_sandboxremote.py: Implement the REAPI client

The remote execution client is implemented as a remote sandbox that
sends sources and build commands to a REAPI server and fetches results
once remotely executed. New file.

#454

buildstream/sandbox/_sandboxremote.py

+#!/usr/bin/env python3
+#
+#  Copyright (C) 2018 Bloomberg LP
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2 of the License, or (at your option) any later version.
+#
+#  This library is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
+#
+#  Authors:
+#        Jim MacArthur <jim.macarthur@codethink.co.uk>
+
+import os
+from urllib.parse import urlparse
+
+import grpc
+
+from . import Sandbox
+from ..storage._filebaseddirectory import FileBasedDirectory
+from ..storage._casbaseddirectory import CasBasedDirectory
+from .._protos.build.bazel.remote.execution.v2 import remote_execution_pb2, remote_execution_pb2_grpc
+from .._artifactcache.cascache import CASCache
+
+
+class SandboxError(Exception):
+    pass
+
+
+# SandboxRemote()
+#
+# This isn't really a sandbox, it's a stub which sends all the sources and build
+# commands to a remote server and retrieves the results from it.
+#
+class SandboxRemote(Sandbox):
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.cascache = None
+
+        url = urlparse(kwargs['server_url'])
+        if not url.scheme or not url.hostname or not url.port:
+            raise SandboxError("Configured remote URL '{}' does not match the expected layout. "
+                               .format(kwargs['server_url']) +
+                               "It should be of the form <protocol>://<domain name>:<port>.")
+        elif url.scheme != 'http':
+            raise SandboxError("Configured remote '{}' uses an unsupported protocol. "
+                               "Only plain HTTP is currenlty supported (no HTTPS).")
+
+        self.server_url = '{}:{}'.format(url.hostname, url.port)
+
+    def _get_cascache(self):
+        if self.cascache is None:
+            self.cascache = CASCache(self._get_context())
+            self.cascache.setup_remotes(use_config=True)
+        return self.cascache
+
+    def run_remote_command(self, command, input_root_digest, working_directory, environment):
+        # Sends an execution request to the remote execution server.
+        #
+        # This function blocks until it gets a response from the server.
+        #
+        environment_variables = [remote_execution_pb2.Command.
+                                 EnvironmentVariable(name=k, value=v)
+                                 for (k, v) in environment.items()]
+
+        # Create and send the Command object.
+        remote_command = remote_execution_pb2.Command(arguments=command,
+                                                      working_directory=working_directory,
+                                                      environment_variables=environment_variables,
+                                                      output_files=[],
+                                                      output_directories=[self._output_directory],
+                                                      platform=None)
+
+        cascache = self._get_cascache()
+        # Upload the Command message to the remote CAS server
+        command_digest = cascache.push_message(self._get_project(), remote_command)
+        if not command_digest or not cascache.verify_digest_pushed(self._get_project(), command_digest):
+            # Command push failed
+            return None
+
+        # Create and send the action.
+        action = remote_execution_pb2.Action(command_digest=command_digest,
+                                             input_root_digest=input_root_digest,
+                                             timeout=None,
+                                             do_not_cache=False)
+
+        # Upload the Action message to the remote CAS server
+        action_digest = cascache.push_message(self._get_project(), action)
+        if not action_digest or not cascache.verify_digest_pushed(self._get_project(), action_digest):
+            # Action push failed
+            return None
+
+        # Next, try to create a communication channel to the BuildGrid server.
+        channel = grpc.insecure_channel(self.server_url)
+        stub = remote_execution_pb2_grpc.ExecutionStub(channel)
+        request = remote_execution_pb2.ExecuteRequest(action_digest=action_digest,
+                                                      skip_cache_lookup=False)
+        try:
+            operation_iterator = stub.Execute(request)
+        except grpc.RpcError:
+            return None
+
+        operation = None
+        with self._get_context().timed_activity("Waiting for the remote build to complete"):
+            # It is advantageous to check operation_iterator.code() is grpc.StatusCode.OK here,
+            # which will check the server is actually contactable. However, calling it when the
+            # server is available seems to cause .code() to hang forever.
+            for operation in operation_iterator:
+                if operation.done:
