整个的transfer.go做了很多操作 ，可以把它理解为http的内部处理或者转换操作 先看几个关键结构体的定义
transferWriter 是为了实现用户可操作填值的头信息处理的数据结构
type transferWriter struct { Method string Body io.Reader BodyCloser io.Closer ResponseToHEAD bool ContentLength int64 // -1 means unknown, 0 means exactly none Close bool TransferEncoding []string Trailer Header IsResponse bool }transferReader
type transferReader struct { // Input Header Header StatusCode int RequestMethod string ProtoMajor int ProtoMinor int // Output Body io.ReadCloser ContentLength int64 TransferEncoding []string Close bool Trailer Header }body定义
type body struct { src io.Reader hdr interface{} // non-nil (Response or Request) value means read trailer r *bufio.Reader // underlying wire-format reader for the trailer closing bool // is the connection to be closed after reading body? doEarlyClose bool // whether Close should stop early mu sync.Mutex // guards following, and calls to Read and Close sawEOF bool closed bool earlyClose bool // Close called and we didn't read to the end of src onHitEOF func() // if non-nil, func to call when EOF is Read }