fixes#2078
A status with invalid utf-8 characters could still be created, but invalid characters will be replaced with [Unicode replacement character](https://en.wikipedia.org/wiki/Specials_(Unicode_block)#Replacement_character) before being sent out. Those bytes will still be percent encoded.
All details added to this invalid status will be dropped.
fixes#2078
A status with invalid utf-8 characters could still be created, but invalid characters will be replaced with [Unicode replacement character](https://en.wikipedia.org/wiki/Specials_(Unicode_block)#Replacement_character) before being sent out. Those bytes will still be percent encoded.
All details added to this invalid status will be dropped.
Reverts grpc/grpc-go#2098
Appengine will fail with the error below:
```
go-app-builder: Failed parsing input: parser: bad import "syscall" in google.golang.org/grpc/channelz/funcs.go from GOPATH
```
The root cause of it is in type_linux.go.
629f6bc5e5/channelz/types_linux.go (L21-L25)
This PR splits out grpclb from grpc. I have made the PR in several commits so you can see more clearly the steps that happened.
There are a few possibly contentious points that I would like to make clear up front:
* grpclb will no longer autoload as a load balancer. I think this is okay, as service config is not widely (at all?) used, and I believe this is the only way to access it.
* `internal` is used more, as a way of having code shared between packages without exposing types
* ConnectivityStateEvaluator, as used by grpclb, is no longer thread safe. I believe there is an outer mutex that guards access, but I want to point out this subtle change up here.
All but one tests pass with this, due to another cyclic dependency. I can fix this, but it is a little more widely scoped (such as exposing grpc.server and grpc.errorDesc in the internal package). This PR is a nearly-passing sample of that last step to get this working.
PTAL @menghanl @dfawley
* Don't send nil requests.
* Fix import name and get rid of condition.
* Let registered encoder deal with nil requests.
* Break encode into encode and compress.
This change introduces some behavior changes that should not impact users that
are following the proper stream protocol. Specifically, one of the following
conditions must be satisfied:
1. The user calls Close on the ClientConn.
2. The user cancels the context provided to NewClientStream, or its deadline
expires. (Note that it if the context is no longer needed before the deadline
expires, it is still recommended to call cancel to prevent bloat.) It is always
recommended to cancel contexts when they are no longer needed, and to
never use the background context directly, so all users should always be
doing this.
3. The user calls RecvMsg (or Recv in generated code) until a non-nil error is
returned.
4. The user receives any error from Header or SendMsg (or Send in generated
code) besides io.EOF. If none of the above happen, this will leak a goroutine
and a context, and grpc will not call the optionally-configured stats handler
with a stats.End message.
Before this change, if a user created a stream and the server ended the stream,
the stats handler would be invoked with a stats.End containing the final status
of the stream. Subsequent calls to RecvMsg would then trigger the stats handler
with InPayloads, which may be unexpected by stats handlers.
New connections can race with GracefulStop such that the server will accept the connection, but then close it immediately. If a connection is accepted before GracefulStop has a chance to effectively cancel the listeners, the server should handle it to avoid client errors.
WithBalancerName dial option specifies the name of the balancer to be used by the ClientConn. Service config updates can NOT override the balancer option.
lyuxuan