bug: http_to_https ret_code 307 not working

[TigerGxl]

Issue description

Environment

• apisix version (cmd: apisix version):1.5
• OS:ubuntu16.04

i use plugin http_to_https and set ret_code 307, like below.

{
  "priority": 0,
  "plugins": {
    "redirect": {
      "ret_code": 307,
      "http_to_https": true
    }
  },
  "uris": [
    "/*"
  ],
  "id": "1a5f4337d",
  "hosts": [
    "demo-apisix.xxxxxxx.com"
  ],
  "upstream": {
    "nodes": {
      "172.16.3.2:80": 100
    },
    "hash_on": "vars",
    "type": "roundrobin"
  }
}

when client sends POST reqeust with http.it's not working, apisix should return 307 and client sends a new request with https again, in fact, apisix return 301 and client sends a new request with https and the method is GET

[TigerGxl]

启用http跳转https后,设置状态码为307不生效.
etcd中存储的状态码是307,但是实际跳转的时候是301,导致原本POST的method在301跳转后变为GET

[membphis]

that is a bug. here is the test case. welcome PR to fix it

=== TEST 1: add plugin with new uri: /test/add
--- config
    location /t {
        content_by_lua_block {
            local t = require("lib.test_admin").test
            local code, body = t('/apisix/admin/routes/1',
                ngx.HTTP_PUT,
                [[{
                    "plugins": {
                        "redirect": {
                            "http_to_https": true,
                            "ret_code": 307
                        }
                    },
                    "uri": "/hello"
                }]]
                )

            if code >= 300 then
                ngx.status = code
            end
            ngx.say(body)
        }
    }
--- request
GET /t
--- response_body
passed
--- no_error_log
[error]



=== TEST 2: redirect
--- request
GET /hello
--- response_headers
Location: /test/add
--- error_code: 307
--- no_error_log
[error]

[moonming]

@liuhengloveyou please take a look

[gy09535]

I thinks when we send redirect to 301 ,some browser default change the request to get, so we should add some logical to handle post request , when the request is post we should send the ret_code to 307, according to https://github.com/apache/apisix/blob/master/apisix/plugins/redirect.lua#L136

[liuhengloveyou]

If the user has explicitly configured ret_code, we should not change it.
Unless the configuration is wrong, we should indicate the range in the documentation.

I think the range of should be 400 > ret_code >= 300?

[spacewander]

@gy09535
I think you mean 308 but not 307: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/308
Code 307 is 'Temporary'.

[gy09535]

@gy09535
I think you mean 308 but not 307: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/308
Code 307 is 'Temporary'.

yeah, should be 308