Fix a compiling issue of the official example because of the following error :
```
error[E0599]: the method `execute` exists for struct `BaseChannel<_, _, UnboundedChannel<ClientMessage<_>, Response<_>>>`, but its trait bounds were not satisfied
--> src/main.rs:39:25
|
39 | tokio::spawn(server.execute(HelloServer.serve()));
| ^^^^^^^ method cannot be called on `BaseChannel<_, _, UnboundedChannel<ClientMessage<_>, Response<_>>>` due to unsatisfied trait bounds
|
= note: the following trait bounds were not satisfied:
`<&BaseChannel<_, _, UnboundedChannel<ClientMessage<_>, Response<_>>> as futures::Stream>::Item = _`
which is required by `&BaseChannel<_, _, UnboundedChannel<ClientMessage<_>, Response<_>>>: tarpc::server::incoming::Incoming<_>`
`&BaseChannel<_, _, UnboundedChannel<ClientMessage<_>, Response<_>>>: futures::Stream`
which is required by `&BaseChannel<_, _, UnboundedChannel<ClientMessage<_>, Response<_>>>: tarpc::server::incoming::Incoming<_>`
= help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope; perhaps add a `use` for it:
|
1 | use tarpc::server::Channel;
|
```
See https://github.com/google/tarpc/pull/358#issuecomment-981953193 for the root cause.
In the interest of the user's attention, some ancillary APIs have been
moved to new submodules:
- server::limits contains what was previously called Throttler and
ChannelFilter. Both of those names were very generic, when the methods
applied by these types were very specific (and also simplistic). Renames
have occurred:
- ThrottlerStream => MaxRequestsPerChannel
- Throttler => MaxRequests
- ChannelFilter => MaxChannelsPerKey
- server::incoming contains the Incoming trait.
- server::tokio contains the tokio-specific helper types.
The 5 structs and 1 enum remaining in the base server module are all
core to the functioning of the server.
tarpc is now instrumented with tracing primitives extended with
OpenTelemetry traces. Using a compatible tracing-opentelemetry
subscriber like Jaeger, each RPC can be traced through the client,
server, amd other dependencies downstream of the server. Even for
applications not connected to a distributed tracing collector, the
instrumentation can also be ingested by regular loggers like env_logger.
# Breaking Changes
## Logging
Logged events are now structured using tracing. For applications using a
logger and not a tracing subscriber, these logs may look different or
contain information in a less consumable manner. The easiest solution is
to add a tracing subscriber that logs to stdout, such as
tracing_subscriber::fmt.
## Context
- Context no longer has parent_span, which was actually never needed,
because the context sent in an RPC is inherently the parent context.
For purposes of distributed tracing, the client side of the RPC has all
necessary information to link the span to its parent; the server side
need do nothing more than export the (trace ID, span ID) tuple.
- Context has a new field, SamplingDecision, which has two variants,
Sampled and Unsampled. This field can be used by downstream systems to
determine whether a trace needs to be exported. If the parent span is
sampled, the expectation is that all child spans be exported, as well;
to do otherwise could result in lossy traces being exported. Note that
if an Openetelemetry tracing subscriber is not installed, the fallback
context will still be used, but the Context's sampling decision will
always be inherited by the parent Context's sampling decision.
- Context::scope has been removed. Context propagation is now done via
tracing's task-local spans. Spans can be propagated across tasks via
Span::in_scope. When a service receives a request, it attaches an
Opentelemetry context to the local Span created before request handling,
and this context contains the request deadline. This span-local deadline
is retrieved by Context::current, but it cannot be modified so that
future Context::current calls contain a different deadline. However, the
deadline in the context passed into an RPC call will override it, so
users can retrieve the current context and then modify the deadline
field, as has been historically possible.
- Context propgation precedence changes: when an RPC is initiated, the
current Span's Opentelemetry context takes precedence over the trace
context passed into the RPC method. If there is no current Span, then
the trace context argument is used as it has been historically. Note
that Opentelemetry context propagation requires an Opentelemetry
tracing subscriber to be installed.
## Server
- The server::Channel trait now has an additional required associated
type and method which returns the underlying transport. This makes it
more ergonomic for users to retrieve transport-specific information,
like IP Address. BaseChannel implements Channel::transport by returning
the underlying transport, and channel decorators like Throttler just
delegate to the Channel::transport method of the wrapped channel.
# References
[1] https://github.com/tokio-rs/tracing
[2] https://opentelemetry.io
[3] https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-jaeger
[4] https://github.com/env-logger-rs/env_logger
1. Renames
Some of the items in this module were renamed to be less generic:
- Handler => Incoming
- ClientHandler => Requests
- ResponseHandler => InFlightRequest
- Channel::{respond_with => requests}
In the case of Handler: handler of *what*? Now it's a bit clearer that
this is a stream of Channels (aka *incoming* connections).
Similarly, ClientHandler was a stream of requests over a single
connection. Hopefully Requests better reflects that.
ResponseHandler was renamed InFlightRequest because it no longer
contains the serving function. Instead, it is just the request, plus
the response channel and an abort hook. As a result of this,
Channel::respond_with underwent a big change: it used to take the
serving function and return a ClientHandler; now it has been renamed
Channel::requests and does not take any args.
2. Execute methods
All methods thats actually result in responses being generated
have been consolidated into methods named `execute`:
- InFlightRequest::execute returns a future that completes when a
response has been generated and sent to the server Channel.
- Requests::execute automatically spawns response handlers for all
requests over a single channel.
- Channel::execute is a convenience for `channel.requests().execute()`.
- Incoming::execute automatically spawns response handlers for all
requests over all channels.
3. Removal of Server.
server::Server was removed, as it provided no value over the Incoming/Channel
abstractions. Additionally, server::new was removed, since it just
returned a Server.
As part of this, I made an optional tokio feature which, when enabled,
adds utility functions that spawn on the default tokio executor. This
allows for the removal of the runtime crate.
On the one hand, this makes the spawning utils slightly less generic. On
the other hand:
- The fns are just helpers and are easily rewritten by the user.
- Tokio is the clear dominant futures executor, so most people will just
use these versions.
Send + 'static was baked in to make it possible to spawn futures onto
the default executor. We can accomplish the same thing by offering
helper fns that do the spawning while not requiring it for the rest of
the functionality.
Fixes https://github.com/google/tarpc/issues/212
- fn serve -> Service::serve
- fn new_stub -> Client::new
This allows the generated function names to remain consistent across
service definitions while preventing collisions.
