Provide custom CheckRedirect for r2.Request.Client.

[dhermes]

By default, if a (net/http).Client hits 10 redirects, it will give up with:

func defaultCheckRedirect(req *Request, via []*Request) error {
	if len(via) >= 10 {
		return errors.New("stopped after 10 redirects")
	}
	return nil
}

but this default can be overridden on a Client.

[dhermes]

As a way to test redirects in general:

package main

import (
	"fmt"
	"net/http"
	"net/http/httptest"
	"net/url"

	"github.com/blend/go-sdk/r2"
)

func main() {
	path := "/v1/auth/token/lookup"
	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path == path {
			http.Redirect(w, r, "/more", http.StatusTemporaryRedirect)
			return
		}
		fmt.Fprintln(w, "Hello, client")
	}))
	defer ts.Close()
	u, err := url.Parse(ts.URL)
	if err != nil {
		panic(err)
	}

	// Do a GET.
	fmt.Println("--- Doing a GET ---")
	opts := []r2.Option{
		r2.OptScheme("http"),
		r2.OptHeaderValue("X-Vault-Token", "bar"),
		r2.OptHost(u.Host),
		r2.OptGet(),
		r2.OptPathf(path),
	}
	body, res, err := r2.New("", opts...).Bytes()
	if err != nil {
		panic(err)
	}
	fmt.Printf("body: %q\n\n%#v\n", string(body), res)

	// Do a POST.
	fmt.Println("--- Doing a POST ---")
	opts = []r2.Option{
		r2.OptScheme("http"),
		r2.OptHeaderValue("X-Vault-Token", "bar"),
		r2.OptHost(u.Host),
		r2.OptPost(),
		r2.OptPathf(path),
		r2.OptJSONBody(map[string]string{"token": "foo"}),
	}
	body, res, err = r2.New("", opts...).Bytes()
	if err != nil {
		panic(err)
	}
	fmt.Printf("body: %q\n\n%#v\n", string(body), res)
}

which produces

--- Doing a GET ---
body: "Hello, client\n"

&http.Response{Status:"200 OK", StatusCode:200, Proto:"HTTP/1.1", ProtoMajor:1, ProtoMinor:1, Header:http.Header{"Content-Length":[]string{"14"}, "Content-Type":[]string{"text/plain; charset=utf-8"}, "Date":[]string{"Sat, 01 Feb 2020 00:01:16 GMT"}}, Body:(*http.bodyEOFSignal)(0xc0001bc100), ContentLength:14, TransferEncoding:[]string(nil), Close:false, Uncompressed:false, Trailer:http.Header(nil), Request:(*http.Request)(0xc0001c8000), TLS:(*tls.ConnectionState)(nil)}
--- Doing a POST ---
body: ""

&http.Response{Status:"307 Temporary Redirect", StatusCode:307, Proto:"HTTP/1.1", ProtoMajor:1, ProtoMinor:1, Header:http.Header{"Content-Length":[]string{"0"}, "Date":[]string{"Sat, 01 Feb 2020 00:01:16 GMT"}, "Location":[]string{"/more"}}, Body:http.noBody{}, ContentLength:0, TransferEncoding:[]string(nil), Close:false, Uncompressed:false, Trailer:http.Header(nil), Request:(*http.Request)(0xc000176420), TLS:(*tls.ConnectionState)(nil)}

[dhermes]

Also more relevant (directly) to this issue would be the case of too many redirects:

package main

import (
	"fmt"
	"net/http"
	"net/http/httptest"
	"net/url"

	"github.com/blend/go-sdk/r2"
)

func main() {
	path := "/v1/auth/token/lookup"
	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, path, http.StatusTemporaryRedirect)
	}))
	defer ts.Close()
	u, err := url.Parse(ts.URL)
	if err != nil {
		panic(err)
	}

	// Do a GET.
	fmt.Println("--- Doing a GET ---")
	opts := []r2.Option{
		r2.OptScheme("http"),
		r2.OptHeaderValue("X-Vault-Token", "bar"),
		r2.OptHost(u.Host),
		r2.OptGet(),
		r2.OptPathf(path),
	}
	_, _, err = r2.New("", opts...).Bytes()
	if err == nil {
		panic("SHOULD ERR")
	}
	unwrapped, ok := err.(*url.Error)
	if !ok {
		panic("SHOULD UNWRAP")
	}

	fmt.Printf("%#v\n", unwrapped)
	fmt.Printf("%#v\n", unwrapped.Err)
}

which produces

--- Doing a GET ---
&url.Error{Op:"Get", URL:"/v1/auth/token/lookup", Err:(*errors.errorString)(0xc0001d4220)}
&errors.errorString{s:"stopped after 10 redirects"}

[dhermes]

Closing this since #176 is merged. I opened #177 to track just the 307 for POST bits.