Upgrade to Proc 4.21.0

Fix error
_message.Message._CheckCalledFromGeneratedFile()
TypeError: Descriptors cannot not be created directly.

Author: Beutlin

README.md

@@ -1,2 +1,8 @@
 # pythonsdk
 Python SDK for gaia pipelines.
+
+## Upgrade Protc / gRPC
+```
+protoc -I . --python_out=. gaiasdk/plugin.proto
+python3 -m grpc_tools.protoc -I . --python_out=. --grpc_python_out=. gaiasdk/plugin.proto
+```

gaiasdk/plugin.proto

@@ -0,0 +1,59 @@
+// plugin.proto
+// Defines the gRPC interface between gaia and the user defined
+// pipelines (plugins). All rpc Methods are called from Gaia and
+// executed in the plugin.
+
+syntax = "proto3";
+
+option java_multiple_files = true;
+option java_package = "io.gaiapipeline.proto";
+option java_outer_classname = "GRPCPlugin";
+
+package proto;
+
+// Job represents a single job
+message Job {
+    uint32              unique_id   = 1;
+    string              title       = 2;
+    string              description = 3;
+    repeated uint32     dependson   = 4;
+    repeated Argument   args        = 5;
+    ManualInteraction   interaction = 6;
+}
+
+// Argument represents an argument passed from a pipeline
+// to gaia and/or from gaia to the pipeline.
+message Argument {
+    string description = 1;
+    string type        = 2;
+    string key         = 3;
+    string value       = 4;
+}
+
+// ManualInteraction represents a manual human interaction
+message ManualInteraction {
+    string description = 1;
+    string type        = 2;
+    string value       = 3;
+}
+
+// JobResult represents the result of an executed job
+message JobResult {
+    uint32 unique_id      = 1;
+    bool   failed         = 2;
+    bool   exit_pipeline  = 3;
+    string message        = 4;
+}
+
+// Empty message
+message Empty {}
+
+service Plugin {
+    // GetJobs returns a stream of Job objects.
+    // Used to expose jobs to gaia.
+    rpc GetJobs(Empty) returns (stream Job);
+
+    // ExecuteJob signals the plugin to execute the given job.
+    // Used to execute one job from a pipeline.
+    rpc ExecuteJob(Job) returns (JobResult);
+}