privval: refactor Remote signers (#3370)

This PR is related to #3107 and a continuation of #3351

It is important to emphasise that in the privval original design, client/server and listening/dialing roles are inverted and do not follow a conventional interaction.

Given two hosts A and B:

    Host A is listener/client
    Host B is dialer/server (contains the secret key)
    When A requires a signature, it needs to wait for B to dial in before it can issue a request.
    A only accepts a single connection and any failure leads to dropping the connection and waiting for B to reconnect.

The original rationale behind this design was based on security.

    Host B only allows outbound connections to a list of whitelisted hosts.
    It is not possible to reach B unless B dials in. There are no listening/open ports in B.

This PR results in the following changes:

    Refactors ping/heartbeat to avoid previously existing race conditions.
    Separates transport (dialer/listener) from signing (client/server) concerns to simplify workflow.
    Unifies and abstracts away the differences between unix and tcp sockets.
    A single signer endpoint implementation unifies connection handling code (read/write/close/connection obj)
    The signer request handler (server side) is customizable to increase testability.
    Updates and extends unit tests

A high level overview of the classes is as follows:

Transport (endpoints): The following classes take care of establishing a connection

    SignerDialerEndpoint
    SignerListeningEndpoint
    SignerEndpoint groups common functionality (read/write/timeouts/etc.)

Signing (client/server): The following classes take care of exchanging request/responses

    SignerClient
    SignerServer

This PR also closes #3601

Commits:

* refactoring - work in progress

* reworking unit tests

* Encapsulating and fixing unit tests

* Improve tests

* Clean up

* Fix/improve unit tests

* clean up tests

* Improving service endpoint

* fixing unit test

* fix linter issues

* avoid invalid cache values (improve later?)

* complete implementation

* wip

* improved connection loop

* Improve reconnections + fixing unit tests

* addressing comments

* small formatting changes

* clean up

* Update node/node.go

Co-Authored-By: jleni <juan.leni@zondax.ch>

* Update privval/signer_client.go

Co-Authored-By: jleni <juan.leni@zondax.ch>

* Update privval/signer_client_test.go

Co-Authored-By: jleni <juan.leni@zondax.ch>

* check during initialization

* dropping connecting when writing fails

* removing break

* use t.log instead

* unifying and using cmn.GetFreePort()

* review fixes

* reordering and unifying drop connection

* closing instead of signalling

* refactored service loop

* removed superfluous brackets

* GetPubKey can return errors

* Revert "GetPubKey can return errors"

This reverts commit 68c06f19b4.

* adding entry to changelog

* Update CHANGELOG_PENDING.md

Co-Authored-By: jleni <juan.leni@zondax.ch>

* Update privval/signer_client.go

Co-Authored-By: jleni <juan.leni@zondax.ch>

* Update privval/signer_dialer_endpoint.go

Co-Authored-By: jleni <juan.leni@zondax.ch>

* Update privval/signer_dialer_endpoint.go

Co-Authored-By: jleni <juan.leni@zondax.ch>

* Update privval/signer_dialer_endpoint.go

Co-Authored-By: jleni <juan.leni@zondax.ch>

* Update privval/signer_dialer_endpoint.go

Co-Authored-By: jleni <juan.leni@zondax.ch>

* Update privval/signer_listener_endpoint_test.go

Co-Authored-By: jleni <juan.leni@zondax.ch>

* updating node.go

* review fixes

* fixes linter

* fixing unit test

* small fixes in comments

* addressing review comments

* addressing review comments 2

* reverting suggestion

* Update privval/signer_client_test.go

Co-Authored-By: Anton Kaliaev <anton.kalyaev@gmail.com>

* Update privval/signer_client_test.go

Co-Authored-By: Anton Kaliaev <anton.kalyaev@gmail.com>

* Update privval/signer_listener_endpoint_test.go

Co-Authored-By: Anton Kaliaev <anton.kalyaev@gmail.com>

* do not expose brokenSignerDialerEndpoint

* clean up logging

* unifying methods

shorten test time
signer also drops

* reenabling pings

* improving testability + unit test

* fixing go fmt + unit test

* remove unused code

* Addressing review comments

* simplifying connection workflow

* fix linter/go import issue

* using base service quit

* updating comment

* Simplifying design + adjusting names

* fixing linter issues

* refactoring test harness + fixes

* Addressing review comments

* cleaning up

* adding additional error check

node/node_test.go

@@ -136,25 +136,29 @@ func TestNodeSetPrivValTCP(t *testing.T) {
 	config.BaseConfig.PrivValidatorListenAddr = addr
 
 	dialer := privval.DialTCPFn(addr, 100*time.Millisecond, ed25519.GenPrivKey())
-	pvsc := privval.NewSignerServiceEndpoint(
+	dialerEndpoint := privval.NewSignerDialerEndpoint(
 		log.TestingLogger(),
-		config.ChainID(),
-		types.NewMockPV(),
 		dialer,
 	)
-	privval.SignerServiceEndpointTimeoutReadWrite(100 * time.Millisecond)(pvsc)
+	privval.SignerDialerEndpointTimeoutReadWrite(100 * time.Millisecond)(dialerEndpoint)
+
+	signerServer := privval.NewSignerServer(
+		dialerEndpoint,
+		config.ChainID(),
+		types.NewMockPV(),
+	)
 
 	go func() {
-		err := pvsc.Start()
+		err := signerServer.Start()
 		if err != nil {
 			panic(err)
 		}
 	}()
-	defer pvsc.Stop()
+	defer signerServer.Stop()
 
 	n, err := DefaultNewNode(config, log.TestingLogger())
 	require.NoError(t, err)
-	assert.IsType(t, &privval.SignerValidatorEndpoint{}, n.PrivValidator())
+	assert.IsType(t, &privval.SignerClient{}, n.PrivValidator())
 }
 
 // address without a protocol must result in error
@@ -178,13 +182,17 @@ func TestNodeSetPrivValIPC(t *testing.T) {
 	config.BaseConfig.PrivValidatorListenAddr = "unix://" + tmpfile
 
 	dialer := privval.DialUnixFn(tmpfile)
-	pvsc := privval.NewSignerServiceEndpoint(
+	dialerEndpoint := privval.NewSignerDialerEndpoint(
 		log.TestingLogger(),
-		config.ChainID(),
-		types.NewMockPV(),
 		dialer,
 	)
-	privval.SignerServiceEndpointTimeoutReadWrite(100 * time.Millisecond)(pvsc)
+	privval.SignerDialerEndpointTimeoutReadWrite(100 * time.Millisecond)(dialerEndpoint)
+
+	pvsc := privval.NewSignerServer(
+		dialerEndpoint,
+		config.ChainID(),
+		types.NewMockPV(),
+	)
 
 	go func() {
 		err := pvsc.Start()
@@ -194,8 +202,7 @@ func TestNodeSetPrivValIPC(t *testing.T) {
 
 	n, err := DefaultNewNode(config, log.TestingLogger())
 	require.NoError(t, err)
-	assert.IsType(t, &privval.SignerValidatorEndpoint{}, n.PrivValidator())
-
+	assert.IsType(t, &privval.SignerClient{}, n.PrivValidator())
 }
 
 // testFreeAddr claims a free port so we don't block on listener being ready.