What version of Go are you using (go version)?

$ go version
go version go1.10.4 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/u/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/yw674/go"
GORACE=""
GOROOT="/usr/lib/go-1.10"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go-1.10/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build154661289=/tmp/go-build -gno-record-gcc-switches"

What did you do?

func readStream(){
        resp, err := http.Get(device.Url)
        if err != nil {
                // handle error
        }
        defer resp.Body.Close()
        log.Printf("%v+", resp.Header)

        contentType := resp.Header.Get("Content-Type");
        if len(contentType) < 1 {
                return
        }

        mediaType, mediaTypeParams, err := mime.ParseMediaType(contentType)
        fmt.Println("parseMessageWithHeader", mediaType)
        if err != nil {
                return
        }
        
        boundary := mediaTypeParams["boundary"]
        log.Printf("boundary %s", boundary)

        mr := multipart.NewReader(resp.Body, boundary)
        for {
                p, err := mr.NextPart()
                if err == io.EOF {
                        return
                }
                if err != nil {
                        log.Fatal("np: ", err)
                }
                slurp, err := ioutil.ReadAll(p)
                if err != nil {
                        log.Fatal("io: ", err)
                }
                fmt.Printf("Part %q: %q\n", p.Header.Get("Foo"), slurp)
        }
}

What did you expect to see?

MJPEG chunks to be read to slurp.

What did you see instead?

2019/08/15 13:30:16 map[Content-Type:[multipart/x-mixed-replace; boundary=--myboundary] Date:[Thu, 15 Aug 2019 11:30:16 GMT]]+
parseMessageWithHeader multipart/x-mixed-replace
2019/08/15 13:30:16 boundary --myboundary
2019/08/15 13:30:16 np: multipart: NextPart: bufio: buffer full

I suspect this is due to peekBufferSize is only 4096 bytes: