Downloading an Object - Streaming (SDK for Go)
Function
This API downloads a file using streaming from OBS to your local computer.
Restrictions
- To download an object, you must be the bucket owner or have the required permission (obs:object:GetObject in IAM or GetObject in a bucket policy). For details, see Introduction to OBS Access Control, IAM Custom Policies, and Configuring an Object Policy.
- The mapping between OBS regions and endpoints must comply with what is listed in Regions and Endpoints.
- Objects in the Archive storage class can be downloaded only when they are in the Restored status.
Method
func (obsClient ObsClient) GetObject(input *GetObjectInput) (output *GetObjectOutput, err error)
Request Parameters
Parameter |
Type |
Mandatory (Yes/No) |
Description |
---|---|---|---|
input |
Yes |
Explanation: Input parameters for a streaming download. For details, see Table 2. |
Parameter |
Type |
Mandatory (Yes/No) |
Description |
---|---|---|---|
Bucket |
string |
Yes |
Explanation: Bucket name Restrictions:
Default value: None |
Key |
string |
Yes |
Explanation: Object name. An object is uniquely identified by an object name in a bucket. An object name is a complete path that does not contain the bucket name. For example, if the address for accessing the object is examplebucket.obs.ap-southeast-1.myhuaweicloud.com/folder/test.txt, the object name is folder/test.txt. Value range: The value must contain 1 to 1,024 characters. Default value: None |
ResponseCacheControl |
string |
No |
Explanation: Cache-Control header in the response. It specifies the cache behavior of the web page when the object is downloaded. Default value: None |
ResponseContentDisposition |
string |
No |
Explanation: Content-Disposition header in the response. It specifies the name of the object when it is downloaded. Default value: None |
ResponseContentEncoding |
string |
No |
Explanation: Content-Encoding header in the response. It specifies the content encoding format when an object is downloaded. Default value: None |
ResponseContentLanguage |
string |
No |
Explanation: Content-Language header in the response. It specifies the content language format when an object is downloaded. Default value: None |
ResponseContentType |
string |
No |
Explanation: Content-Type header in the response. It specifies the object file type. Default value: None |
ResponseExpires |
string |
No |
Explanation: Expires header in the response. It specifies the cache expiration time of the web page when the object is downloaded. Default value: None |
VersionId |
string |
No |
Explanation: Object version ID, for example, G001117FCE89978B0000401205D5DC9 Value range: The value must contain 32 characters. Default value: None. If this parameter is left blank, the latest version of the object is obtained. |
ImageProcess |
string |
No |
Explanation: Image processing command or style. Example for resizing and rotating an image: image/resize,m_fixed,w_100,h_100/rotate,90 Value range: Command format: image/commands Style format: style/style name For details about image processing parameters, see Processing Images. Default value: If no commands are entered, the original image is returned. |
RangeStart |
int64 |
No |
Explanation: Start position for object download Value range: 0 to the object length, in bytes. Default value: 0, indicating the download starts from the first byte of the object. |
RangeEnd |
int64 |
No |
Explanation: End position for object download Value range:
Default value: None |
IfMatch |
string |
No |
Explanation: Preset ETag. If the ETag of the object to be downloaded is the same as the preset ETag, the object is returned. Otherwise, an error is returned. Value range: The value must contain 32 characters. Default value: None |
IfNoneMatch |
string |
No |
Explanation: Preset ETag. If the ETag of the object to be downloaded is different from the preset ETag, the object is returned. Otherwise, an error is returned. Value range: The value must contain 32 characters. Default value: None |
IfModifiedSince |
time.Time |
No |
Explanation: The object is returned if it has been modified since the specified time; otherwise, an error is returned. Restrictions: The time must be in the ISO8601 format, for example, 2018-01-01T00:00:00.000Z. Sample code: time.Now().Add(time.Duration(24) * time.Hour) Default value: None |