+                    break
+
+        return operation
+
+    def process_job_output(self, output_directories, output_files):
+        # Reads the remote execution server response to an execution request.
+        #
+        # output_directories is an array of OutputDirectory objects.
+        # output_files is an array of OutputFile objects.
+        #
+        # We only specify one output_directory, so it's an error
+        # for there to be any output files or more than one directory at the moment.
+        #
+        if output_files:
+            raise SandboxError("Output files were returned when we didn't request any.")
+        elif not output_directories:
+            error_text = "No output directory was returned from the build server."
+            raise SandboxError(error_text)
+        elif len(output_directories) > 1:
+            error_text = "More than one output directory was returned from the build server: {}."
+            raise SandboxError(error_text.format(output_directories))
+
+        tree_digest = output_directories[0].tree_digest
+        if tree_digest is None or not tree_digest.hash:
+            raise SandboxError("Output directory structure had no digest attached.")
+
+        cascache = self._get_cascache()
+        # Now do a pull to ensure we have the necessary parts.
+        dir_digest = cascache.pull_tree(self._get_project(), tree_digest)
+        if dir_digest is None or not dir_digest.hash or not dir_digest.size_bytes:
+            raise SandboxError("Output directory structure pulling from remote failed.")
+
+        path_components = os.path.split(self._output_directory)
+
+        # Now what we have is a digest for the output. Once we return, the calling process will
+        # attempt to descend into our directory and find that directory, so we need to overwrite
+        # that.
+
+        if not path_components:
+            # The artifact wants the whole directory; we could just return the returned hash in its
+            # place, but we don't have a means to do that yet.
+            raise SandboxError("Unimplemented: Output directory is empty or equal to the sandbox root.")
+
+        # At the moment, we will get the whole directory back in the first directory argument and we need
+        # to replace the sandbox's virtual directory with that. Creating a new virtual directory object
+        # from another hash will be interesting, though...
+
+        new_dir = CasBasedDirectory(self._get_context(), ref=dir_digest)
+        self._set_virtual_directory(new_dir)
+
+    def run(self, command, flags, *, cwd=None, env=None):
+        # Upload sources
+        upload_vdir = self.get_virtual_directory()
+
+        if isinstance(upload_vdir, FileBasedDirectory):
+            # Make a new temporary directory to put source in
+            upload_vdir = CasBasedDirectory(self._get_context(), ref=None)
+            upload_vdir.import_files(self.get_virtual_directory()._get_underlying_directory())
+
+        upload_vdir.recalculate_hash()
+
+        cascache = self._get_cascache()
+        # Now, push that key (without necessarily needing a ref) to the remote.
+        vdir_digest = cascache.push_directory(self._get_project(), upload_vdir)
+        if not vdir_digest or not cascache.verify_digest_pushed(self._get_project(), vdir_digest):
+            raise SandboxError("Failed to verify that source has been pushed to the remote artifact cache.")
+
+        # Set up environment and working directory
+        if cwd is None:
+            cwd = self._get_work_directory()
+
+        if cwd is None:
+            cwd = '/'
+
+        if env is None:
+            env = self._get_environment()
+
+        # We want command args as a list of strings
+        if isinstance(command, str):
+            command = [command]
+
+        # Now transmit the command to execute
+        operation = self.run_remote_command(command, upload_vdir.ref, cwd, env)
+
+        if operation is None:
+            # Failure of remote execution, usually due to an error in BuildStream
+            # NB This error could be raised in __run_remote_command
+            raise SandboxError("No response returned from server")
+
+        assert not operation.HasField('error') and operation.HasField('response')
+
+        execution_response = remote_execution_pb2.ExecuteResponse()
+        # The response is expected to be an ExecutionResponse message
+        assert operation.response.Is(execution_response.DESCRIPTOR)
+
+        operation.response.Unpack(execution_response)
+
+        if execution_response.status.code != 0:
+            # A normal error during the build: the remote execution system
+            # has worked correctly but the command failed.
+            # execution_response.error also contains 'message' (str) and
+            # 'details' (iterator of Any) which we ignore at the moment.
+            return execution_response.status.code
+
+        action_result = execution_response.result
+
+        self.process_job_output(action_result.output_directories, action_result.output_files)
+
+        return 0