Go:恐慌:运行时错误:无效的内存地址或零指针取消引用 [英] Go: panic: runtime error: invalid memory address or nil pointer dereference
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问题描述
运行我的 Go 程序时，它会发生恐慌并返回以下内容:
When running my Go program, it panics and returns the following:
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x38 pc=0x26df]
goroutine 1 [running]:
main.getBody(0x1cdcd4, 0xf800000004, 0x1f2b44, 0x23, 0xf84005c800, ...)
/Users/matt/Dropbox/code/go/scripts/cron/fido.go:65 +0x2bb
main.getToken(0xf84005c7e0, 0x10)
/Users/matt/Dropbox/code/go/scripts/cron/fido.go:140 +0x156
main.main()
/Users/matt/Dropbox/code/go/scripts/cron/fido.go:178 +0x61
goroutine 2 [syscall]:
created by runtime.main
/usr/local/Cellar/go/1.0.3/src/pkg/runtime/proc.c:221
goroutine 3 [syscall]:
syscall.Syscall6()
/usr/local/Cellar/go/1.0.3/src/pkg/syscall/asm_darwin_amd64.s:38 +0x5
syscall.kevent(0x6, 0x0, 0x0, 0xf840085188, 0xa, ...)
/usr/local/Cellar/go/1.0.3/src/pkg/syscall/zsyscall_darwin_amd64.go:199 +0x88
syscall.Kevent(0xf800000006, 0x0, 0x0, 0xf840085188, 0xa0000000a, ...)
/usr/local/Cellar/go/1.0.3/src/pkg/syscall/syscall_bsd.go:546 +0xa4
net.(*pollster).WaitFD(0xf840085180, 0xf840059040, 0x0, 0x0, 0x0, ...)
/usr/local/Cellar/go/1.0.3/src/pkg/net/fd_darwin.go:96 +0x185
net.(*pollServer).Run(0xf840059040, 0x0)
/usr/local/Cellar/go/1.0.3/src/pkg/net/fd.go:236 +0xe4
created by net.newPollServer
/usr/local/Cellar/go/1.0.3/src/pkg/net/newpollserver.go:35 +0x382
我查看了其他人对相同异常的响应，但看不到任何简单的内容(即未处理的错误).
I've looked at the responses others have had to the same exception, but can't see anything simple (i.e. an unhandled error).
我正在一台无法访问代码中列出的 API 服务器的机器上运行它，但我希望它会返回一个适当的错误(因为我已经尝试捕获此类错误).
I am running it on a machine that does not have access to the API servers listed in the code, but I was hoping it'd return an appropriate error (as I've attempted to catch errors of that kind).
package main
/*
Fido fetches the list of public images from the Glance server, captures the IDs of images with 'status': 'active' and then queues the images for pre-fetching with the Glance CLI utility `glance-cache-manage`. Once the images are added to the queue, `glance-cache-prefetcher` is called to actively fetch the queued images into the local compute nodes' image cache.
See http://docs.openstack.org/developer/glance/cache.html for further details on the Glance image cache.
*/
import (
"bytes"
"encoding/json"
"fmt"
"io/ioutil"
/*
"log"
"log/syslog"
*/
"net/http"
"os"
"os/exec"
)
func prefetchImages() error {
cmd := exec.Command("glance-cache-prefetcher")
err := cmd.Run()
if err != nil {
return fmt.Errorf("glance-cache-prefetcher failed to execute properly: %v", err)
}
return nil
}
func queueImages(hostname string, imageList []string) error {
for _, image := range imageList {
cmd := exec.Command("glance-cache-manage", "--host=", hostname, "queue-image", image)
err := cmd.Run()
if err != nil {
return fmt.Errorf("glance-cache-manage failed to execute properly: %v", err)
} else {
fmt.Printf("Image %s queued", image)
}
}
return nil
}
func getBody(method string, url string, headers map[string]string, body []byte) ([]byte, error) {
client := &http.Client{}
req, err := http.NewRequest(method, url, bytes.NewReader(body))
if err != nil {
return nil, err
}
for key, value := range headers {
req.Header.Add(key, value)
}
res, err := client.Do(req)
defer res.Body.Close()
if err != nil {
return nil, err
}
var bodyBytes []byte
if res.StatusCode == 200 {
bodyBytes, err = ioutil.ReadAll(res.Body)
} else if err != nil {
return nil, err
} else {
return nil, fmt.Errorf("The remote end did not return a HTTP 200 (OK) response.")
