Use favicon if OG image URL is not specified (#52)

src/MyWebLog.Domain/SupportTypes.fs

@@ -508,9 +508,10 @@ type OpenGraphImage = {
 
     /// <summary>The <c>meta</c> properties for this image</summary>
     /// <param name="urlTransform">A function to convert relative URLs to absolute URLs</param>
+    /// <param name="fallbackImage">A relative URL to use for the image if the image property is blank</param>
     /// <returns>A sequence of key/value pairs for this OpenGraph image file</returns>
-    member this.ToProperties(urlTransform: string -> string) = seq {
+    member this.ToProperties(urlTransform: string -> string, fallbackImage: string option) = seq {
-        let url = urlTransform this.Url
+        let url = urlTransform (if this.Url = "" then defaultArg fallbackImage "" else this.Url)
         yield "og:image", url
         if url.StartsWith "https:" then yield "og:image:secure_url", url
         match this.Type with
@@ -691,10 +692,11 @@ type OpenGraphProperties = {
 
     /// <summary>The <c>meta</c> properties for this page or post</summary>
     /// <param name="urlTransform">A function to convert relative URLs to absolute URLs</param>
+    /// <param name="fallbackImage">A relative URL to use for the image if the image property is blank</param>
     /// <returns>A sequence of key/value pairs for this set of OpenGraph properties</returns>
-    member this.ToProperties urlTransform = seq {
+    member this.ToProperties urlTransform fallbackImage = seq {
         yield "og:type", string this.Type
-        yield! this.Image.ToProperties urlTransform
+        yield! this.Image.ToProperties(urlTransform, fallbackImage)
         match this.Description with Some desc -> yield "og:description", desc | None -> ()
         match this.Determiner  with Some det  -> yield "og:determiner",  det  | None -> ()
         match this.Locale      with Some loc  -> yield "og:locale",      loc  | None -> ()

