[config] introduce config package (#4376)

* [config] introduce config package

This change introduces the config package with the following changes:

- add go-jsonschema tool to tools.go
- add `make genjsonschema` target to Makefile
- run the genjsonschema target to generate the code from the opentelemetry configuration schema
- add a readme for the package

Signed-off-by: Alex Boten <aboten@lightstep.com>

.github/dependabot.yml

@@ -109,6 +109,15 @@ updates:
     schedule:
       interval: weekly
       day: sunday
+  - package-ecosystem: gomod
+    directory: /config
+    labels:
+      - dependencies
+      - go
+      - Skip Changelog
+    schedule:
+      interval: weekly
+      day: sunday
   - package-ecosystem: gomod
     directory: /detectors/aws/ec2
     labels:

CHANGELOG.md

@@ -12,6 +12,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Add the new `go.opentelemetry.io/contrib/instrgen` package to provide auto-generated source code instrumentation. (#3068, #3108)
 - Add `"go.opentelemetry.io/contrib/samplers/jaegerremote".WithSamplingStrategyFetcher` which sets custom fetcher implementation. (#4045)
+- Add `"go.opentelemetry.io/contrib/config"` package that includes configuration models generated via go-jsonschema (#4376)
 
 ### Changed
 

Makefile

@@ -74,6 +74,9 @@ $(GOTMPL): PACKAGE=go.opentelemetry.io/build-tools/gotmpl
 GORELEASE = $(TOOLS)/gorelease
 $(GORELEASE): PACKAGE=golang.org/x/exp/cmd/gorelease
 
+GOJSONSCHEMA = $(TOOLS)/go-jsonschema
+$(GOJSONSCHEMA): PACKAGE=github.com/atombender/go-jsonschema
+
 tools: $(GOLANGCI_LINT) $(MISSPELL) $(GOCOVMERGE) $(STRINGER) $(PORTO) $(MULTIMOD) $(DBOTCONF) $(CROSSLINK) $(GOTMPL) $(GORELEASE)
 
 # Generate
@@ -283,3 +286,33 @@ COMMIT ?= "HEAD"
 add-tags: | $(MULTIMOD)
 	@[ "${MODSET}" ] || ( echo ">> env var MODSET is not set"; exit 1 )
 	$(MULTIMOD) verify && $(MULTIMOD) tag -m ${MODSET} -c ${COMMIT}
+
+# The source directory for opentelemetry-configuration schema.
+OPENTELEMETRY_CONFIGURATION_JSONSCHEMA_SRC_DIR=tmp/opentelememetry-configuration
+
+# The SHA matching the current version of the opentelemetry-configuration schema to use
+OPENTELEMETRY_CONFIGURATION_JSONSCHEMA_VERSION=v0.1.0
+
+# Cleanup temporary directory
+genjsonschema-cleanup:
+	rm -Rf ${OPENTELEMETRY_CONFIGURATION_JSONSCHEMA_SRC_DIR}
+
+GENERATED_CONFIG=./config/generated_config.go
+
+# Generate structs for configuration from opentelemetry-configuration schema
+genjsonschema: genjsonschema-cleanup $(GOJSONSCHEMA)
+	mkdir -p ${OPENTELEMETRY_CONFIGURATION_JSONSCHEMA_SRC_DIR}
+	curl -sSL https://api.github.com/repos/open-telemetry/opentelemetry-configuration/tarball/${OPENTELEMETRY_CONFIGURATION_JSONSCHEMA_VERSION} | tar xz --strip 1 -C ${OPENTELEMETRY_CONFIGURATION_JSONSCHEMA_SRC_DIR}
+	$(GOJSONSCHEMA) \
+		--capitalization ID \
+		--capitalization OTLP \
+		--struct-name-from-title \
+		--package config \
+		--tags mapstructure \
+		--output ${GENERATED_CONFIG} \
+		${OPENTELEMETRY_CONFIGURATION_JSONSCHEMA_SRC_DIR}/schema/opentelemetry_configuration.json
+	@echo Modify jsonschema generated files.
+	sed -f ./config/jsonschema_patch.sed ${GENERATED_CONFIG} > ${GENERATED_CONFIG}.tmp
+	mv ${GENERATED_CONFIG}.tmp ${GENERATED_CONFIG}
+	$(MAKE) lint
+	$(MAKE) genjsonschema-cleanup

config/README.md

@@ -0,0 +1,31 @@
+# Configuration Library
+
+This package can be used to parse a configuration file that follows the JSON
+Schema defined by the [OpenTelemetry Configuration] schema.
+
+The package contains:
+
+- models generated via the JSON schema using the [go-jsonschema] library
+- a `Create` function that interprets [configuration model] and return SDK components (TODO)
+- a `Parse` function that parses and validates a [configuration file] (TODO)
+
+## Using the generate model code
+
+The `generated_config.go` code in versioned submodule can be used directly as-is to programmatically
+produce a configuration model that can be then used as a parameter to the `Create` function. Note
+that the package is versioned to match the release versioning of the opentelemetry-configuration
+repository.
+
+## Using the `Create` function (TODO)
+
+## Using the `Parse` function (TODO)
+
+The original code from the package comes from the [OpenTelemetry Collector's service] telemetry
+configuration code. The intent being to share this code across implementations and reduce
+duplication where possible.
+
+[OpenTelemetry Configuration]: https://github.com/open-telemetry/opentelemetry-configuration/
+[go-jsonschema]: https://github.com/omissis/go-jsonschema
+[configuration model]: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/file-configuration.md#configuration-model
+[configuration file]: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/file-configuration.md#configuration-file
+[OpenTelemetry Collector's service]: https://github.com/open-telemetry/opentelemetry-collector/blob/7c5ecef11dff4ce5501c9683b277a25a61ea0f1a/service/telemetry/generated_config.go