[bugfix] Relax outgoing http request queue (#760)

* add request queue trace logging

* fix  misleading wording

* implement request slots per host per method

* undo formatting change (?)

* remove gratuitous trace logging

* rename done -> release
avoids confusion with ctx.Done

internal/httpclient/queue_test.go

@@ -0,0 +1,106 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package httpclient
+
+import (
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/suite"
+)
+
+type QueueTestSuite struct {
+	suite.Suite
+}
+
+func (suite *QueueTestSuite) TestQueue() {
+	maxOpenConns := 5
+	waitTimeout := 1 * time.Second
+
+	rc := &requestQueue{
+		maxOpenConns: maxOpenConns,
+	}
+
+	// fill all the open connections
+	var release func()
+	for i, n := range make([]interface{}, maxOpenConns) {
+		w, r := rc.getWaitSpot("example.org", http.MethodPost)
+		w <- n
+		if i == maxOpenConns-1 {
+			// save the last release function
+			release = r
+		}
+	}
+
+	// try to wait again for the same host/method combo, it should timeout
+	waitAgain, _ := rc.getWaitSpot("example.org", "post")
+
+	select {
+	case waitAgain <- struct{}{}:
+		suite.FailNow("first wait did not time out")
+	case <-time.After(waitTimeout):
+		break
+	}
+
+	// now close the final release that we derived earlier
+	release()
+
+	// try waiting again, it should work this time
+	select {
+	case waitAgain <- struct{}{}:
+		break
+	case <-time.After(waitTimeout):
+		suite.FailNow("second wait timed out")
+	}
+
+	// the POST queue is now sitting on full
+	suite.Len(waitAgain, maxOpenConns)
+
+	// we should still be able to make a GET for the same host though
+	getWait, getRelease := rc.getWaitSpot("example.org", http.MethodGet)
+	select {
+	case getWait <- struct{}{}:
+		break
+	case <-time.After(waitTimeout):
+		suite.FailNow("get wait timed out")
+	}
+
+	// the GET queue has one request waiting
+	suite.Len(getWait, 1)
+	// clear it...
+	getRelease()
+	suite.Empty(getWait)
+
+	// even though the POST queue for example.org is full, we
+	// should still be able to make a POST request to another host :)
+	waitForAnotherHost, _ := rc.getWaitSpot("somewhere.else", http.MethodPost)
+	select {
+	case waitForAnotherHost <- struct{}{}:
+		break
+	case <-time.After(waitTimeout):
+		suite.FailNow("get wait timed out")
+	}
+
+	suite.Len(waitForAnotherHost, 1)
+}
+
+func TestQueueTestSuite(t *testing.T) {
+	suite.Run(t, &QueueTestSuite{})
+}