bugfix nil pointer no target discovered

[kpango]

Signed-off-by: kpango [email protected]

Description:

@datelier reports this bug in the commit c1addd2
when no target connection found gRPC client continue to discover and connect to target,
but there is no target Connect method returns Error and nil connection which makes nil-pointer panic for logging.

2021-03-02 15:00:37     [WARN]: recovered: %+v                                                                                                                                                               
stacktrace:                                                                                                                                                                                                  
%s runtime error: invalid memory address or nil pointer dereference goroutine 119 [running]:                                                                                                                 
runtime/debug.Stack(0xc0004f3590, 0x11a3aa0, 0x1cea7d0)                                                                                                                                                      
        runtime/debug/stack.go:24 +0x9f                                                                                                                                                                      
github.com/vdaas/vald/internal/safety.recoverFunc.func1.1(0xc0004f3e30, 0x1)                                                                                                                                 
        github.com/vdaas/vald/internal/safety/safety.go:41 +0x79                                                                                                                                             
panic(0x11a3aa0, 0x1cea7d0)                                                                                                                                                                                  
        runtime/panic.go:969 +0x1b9                                                                                                                                                                          
github.com/vdaas/vald/internal/net/grpc.(*gRPCClient).Connect.func2(0xc000682dc0, 0x1, 0xc0003eb4d0, 0x10fa580)                                                                                              
        github.com/vdaas/vald/internal/net/grpc/client.go:570 +0x1093                                                                                                                                        
github.com/vdaas/vald/internal/singleflight.(*group).Do(0xc000422f60, 0x1545be0, 0xc000804f60, 0xc0003b6c90, 0x2b, 0xc000824eb0, 0x2b, 0x479f49, 0x203000, 0x203000, ...)                                    
        github.com/vdaas/vald/internal/singleflight/singleflight.go:62 +0xd8                                                                                                                                 
github.com/vdaas/vald/internal/net/grpc.(*gRPCClient).Connect(0xc00032c500, 0x1545be0, 0xc000804f60, 0xc0000440f0, 0x23, 0x0, 0x0, 0x0, 0x0, 0x0, ...)                                                       
        github.com/vdaas/vald/internal/net/grpc/client.go:556 +0x274                                                                                                                                         
github.com/vdaas/vald/internal/net/grpc.(*gRPCClient).StartConnectionMonitor.func1.3(0x11390c0, 0xc0003fd690, 0x1124440, 0x1ca8060, 0xc0004f3b00)                                                            
        github.com/vdaas/vald/internal/net/grpc/client.go:261 +0x190                                                                                                                                         
sync.(*Map).Range(0xc00032c600, 0xc0004f3cc0)                                                                                                                                                                
        sync/map.go:345 +0x1d9                                                                                                                                                                               
github.com/vdaas/vald/internal/net/grpc.(*gRPCClient).StartConnectionMonitor.func1(0x0, 0x0)                                                                                                                 
        github.com/vdaas/vald/internal/net/grpc/client.go:245 +0x40c                                                                                                                                         
github.com/vdaas/vald/internal/safety.recoverFunc.func1(0x0, 0x0)                                                                                                                                            
        github.com/vdaas/vald/internal/safety/safety.go:63 +0x65                                                                                                                                             
github.com/vdaas/vald/internal/errgroup.(*group).Go.func1(0xc00022ec80, 0xc0005e85c0)                                                                                                                        
        github.com/vdaas/vald/internal/errgroup/group.go:110 +0xd6                                                                                                                                           
created by github.com/vdaas/vald/internal/errgroup.(*group).Go                                                                                                                                               
        github.com/vdaas/vald/internal/errgroup/group.go:100 +0x7a

Related Issue:

How Has This Been Tested?:

Environment:

• Go Version: 1.16
• Docker Version: 19.03.8
• Kubernetes Version: 1.18.2
• NGT Version: 1.12.3

Types of changes:

• Bug fix [type/bug]
• New feature [type/feature]
• Add tests [type/test]
• Security related changes [type/security]
• Add documents [type/documentation]
• Refactoring [type/refactoring]
• Update dependencies [type/dependency]
• Update benchmarks and performances [type/bench]
• Update CI [type/ci]

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

Checklist:

• I have read the CONTRIBUTING document.
• I have checked open Pull Requests for the similar feature or fixes?
• I have added tests and benchmarks to cover my changes.
• I have ensured all new and existing tests passed.
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly.

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[codecov]

Codecov Report

Merging #1055 (476f5f9) into master (691e2f7) will decrease coverage by 0.58%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1055      +/-   ##
==========================================
- Coverage   15.02%   14.43%   -0.59%     
==========================================
  Files         497      494       -3     
  Lines       28703    28351     -352     
==========================================
- Hits         4313     4093     -220     
+ Misses      24119    24007     -112     
+ Partials      271      251      -20     

Impacted Files	Coverage Δ
internal/net/grpc/client.go	0.00% <0.00%> (ø)
internal/net/grpc/pool/pool.go	0.00% <0.00%> (ø)
internal/worker/queue.go	95.00% <0.00%> (-3.34%)	⬇️
internal/net/dialer.go
internal/net/net.go
internal/net/option.go
internal/db/storage/blob/s3/reader/reader.go	94.56% <0.00%> (+31.52%)	⬆️

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