memlogd: add test cases

- check writing to the log does not block
- check the log doesn't expand -- it should be finite
- check that client connections don't buffer arbitrary amounts of
  data if the client is slow

Signed-off-by: David Scott <dave.scott@docker.com>

pkg/memlogd/cmd/memlogd/main_test.go

@@ -0,0 +1,133 @@
+package main
+
+import (
+	"bufio"
+	"io"
+	"log"
+	"net"
+	"os"
+	"syscall"
+	"testing"
+	"time"
+)
+
+func TestNonblock(t *testing.T) {
+	// Test that writes to the logger don't block because it is full
+	linesInBuffer := 10
+
+	logCh := make(chan logEntry)
+	queryMsgChan := make(chan queryMessage)
+
+	go ringBufferHandler(linesInBuffer, linesInBuffer, logCh, queryMsgChan)
+
+	// Overflow the log to make sure it doesn't block
+	for i := 0; i < 2*linesInBuffer; i++ {
+		select {
+		case logCh <- logEntry{time: time.Now(), source: "memlogd", msg: "hello TestNonblock"}:
+			continue
+		case <-time.After(time.Second):
+			t.Errorf("write to the logger blocked for over 1s after %d (size was set to %d)", i, linesInBuffer)
+		}
+	}
+}
+
+func TestFinite(t *testing.T) {
+	// Test that the logger doesn't store more than its configured maximum size
+	linesInBuffer := 10
+
+	logCh := make(chan logEntry)
+	queryMsgChan := make(chan queryMessage)
+
+	go ringBufferHandler(linesInBuffer, linesInBuffer, logCh, queryMsgChan)
+
+	// Overflow the log by 2x
+	for i := 0; i < 2*linesInBuffer; i++ {
+		logCh <- logEntry{time: time.Now(), source: "memlogd", msg: "hello TestFinite"}
+	}
+	a, b := socketpair()
+	defer a.Close()
+	defer b.Close()
+	queryM := queryMessage{
+		conn: a,
+		mode: logDump,
+	}
+	queryMsgChan <- queryM
+	r := bufio.NewReader(b)
+	count := 0
+	for {
+		_, err := r.ReadString('\n')
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			log.Fatalf("Unexpected error reading from socket: %s", err)
+		}
+		count++
+	}
+	if linesInBuffer != count {
+		t.Errorf("Read %d lines but expected %d", count, linesInBuffer)
+	}
+}
+
+func TestFinite2(t *testing.T) {
+	// Test that the query connection doesn't store more than the configured
+	// maximum size.
+	linesInBuffer := 10
+	// the output buffer size will be 1/2 of the ring
+	outputBufferSize := linesInBuffer / 2
+	logCh := make(chan logEntry)
+	queryMsgChan := make(chan queryMessage)
+
+	go ringBufferHandler(linesInBuffer, outputBufferSize, logCh, queryMsgChan)
+
+	// fill the ring
+	for i := 0; i < linesInBuffer; i++ {
+		logCh <- logEntry{time: time.Now(), source: "memlogd", msg: "hello TestFinite2"}
+	}
+
+	a, b := socketpair()
+	defer a.Close()
+	defer b.Close()
+	queryM := queryMessage{
+		conn: a,
+		mode: logDump,
+	}
+	queryMsgChan <- queryM
+	// since the ring won't fit in the output buffer some should be dropped
+
+	r := bufio.NewReader(b)
+	count := 0
+	for {
+		_, err := r.ReadString('\n')
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			log.Fatalf("Unexpected error reading from socket: %s", err)
+		}
+		count++
+	}
+	if count != outputBufferSize {
+		t.Errorf("Read %d lines but expected %d", count, outputBufferSize)
+	}
+}
+
+func socketpair() (net.Conn, net.Conn) {
+	fds, err := syscall.Socketpair(syscall.AF_UNIX, syscall.SOCK_STREAM, 0)
+	if err != nil {
+		log.Fatal("Unable to create socketpair: ", err)
+	}
+	f := os.NewFile(uintptr(fds[0]), "a")
+	a, err := net.FileConn(f)
+	if err != nil {
+		log.Fatal("Unable to create net.Conn from socketpair: ", err)
+	}
+	_ = f.Close()
+	f = os.NewFile(uintptr(fds[1]), "b")
+	b, err := net.FileConn(f)
+	if err != nil {
+		log.Fatal("Unable to create net.Conn from socketpair: ", err)
+	}
+	_ = f.Close()
+	return a, b
+}