IfUnmodifiedSince |
time.Time |
No |
Explanation: The object is returned if it has not been modified since the specified time; otherwise, an error is returned. Restrictions: The time must be in the ISO8601 format, for example, 2018-01-01T00:00:00.000Z. Sample code: time.Now().Add(time.Duration(24) * time.Hour) Default value: None |
SseHeader |
No |
Explanation: Server-side decryption headers. For details, see Table 3. Restrictions: If the object uploaded to a server is encrypted with the key provided by the client, the key must also be provided in the message for downloading the object. |
Parameter |
Type |
Mandatory (Yes/No) |
Description |
---|---|---|---|
Encryption |
string |
Yes if used as a request parameter |
Explanation: SSE-C used for encrypting objects Value range: AES256, indicating objects are encrypted using SSE-C Default value: None |
Key |
string |
Yes if used as a request parameter |
Explanation: Key for encrypting the object when SSE-C is used Restrictions: The value is a Base64-encoded 256-bit key, for example, K7QkYpBkM5+hca27fsNkUnNVaobncnLht/rCB2o/9Cw=. Default value: None |
KeyMD5 |
string |
No if used as a request parameter |
Explanation: MD5 value of the key for encrypting objects when SSE-C is used. This value is used to check whether any error occurs during the transmission of the key. Restrictions: The value is encrypted by MD5 and then encoded by Base64, for example, 4XvB3tbNTN+tIEVa0/fGaQ==. Default value: None |
Responses
Parameter |
Type |
Description |
---|---|---|
output |
Explanation: Returned results. For details, see Table 5. |
|
err |
error |
Explanation: Error messages returned by the API |
Parameter |
Type |
Description |
---|---|---|
StatusCode |
int |
Explanation: HTTP status code Value range: A status code is a group of digits that can be 2xx (indicating successes) or 4xx or 5xx (indicating errors). It indicates the status of a response. For more information, see Status Code. Default value: None |
RequestId |
string |
Explanation: Request ID returned by the OBS server Default value: None |
ResponseHeaders |
map[string][]string |
Explanation: HTTP response headers Default value: None |
Body |
io.ReadCloser |
Explanation: Object data stream to download Default value: None |
StorageClass |
Explanation: Object storage class Value range: See Table 6. Default value: None |
|
AllowOrigin |
string |
Explanation: If Origin in the request meets the CORS rules of the bucket, AllowedOrigin in the CORS rules is returned. AllowedOrigin indicates the origin from which the requests can access the bucket. Restrictions: Domain name of the origin. Each origin can contain only one wildcard character (*), for example, https://*.vbs.example.com. Default value: None |
AllowHeader |
string |
Explanation: If RequestHeader in the request meets the CORS rules of the bucket, AllowedHeader in the CORS rules is returned. AllowedHeader indicates the allowed headers for cross-origin requests. Only CORS requests matching the allowed headers are valid. Restrictions: Each header can contain only one wildcard character (*). Spaces, ampersands (&), colons (:), and less-than signs (<) are not allowed. Default value: None |
AllowMethod |
string |
Explanation: AllowedMethod in the CORS rules of the bucket. It specifies the HTTP method of cross-origin requests, that is, the operation type of buckets and objects. Value range: The following HTTP methods are supported:
Default value: None |
ExposeHeader |
string |
Explanation: ExposeHeader in the CORS rules of the bucket. It specifies the CORS-allowed additional headers in the response. These headers provide additional information to clients. By default, your browser can only access headers Content-Length and Content-Type. If your browser needs to access other headers, add them to a list of the allowed additional headers. Restrictions: Spaces, wildcard characters (*), ampersands (&), colons (:), and less-than signs (<) are not allowed. Default value: None |
MaxAgeSeconds |
int |
Explanation: MaxAgeSeconds in the CORS rules of the bucket. It specifies the time your client can cache the response for a cross-origin request. Restrictions: Each CORS rule can specify only one value for MaxAgeSeconds. Value range: 0 to (231 – 1), in seconds Default value: 100 |
ContentLength |
int64 |
Explanation: Object size in bytes Value range: The value ranges from 0 TB to 48.8 TB, in bytes. Default value: None |
