Increase Stat() buffer size (prometheus#547)

Increase the /proc/stat scanner tokens size from the default of 65k to
1024k. This allows for scanning of large `intr` lines with > 65k
columns.
* Increase the scanner buffer from the default 4kB to 8kB bytes at a time.

Fixes: prometheus#546

Signed-off-by: SuperQ <[email protected]>

Author: SuperQ

stat.go

@@ -187,6 +187,10 @@ func parseStat(r io.Reader, fileName string) (Stat, error) {
 		err error
 	)
 
+	// Increase default scanner buffer to handle very long `intr` lines.
+	buf := make([]byte, 0, 8*1024)
+	scanner.Buffer(buf, 1024*1024)
+
 	for scanner.Scan() {
 		line := scanner.Text()
 		parts := strings.Fields(scanner.Text())

stat_test.go

@@ -30,7 +30,7 @@ func TestStat(t *testing.T) {
 	}
 
 	// intr
-	if want, have := uint64(8885917), s.IRQTotal; want != have {
+	if want, have := uint64(73777505), s.IRQTotal; want != have {
 		t.Errorf("want irq/total %d, have %d", want, have)
 	}
 	if want, have := uint64(1), s.IRQ[8]; want != have {