ]
+                    for table in table_names:
+                        tables[table] = conn.execute('select count(*) from "{}"'.format(table)).fetchone()[0]
 
-            metadata[name] = {
-                'hash': m.hexdigest(),
-                'file': str(path),
-                'tables': tables,
-            }
-        self._metadata = metadata
-        return metadata
+                self._inspect[name] = {
+                    'hash': m.hexdigest(),
+                    'file': str(path),
+                    'tables': tables,
+                }
+        return self._inspect
 
     def app(self):
         app = Sanic(__name__)