目录
现象
A服务通过post请求访问B服务的时候，B服务返回了一个301，让A服务去访问C服务。在这期间method没有改变，只是修改了location。
但是当A服务通过301访问到C服务的时候，method竟然由post变成了get请求。
源码
net/http/client.go
func (c *Client) do(req *Request) (retres *Response, reterr error) {
if testHookClientDoResult != nil {
defer func() { testHookClientDoResult(retres, reterr) }()
}
if req.URL == nil {
req.closeBody()
return nil, &url.Error{
Op: urlErrorOp(req.Method),
Err: errors.New("http: nil Request.URL"),
}
}
var (
deadline = c.deadline()
reqs []*Request
resp *Response
copyHeaders = c.makeHeadersCopier(req)
reqBodyClosed = false // have we closed the current req.Body?
// Redirect behavior:
redirectMethod string
includeBody bool
)
uerr := func(err error) error {
// the body may have been closed already by c.send()
if !reqBodyClosed {
req.closeBody()
}
var urlStr string
if resp != nil && resp.Request != nil {
urlStr = stripPassword(resp.Request.URL)
} else {
urlStr = stripPassword(req.URL)
}
return &url.Error{
Op: urlErrorOp(reqs[0].Method),
URL: urlStr,
Err: err,
}
}
for {
// For all but the first request, create the next
// request hop and replace req.
if len(reqs) > 0 {
loc := resp.Header.Get("Location")
if loc == "" {
resp.closeBody()
return nil, uerr(fmt.Errorf("%d response missing Location header", resp.StatusCode))
}
u, err := req.URL.Parse(loc)
if err != nil {
resp.closeBody()
return nil, uerr(fmt.Errorf("failed to parse Location header %q: %v", loc, err))
}
host := ""
if req.Host != "" && req.Host != req.URL.Host {
// If the caller specified a custom Host header and the
// redirect location is relative, preserve the Host header
// through the redirect. See issue #22233.
if u, _ := url.Parse(loc); u != nil && !u.IsAbs() {
host = req.Host
}
}
ireq := reqs[0]
req = &Request{
Method: redirectMethod,
Response: resp,
URL: u,
Header: make(Header),
Host: host,
Cancel: ireq.Cancel,
ctx: ireq.ctx,
}
if includeBody && ireq.GetBody != nil {
req.Body, err = ireq.GetBody()
if err != nil {
resp.closeBody()
return nil, uerr(err)
}
req.ContentLength = ireq.ContentLength
}
// Copy original headers before setting the Referer,
// in case the user set Referer on their first request.
// If they really want to override, they can do it in
// their CheckRedirect func.
copyHeaders(req)
// Add the Referer header from the most recent
// request URL to the new one, if it's not https->http:
if ref := refererForURL(reqs[len(reqs)-1].URL, req.URL); ref != "" {
req.Header.Set("Referer", ref)
}
err = c.checkRedirect(req, reqs)
// Sentinel error to let users select the
// previous response, without closing its
// body. See Issue 10069.
if err == ErrUseLastResponse {
return resp, nil
}
// Close the previous response's body. But
// read at least some of the body so if it's
// small the underlying TCP connection will be
// re-used. No need to check for errors: if it
// fails, the Transport won't reuse it anyway.
const maxBodySlurpSize = 2 << 10
if resp.ContentLength == -1 || resp.ContentLength <= maxBodySlurpSize {
io.CopyN(ioutil.Discard, resp.Body, maxBodySlurpSize)
}
resp.Body.Close()
if err != nil {
// Special case for Go 1 compatibility: return both the response
// and an error if the CheckRedirect function failed.
// See https://golang.org/issue/3795
// The resp.Body has already been closed.
ue := uerr(err)
ue.(*url.Error).URL = loc
return resp, ue
}
}
reqs = append(reqs, req)
var err error
var didTimeout func() bool
if resp, didTimeout, err = c.send(req, deadline); err != nil {
// c.send() always closes req.Body
reqBodyClosed = true
if !deadline.IsZero() && didTimeout() {
err = &httpError{
// TODO: early in cycle: s/Client.Timeout exceeded/timeout or context cancellation/
err: err.Error() + " (Client.Timeout exceeded while awaiting headers)",
timeout: true,
}
}
return nil, uerr(err)
}
var shouldRedirect bool
// 处理redirect请求
redirectMethod, shouldRedirect, includeBody = redirectBehavior(req.Method, resp, reqs[0])
if !shouldRedirect {
return resp, nil
}
req.closeBody()
}
}
// 处理redirect请求
// redirectBehavior describes what should happen when the
// client encounters a 3xx status code from the server
func redirectBehavior(reqMethod string, resp *Response, ireq *Request) (redirectMethod string, shouldRedirect, includeBody bool) {
switch resp.StatusCode {
case 301, 302, 303:
redirectMethod = reqMethod
shouldRedirect = true
includeBody = false
// RFC 2616 allowed automatic redirection only with GET and
// HEAD requests. RFC 7231 lifts this restriction, but we still
// restrict other methods to GET to maintain compatibility.
// See Issue 18570.
if reqMethod != "GET" && reqMethod != "HEAD" {
redirectMethod = "GET"
}
case 307, 308:
redirectMethod = reqMethod
shouldRedirect = true
includeBody = true
// Treat 307 and 308 specially, since they're new in
// Go 1.8, and they also require re-sending the request body.
if resp.Header.Get("Location") == "" {
// 308s have been observed in the wild being served
// without Location headers. Since Go 1.7 and earlier
// didn't follow these codes, just stop here instead
// of returning an error.
// See Issue 17773.
shouldRedirect = false
break
}
if ireq.GetBody == nil && ireq.outgoingLength() != 0 {
// We had a request body, and 307/308 require
// re-sending it, but GetBody is not defined. So just
// return this response to the user instead of an
// error, like we did in Go 1.7 and earlier.
shouldRedirect = false
}
}
return redirectMethod, shouldRedirect, includeBody
}
原因
根据源码：
redirectBehavior(reqMethod string, resp *Response, ireq *Request)
可知，当状态码为301，302，303的时候，会把请求method变为get，当状态码为307，308的时候回维持原来的method不变。
解决
B服务不再返回301，返回307或者308