rpcsrv: close idle client connections in doRPCCallOverHTTP

[roman-khimov]

This doesn't fix anything, but why not (at least let's see how it behaves on GH).

Just FYI, I've also tried

--- a/pkg/services/rpcsrv/server_test.go
+++ b/pkg/services/rpcsrv/server_test.go
@@ -2223,7 +2223,16 @@ var rpcTestCases = map[string][]rpcTestCase{
 
 func TestRPC(t *testing.T) {
        t.Run("http", func(t *testing.T) {
-               testRPCProtocol(t, doRPCCallOverHTTP)
+               cl := http.Client{Timeout: time.Second}
+               testRPCProtocol(t, func(rpcCall string, url string, t *testing.T) []byte {
+                       resp, err := cl.Post(url, "application/json", strings.NewReader(rpcCall))
+                       require.NoErrorf(t, err, "could not make a POST request")
+                       body, err := gio.ReadAll(resp.Body)
+                       resp.Body.Close()
+                       assert.NoErrorf(t, err, "could not read response from the request: %s", rpcCall)
+                       return bytes.TrimSpace(body)
+               })
+               cl.CloseIdleConnections()
        })
 
        t.Run("websocket", func(t *testing.T) {

as optimization, but it doesn't affect test time in any way.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.71%. Comparing base (54c53cf) to head (86faf7b).
Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3350   +/-   ##
=======================================
  Coverage   84.70%   84.71%           
=======================================
  Files         331      331           
  Lines       44932    44932           
=======================================
+ Hits        38060    38062    +2     
  Misses       5362     5362           
+ Partials     1510     1508    -2     

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[AnnaShaleva]

BTW, the interesting fact is that we do the same with our real client:

neo-go/pkg/rpcclient/client.go

Lines 168 to 172 in 67d3917

	// Close closes unused underlying networks connections.
	func (c *Client) Close() {
	c.ctxCancel()
	c.cli.CloseIdleConnections()
	}