feat(otlp): add openssl feature flags for grpcio (#367)

opentelemetry-otlp/Cargo.toml

@@ -27,6 +27,10 @@ grpcio = "0.6"
 opentelemetry = { version = "0.10", default-features = false, features = ["trace"], path = "../opentelemetry" }
 protobuf = "2.18"
 
+[features]
+openssl = ["grpcio/openssl"]
+openssl-vendored = ["grpcio/openssl-vendored"]
+
 [build-dependencies]
 protobuf-codegen = "2.16"
 protoc-grpcio = "2.0"

opentelemetry-otlp/README.md

@@ -120,3 +120,16 @@ fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>> {
     Ok(())
 }
 ```
+
+## Feature flags
+
+By default `opentelemetry-otlp` uses `boringssl` for grpc crypto. You can switch
+this to use `openssl` by enabling the `openssl` feature:
+
+```toml
+[dependencies]
+opentelemetry-otlp = { version = "*", features = ["openssl"] }
+```
+
+If you would like to use a vendored `openssl` version, use the `openssl-vendored` feature.
+For more info, see https://github.com/tikv/grpc-rs#feature-openssl-and-openssl-vendored.

opentelemetry-otlp/src/lib.rs

@@ -95,6 +95,18 @@
 //!     Ok(())
 //! }
 //! ```
+//! ## Feature flags
+//!
+//! By default `opentelemetry-otlp` uses `boringssl` for grpc crypto. You can switch
+//! this to use `openssl` by enabling the `openssl` feature:
+//!
+//! ```toml
+//! [dependencies]
+//! opentelemetry-otlp = { version = "*", features = ["openssl"] }
+//! ```
+//!
+//! If you would like to use a vendored `openssl` version, use the `openssl-vendored` feature.
+//! For more info, see https://github.com/tikv/grpc-rs#feature-openssl-and-openssl-vendored.
 #![warn(
     future_incompatible,
     missing_debug_implementations,