src/MyWebLog.Tests/Domain/SupportTypesTests.fs

@@ -356,12 +356,24 @@ let openGraphImageTests = testList "OpenGraphImage" [
     let transform = webLog.UrlToAbsolute
     testList "ToProperties" [
         test "succeeds with minimum required" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "http://test.url" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "http://test.url" }.ToProperties(transform, None))
             Expect.hasLength props 1 "There should be one property"
             Expect.equal props[0] ("og:image", "http://test.url") "The URL was not written correctly"
         }
+        test "succeeds with fallback URL" {
+            let props = Array.ofSeq (OpenGraphImage.Empty.ToProperties(transform, Some "theme/it/favicon.ico"))
+            Expect.hasLength props 2 "There should be one property"
+            Expect.equal
+                props[0] ("og:image", "https://unit.test/taco/theme/it/favicon.ico") "The URL was not written correctly"
+            Expect.equal
+                props[1]
+                ("og:image:secure_url", "https://unit.test/taco/theme/it/favicon.ico")
+                "The secure URL was not written correctly"
+        }
         test "succeeds with secure URL" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "https://secure.url" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "https://secure.url" }.ToProperties(transform, None))
             Expect.hasLength props 2 "There should be two properties"
             Expect.equal props[0] ("og:image", "https://secure.url") "The URL was not written correctly"
             Expect.equal
@@ -373,7 +385,7 @@ let openGraphImageTests = testList "OpenGraphImage" [
                   Type   = Some "image/jpeg"
                   Width  = Some 400
                   Height = Some 600
-                  Alt    = Some "This ought to be good" }.ToProperties transform
+                  Alt    = Some "This ought to be good" }.ToProperties(transform, None)
                 |> Array.ofSeq
             Expect.hasLength props 5 "There should be five properties"
             Expect.equal props[0] ("og:image", "http://test.this") "The URL was not written correctly"
@@ -383,7 +395,8 @@ let openGraphImageTests = testList "OpenGraphImage" [
             Expect.equal props[4] ("og:image:alt", "This ought to be good") "The alt text was not written correctly"
         }
         test "succeeds when deriving BMP and transforming URL" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "old/windows.bmp" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "old/windows.bmp" }.ToProperties(transform, None))
             Expect.hasLength props 3 "There should be three properties"
             Expect.equal
                 props[0] ("og:image", "https://unit.test/taco/old/windows.bmp") "The URL was not transformed correctly"
@@ -394,48 +407,55 @@ let openGraphImageTests = testList "OpenGraphImage" [
             Expect.equal props[2] ("og:image:type", "image/bmp") "The MIME type for BMP was not derived correctly"
         }
         test "succeeds when deriving GIF" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "its.a.soft.g.gif" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "its.a.soft.g.gif" }.ToProperties(transform, None))
             Expect.hasLength props 3 "There should be three properties"
             Expect.equal props[2] ("og:image:type", "image/gif") "The MIME type for GIF was not derived correctly"
         }
         test "succeeds when deriving ICO" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "favicon.ico" }.ToProperties transform)
+            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "favicon.ico" }.ToProperties(transform, None))
             Expect.hasLength props 3 "There should be three properties"
             Expect.equal
                 props[2] ("og:image:type", "image/vnd.microsoft.icon") "The MIME type for ICO was not derived correctly"
         }
         test "succeeds when deriving JPEG" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "big/name/photo.jpeg" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "big/name/photo.jpeg" }.ToProperties(transform, None))
             Expect.hasLength props 3 "There should be three properties"
             Expect.equal props[2] ("og:image:type", "image/jpeg") "The MIME type for JPEG was not derived correctly"
         }
         test "succeeds when deriving PNG" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "some/nice/graphic.png" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "some/nice/graphic.png" }.ToProperties(transform, None))
             Expect.hasLength props 3 "There should be three properties"
             Expect.equal props[2] ("og:image:type", "image/png") "The MIME type for PNG was not derived correctly"
         }
         test "succeeds when deriving SVG" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "fancy-new-vector.svg" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "fancy-new-vector.svg" }.ToProperties(transform, None))
             Expect.hasLength props 3 "There should be three properties"
             Expect.equal props[2] ("og:image:type", "image/svg+xml") "The MIME type for SVG was not derived correctly"
         }
         test "succeeds when deriving TIF" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "tagged/file.tif" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "tagged/file.tif" }.ToProperties(transform, None))
             Expect.hasLength props 3 "There should be three properties"
             Expect.equal props[2] ("og:image:type", "image/tiff") "The MIME type for TIF was not derived correctly"
         }
         test "succeeds when deriving TIFF" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "tagged/file.two.tiff" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "tagged/file.two.tiff" }.ToProperties(transform, None))
             Expect.hasLength props 3 "There should be three properties"
             Expect.equal props[2] ("og:image:type", "image/tiff") "The MIME type for TIFF was not derived correctly"
         }
         test "succeeds when deriving WEBP" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "modern/photo.webp" }.ToProperties transform)
+            let props =
+                Array.ofSeq ({ OpenGraphImage.Empty with Url = "modern/photo.webp" }.ToProperties(transform, None))
             Expect.hasLength props 3 "There should be three properties"
             Expect.equal props[2] ("og:image:type", "image/webp") "The MIME type for WEBP was not derived correctly"
         }
         test "succeeds when type cannot be derived" {
-            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "intro.mp3" }.ToProperties transform)
+            let props = Array.ofSeq ({ OpenGraphImage.Empty with Url = "intro.mp3" }.ToProperties(transform, None))
             Expect.hasLength props 2 "There should be two properties (only URLs; no type derived)"
         }
     ]
@@ -630,7 +650,7 @@ let openGraphPropertiesTests = testList "OpenGraphProperties" [
             let props =
                 { OpenGraphProperties.Empty with
                     Image = { OpenGraphImage.Empty with Url = "http://this.aint.nothing" } }
-                    .ToProperties WebLog.Empty.UrlToAbsolute
+                    .ToProperties WebLog.Empty.UrlToAbsolute None
                 |> Array.ofSeq
             Expect.hasLength props 2 "There should have been two properties"
             Expect.equal props[0] ("og:type", "article") "Type not written correctly"
@@ -647,7 +667,7 @@ let openGraphPropertiesTests = testList "OpenGraphProperties" [
                   LocaleAlternate = Some [ "en_UK"; "es_MX" ]
                   Video           = Some { OpenGraphVideo.Empty with Url = "http://this.video.file" }
                   Other           = Some [ { Name = "book.publisher"; Value = "Yep" } ] }
-                    .ToProperties WebLog.Empty.UrlToAbsolute
+                    .ToProperties WebLog.Empty.UrlToAbsolute None
                 |> Array.ofSeq
             Expect.hasLength props 10 "There should have been ten properties"
             Expect.equal props[0] ("og:type", "book") "Type not written correctly"

src/MyWebLog/Template.fs

@@ -219,8 +219,11 @@ let parser =
                 |> Permalink
                 |> app.WebLog.AbsoluteUrl
                 |> function url -> writeOgProp ("og:url", url)
+                let fallback =
+                    if assetExists "favicon.ico" app.WebLog then Some $"theme/{app.WebLog.ThemeId}/favicon.ico"
+                    else None
                 match if app.IsPage then app.Page.OpenGraph else app.Posts.Posts[0].OpenGraph with
-                | Some props -> props.ToProperties app.WebLog.UrlToAbsolute |> Seq.iter writeOgProp
+                | Some props -> props.ToProperties app.WebLog.UrlToAbsolute fallback |> Seq.iter writeOgProp
                 | None -> ()
 
             writer.WriteLine $"""{s}<meta name=generator content="{app.Generator}">"""