Support sending a serialized envelope via Transport

[kornelski]

I need to report errors from a process that runs in an off-line sandbox, without its own access to a network. The process can serialize and pass on messages to be sent from another process (like Chrome Renderer helper and Chrome root process). Related to #281

Sentry supports pluggable Transport which can be used to capture an Envelope, and Envelope supports serialization via to_writer, so I can move it between processes easily. However, the Transport trait can't send a serialized &[u8] representation of the envelope, so I can't reuse Sentry's implementation of networked transports. I need to reinvent the whole transport logic myself, including retry-after and rate limiting logic, which I'd rather not duplicate.

• Could you extend the Transport trait to support sending of an already-serialized envelope from &[u8] or Vec<u8> representation?

• Or, could you make it possible to parse Envelope object back from its serialized representation, so that I can feed it back to a Transport?

• Alternatively, could you make TransportThread public, so I would only need to copy-paste only the easy parts of an http client implementation?

[Swatinem]

I think one way to solve this would be to create a "raw" Envelope, similar to what we have in sentry-native.

Also, I wanted to expose the retry-after and rate-limiting logic so that it can be reused by third parties. I think we will be doing that soon-ish.

[kamilogorek]

@Swatinem please ping me once it's decided and implemented, so I'll pull this down to sentry-cli as well :)

[smeubank]

@Swatinem any update on this? We added this to our sentry-cli roadmap #1168

[Swatinem]

We haven’t planned for this yet. However I don’t expect this to be a huge change.