7. 错误处理

1.通用的错误处理：

S3有一个通用的错误处理类：awserr.Error，通过了以下方法获取出错信息：

方法	说明
Code	returns the classification code by which related errors are grouped.
Message	returns a description of the error.
OrigError	returns the original error of type error that is wrapped by the awserr.Error interface, such as a standard library error or a service error.

awserr.Error的定义如下：

type Error interface {
    // Satisfy the generic error interface.
    error

    // Returns the short phrase depicting the classification of the error.
    Code() string

    // Returns the error details message.
    Message() string

    // Returns the original error if one was set.  Nil is returned if not set.
    OrigErr() error
}

2.处理特殊的出错

svc := s3.New(sess)
resp, err := svc.GetObject(&s3.GetObjectInput{
    Bucket: aws.String(os.Args[1]),
    Key:    aws.String(os.Args[2]),
})

if err != nil {
    // http://docs.aws.amazon.com/AmazonS3/latest/API/ErrorResponses.html
    if aerr, ok := err.(awserr.Error); ok {
        switch aerr.Code() {
        case s3.ErrCodeNoSuchBucket:
            exitErrorf("bucket %s does not exist", os.Args[1])
        case s3.ErrCodeNoSuchKey:
            exitErrorf("object with key %s does not exist in bucket %s", os.Args[2], os.Args[1])
        }
    }
}

Code	description
ErrCodeNoSuchBucket	桶不存在
ErrCodeNoSuchKey	对象不存在
ErrCodeBucketAlreadyExists	桶已经被创建了，不属于您
ErrCodeBucketAlreadyOwnedByYou	桶已经被创建了，且是您创建的
ErrCodeNoSuchUpload	分块上传不存在

3.特殊的错误接口：MultiUploadFailure

接口定义如下：

type MultiUploadFailure interface {
    awserr.Error

    // Returns the upload id for the S3 multipart upload that failed.
    UploadID() string
}