HTTP client API for exporter developers

[open-telemetry]

HTTP client API for exporter developers

[jajanet]

Was this addressed in #217? Maybe we can update this issue to needing to add thread-safety, optimizations, or other measures if so?

[SamuelMarks]

I started working on a common interface last quarter, but it's very much a WiP:

libacquire

The core for your package manager, minus the dependency graph components. Features: download, verify, and extract.

By default—for HTTP, HTTPS, and FTP—this uses libfetch on FreeBSD; wininet on Windows; and libcurl everywhere else. Override with -DUSE_LIBCURL or -DUSE_LIBFETCH.

By default—for MD5, SHA256, SHA512—this uses wincrypt on Windows; and OpenSSL everywhere else. Note that on macOS this uses the builtin CommonCrypto/CommonDigest.h header, and on OpenBSD it uses LibreSSL; however in both of these cases it's the OpenSSL API with different headers. Override with -DUSE_OPENSSL.

Mentioning here not so that you follow my implementation, but rather the reverse; the common interface you come up with I'll [likely follow and] implement for Solaris, Linux, BSD, macOS, and Windows.

(though maybe you'll be inspired by the idea of libacquire in defining said interface)

[kyessenov]

Please consider adding nghttp2-based stacks (https://github.com/envoyproxy/envoy) to the list.

[SamuelMarks]

You might want to start from https://github.com/aws/aws-sdk-cpp/tree/master/aws-cpp-sdk-core/source/http

[lalitb]

#217 brings only http server, we still are missing client part. So either we can modify it to work as thread-safe, optimised http client/server library, or else use header only c++11 cross platform library like https://github.com/yhirose/cpp-httplib. Anyway, I can own this if no one is working on it. We would anyway need it for zipkin support.

[kyessenov]

I think we want a portable interface but not an implementation. Consider the use case of compiling this library to Wasm and substituting regular POSIX calls with Wasm externs. Anything that talks over the network cannot be directly translated to Wasm.