$ GOMAXPROCS=4 go test -bench='HTTPClient(Do|GetEndToEnd)' -benchmem -benchtime=10s
BenchmarkNetHTTPClientDoFastServer-4                      2000000       8774 ns/op     2619 B/op       35 allocs/op
BenchmarkNetHTTPClientGetEndToEnd1TCP-4                    500000      22951 ns/op     5047 B/op       56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd10TCP-4                  1000000      19182 ns/op     5037 B/op       55 allocs/op
BenchmarkNetHTTPClientGetEndToEnd100TCP-4                 1000000      16535 ns/op     5031 B/op       55 allocs/op
BenchmarkNetHTTPClientGetEndToEnd1Inmemory-4              1000000      14495 ns/op     5038 B/op       56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd10Inmemory-4             1000000      10237 ns/op     5034 B/op       56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd100Inmemory-4            1000000      10125 ns/op     5045 B/op       56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd1000Inmemory-4           1000000      11132 ns/op     5136 B/op       56 allocs/op

$ GOMAXPROCS=4 go test -bench='kClient(Do|GetEndToEnd)' -benchmem -benchtime=10s
BenchmarkClientDoFastServer-4                            50000000        397 ns/op        0 B/op        0 allocs/op
BenchmarkClientGetEndToEnd1TCP-4                          2000000       7388 ns/op        0 B/op        0 allocs/op
BenchmarkClientGetEndToEnd10TCP-4                         2000000       6689 ns/op        0 B/op        0 allocs/op
BenchmarkClientGetEndToEnd100TCP-4                        3000000       4927 ns/op        1 B/op        0 allocs/op
BenchmarkClientGetEndToEnd1Inmemory-4                    10000000       1604 ns/op        0 B/op        0 allocs/op
BenchmarkClientGetEndToEnd10Inmemory-4                   10000000       1458 ns/op        0 B/op        0 allocs/op
BenchmarkClientGetEndToEnd100Inmemory-4                  10000000       1329 ns/op        0 B/op        0 allocs/op
BenchmarkClientGetEndToEnd1000Inmemory-4                 10000000       1316 ns/op        5 B/op        0 allocs/op

// workerpool.go
type workerPool struct {
    ready []*workerChan

    workerChanPool sync.Pool
}

type workerChan struct {
    lastUseTime time.Time
    ch          chan net.Conn
}

// client.go

var (
    requestPool  sync.Pool
    responsePool sync.Pool
)

// 从对象池中获取 Request 对象
func AcquireRequest() *Request {
    ...
}

// 归还 Request 对象到对象池中
func ReleaseRequest(req *Request) {
    ...
}

// 从对象池中获取 Response 对象
func AcquireResponse() *Response {
    ...
}

// 归还 Response 对象到对象池中
func ReleaseResponse(resp *Response) {
    ...
}

// cookie.go

var cookiePool = &sync.Pool{
    New: func() interface{} {
        return &Cookie{}
    },
}

// 从对象池中获取 Cookie 对象
func AcquireCookie() *Cookie {
    ...
}

// 归还 Cookie 对象到对象池中
func ReleaseCookie(c *Cookie) {
    ...
}

$ grep -inr --include \*.go "sync.Pool" $(go list -f {{.Dir}} github.com/valyala/fasthttp) | wc -l

# 输出如下
38

// 重置 URI 对象
// 从方法的内部实现中可以看到，类型为 []byte 的所有字段都被复用了
func (u *URI) Reset() {
    u.pathOriginal = u.pathOriginal[:0]
    u.scheme = u.scheme[:0]
    u.path = u.path[:0]
    u.queryString = u.queryString[:0]
    u.hash = u.hash[:0]
    u.username = u.username[:0]
    u.password = u.password[:0]

    u.host = u.host[:0]
    ...
}

func (c *Cookie) SetValue(value string) {
    c.value = append(c.value[:0], value...)
}

func (c *Cookie) SetValueBytes(value []byte) {
    c.value = append(c.value[:0], value...)
}

func (c *Cookie) SetKey(key string) {
    c.key = append(c.key[:0], key...)
}

func (c *Cookie) SetKeyBytes(key []byte) {
    c.key = append(c.key[:0], key...)
}

// s2b_new.go
func b2s(b []byte) string {
    return *(*string)(unsafe.Pointer(&b))
}

// b2s_new.go
func s2b(s string) (b []byte) {
    bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
    sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
    bh.Data = sh.Data
    bh.Cap = sh.Len
    bh.Len = sh.Len
    return b
}

// cookie.go
// Cookie 对象拷贝实现
func (c *Cookie) CopyTo(src *Cookie) {
    c.Reset()
    c.key = append(c.key, src.key...)
    c.value = append(c.value, src.value...)
    c.expire = src.expire
    c.maxAge = src.maxAge
    c.domain = append(c.domain, src.domain...)
    c.path = append(c.path, src.path...)
    c.httpOnly = src.httpOnly
    c.secure = src.secure
    c.sameSite = src.sameSite
}

// client.go
func (req *Request) CopyTo(dst *Request) {
    ...
}

func (resp *Response) CopyTo(dst *Response) {
  ...
}