[RFC PATCH 4/8] hashserv: Support read-only server

["Paul Barker" <pbarker@konsulko.com>]

The -r/--readonly argument is added to the bitbake-hashserv app. If this
argument is given then clients may only perform read operations against
the server. The read-only mode is implemented by simply not installing
handlers for write operations, this keeps the permission model simple
and reduces the risk of accidentally allowing write operations.

As a sqlite database can be safely opened by multiple processes in
parallel, it's possible to start two hashserv instances against a single
database if you wish to export both a read-only port and a read-write
port.

Signed-off-by: Paul Barker <pbarker@konsulko.com>
---
 bin/bitbake-hashserv     |  3 ++-
 lib/hashserv/__init__.py |  4 ++--
 lib/hashserv/server.py   | 25 ++++++++++++++++++-------
 3 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/bin/bitbake-hashserv b/bin/bitbake-hashserv
index 1bc1f91f3..2669bbd13 100755
--- a/bin/bitbake-hashserv
+++ b/bin/bitbake-hashserv
@@ -33,6 +33,7 @@ def main():
     parser.add_argument('--bind', default=DEFAULT_BIND, help='Bind address (default "%(default)s")')
     parser.add_argument('--database', default='./hashserv.db', help='Database file (default "%(default)s")')
     parser.add_argument('--log', default='WARNING', help='Set logging level')
+    parser.add_argument('-r', '--read-only', action='store_true', help='Disallow write operations from clients')
 
     args = parser.parse_args()
 
@@ -47,7 +48,7 @@ def main():
     console.setLevel(level)
     logger.addHandler(console)
 
-    server = hashserv.create_server(args.bind, args.database)
+    server = hashserv.create_server(args.bind, args.database, read_only=args.read_only)
     server.serve_forever()
     return 0
 
diff --git a/lib/hashserv/__init__.py b/lib/hashserv/__init__.py
index 55f48410d..5f2e101e5 100644
--- a/lib/hashserv/__init__.py
+++ b/lib/hashserv/__init__.py
@@ -94,10 +94,10 @@ def chunkify(msg, max_chunk):
         yield "\n"
 
 
-def create_server(addr, dbname, *, sync=True, upstream=None):
+def create_server(addr, dbname, *, sync=True, upstream=None, read_only=False):
     from . import server
     db = setup_database(dbname, sync=sync)
-    s = server.Server(db, upstream=upstream)
+    s = server.Server(db, upstream=upstream, read_only=read_only)
 
     (typ, a) = parse_address(addr)
     if typ == ADDR_TYPE_UNIX:
diff --git a/lib/hashserv/server.py b/lib/hashserv/server.py
index fa0d3410b..b1e8b2f89 100644
--- a/lib/hashserv/server.py
+++ b/lib/hashserv/server.py
@@ -112,6 +112,9 @@ class Stats(object):
 class ClientError(Exception):
     pass
 
+class ServerError(Exception):
+    pass
+
 def insert_task(cursor, data, ignore=False):
     keys = sorted(data.keys())
     query = '''INSERT%s INTO tasks_v2 (%s) VALUES (%s)''' % (
@@ -138,7 +141,7 @@ class ServerClient(object):
     FAST_QUERY = 'SELECT taskhash, method, unihash FROM tasks_v2 WHERE method=:method AND taskhash=:taskhash ORDER BY created ASC LIMIT 1'
     ALL_QUERY =  'SELECT *                         FROM tasks_v2 WHERE method=:method AND taskhash=:taskhash ORDER BY created ASC LIMIT 1'
 
-    def __init__(self, reader, writer, db, request_stats, backfill_queue, upstream):
+    def __init__(self, reader, writer, db, request_stats, backfill_queue, upstream, read_only):
         self.reader = reader
         self.writer = writer
         self.db = db
@@ -149,15 +152,19 @@ class ServerClient(object):
 
         self.handlers = {
             'get': self.handle_get,
-            'report': self.handle_report,
-            'report-equiv': self.handle_equivreport,
             'get-stream': self.handle_get_stream,
             'get-stats': self.handle_get_stats,
-            'reset-stats': self.handle_reset_stats,
             'chunk-stream': self.handle_chunk,
-            'backfill-wait': self.handle_backfill_wait,
         }
 
+        if not read_only:
+            self.handlers.update({
+                'report': self.handle_report,
+                'report-equiv': self.handle_equivreport,
+                'reset-stats': self.handle_reset_stats,
+                'backfill-wait': self.handle_backfill_wait,
+            })
+
     async def process_requests(self):
         if self.upstream is not None:
             self.upstream_client = await create_async_client(self.upstream)
@@ -455,7 +462,10 @@ class ServerClient(object):
 
 
 class Server(object):
-    def __init__(self, db, loop=None, upstream=None):
+    def __init__(self, db, loop=None, upstream=None, read_only=False):
+        if upstream and read_only:
+            raise ServerError("Read-only hashserv cannot pull from an upstream server")
+
         self.request_stats = Stats()
         self.db = db
 
@@ -467,6 +477,7 @@ class Server(object):
             self.close_loop = False
 
         self.upstream = upstream
+        self.read_only = read_only
 
         self._cleanup_socket = None
 
@@ -510,7 +521,7 @@ class Server(object):
     async def handle_client(self, reader, writer):
         # writer.transport.set_write_buffer_limits(0)
         try:
-            client = ServerClient(reader, writer, self.db, self.request_stats, self.backfill_queue, self.upstream)
+            client = ServerClient(reader, writer, self.db, self.request_stats, self.backfill_queue, self.upstream, self.read_only)
             await client.process_requests()
         except Exception as e:
             import traceback
-- 
2.26.2