First pass implementation

Ooui.Forms/Forms.cs

@@ -1,6 +1,4 @@
 using System;
-using System.Diagnostics;
-using Xamarin.Forms;
 using Xamarin.Forms.Internals;
 using Ooui.Forms;
 using System.IO;
@@ -8,6 +6,7 @@ using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
 using Ooui;
+using System.Net.Http;
 
 namespace Xamarin.Forms
 {
@@ -37,6 +36,9 @@ namespace Xamarin.Forms
 
         public static event EventHandler<ViewInitializedEventArgs> ViewInitialized;
 
+        public static HttpClientHandler HttpClientHandler { get; set; }
+
+
         public static void SendViewInitialized (this VisualElement self, Ooui.Element nativeView)
         {
             ViewInitialized?.Invoke (self, new ViewInitializedEventArgs { View = self, NativeView = nativeView });
@@ -69,7 +71,7 @@ namespace Xamarin.Forms
 
             public string GetMD5Hash (string input)
             {
-                throw new NotImplementedException ();
+                return Utilities.GetMd5Hash(input);
             }
 
             public double GetNamedSize (NamedSize size, Type targetElementType, bool useOldSizes)
@@ -89,9 +91,30 @@ namespace Xamarin.Forms
                 }
             }
 
-            public Task<Stream> GetStreamAsync (Uri uri, CancellationToken cancellationToken)
+
+            public async Task<Stream> GetStreamAsync (Uri uri, CancellationToken cancellationToken)
             {
-                throw new NotImplementedException ();
+                //NOTE:  Wanted to use the same facility that ImageLoaderSourceHandler uses,
+                //       but couldn't find an optional way to ignore certificate errors with self-signed 
+                //       certificates with that approach.  Calling:
+                //          ServicePointManager.ServerCertificateValidationCallback += (o, cert, chain, errors) => true;
+                //       in web application seemed to get ignored.
+
+                //var imageSource = new UriImageSource() { Uri = uri };
+                //return imageSource.GetStreamAsync(cancellationToken);
+
+                using (var client = HttpClientHandler == null ? new HttpClient() : new HttpClient(HttpClientHandler))
+                {
+                    HttpResponseMessage streamResponse = await client.GetAsync(uri.AbsoluteUri).ConfigureAwait(false);
+
+                    if (!streamResponse.IsSuccessStatusCode)
+                    {
+                        Log.Warning("HTTP Request", $"Could not retrieve {uri}, status code {streamResponse.StatusCode}");
+                        return null;
+                    }
+
+                    return await streamResponse.Content.ReadAsStreamAsync().ConfigureAwait(false);
+                }
             }
 
             public IIsolatedStorageFile GetUserStoreForApplication ()

Ooui.Forms/Renderers/ImageRenderer.cs

@@ -213,7 +213,7 @@ namespace Ooui.Forms.Renderers
                         using (var outputStream = new System.IO.MemoryStream (data)) {
                             await streamImage.CopyToAsync (outputStream, 4096, cancelationToken).ConfigureAwait (false);
                         }
-                        var hash = Ooui.Utilities.Hash (data);
+                        var hash = Ooui.Utilities.GetShaHash (data);
                         var etag = "\"" + hash + "\"";
                         image = "/images/" + hash;
                         if (Ooui.UI.TryGetFileContentAtPath (image, out var file) && file.Etag == etag) {

Ooui/UI.cs

@@ -85,7 +85,7 @@ namespace Ooui
                     clientJsBytes = Encoding.UTF8.GetBytes (r.ReadToEnd ());
                 }
             }
-            clientJsEtag = "\"" + Utilities.Hash (clientJsBytes) + "\"";
+            clientJsEtag = "\"" + Utilities.GetShaHash (clientJsBytes) + "\"";
         }
 
         static void Publish (string path, RequestHandler handler)
@@ -117,13 +117,13 @@ namespace Ooui
             if (contentType == null) {
                 contentType = GuessContentType (path, filePath);
             }
-            var etag = "\"" + Utilities.Hash (data) + "\"";
+            var etag = "\"" + Utilities.GetShaHash (data) + "\"";
             Publish (path, new DataHandler (data, etag, contentType));
         }
 
         public static void PublishFile (string path, byte[] data, string contentType)
         {
-            var etag = "\"" + Utilities.Hash (data) + "\"";
+            var etag = "\"" + Utilities.GetShaHash (data) + "\"";
             Publish (path, new DataHandler (data, etag, contentType));
         }
 
@@ -168,7 +168,7 @@ namespace Ooui
         public static void PublishJson (string path, object value)
         {
             var data = JsonHandler.GetData (value);
-            var etag = "\"" + Utilities.Hash (data) + "\"";
+            var etag = "\"" + Utilities.GetShaHash (data) + "\"";
             Publish (path, new DataHandler (data, etag, JsonHandler.ContentType));
         }
 

Ooui/Utilities.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Security.Cryptography;
 using System.Text;
 
 namespace Ooui
@@ -6,20 +7,53 @@ namespace Ooui
     public static class Utilities
     {
         [ThreadStatic]
-        static System.Security.Cryptography.SHA256 sha256;
+        static SHA256 sha256;
 
-        public static string Hash (byte[] bytes)
+        [ThreadStatic]
+        static MD5 md5;
+
+        public static string GetShaHash(byte[] bytes)
         {
             var sha = sha256;
-            if (sha == null) {
+            if (sha == null)
-                sha = System.Security.Cryptography.SHA256.Create ();
+            {
+                sha = SHA256.Create();
                 sha256 = sha;
             }
             var data = sha.ComputeHash(bytes);
+
+            return BytesToString(data);
+        }
+
+        public static string GetMd5Hash(string input)
+        {
+            var md = md5;
+            if (md == null)
+            {
+                md = MD5.Create();
+                md5 = md;
+            }
+            
+            // Convert the input string to a byte array and compute the hash.
+            byte[] data = md.ComputeHash(Encoding.UTF8.GetBytes(input));
+
+            return BytesToString(data);
+        }
+
+        private static string BytesToString(byte[] data)
+        {
+            // Create a new Stringbuilder to collect the bytes
+            // and create a string.
             StringBuilder sBuilder = new StringBuilder();
-            for (int i = 0; i < data.Length; i++) {
+
+            // Loop through each byte of the hashed data 
+            // and format each one as a hexadecimal string.
+            for (int i = 0; i < data.Length; i++)
+            {
                 sBuilder.Append(data[i].ToString("x2"));
             }
+
+            // Return the hexadecimal string.
             return sBuilder.ToString();
         }
     }