CacheControl |
string |
Explanation: Cache-Control header in the response. It specifies cache behaviors of the web page when an object is downloaded. Default value: None |
ContentDisposition |
string |
Explanation: Content-Disposition header in the response Default value: None |
ContentEncoding |
string |
Explanation: Content-Encoding header in the response Default value: None |
ContentLanguage |
string |
Explanation: Content-Language header in the response Default value: None |
ContentType |
string |
Explanation: MIME type of the file to be downloaded. MIME type is a standard way of describing a data type and is used by the browser to decide how to display data. Value range: See What Is Content-Type (MIME)? Default value: If you do not specify this parameter when uploading an object, the SDK determines the object type based on the suffix of the specified object name and automatically assigns a value to this parameter. |
Expires |
string |
Explanation: Expires header in the response Default value: None |
LastModified |
time.Time |
Explanation: Time when the last modification was made to the object Restrictions: The time must be in the ISO8601 format, for example, 2018-01-01T00:00:00.000Z. Default value: None |
ETag |
string |
Explanation: Base64-encoded, 128-bit MD5 value of an object. ETag is the unique identifier of the object content. It can be used to determine whether the object content is changed. For example, if the ETag value is A when an object is uploaded, but changes to B when the object is downloaded, it indicates that the object content has been changed. The ETag reflects changes to the object content, rather than the object metadata. An uploaded or copied object has a unique ETag after being encrypted using MD5. Restrictions: If an object is encrypted using server-side encryption, the ETag is not the MD5 value of the object. Value range: The value must contain 32 characters. Default value: None |
VersionId |
string |
Explanation: Object version ID Value range: The value must contain 32 characters. Default value: None |
Restore |
string |
Explanation: Restore status of an object. For an Archive object that is being restored or has been restored, this header is returned. For example, ongoing-request="true" indicates that the object is being restored. ongoing-request="false", expiry-date="Wed, 7 Nov 2012 00:00:00 GMT" indicates that the object has been restored. expiry-date indicates when the restored object expires. Restrictions: This parameter is only available for Archive objects. Default value: None |
Expiration |
string |
Explanation: Expiration details of the object. Example: "expiry-date=\"Mon, 11 Sep 2023 00:00:00 GMT\"" Default value: None |
SseHeader |
Explanation: Server-side encryption header information. If SSE-C is used, see Table 7. If SSE-KMS is used, see Table 8. |
|
WebsiteRedirectLocation |
string |
Explanation: If the bucket is configured with website hosting, the request for obtaining the object can be redirected to another object in the bucket or an external URL. This parameter specifies the address the request for the object is redirected to. The request is redirected to object anotherPage.html in the same bucket: WebsiteRedirectLocation:/anotherPage.html The request is redirected to an external URL http://www.example.com/: WebsiteRedirectLocation:http://www.example.com/ OBS obtains the specified value from the header and stores it in the object metadata WebsiteRedirectLocation. Restrictions:
Default value: None |
Metadata |
map[string]string |
Explanation: Custom object metadata. You can add a header starting with x-obs-meta- in the request to define metadata. The custom metadata will be returned in the response when you retrieve the object or query the object metadata. Restrictions:
Default value: None |
Constant |
Default Value |
Description |
---|---|---|
StorageClassStandard |
STANDARD |
OBS Standard Features low access latency and high throughput and is used for storing massive, frequently accessed (multiple times a month) or small objects (< 1 MB) requiring quick response. |
StorageClassWarm |
WARM |
OBS Infrequent Access Used for storing data that is semi-frequently accessed (fewer than 12 times a year) but is instantly available when needed. |
StorageClassCold |
COLD |
