Question

我在尝试从AWS S3读取GZIP文件时遇到了一些麻烦。我只有一个简单的代码，我收到错误panic: runtime error: invalid memory address or nil pointer dereference。但它仍然很难找到问题。

错误消息是gzip.NewReader...。为什么golang会举报？我怎么能解决它？

goroutine 1 [running]:
github.com/hensg/pushego/aws.GetGZIPProductsDump(0x7ffead44098f, 0xc, 0x7ffead44099f, 0x2f, 0x0, 0xc420190580, 0x0, 0x0)
        /home/henrique/go/src/github.com/hensg/pushego/aws/s3.go:47 +0x2e7
main.main()
        /home/henrique/go/src/github.com/hensg/pushego/pushego.go:28 +0x249

主要代码（pushego.go）

package main

import (
    "bufio"
    "flag"
    "log"
    "os"
    "time"

    "github.com/hensg/pushego/aws"
)

func init() {
    log.SetOutput(os.Stdout)
}

func main() {
    log.Println("Starting...")

    var bucket, key string
    var timeout time.Duration

    flag.StringVar(&bucket, "b", "", "Bucket name")
    flag.StringVar(&key, "k", "", "Object key name")
    flag.DurationVar(&timeout, "d", 0, "Download timeout")
    flag.Parse()

    gzipReader, err := aws.GetGZIPDump(bucket, key, timeout) // line 28
    if err != nil {
        log.Fatal("Failed to create GZIP reader")
    }
   defer gzipReader.Close()

    scanner := bufio.NewScanner(gzipReader)
    for scanner.Scan() {
        log.Printf("Read: %s\n", scanner.Text())
    }

    log.Printf("Successfully download file from %s/%s\n", bucket, key)
}

Aws代码（aws / s3.go）

package aws

import (
    "compress/gzip"
    "context"
    "log"
    "time"

    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/aws/awserr"
    "github.com/aws/aws-sdk-go/aws/request"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/s3"
)

func GetGZIPProductsDump(bucket, key string, timeout time.Duration) (*gzip.Reader, error) {
    sess := session.Must(session.NewSession())
    svc := s3.New(sess)

    // Create a context with a timeout that will abort the download if it takes
    // more than the passed in timeout.
    ctx := context.Background()
    var cancelFn func()
    if timeout > 0 {
        ctx, cancelFn = context.WithTimeout(ctx, timeout)
    }
    // Ensure the context is canceled to prevent leaking.
    // See context package for more information, https://golang.org/pkg/context/
    defer cancelFn()

    // Uploads the object to S3. The Context will interrupt the request if the
    // timeout expires.
    resp, err := svc.GetObjectWithContext(ctx, &s3.GetObjectInput{
        Bucket: aws.String(bucket),
        Key:    aws.String(key),
    })
    if err != nil {
        if aerr, ok := err.(awserr.Error); ok && aerr.Code() == request.CanceledErrorCode {
            // If the SDK can determine the request or retry delay was canceled
            // by a context the CanceledErrorCode error code will be returned.
            log.Fatal("Download canceled due to timeout, %v\n", err)
        } else {
            log.Fatal("Failed to download object, %v\n", err)
        }
    }

    return gzip.NewReader(resp.Body) // line 47
}

Answer 1

问题与defer cancelFn()有关，目前如果超时为0则未设置func，这会引发带有空指针的恐慌，因此，您应该移动defer内部的之前的if语句，因为它是唯一需要使用的时间点。 aws/s3.go的代码必须如下所示。

...
// Create a context with a timeout that will abort the download if it takes
// more than the passed in timeout.
ctx := context.Background()
var cancelFn func()
if timeout > 0 {
    ctx, cancelFn = context.WithTimeout(ctx, timeout)
    // Ensure the context is canceled to prevent leaking.
    // See context package for more information, https://golang.org/pkg/context/
    defer cancelFn()
}
...

Golang IO读取文件无效的内存地址

1 个答案: