如何从一个bytes.Buffer读取多次？

I'm trying to create two HTTP requests with the same request body. Unfortunately, the second request sends an empty body.

w := httptest.NewRecorder()
w2 := httptest.NewRecorder()
pd := &postData{
    Data: 5,
}
b := new(bytes.Buffer)
json.NewEncoder(b).Encode(pd)
req, _ := http.NewRequest("PUT", "/v1/jobs/echo", b)
server.ServeHTTP(w, req)

req, _ = http.NewRequest("PUT", "/v1/jobs/echo", b)
server.ServeHTTP(w2, req)

Reading through the documentation and the source code for bytes.Buffer, it looks like there's no way to reset the buffer to 0 - there's a Reset method, but this also wipes the buffer's internal state.

Is there a way to "replay" any reader in Go? A bytes.Buffer or any other Reader.

OK. So I wouldn't consider this ideal and it would be better to just init a reader in the first place but if you put your data in a bytes.Reader instead of bytes.Buffer then you'll be able to seek back to the beginning after the first call to NewRequest has read to the end.

w := httptest.NewRecorder()
w2 := httptest.NewRecorder()
pd := &postData{
    Data: 5,
}
b := new(bytes.Buffer)
json.NewEncoder(b).Encode(pd)
r := bytes.NewReader(b.Bytes())
req, _ := http.NewRequest("PUT", "/v1/jobs/echo", r)
server.ServeHTTP(w, req)

r.Seek(0, 0)
req, _ = http.NewRequest("PUT", "/v1/jobs/echo", r)
server.ServeHTTP(w2, req)