OBS Archive Used for storing rarely accessed (once a year) data. |
Parameter |
Type |
Mandatory (Yes/No) |
Description |
---|---|---|---|
Encryption |
string |
Yes if used as a request parameter |
Explanation: SSE-C used for encrypting objects Value range: AES256, indicating objects are encrypted using SSE-C Default value: None |
Key |
string |
Yes if used as a request parameter |
Explanation: Key for encrypting the object when SSE-C is used Restrictions: The value is a Base64-encoded 256-bit key, for example, K7QkYpBkM5+hca27fsNkUnNVaobncnLht/rCB2o/9Cw=. Default value: None |
KeyMD5 |
string |
No if used as a request parameter |
Explanation: MD5 value of the key for encrypting objects when SSE-C is used. This value is used to check whether any error occurs during the transmission of the key. Restrictions: The value is encrypted by MD5 and then encoded by Base64, for example, 4XvB3tbNTN+tIEVa0/fGaQ==. Default value: None |
Parameter |
Type |
Mandatory (Yes/No) |
Description |
---|---|---|---|
Encryption |
string |
Yes if used as a request parameter |
Explanation: SSE-KMS used for encrypting objects Value range: kms, indicating objects are encrypted using SSE-KMS Default value: None |
Key |
string |
No if used as a request parameter |
Explanation: ID of the KMS master key when SSE-KMS is used Value range: Valid value formats are as follows:
In the preceding formats:
Default value:
|
Code Examples
This example downloads example/objectname from examplebucket using streaming.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 |
package main import ( "fmt" "os" obs "github.com/huaweicloud/huaweicloud-sdk-go-obs/obs" ) func main() { //Obtain an AK/SK pair using environment variables or import an AK/SK pair in other ways. Using hard coding may result in leakage. //Obtain an AK/SK pair on the management console. For details, see https://support.huaweicloud.com/intl/en-us/usermanual-ca/ca_01_0003.html. ak := os.Getenv("AccessKeyID") sk := os.Getenv("SecretAccessKey") // (Optional) If you use a temporary AK/SK pair and a security token to access OBS, you are advised not to use hard coding to reduce leakage risks. You can obtain an AK/SK pair using environment variables or import an AK/SK pair in other ways. // securityToken := os.Getenv("SecurityToken") // Enter the endpoint corresponding to the bucket. CN-Hong Kong is used here as an example. Replace it with the one currently in use. endPoint := "https://obs.ap-southeast-1.myhuaweicloud.com" // Create an obsClient instance. // If you use a temporary AK/SK pair and a security token to access OBS, use the obs.WithSecurityToken method to specify a security token when creating an instance. obsClient, err := obs.New(ak, sk, endPoint/*, obs.WithSecurityToken(securityToken)*/) if err != nil { fmt.Printf("Create obsClient error, errMsg: %s", err.Error()) } input := &obs.GetObjectInput{} // Specify a bucket name. input.Bucket = "examplebucket" // Specify the object (example/objectname as an example) to download. input.Key = "example/objectname" // Download the object using streaming. output, err := obsClient.GetObject(input) if err == nil { // Close output.Body after using it, to avoid connection leakage. defer output.Body.Close() fmt.Printf("Get object(%s) under the bucket(%s) successful!\n", input.Key, input.Bucket) fmt.Printf("StorageClass:%s, ETag:%s, ContentType:%s, ContentLength:%d, LastModified:%s\n", output.StorageClass, output.ETag, output.ContentType, output.ContentLength, output.LastModified) // Read the object content. p := make([]byte, 1024) var readErr error var readCount int for { readCount, readErr = output.Body.Read(p) if readCount > 0 { fmt.Printf("%s", p[:readCount]) } if readErr != nil { break } } return } fmt.Printf("List objects under the bucket(%s) fail!\n", input.Bucket) if obsError, ok := err.(obs.ObsError); ok { fmt.Println("An ObsError was found, which means your request sent to OBS was rejected with an error response.") fmt.Println(obsError.Error()) } else { fmt.Println("An Exception was found, which means the client encountered an internal problem when attempting to communicate with OBS, for example, the client was unable to access the network.") fmt.Println(err) } } |
Readable streams obtained by GetObjectOutput.Body must be closed explicitly. Otherwise, resource leakage occurs.
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