Go panic runtime error invalid memory address or nil pointer dereference

Question

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   I ve looked at the responses others have had to the same exception  but can t see anything simple  i e  an unhandled error    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     amp 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   amp 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    lt password gt      tenantId    lt tenantkeygoeshere gt            bodyBytes  err    getBody method  url  headers  creds       if err    nil           return     err            var keystone TokenResponse     err   json Unmarshal bodyBytes   amp 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

User · Answer

Since I got here with my problem I will add this answer although it is not exactly relevant to the original question. When you are implementing an interface make sure you do not forget to add the type pointer on your member function declarations. Example:

type AnimalSounder interface {
    MakeNoise()
}

type Dog struct {
    Name string
    mean bool
    BarkStrength int
}

func (dog *Dog) MakeNoise() {
    //implementation
}

I forgot the *(dog Dog) part, I do not recommend it. Then you get into ugly trouble when calling MakeNoice on an AnimalSounder interface variable of type Dog.

User · Answer

The nil pointer dereference is in line 65 which is the defer in  res  err    client Do req  defer res Body Close    if err    nil       return nil  err     If err   nil then res  nil and res Body panics  Handle err before defering the res Body Close

User · Answer

According to the docs for func   Client  Do    quot An error is returned if caused by client policy  such as CheckRedirect   or if there was an HTTP protocol error  A non-2xx response doesn t cause an error  When err is nil  resp always contains a non-nil resp Body  quot   Then looking at this code  res  err    client Do req  defer res Body Close    if err    nil       return nil  err    I m guessing that err is not nil  You re accessing the  Close   method on res Body before you check for the err  The defer only defers the function call  The field and method are accessed immediately   So instead  try checking the error immediately  res  err    client Do req   if err    nil       return nil  err   defer res Body Close

User · Answer

for me one solution for this problem  was to add in sql Open     sslmode disable

User · Answer

Make sure that you handle all the errors by sending a return value   if err  nil      return nil  err

[go] Go: panic: runtime error: invalid memory address or nil pointer dereference

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