Allow for embedded images in markdown

Package.resolved

@@ -9,6 +9,33 @@
         "version" : "6.0.0"
       }
     },
+    {
+      "identity" : "sdwebimage",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/SDWebImage/SDWebImage.git",
+      "state" : {
+        "revision" : "cac9a55a3ae92478a2c95042dcc8d9695d2129ca",
+        "version" : "5.21.0"
+      }
+    },
+    {
+      "identity" : "sdwebimageswiftui",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/SDWebImage/SDWebImageSwiftUI",
+      "state" : {
+        "revision" : "53573d6dd017e354c0e7d8f1c86b77ef1383c996",
+        "version" : "2.2.7"
+      }
+    },
+    {
+      "identity" : "splash",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/JohnSundell/Splash",
+      "state" : {
+        "revision" : "7f4df436eb78fe64fe2c32c58006e9949fa28ad8",
+        "version" : "0.16.0"
+      }
+    },
     {
       "identity" : "swift-cmark",
       "kind" : "remoteSourceControl",

Sources/MarkdownUI/Extensibility/DefaultEmbeddedImageProvider.swift

@@ -0,0 +1,35 @@
+import SwiftUI
+
+public struct DefaultEmbeddedImageProvider: EmbeddedImageProvider {
+
+  public func makeImage(data: Data) -> Image {
+    Image(data: data) ?? Image(systemName: "")
+  }
+
+}
+
+private extension Image {
+
+  init?(data: Data) {
+#if os(iOS)
+    guard let image = UIImage(data: data) else {
+      return nil
+    }
+
+    self.init(uiImage: image)
+#elseif os(macOS)
+    guard let image = NSImage(data: data) else {
+      return nil
+    }
+
+    self.init(nsImage: image)
+#endif
+  }
+
+}
+
+extension EmbeddedImageProvider where Self == DefaultEmbeddedImageProvider {
+  public static var `default`: Self {
+    .init()
+  }
+}

Sources/MarkdownUI/Extensibility/EmbeddedImageProvider.swift

@@ -0,0 +1,6 @@
+import SwiftUI
+
+public protocol EmbeddedImageProvider {
+
+  @ViewBuilder func makeImage(data: Data) -> Image
+}

Sources/MarkdownUI/Views/Environment/Environment+EmbeddedImageProvider.swift

@@ -0,0 +1,21 @@
+import SwiftUI
+
+extension View {
+  /// Sets the embedded image provider to use for Markdown images that have the image content embedded inside the document
+  /// - Parameter provider: the image provider to use for embedded images
+  /// - Returns: A view that has the specified provider set as an environment variable
+  public func embeddedImageProvider(_ provider: EmbeddedImageProvider) -> some View {
+    environment(\.embeddedImageProvider, provider)
+  }
+}
+
+extension EnvironmentValues {
+  var embeddedImageProvider: EmbeddedImageProvider {
+    get { self[EmbeddedImageProviderKey.self] }
+    set { self[EmbeddedImageProviderKey.self] = newValue }
+  }
+}
+
+private struct EmbeddedImageProviderKey: EnvironmentKey {
+  static let defaultValue: EmbeddedImageProvider = .default
+}

Sources/MarkdownUI/Views/Inlines/ImageView.swift

@@ -3,6 +3,7 @@ import SwiftUI
 struct ImageView: View {
   @Environment(\.theme.image) private var image
   @Environment(\.imageProvider) private var imageProvider
+  @Environment(\.embeddedImageProvider) private var embeddedImageProvider: EmbeddedImageProvider
   @Environment(\.imageBaseURL) private var baseURL
 
   private let data: RawImageData
@@ -20,8 +21,31 @@ struct ImageView: View {
     )
   }
 
+  @ViewBuilder
   private var label: some View {
-    self.imageProvider.makeImage(url: self.url)
+    if let imageData = Data(base64Encoded: base64String) {
+      self.embeddedImageForData(imageData)
+    } else if let url = self.url {
+      self.remoteImageForURL(url)
+    }
+  }
+
+  private var base64String: String {
+    self.data.source.replacingOccurrences(of: "data:image/[a-z]+;base64,", with: "", options: .regularExpression)
+  }
+
+  @ViewBuilder
+  private func remoteImageForURL(_ url: URL) -> some View {
+    self.imageProvider.makeImage(url: url)
+      .link(destination: self.data.destination)
+      .accessibilityLabel(self.data.alt)
+  }
+
+  @ViewBuilder
+  private func embeddedImageForData(_ imageData: Data) -> some View {
+    self.embeddedImageProvider.makeImage(data: imageData)
+      .resizable()
+      .scaledToFit()
       .link(destination: self.data.destination)
       .accessibilityLabel(self.data.alt)
   }