英文:
Runtime error when attempting to read *http.Response Body, having used urlfetch.Transport
问题
App Engine不允许使用DefaultClient,而是提供了urlfetch服务。以下是一个最小化的示例,部署和工作效果基本符合预期:
package app
import (
"fmt"
"net/http"
"appengine"
"appengine/urlfetch"
"code.google.com/p/goauth2/oauth"
)
func init () {
http.HandleFunc("/", home)
}
func home(w http.ResponseWriter, r *http.Request) {
c := appengine.NewContext(r)
config := &oauth.Config{
ClientId: "<redacted>",
ClientSecret: "<redacted>",
Scope: "email",
AuthURL: "https://www.facebook.com/dialog/oauth",
TokenURL: "https://graph.facebook.com/oauth/access_token",
RedirectURL: "http://example.com/",
}
code := r.FormValue("code")
if code == "" {
http.Redirect(w, r, config.AuthCodeURL("foo"), http.StatusFound)
}
t := &oauth.Transport{Config: config, Transport: &urlfetch.Transport{Context: c}}
tok, _ := t.Exchange(code)
graphResponse, _ := t.Client().Get("https://graph.facebook.com/me")
fmt.Fprintf(w, "<pre>%s<br />%s</pre>", tok, graphResponse)
}
使用正确的ClientId、ClientSecret和RedirectURL,这将产生以下输出(为了简洁起见进行了编辑):
&{AAADTWGsQ5<snip>kMdjh5VKwZDZD 0001-01-01 00:00:00 +0000 UTC}
&{200 OK %!s(int=200) HTTP/1.1 %!s(int=1) %!s(int=1)
map[Connection:[keep-alive] Access-Control-Allow-Origin:[*]
<snip>
Content-Type:[text/javascript; charset=UTF-8]
Date:[Wed, 06 Feb 2013 12:06:45 GMT] X-Google-Cache-Control:[remote-fetch]
Cache-Control:[private, no-cache, no-store, must-revalidate] Pragma:[no-cache]
X-Fb-Rev:[729873] Via:[HTTP/1.1 GWA] Expires:[Sat, 01 Jan 2000 00:00:00 GMT]]
%!s(*urlfetch.bodyReader=&{[123 34 105 100 <big snip> 48 48 34 125] false false})
%!s(int64=306) [] %!s(bool=true) map[] %!s(*http.Request=&{GET 0xf840087230
HTTP/1.1 1 1 map[Authorization:[Bearer AAADTWGsQ5NsBAC4yT0x1shZAJAtODOIx0tZCb
TYTjxFC4esEqCjPDi3REMKHBUjZCX4FIKLO1UjMpJxhJZCfGFcOJlFu7UvehkMdjh5VKwZDZD]]
0 [] false graph.facebook.com map[] map[] })}
看起来我一直得到了一个*http.Response,所以我期望能够从响应体中读取。然而,任何对Body的提及,例如:
defer graphResponse.Body.Close()
编译、部署,但会导致以下运行时错误:
panic: runtime error: invalid memory address or nil pointer dereference
runtime.panic go/src/pkg/runtime/proc.c:1442
runtime.panicstring go/src/pkg/runtime/runtime.c:128
runtime.sigpanic go/src/pkg/runtime/thread_linux.c:199
app.home app/app.go:33
net/http.HandlerFunc.ServeHTTP go/src/pkg/net/http/server.go:704
net/http.(*ServeMux).ServeHTTP go/src/pkg/net/http/server.go:942
appengine_internal.executeRequestSafely go/src/pkg/appengine_internal/api_prod.go:240
appengine_internal.(*server).HandleRequest go/src/pkg/appengine_internal/api_prod.go:190
reflect.Value.call go/src/pkg/reflect/value.go:526
reflect.Value.Call go/src/pkg/reflect/value.go:334
_ _.go:316
runtime.goexit go/src/pkg/runtime/proc.c:270
我错过了什么?这是因为使用了urlfetch而不是DefaultClient吗?
