[BP 7.0.2 MB-47475] - Prevent Indexer Crash with PlasmaDiag invalid DB instance

Today, we pass db instance which are basically golang pointers as argument for plasmaDiag REST API calls. If we provide garbage as instance ids, dereferencing can either lead to panics or unhandled exceptions such as the one below. For the latter, is not a recoverable error in golang and results in crashing the indexer.
 
   In addition from security point of view, it is not advisable to expose internal memory addresses through any REST APIs.
 
indexer.log:
 
2021-07-15T18:35:00.300-07:00 [Info] ServiceMgr::GetCurrentTopology returns &{[0 0 0 0 0 0 0 8] [c62eca2248e32c85977ca9f23b06526d 401ed77c7ecd37ba800de7ef65c10cc4 4af441577ad164362dd80795081f7ab1 47679e6d345699b6db3e938577573f32] true []}
2021-07-15T18:35:00.303-07:00 [Info] ServiceMgr::GetCurrentTopology [0 0 0 0 0 0 0 8]
2021-07-15T18:35:11.696-07:00 [Info] ServiceMgr::rebalanceJanitor Running Periodic Cleanup
unexpected fault address 0x6967
fatal error: fault
[signal SIGSEGV: segmentation violation code=0x1 addr=0x6967 pc=0x491846b]
 
goroutine 4338 [running]:
runtime.throw(0x4ea51a3, 0x5)
/Users/saptarshisen/.cbdepscache/exploded/x86_64/go-1.16.5/go/src/runtime/panic.go:1117 +0x72 fp=0xc00561ebb8 sp=0xc00561eb88 pc=0x403bbb2
runtime.sigpanic()
/Users/saptarshisen/.cbdepscache/exploded/x86_64/go-1.16.5/go/src/runtime/signal_unix.go:741 +0x276 fp=0xc00561ebf0 sp=0xc00561ebb8 pc=0x4053216
github.com/couchbase/plasma.(*Plasma).getStats(0x63df, 0x4ec8f00, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
/Users/saptarshisen/ws/couchbase_svr/goproj/src/github.com/couchbase/plasma/plasma.go:851 +0xab fp=0xc00561eed8 sp=0xc00561ebf0 pc=0x491846b
github.com/couchbase/plasma.(*Plasma).GetStats(...)
/Users/saptarshisen/ws/couchbase_svr/goproj/src/github.com/couchbase/plasma/plasma.go:834
github.com/couchbase/plasma.(*diag).Command(0x5940568, 0xc0062f6bc8, 0x5, 0xc005f7ed00, 0xc005f7ecc0, 0x1, 0x4)
/Users/saptarshisen/ws/couchbase_svr/goproj/src/github.com/couchbase/plasma/diag.go:164 +0xe4d fp=0xc00561f9d0 sp=0xc00561eed8 pc=0x48e284d
github.com/couchbase/plasma.(*diag).HandleHttp(0x5940568, 0x50596c0, 0xc000277b20, 0xc004a72a00)
/Users/saptarshisen/ws/couchbase_svr/goproj/src/github.com/couchbase/plasma/diag.go:362 +0x19e fp=0xc00561fa58 sp=0xc00561f9d0 pc=0x48e327e
github.com/couchbase/indexing/secondary/indexer.(*settingsManager).handlePlasmaDiag(0xc0001541e0, 0x50596c0, 0xc000277b20, 0xc004a72a00)
/Users/saptarshisen/ws/couchbase_svr/goproj/src/github.com/couchbase/indexing/secondary/indexer/settings.go:240 +0xfa fp=0xc00561fab8 sp=0xc00561fa58 pc=0x4b46e1a
github.com/couchbase/indexing/secondary/indexer.(*settingsManager).handlePlasmaDiag-fm(0x50596c0, 0xc000277b20, 0xc004a72a00)
/Users/saptarshisen/ws/couchbase_svr/goproj/src/github.com/couchbase/indexing/secondary/indexer/settings.go:230 +0x51 fp=0xc00561fae8 sp=0xc00561fab8 pc=0x4beceb1
net/http.HandlerFunc.ServeHTTP(0xc000629730, 0x50596c0, 0xc000277b20, 0xc004a72a00)
/Users/saptarshisen/.cbdepscache/exploded/x86_64/go-1.16.5/go/src/net/http/server.go:2069 +0x44 fp=0xc00561fb10 sp=0xc00561fae8 pc=0x42ce484
net/http.(*ServeMux).ServeHTTP(0xc00061f1c0, 0x50596c0, 0xc000277b20, 0xc004a72a00)
/Users/saptarshisen/.cbdepscache/exploded/x86_64/go-1.16.5/go/src/net/http/server.go:2448 +0x1ad fp=0xc00561fb70 sp=0xc00561fb10 pc=0x42d030d
net/http.serverHandler.ServeHTTP(0xc0006627e0, 0x50596c0, 0xc000277b20, 0xc004a72a00)
/Users/saptarshisen/.cbdepscache/exploded/x86_64/go-1.16.5/go/src/net/http/server.go:2887 +0xa3 fp=0xc00561fba0 sp=0xc00561fb70 pc=0x42d1a43
net/http.(*conn).serve(0xc005993680, 0x5063860, 0xc005f7eb80)
/Users/saptarshisen/.cbdepscache/exploded/x86_64/go-1.16.5/go/src/net/http/server.go:1952 +0x8cd fp=0xc00561ffc8 sp=0xc00561fba0 pc=0x42ccf6d
runtime.goexit()
/Users/saptarshisen/.cbdepscache/exploded/x86_64/go-1.16.5/go/src/runtime/asm_amd64.s:1371 +0x1 fp=0xc00561ffd0 sp=0xc00561ffc8 pc=0x4075281
created by net/http.(*Server).Serve
/Users/saptarshisen/.cbdepscache/exploded/x86_64/go-1.16.5/go/src/net/http/server.go:3013 +0x39b
 
client side:
python3 diag_client.py --port 9102 --stats 1

default/#primary/Mainstore#3083721504090702076:0

Traceback (most recent call last):

  File "/usr/local/lib/python3.9/site-packages/urllib3/connectionpool.py", line 699, in urlopen

    httplib_response = self._make_request(

  File "/usr/local/lib/python3.9/site-packages/urllib3/connectionpool.py", line 445, in _make_request

    six.raise_from(e, None)

  File "<string>", line 3, in raise_from

  File "/usr/local/lib/python3.9/site-packages/urllib3/connectionpool.py", line 440, in _make_request

    httplib_response = conn.getresponse()

  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 1347, in getresponse

    response.begin()

  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 307, in begin

    version, status, reason = self._read_status()

  File "/usr/local/Cellar/python@3.9/3.9.2_4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/http/client.py", line 276, in _read_status

    raise RemoteDisconnected("Remote end closed connection without"

http.client.RemoteDisconnected: Remote end closed connection without response