}
return bodyBytes, nil
}
func getImages(authToken string) ([]string, error) {
type GlanceDetailResponse struct {
Images []struct {
Name string `json:"name"`
Status string `json:"status"`
ID string `json:"id"`
}
}
method := "GET"
url := "http://192.168.1.2:9292/v1.1/images/detail"
headers := map[string]string{"X-Auth-Token": authToken}
bodyBytes, err := getBody(method, url, headers, nil)
if err != nil {
return nil, fmt.Errorf("unable to retrieve the response body from the Glance API server: %v", err)
}
var glance GlanceDetailResponse
err = json.Unmarshal(bodyBytes, &glance)
if err != nil {
return nil, fmt.Errorf("unable to parse the JSON response:", err)
}
imageList := make([]string, 10)
for _, image := range glance.Images {
if image.Status == "active" {
imageList = append(imageList, image.ID)
}
}
return imageList, nil
}
func getToken() (string, error) {
type TokenResponse struct {
Auth []struct {
Token struct {
Expires string `json:"expires"`
ID string `json:"id"`
}
}
}
method := "POST"
url := "http://192.168.1.2:5000/v2.0/tokens"
headers := map[string]string{"Content-type": "application/json"}
creds := []byte(`{"auth":{"passwordCredentials":{"username": "glance", "password":"<password>"}, "tenantId":"<tenantkeygoeshere>"}}`)
bodyBytes, err := getBody(method, url, headers, creds)
if err != nil {
return "", err
}
var keystone TokenResponse
err = json.Unmarshal(bodyBytes, &keystone)
if err != nil {
return "", err
}
authToken := string((keystone.Auth[0].Token.ID))
return authToken, nil
}
func main() {
/*
slog, err := syslog.New(syslog.LOG_ERR, "[fido]")
if err != nil {
log.Fatalf("unable to connect to syslog: %v", err)
os.Exit(1)
} else {
defer slog.Close()
}
*/
hostname, err := os.Hostname()
if err != nil {
// slog.Err("Hostname not captured")
os.Exit(1)
}
authToken, err := getToken()
if err != nil {
// slog.Err("The authentication token from the Glance API server was not retrieved")
os.Exit(1)
}
imageList, err := getImages(authToken)
err = queueImages(hostname, imageList)
if err != nil {
// slog.Err("Could not queue the images for pre-fetching")
os.Exit(1)
}
err = prefetchImages()
if err != nil {
// slog.Err("Could not queue the images for pre-fetching")
os.Exit(1)
}
return
}
推荐答案
"如果由客户端策略(例如 CheckRedirect)引起，或者存在 HTTP 协议错误，则会返回错误.非 2xx 响应不会导致错误.
当err为nil时，resp总是包含一个非nil的resp.Body."
然后看这段代码:
res, err := client.Do(req)
defer res.Body.Close()
if err != nil {
return nil, err
}
我猜err 不是nil.在检查 err 之前，您正在访问 res.Body 上的 .Close() 方法.
I'm guessing that err is not nil. You're accessing the .Close() method on res.Body before you check for the err.
defer 只延迟函数调用.立即访问字段和方法.
The defer only defers the function call. The field and method are accessed immediately.
因此，请立即尝试检查错误.
So instead, try checking the error immediately.
res, err := client.Do(req)
if err != nil {
return nil, err
}
defer res.Body.Close()
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