Updated Yahoo Weather API - .NET - yahoo-weather-api

Question

I'm trying to implement the newest yahoo weather API in a .NET application (the one we were using was discontinued in favor of this new one): https://developer.yahoo.com/weather/documentation.html#commercial
Their only examples are in PHP and Java. I've done my best to convert the Java example to .NET but I still am getting a "401 - Unauthorized" response. I've gone over my code several times and cannot find any problems so I'm hoping someone else will be able to see where I went wrong. Code is below.
Private Sub _WeatherLoader_DoWork(sender As Object, e As DoWorkEventArgs)
Try
Dim oauth As New OAuth.OAuthBase
Dim forecastRssResponse As query
Dim appId As String = My.Settings.YahooAppID
Dim consumerKey As String = My.Settings.YahooAPIConsumerKey
Dim yahooUri As String = String.Format("{0}?location=billings,mt&format=xml", YAHOO_WEATHER_API_BASE_ENDPOINT)
Dim oAuthTimestamp As Integer = oauth.GenerateTimeStamp()
Dim oAuthNonce As String = oauth.GenerateNonce()
Dim parameters As New List(Of String)
Try
parameters.Add(String.Format("oauth_consumer_key={0}", consumerKey))
parameters.Add(String.Format("oauth_nonce={0}", oAuthNonce))
parameters.Add("oauth_signature_method=HMAC-SHA1")
parameters.Add(String.Format("oauth_timestamp={0}", oAuthTimestamp.ToString()))
parameters.Add("oauth_version=1.0")
' Encode the location
parameters.Add(String.Format("location={0}", HttpUtility.UrlEncode("billings,mt", Encoding.UTF8)))
parameters.Add("format=xml")
' Sort parameters ascending
parameters = parameters.OrderBy(Function(item) item).ToList()
Dim i As Integer = 0
Dim builder As New StringBuilder()
Do While (i < parameters.Count())
builder.Append(String.Format("{0}{1}", If(i > 0, "&", String.Empty), parameters(i)))
i += 1
Loop
Dim signatureString As String = String.Format("GET&{0}&{1}", HttpUtility.UrlEncode(YAHOO_WEATHER_API_BASE_ENDPOINT, Encoding.UTF8), HttpUtility.UrlEncode(builder.ToString(), Encoding.UTF8))
Dim oAuthSignature As String = _CreateOauthSignature(signatureString)
Dim authorizationLine As String = String.Format("OAuth oauth_consumer_key={0}, oauth_nonce={1}, oauth_timestamp={2}, oauth_signature_method=HMAC-SHA1, oauth_signature={3}, oauth_version=1.0", consumerKey, oAuthNonce, oAuthTimestamp, oAuthSignature)
Dim forecastRequest As WebRequest = WebRequest.Create(yahooUri)
forecastRequest.Headers.Add("Authorization", authorizationLine)
forecastRequest.Headers.Add("Yahoo-App-Id", appId)
' Cast to HttpWebRequest to set ContentType through property
CType(forecastRequest, HttpWebRequest).ContentType = "text/xml"
Dim forecastResponse As WebResponse = forecastRequest.GetResponse()
If forecastResponse IsNot Nothing Then
Using responseStream As Stream = forecastResponse.GetResponseStream()
Dim rssDoc As New XmlDocument()
rssDoc.Load(responseStream)
forecastRssResponse = rssDoc.OuterXml().FromXml(Of query)()
End Using
e.Result = forecastRssResponse
End If
Catch ex As Exception
e.Result = Nothing
LoadingManually = False
End Try
Catch ex As Exception
modMain.SendDevErrorEmail(ex, "_WeatherLoader_DoWork in WeatherWidget", "Catch around dowork code in fired from refresh timer event in wether widget")
e.Result = Nothing
LoadingManually = False
End Try
End Sub
Private Function _CreateOauthSignature(baseInfo As String) As String
Dim secretKey As String = String.Format("{0}&", My.Settings.YahooAPIConsumerSecretKey)
Dim encoding As New System.Text.ASCIIEncoding()
Dim keyBytes As Byte() = encoding.GetBytes(secretKey)
Dim messageBytes As Byte() = encoding.GetBytes(baseInfo)
Dim hashMessage As Byte()
Using hmac As New HMACSHA1(keyBytes)
hashMessage = hmac.ComputeHash(messageBytes)
End Using
Return Convert.ToBase64String(hashMessage)
End Function

Answer 1

After painstakingly creating a Java app, pasting in the Java example and stepping through it I found that the issue is in a poorly implemented URL Decode function on the receiving end.
In the Java app, URL Encode uses upper case characters while in .NET HTTPUtility.URLEncode uses lower case characters. This is enough to throw off your signature and cause a 401 - Unauthorized error.
My solution was to create a string extension method that will URL Encode in upper case:
<Extension>
Public Function UppercaseURLEncode(ByVal sourceString As String) As String
Dim temp As Char() = HttpUtility.UrlEncode(sourceString).ToCharArray()
For i As Integer = 0 To temp.Length - 2
If temp(i).ToString().Equals("%", StringComparison.OrdinalIgnoreCase) Then
temp(i + 1) = Char.ToUpper(temp(i + 1))
temp(i + 2) = Char.ToUpper(temp(i + 2))
End If
Next
Return New String(temp)
End Function
Using this extension method my signature gets created exactly like the one in the Java app and I am able to retrieve the response.
Hope this helps other .net programmers with this issue!