Azure PUT Blob authentication fails in R

Question

I would like to use R and the Azure Storage's Put Blob API to put files into my blob storage account but it fails to authenticate my request. Unfortunately, I couldn't find any documentation or sample code for R. General documentation of Put Blob API: https://docs.microsoft.com/en-us/rest/api/storageservices/put-blob

Here is the code that I tried to use:

library(httr)  

account <- "myAccount"  
container <- "myContainer"  
filename <- "test.txt"  
key <- "primaryKey"  
object <- "Hello World" 

url <- paste0("https://", account, ".blob.core.windows.net/", container, "/", filename)
requestdate <- format(Sys.time(),"%a, %d %b %Y %H:%M:%S %Z", tz="GMT")  
content_length <- nchar(object, type = "bytes")  

signature_string <- paste0("PUT", "\n", "\n", "\n",
                       content_length, "\n", 
                       "\n",
                       "x-ms-date:",requestdate, "\n", 
                       "x-ms-version:2015-02-21", "\n",
                       "x-ms-blob-type:BlockBlob", "\n",
                       "Content-Type:text/plain",  "\n",
                       "\n",
                       "x-ms-blob-content-dis filename=", filename, "\n",
                       "\n",
                       "/",account, "/",container,"/", filename)

headerstuff <- add_headers(Authorization=paste0("SharedKey ",account,":", 
                       RCurl::base64(digest::hmac(key = 
RCurl::base64Decode(key, mode = "raw"),
                       object = enc2utf8(signature_string),
                       algo = "sha256", raw = TRUE))),
                       `Content-Length` = content_length,
                       `x-ms-date`= requestdate,
                       `x-ms-version`= "2015-02-21",
                       `x-ms-blob-type`="BlockBlob",
                       `Content-Type`="text/plain")

content(PUT(url, config = headerstuff, body = object, verbose()), as = "text")`

Request it sends:

-> PUT /myContainer/test.txt HTTP/1.1
-> Host: myAccount.blob.core.windows.net
-> User-Agent: libcurl/7.49.1 r-curl/2.3 httr/1.2.1
-> Accept-Encoding: gzip, deflate
-> Accept: application/json, text/xml, application/xml, */*
-> Authorization: SharedKey myAccount:hashedSignatureString
-> Content-Length: 11
-> x-ms-date: Tue, 13 Jun 2017 08:50:38 GMT
-> x-ms-version: 2015-02-21
-> x-ms-blob-type: BlockBlob
-> Content-Type: text/plain
-> 
>> Hello World

Response:

<- HTTP/1.1 403 Server failed to authenticate the request. Make sure the 
value of Authorization header is formed correctly including the signature.
<- Content-Length: 693
<- Content-Type: application/xml
<- Server: Microsoft-HTTPAPI/2.0
<- x-ms-request-id: efc2c8de-0001-00a9-3d21-e41b06000000
<- Date: Tue, 13 Jun 2017 08:48:56 GMT

I tried the same with the List Blobs API (with some minor changes in the formatting of the headers) and it works well, but I can't make it work with Put Blob. List Blob solution from here: https://stackoverflow.com/a/29286040/8085694

Could you please provide some sample R code for Authentication header creation at Put Blob or help me resolve this issue?

Also, if I go further, is it possible somehow to upload R objects as blobs to the storage?

Thanks in advance,

Gábor

Answer 1

I managed to resolve this issue by putting the "\n" characters and everything in the right place. Based on Gaurav Mantri's help, I used:
https://docs.microsoft.com/en-us/rest/api/storageservices/authentication-for-the-azure-storage-services

The following changes in the 'signature_string' worked:

signature_string <- paste0("PUT", "\n",            # HTTP Verb
                           "\n",                   # Content-Encoding  
                           "\n",                   # Content-Language
                           content_length, "\n",   # Content-Length
                           "\n",                   # Content-MD5
                           "text/plain", "\n",     # Content-Type
                           "\n",                   # Date
                           "\n",                   # If-Modified-Since
                           "\n",                   # If-Match  
                           "\n",                   # If-None-Match
                           "\n",                   # If-Unmodified-Since
                           "\n",                   # Range
                           # Here comes the Canonicalized Headers
                           "x-ms-blob-type:BlockBlob","\n",
                           "x-ms-date:",requestdate,"\n",
                           "x-ms-version:2015-02-21","\n",
                           # Here comes the Canonicalized Resource
                           "/",account, "/",container,"/", filename)

Answer 2

There is an Azure offical R package Microsoft/AzureSMR on GitHub, which can help you easier using R & Azure Blob Storage, you can refer to its tutorial to know more details.

If you just want to use some Azure services like Blob Storage, not else, I think some source codes of this project are very valuable for rebuilding your code better, such as createAzureStorageSignature method which can directly help building the signature to resolve your issue.