Document OSS dependencies and their license (#844)

README.md

@@ -37,6 +37,10 @@ of the current project.
 In general, the code shipped from this repository should build on all platforms
 having C++ compiler with [supported C++ standards](#supported-c-versions).
 
+## Dependencies
+
+Please refer to [Dependencies.md](docs/dependencies.md) for OSS Dependencies and license requirements.
+
 ## Installation
 
 Please refer to [INSTALL.md](./INSTALL.md).

docs/dependencies.md

@@ -0,0 +1,64 @@
+# Dependencies and Licenses
+
+There are
+
+- External dependencies as linkable libraries or externally installed headers, and
+- Internal dependencies as the part of code from external libraries backported/copied in main repo.
+
+Both these dependencies are listed here:
+
+## Internal dependencies
+
+- [nostd::variant](https://github.com/open-telemetry/opentelemetry-cpp/blob/v1.0.0-rc1/api/include/opentelemetry/nostd/absl/types/variant.h): This is backported from [Abseil C++ libraries](https://github.com/abseil/abseil-cpp) and used as default variant implementation. License: `Apache License 2.0`
+- [nostd::span](https://github.com/open-telemetry/opentelemetry-cpp/blob/v1.0.0-rc1/api/include/opentelemetry/nostd/span.h): This is backported from libstdc++-v3 and used as default span implementation. License: `GNU General Public License`
+- [TraceLoggingDynamic](https://github.com/open-telemetry/opentelemetry-cpp/blob/v1.0.0-rc1/exporters/etw/include/opentelemetry/exporters/etw/TraceLoggingDynamic.h): Dynamic TraceLogging Provider API for C++ used by ETW exporter. License: `MIT License`
+
+## External dependencies
+
+- [API](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/api) & [SDK](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/sdk):
+  - Uses Standard C++ library for latest features (std::string_view, std::variant, std::span, std::shared_ptr, std::unique_ptr) with  C++14/17/20 compiler if `WITH_STL` cmake option is enabled or `HAVE_CPP_STDLIB` macro is defined. License: `GNU General Public License`
+    - For C++11/14/17 compilers, fallback to gsl::span if [GSL C++ library](https://github.com/microsoft/GSL) is installed. License: `MIT License`
+  - Uses Abseil C++ Library for `absl::variant` as default `nostd::variant` if `WITH_ABSEIL` cmake option is enabled. License: `Apache License 2.0`
+
+- [OTLP/HTTP+JSON](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/exporters/otlp) exporter:
+  - [protobuf](https://github.com/protocolbuffers/protobuf):  Library to serialize structured data.
+    - OTLP messages are constructed as protobuf payloads.
+    - `protoc` compiler is used to generate C++ stubs for proto files provided by `opentelemetry-proto`.
+    - `libprotobuf` library is used for generating serialised trace/metrics/log data to be sent to opentelemetry collector.
+    - License: The library is licensed [here](https://github.com/protocolbuffers/protobuf/blob/master/LICENSE). The  code generated by protoc compiler is owned by the owner of `.proto` file.
+  - [libcurl](https://curl.se/libcurl/) : the multiprotocol file transfer library.
+    - Export connects with opentelemetry collector over HTTP protocol using libcurl library
+    - License: Inspired by `MIT/X` but not same. <https://curl.se/docs/copyright.html>
+  - [nlohmann/json](https://github.com/nlohmann/json): JSON for Modern C++.
+    - protobuf serialized otlp messages are encoded in JSON format using this library.
+    - License: `MIT License`
+
+- [OTLP/gRPC](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/exporters/otlp) exporter:
+  - `protobuf`  OTLP messages are constructed as protobuf payloads.
+  - [gRPC](https://github.com/grpc/grpc): An RPC library and framework
+    - Exporter communicates with OTLP collector using gRPC transport mechanism.
+    - License: `Apache License 2.0`
+
+- [Zipkin](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/exporters/zipkin) exporter:
+  - `libcurl` for connecting with Zipkin server over HTTP protocol.
+  - `nlohmann/json` for encoding Zipkin messages.
+
+- [Jaeger](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/exporters/jaeger) exporter:
+  - [Thrift](https://github.com/apache/thrift) - Serialization and RPC framework.
+    - `thrift` compiler to generate C++ stubs for IDL data model for Jaeger.
+    - `libthrift`  library to generate serialised trace/metrics/log data to be sent to remote Jaeger service.
+    - License: `Apache License 2.0`
+
+- [ETW](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/exporters/etw) exporter:
+  - `nlohmann/json` for generating MessagePack serialization for message to be transmitted to ETW.
+
+- [Prometheus](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/exporters/prometheus) exporter:
+  - [`prometheus-cpp`](https://github.com/jupp0r/prometheus-cpp) Prometheus Client Library for Modern C++
+    - License: `MIT License`
+
+- [ElasticSearch](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/exporters/elasticsearch) exporter:
+  - `libcurl` for connecting with Elasticsearch server over HTTP protocol.
+  - `nlohmann/json` for encoding Elastic Search messages.
+
+- [Zpages](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/ext/src/zpages):
+  - None