Daily Perf Improver: Optimize HTML parser CharList with StringBuilder

src/FSharp.Data.Html.Core/HtmlParser.fs

@@ -77,16 +77,15 @@ module internal HtmlParser =
             String(buffer)
 
     type CharList =
-        { mutable Contents: char list }
+        { mutable Contents: StringBuilder }
 
-        static member Empty = { Contents = [] }
+        static member Empty = { Contents = StringBuilder() }
 
-        override x.ToString() =
-            String(x.Contents |> List.rev |> List.toArray)
+        override x.ToString() = x.Contents.ToString()
 
-        member x.Cons(c) = x.Contents <- c :: x.Contents
+        member x.Cons(c: char) = x.Contents.Append(c) |> ignore
         member x.Length = x.Contents.Length
-        member x.Clear() = x.Contents <- []
+        member x.Clear() = x.Contents.Clear() |> ignore
 
     type InsertionMode =
         | DefaultMode
@@ -116,8 +115,8 @@ module internal HtmlParser =
 
         static member Create(reader: TextReader) =
             { Attributes = []
-              CurrentTag = CharList.Empty
-              Content = CharList.Empty
+              CurrentTag = { Contents = StringBuilder() }
+              Content = { Contents = StringBuilder() }
               HasFormattedParent = false
               InsertionMode = DefaultMode
               Tokens = []
@@ -133,7 +132,7 @@ module internal HtmlParser =
         member x.ContentLength = x.Content.Length
 
         member x.NewAttribute() =
-            x.Attributes <- (CharList.Empty, CharList.Empty) :: x.Attributes
+            x.Attributes <- ({ Contents = StringBuilder() }, { Contents = StringBuilder() }) :: x.Attributes
 
         member x.ConsAttrName() =
             match x.Attributes with
@@ -170,7 +169,7 @@ module internal HtmlParser =
         member x.EmitSelfClosingTag() =
             let name = x.CurrentTag.ToString().Trim()
             let result = Tag(true, name, x.GetAttributes())
-            x.CurrentTag <- CharList.Empty
+            x.CurrentTag <- { Contents = StringBuilder() }
             x.InsertionMode <- DefaultMode
             x.Attributes <- []
             x.Tokens <- result :: x.Tokens
@@ -212,7 +211,7 @@ module internal HtmlParser =
                 else
                     DefaultMode
 
-            x.CurrentTag <- CharList.Empty
+            x.CurrentTag <- { Contents = StringBuilder() }
             x.Attributes <- []
             x.Tokens <- result :: x.Tokens
 
@@ -223,7 +222,7 @@ module internal HtmlParser =
             for c in content.ToCharArray() do
                 x.ConsAttrValue c
 
-            x.Content <- CharList.Empty
+            x.Content <- { Contents = StringBuilder() }
             x.InsertionMode <- DefaultMode
 
         member x.Emit() : unit =
@@ -247,17 +246,17 @@ module internal HtmlParser =
                 | DocTypeMode -> DocType content
                 | CDATAMode -> CData(content.Replace("<![CDATA[", "").Replace("]]>", ""))
 
-            x.Content <- CharList.Empty
+            x.Content <- { Contents = StringBuilder() }
             x.InsertionMode <- DefaultMode
 
             match result with
             | Text t when String.IsNullOrEmpty(t) -> ()
             | _ -> x.Tokens <- result :: x.Tokens
 
         member x.Cons() = x.Content.Cons(x.Reader.ReadChar())
-        member x.Cons(char) = x.Content.Cons(char)
-        member x.Cons(char) = Array.iter (x.Content.Cons) char
-        member x.Cons(char: string) = x.Cons(char.ToCharArray())
+        member x.Cons(char: char) = x.Content.Cons(char)
+        member x.Cons(chars: char array) = Array.iter (x.Content.Cons) chars
+        member x.Cons(chars: string) = x.Cons(chars.ToCharArray())
 
         member x.ConsTag() =
             match x.Reader.ReadChar() with

tests/FSharp.Data.Benchmarks/FSharp.Data.Benchmarks.fsproj

@@ -14,6 +14,7 @@
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </EmbeddedResource>
     <Compile Include="JsonBenchmarks.fs" />
+    <Compile Include="HtmlBenchmarks.fs" />
     <Compile Include="Program.fs" />
   </ItemGroup>
   <ItemGroup>

tests/FSharp.Data.Benchmarks/HtmlBenchmarks.fs

@@ -0,0 +1,47 @@
+namespace FSharp.Data.Benchmarks
+
+open System
+open System.IO
+open BenchmarkDotNet.Attributes
+open FSharp.Data
+
+[<MemoryDiagnoser>]
+[<SimpleJob>]
+type HtmlBenchmarks() =
+
+    let mutable simpleHtmlText = ""
+    let mutable zooplaHtmlText = ""
+    let mutable usPresidentsHtmlText = ""
+    let mutable doctorWhoHtmlText = ""
+    let mutable wimbledonHtmlText = ""
+
+    [<GlobalSetup>]
+    member this.Setup() =
+        let dataPath = Path.Combine(__SOURCE_DIRECTORY__, "../FSharp.Data.Tests/Data")
+
+        // Load various HTML files of different sizes and complexity
+        simpleHtmlText <- File.ReadAllText(Path.Combine(dataPath, "SimpleHtmlTablesWithTr.html"))
+        zooplaHtmlText <- File.ReadAllText(Path.Combine(dataPath, "zoopla.html"))  // ~773KB
+        usPresidentsHtmlText <- File.ReadAllText(Path.Combine(dataPath, "us_presidents_wikipedia.html"))  // ~698KB
+        doctorWhoHtmlText <- File.ReadAllText(Path.Combine(dataPath, "doctor_who2.html"))  // ~518KB
+        wimbledonHtmlText <- File.ReadAllText(Path.Combine(dataPath, "wimbledon_wikipedia.html"))  // ~411KB
+
+    [<Benchmark>]
+    member this.ParseSimpleHtml() =
+        HtmlDocument.Parse(simpleHtmlText)
+
+    [<Benchmark>]
+    member this.ParseZooplaHtml() =
+        HtmlDocument.Parse(zooplaHtmlText)
+
+    [<Benchmark>]
+    member this.ParseUsPresidentsHtml() =
+        HtmlDocument.Parse(usPresidentsHtmlText)
+
+    [<Benchmark>]
+    member this.ParseDoctorWhoHtml() =
+        HtmlDocument.Parse(doctorWhoHtmlText)
+
+    [<Benchmark>]
+    member this.ParseWimbledonHtml() =
+        HtmlDocument.Parse(wimbledonHtmlText)