英文:
App Engine does not allow use of DefaultClient, providing the urlfetch service instead. The following minimal example deploys and works pretty much as expected:
package app
import (
"fmt"
"net/http"
"appengine"
"appengine/urlfetch"
"code.google.com/p/goauth2/oauth"
)
func init () {
http.HandleFunc("/", home)
}
func home(w http.ResponseWriter, r *http.Request) {
c := appengine.NewContext(r)
config := &oauth.Config{
ClientId: "<redacted>",
ClientSecret: "<redacted>",
Scope: "email",
AuthURL: "https://www.facebook.com/dialog/oauth",
TokenURL: "https://graph.facebook.com/oauth/access_token",
RedirectURL: "http://example.com/",
}
code := r.FormValue("code")
if code == "" {
http.Redirect(w, r, config.AuthCodeURL("foo"), http.StatusFound)
}
t := &oauth.Transport{Config: config, Transport: &urlfetch.Transport{Context: c}}
tok, _ := t.Exchange(code)
graphResponse, _ := t.Client().Get("https://graph.facebook.com/me")
fmt.Fprintf(w, "<pre>%s<br />%s</pre>", tok, graphResponse)
}
With correct ClientId, ClientSecret and RedirectURL, this produces the following output (edited for brevity):
&{AAADTWGsQ5<snip>kMdjh5VKwZDZD 0001-01-01 00:00:00 +0000 UTC}
&{200 OK %!s(int=200) HTTP/1.1 %!s(int=1) %!s(int=1)
map[Connection:[keep-alive] Access-Control-Allow-Origin:[*]
<snip>
Content-Type:[text/javascript; charset=UTF-8]
Date:[Wed, 06 Feb 2013 12:06:45 GMT] X-Google-Cache-Control:[remote-fetch]
Cache-Control:[private, no-cache, no-store, must-revalidate] Pragma:[no-cache]
X-Fb-Rev:[729873] Via:[HTTP/1.1 GWA] Expires:[Sat, 01 Jan 2000 00:00:00 GMT]]
%!s(*urlfetch.bodyReader=&{[123 34 105 100 <big snip> 48 48 34 125] false false})
%!s(int64=306) [] %!s(bool=true) map[] %!s(*http.Request=&{GET 0xf840087230
HTTP/1.1 1 1 map[Authorization:[Bearer AAADTWGsQ5NsBAC4yT0x1shZAJAtODOIx0tZCb
TYTjxFC4esEqCjPDi3REMKHBUjZCX4FIKLO1UjMpJxhJZCfGFcOJlFu7UvehkMdjh5VKwZDZD]]
0 [] false graph.facebook.com map[] map[] })}
It certainly seems like I'm consistently getting an *http.Response back, so I would expect to be able to read from the response Body. However, any mention of Body--for example with:
defer graphResponse.Body.Close()
compiles, deploys, but results in the following runtime error:
panic: runtime error: invalid memory address or nil pointer dereference
runtime.panic go/src/pkg/runtime/proc.c:1442
runtime.panicstring go/src/pkg/runtime/runtime.c:128
runtime.sigpanic go/src/pkg/runtime/thread_linux.c:199
app.home app/app.go:33
net/http.HandlerFunc.ServeHTTP go/src/pkg/net/http/server.go:704
net/http.(*ServeMux).ServeHTTP go/src/pkg/net/http/server.go:942
appengine_internal.executeRequestSafely go/src/pkg/appengine_internal/api_prod.go:240
appengine_internal.(*server).HandleRequest go/src/pkg/appengine_internal/api_prod.go:190
reflect.Value.call go/src/pkg/reflect/value.go:526
reflect.Value.Call go/src/pkg/reflect/value.go:334
_ _.go:316
runtime.goexit go/src/pkg/runtime/proc.c:270
What am I missing? Is this because of the use of urlfetch rather than DefaultClient?
答案1
得分: 0
好的,这当然是我的愚蠢错误,但我可以看出其他人可能会陷入同样的陷阱,所以这是解决方案,由Andrew Gerrand和Kyle Lemons在这个google-appengine-go主题中提出(谢谢你们)。
首先,我没有处理对favicon.ico的请求。可以通过按照这里的说明并在app.yaml中添加一个部分来解决:
- url: /favicon\.ico
static_files: images/favicon.ico
upload: images/favicon\.ico
这解决了对favicon请求的恐慌,但对于对'/'的请求仍然会产生恐慌。问题是,我假设http.Redirect在那一点上结束处理程序的执行。它并不是这样。需要的是在重定向后添加一个return语句,或者添加一个else子句:
code := r.FormValue("code")
if code == "" {
http.Redirect(w, r, config.AuthCodeURL("foo"), http.StatusFound)
} else {
t := &oauth.Transport{Config: config, Transport: &urlfetch.Transport{Context: c}}
tok, _ := t.Exchange(code)
fmt.Fprintf(w, "%s", tok.AccessToken)
// ...
}
当然,我不建议忽略错误,但这个部署和运行如预期,生成一个有效的令牌。
英文:
Okay, this was of course my own silly fault but I can see how others could fall into the same trap so here's the solution, prompted by Andrew Gerrand and Kyle Lemons in this google-appengine-go topic (thanks guys).
First of all, I wasn't handling requests to favicon.ico. That can be taken care of by following the instructions here and adding a section to app.yaml:
- url: /favicon\.ico
static_files: images/favicon.ico
upload: images/favicon\.ico
This fixed panics on favicon requests, but not panics on requests to '/'. Problem was, I'd assumed that an http.Redirect ends handler execution at that point. It doesn't. What was needed was either a return statement following the redirect, or an else clause:
code := r.FormValue("code")
if code == "" {
http.Redirect(w, r, config.AuthCodeURL("foo"), http.StatusFound)
} else {
t := &oauth.Transport{Config: config, Transport: &urlfetch.Transport{Context: c}}
tok, _ := t.Exchange(code)
fmt.Fprintf(w, "%s", tok.AccessToken)
// ...
}
I don't recommend ignoring the error of course but this deploys and runs as expected, producing a valid token.
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