Refactored code generation (#65)

This commit refactored the codebase in order to address our internal build issue. It additionally added checks to the Makefile, that ensure that code is generated via suitable versions of protoc-gen-go and protoc-gen-go-grpc going forward.

.gitignore

@@ -13,3 +13,6 @@
 
 # Dependency directories (remove the comment below to include it)
 # vendor/
+
+# Ignore direnv files
+/.envrc

Makefile

@@ -2,6 +2,16 @@
 Q=$(if $V,,@)
 SRC=$(shell find . -type f -name '*.go')
 
+# protoc-gen-go constraints
+GEN_GO_BIN ?= protoc-gen-go
+GEN_GO_MIN_VERSION ?= 1.31.0
+GEN_GO_VERSION ?= $(shell $(GEN_GO_BIN) --version | awk -F ' v' '{print $$NF}')
+
+# protoc-gen-go-grpc constraints
+GEN_GRPC_BIN ?= protoc-gen-go-grpc
+GEN_GRPC_MIN_VERSION ?= 1.3.0
+GEN_GRPC_VERSION ?= $(shell $(GEN_GRPC_BIN) --version | awk -F ' ' '{print $$NF}')
+
 all: lint generate test
 
 ci: test
@@ -55,7 +65,39 @@ lint:
 # Generate
 #########################################
 
-generate:
-	protoc --proto_path=. --go_out=. --go-grpc_out=. --go_opt=paths=source_relative --go-grpc_opt=paths=source_relative provisioners.proto admin.proto config.proto eab.proto majordomo.proto policy.proto
+generate: check-gen-go-version check-gen-grpc-version
+	@# remove any previously generated protobufs & gRPC files
+	@find . \
+		-type f \
+		-name "*.pb.go" \
+		-delete
+
+	@# generate the corresponding protobufs & gRPC code files
+	find spec -type f -name "*.proto" -print0 | xargs -0 protoc \
+		--proto_path=spec \
+		--go_opt=paths=source_relative \
+		--go_out=.. \
+		--go-grpc_opt=paths=source_relative \
+		--go-grpc_out=..
 
 .PHONY: generate
+
+#########################################
+# Tool constraints
+#########################################
+
+check-gen-go-version:
+	@if ! printf "%s\n%s" "$(GEN_GO_MIN_VERSION)" "$(GEN_GO_VERSION)" | sort -V -C; then \
+		echo "Your $(GEN_GO_BIN) version (v$(GEN_GO_VERSION)) is older than the minimum required (v$(GEN_GO_MIN_VERSION))."; \
+		exit 1; \
+	fi
+
+.PHONY: check-gen-go-version
+
+check-gen-grpc-version:
+	@if ! printf "%s\n%s" "$(GEN_GRPC_MIN_VERSION)" "$(GEN_GRPC_VERSION)" | sort -V -C; then \
+		echo "Your $(GEN_GRPC_BIN) version (v$(GEN_GRPC_VERSION)) is older than the minimum required (v$(GEN_GRPC_MIN_VERSION))."; \
+		exit 1; \
+	fi
+
+.PHONY: check-gen-grpc-version