Displaying Images of File Service from Azure in external system + REST API - rest

Question

I have created a method using GETFILE() service of azure. Reference: https://learn.microsoft.com/en-us/rest/api/storageservices/get-file
public void getImage(){
string storageKey = 'xxxxStorageKeyxxx';
string storageName = '<storageName>';
Datetime dt = Datetime.now();
string formattedDate = dt.formatGMT('EEE, dd MMM yyyy HH:mm:ss')+ ' GMT';
string CanonicalizedHeaders = 'x-ms-date:'+formattedDate+'\nx-ms-version:2016-05-31';
string CanonicalizedResource = '/' + storageName + '/<shareName>/<dirName>/<File Name>\ntimeout:20';
string StringToSign = 'GET\n\n\n\n\napplication/octet-stream\n\n\n\n\n\n\n' + CanonicalizedHeaders+'\n'+CanonicalizedResource;
Blob temp = EncodingUtil.base64Decode(storageKey);
Blob hmac = Crypto.generateMac('HmacSHA256',Blob.valueOf(StringToSign),temp ); //StringToSign
system.debug('oo-'+EncodingUtil.base64Encode(hmac));
HttpRequest req = new HttpRequest();
req.setMethod('GET');
req.setHeader('x-ms-version','2016-05-31' );
req.setHeader('x-ms-date', formattedDate);
req.setHeader('content-type','application/octet-stream');
string signature = EncodingUtil.base64Encode(hmac);
string authHeader = 'SharedKey <storageName>'+':'+signature;
req.setHeader('Authorization',authHeader);
req.setEndpoint('https://<storageName>.file.core.windows.net/<shareName>/<dirName>/<file Name>?timeout=20');
Http http = new Http();
HTTPResponse res;
res = http.send(req);
}
The above was working fine and giving the 200 as response code. But, my main goal is to display/download the respective image which i retrieved through REST API. How can i achieve that?

Answer 1

So a few things before I answer your question:
File storage is not really suitable for what you're trying to accomplish (it's possible though).
You should look at Blob storage for this as blob storage is more suitable for this kind of scenario.
Assuming you go with Blob storage, there are a few things you could do:
If the blob container (equivalent to a share in file storage) has an ACL is Blob or Container (i.e. blobs in a container are publicly available), you could simply return the blob's URL (Same is your request URL in code above) in your response and then create a link in your application with href set to this URL.
If the blob container has an ACL as Private (i.e. blobs are not publicly available), you would need to create a Shared Access Signature (SAS) token on that blob with at least Read permission and then create a SAS URL. A SAS URL is simply blob URL + SAS token and return this SAS URL in your response and then create a link in your application with href set to this URL.
Since an Azure File Share is always private, if you were to use Azure File service to serve a file, you would do the same thing as 2nd option I listed above. You will create a SAS token on the file with at least Read permission and then return the SAS URL in the response and then create a link in your application with href set to this URL.
To read about Shared Access Signature, you may find this link helpful: https://learn.microsoft.com/en-us/azure/storage/common/storage-dotnet-shared-access-signature-part-1.
To create a Shared Access Signature using REST API, you may find this link helpful: https://learn.microsoft.com/en-us/rest/api/storageservices/Constructing-a-Service-SAS?redirectedfrom=MSDN