thetorpedodog commented on a change in pull request #11413: [BEAM-9746] check 
for 0 length copies from state
URL: https://github.com/apache/beam/pull/11413#discussion_r408403890
 
 

 ##########
 File path: sdks/go/pkg/beam/core/runtime/harness/statemgr_test.go
 ##########
 @@ -258,6 +261,167 @@ func TestStateChannel(t *testing.T) {
        }
 }
 
+// TestStateKeyReader validates ordinary Read cases
+func TestStateKeyReader(t *testing.T) {
+       const readLen = 4
+       tests := []struct {
+               name     string
+               buflens  []int // sizes of the buffers received on the state 
channel.
+               numReads int
+               closed   bool // tries to read from closed reader
+               noGet    bool // tries to read from nil get response reader
+       }{
+               {
+                       name:     "emptyData",
+                       buflens:  []int{-1},
+                       numReads: 1,
+               }, {
+                       name:     "singleBufferSingleRead",
+                       buflens:  []int{readLen},
+                       numReads: 2,
+               }, {
+                       name:     "singleBufferMultipleReads",
+                       buflens:  []int{2 * readLen},
+                       numReads: 3,
+               }, {
+                       name:     "singleBufferShortRead",
+                       buflens:  []int{readLen - 1},
+                       numReads: 2,
+               }, {
+                       name:     "multiBuffer",
+                       buflens:  []int{readLen, readLen},
+                       numReads: 3,
+               }, {
+                       name:     "multiBuffer-short-reads",
+                       buflens:  []int{readLen - 1, readLen - 1, readLen - 2},
+                       numReads: 4,
+               }, {
+                       name:     "emptyDataFirst", // Shouldn't happen, but 
not unreasonable to handle.
+                       buflens:  []int{-1, readLen, readLen},
+                       numReads: 4,
+               }, {
+                       name:     "emptyDataMid", // Shouldn't happen, but not 
unreasonable to handle.
+                       buflens:  []int{readLen, readLen, -1, readLen},
+                       numReads: 5,
+               }, {
+                       name:     "emptyDataLast", // Shouldn't happen, but not 
unreasonable to handle.
+                       buflens:  []int{readLen, readLen, -1},
+                       numReads: 3,
+               }, {
+                       name:     "emptyDataLast-short",
+                       buflens:  []int{3*readLen - 2, -1},
+                       numReads: 4,
+               }, {
+                       name:     "closed",
+                       buflens:  []int{-1, -1},
+                       numReads: 1,
+                       closed:   true,
+               }, {
+                       name:     "noGet",
+                       buflens:  []int{-1},
+                       numReads: 1,
+                       noGet:    true,
+               },
+       }
+       for _, test := range tests {
+               t.Run(test.name, func(t *testing.T) {
+                       ctx, cancelFn := 
context.WithCancel(context.Background())
+                       ch := &StateChannel{
+                               id:        "test",
+                               requests:  make(chan *fnpb.StateRequest),
+                               responses: make(map[string]chan<- 
*fnpb.StateResponse),
+                               cancelFn:  cancelFn,
+                               DoneCh:    ctx.Done(),
+                       }
+
+                       // Handle the channel behavior asynchronously.
+                       go func() {
+                               for i := 0; i < len(test.buflens); i++ {
+                                       token := []byte(strconv.Itoa(i))
+                                       var buf []byte
+                                       if test.buflens[i] >= 0 {
+                                               buf = bytes.Repeat([]byte{42}, 
test.buflens[i])
+                                       }
+                                       // On the last request response pair, 
send no token.
+                                       if i+1 == len(test.buflens) {
+                                               token = nil
+                                       }
 
 Review comment:
   rearranging this so that all the initialization for this variable is 
together might make it easier to follow:
   
   ```go
   var buf []byte
   if ... {
     ...
   }
   
   // I can see it making sense to reverse the if-statement here to match the 
one above,
   // but it there is a case to keep it as-is so that the common case is 
outside the 'if'.
   // Up to you.
   var token []byte
   if (not last entry) {
     // Maybe use fmt.Sprint() here rather than Itoa to avoid needing the 
strconv package?
     token = []byte(fmt.Sprint(i))
   }
   
   ch.responses[...] <- ...
   ```

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