If a bucket domain name is in the format of <BucketName-APPID>.cos.<Region>.<Main Domain>, it is an XML domain name. Any file type supported by the browser for direct preview can be previewed in the browser by accessing the object link corresponding to this domain name format.

If a bucket domain name is in the format of <BucketName-APPID>.<region>.<Main Domain>, it is a JSON domain name. Accessing the object link corresponding to the JSON domain name in the browser will prompt a download. There are two ways for you to preview the file in the browser:

Upgrade your COS console to the new console and use the object link corresponding to the XML domain name for access (strongly recommended).
Bind a custom domain and enable a static website to use the custom domain for access.

Example:

Take the picture.jpg file in the root directory of the examplebucket-1250000000 bucket in the Beijing region as an example:

If the object address is in the format of https://examplebucket-1250000000.cos.city.yfm4.fsphere.cn/picture.jpg, you can directly use this address to preview the picture.jpg file in the browser.
If the object address is in the format of https://examplebucket-1250000000.cos.city.yfm4.fsphere.cn/picture.jpg, there are two ways for you to directly preview the object in the browser:
1. Upgrade your COS console to the new console and use the object link corresponding to the XML domain name for access (strongly recommended).
2. Bind a custom domain and enable a static website to use the custom domain for access.

How Do I Directly Download a File in My Browser Without Previewing It?

You can go to the COS console and set the parameter value of Content-Disposition in the custom object headers to attachment. For the operation guide on the console, see Custom Headers.
You can also set the value of the response-content-disposition in the GET Object API request to attachment to make your browser pop up a window for you to download the file. For reference, see the document GET Object.

Note:

To use the response-* parameter in a request, the request must be signed.

How Do I Determine If I Am Accessing COS Over a Private Network?

Intelligent DNS resolution is adopted for COS access endpoints, and the optimal linkage will be detected and provided for you to access COS over the Internet with different Internet Service Providers (ISPs). If you have deployed a service within the cloud platform for accessing COS, intra-region access will be automatically routed to a private network address. Cross-region requests do not support private network access and will be resolved to a public network address by default.

Ways to Determine Access Over a Private Network

Cloud products within the same region automatically access each other through private network connections, and the generated private network traffic incurs no traffic fees. Therefore, when you purchase different products, it is recommended that you choose the same region to save on fees.
To determine access over a private network, see the following method:
For example, when a CVM accesses COS, to determine whether a private network is used to access COS, use the nslookup command on the CVM to resolve the COS endpoint. If a private IP address is returned, the access between the CVM and COS is over a private network; otherwise, it is over a public network.

Note:

Generally, a private IP address takes the form of 10.*.*.* or 100.*.*.*, and a VPC IP address takes the form of 169.254.*.*.

Assume that examplebucket-1250000000.cos.city.yfm4.fsphere.cn is the address of the destination bucket; the Address: 10.148.214.13 below indicates that the access is over a private network.

nslookup examplebucket-1250000000.cos.city.yfm4.fsphere.cn

Server:         10.138.224.65
Address:        10.138.224.65  #53

Name:   examplebucket-1250000000.cos.city.yfm4.fsphere.cn
Address: 10.148.214.13
Name:   examplebucket-1250000000.cos.city.yfm4.fsphere.cn
Address: 10.148.214.14

What if the error 403 forbidden occurs or access permission is rejected when I perform upload/download and other operations?

Follow the steps below to troubleshoot the issue step by step:

Check if the following configuration information is correct:
BucketName, APPID, Region, SecretId, and SecretKey.
After ensuring that the above information is correct, check if you are using a sub-account for operations. If you are, check whether the root account has granted the sub-account the permissions. Otherwise, log in to the root account to grant the sub-account the permissions. For operations on granting permissions, see Authorization Cases.
If you are using a temporary key for operations, check whether the current operation is within the policy set when you get the key.
If you still cannot solve the problem after following the steps above, submit a ticket and contact us.

When I Upload a New File to a Bucket in Which Another File of the Same Name Exists, Will the Old File Be Overwritten or Will the New File Be Saved with a Different Version Name?

COS now supports the versioning feature. If versioning is not enabled for the bucket, when you upload a file to the bucket in which another file of the same name already exists, the old file will be directly overwritten; if versioning is enabled for the bucket, when you upload files to the bucket in which another file of the same name already exists, multiple versions of the object will co-exist.

What Is the Minimum Part Size of a Multipart Upload in COS?

1 MB minimum per part. For more information, see the document Specifications and Limits.

When Uploading a Large File with Multipart Upload, Can I Replace an Invalid Signature to Continue the Multipart Upload?

Yes.