Prevent overflow and panic on large HTTP responses (#1351)

http.go

@@ -8,6 +8,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"math"
 	"mime/multipart"
 	"net"
 	"os"
@@ -2278,5 +2279,10 @@ func round2(n int) int {
 	x |= x >> 8
 	x |= x >> 16
 
+	// Make sure we don't return 0 due to overflow, even on 32 bit systems
+	if x >= uint32(math.MaxInt32) {
+		return math.MaxInt32
+	}
+
 	return int(x + 1)
 }

http_test.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"math"
 	"mime/multipart"
 	"net/http"
 	"net/http/httptest"
@@ -1963,6 +1964,7 @@ func TestRound2(t *testing.T) {
 	testRound2(t, 8, 8)
 	testRound2(t, 9, 16)
 	testRound2(t, 0x10001, 0x20000)
+	testRound2(t, math.MaxInt32-1, math.MaxInt32)
 }
 
 func testRound2(t *testing.T, n, expectedRound2 int) {