fix: give each plot request its own PNG and make the Python path configurable

iceHub82 · claude · iceHub82 · commit 1f07ee7d2bc8 · 2026-08-04T23:00:57.000+02:00
A fixed wwwroot/plots/plot_{ticker}.png let two callers requesting the same
ticker overwrite each other between SavePlot and the browser's follow-up GET.
Each request now renders to plot_{ticker}_{guid}.png, with stale files swept on
the next request. Program.cs resolves the Python home and venv from
configuration (Python:Home / Python:VirtualEnvironment) before falling back to
the sibling-directory default, and creates the plots directory if it is absent.

Also drops the ~45 lines of commented-out copy-paste inside the work-in-progress
backtest endpoint - it duplicated the stock endpoint verbatim and git has it.

Co-Authored-By: Claude Opus 5 (1M context) &lt;noreply@anthropic.com&gt;
diff --git a/PythonNet.App.Web.Tests/MinimalApiExtensionTests.cs b/PythonNet.App.Web.Tests/MinimalApiExtensionTests.cs
@@ -9,21 +9,35 @@ public class MinimalApiExtensionTests
     private static readonly DateTime Start = new(2024, 10, 24);
     private static readonly DateTime End = new(2024, 10, 27);
 
-    // Renders nothing but a marker so the assertions can tell "reached Python" from "rejected early".
-    private static string Marker(Stock s, string start, string end) => $"{s.Ticker}|{s.FileName}|{start}|{end}";
+    /// <summary>Stands in for the Python call chain, recording what the endpoint asked it to render.</summary>
+    private sealed class Recorder
+    {
+        public List<(Stock Stock, string Start, string End, string PlotName)> Calls { get; } = [];
+
+        public void Save(Stock stock, string start, string end, string plotName) =>
+            Calls.Add((stock, start, end, plotName));
+    }
 
     [Theory]
     [InlineData(1, "AAPL", "Apple", "aapl_27.10.24-24.10.24.csv")]
     [InlineData(2, "MSFT", "Microsoft", "msft_27.10.24-24.10.24.csv")]
     [InlineData(3, "IBM", "IBM", "ibm_27.10.24-24.10.24.csv")]
-    public void KnownTicker_RendersWithResolvedStock(int id, string ticker, string title, string file)
+    public void KnownTicker_PassesResolvedStockAndIsoDates(int id, string ticker, string title, string file)
     {
-        var result = MinimalApiExtension.StockPlot(id, Start, End, Marker);
+        var recorder = new Recorder();
+
+        var result = MinimalApiExtension.StockPlot(id, Start, End, recorder.Save);
+
+        var call = Assert.Single(recorder.Calls);
+        Assert.Equal(ticker, call.Stock.Ticker);
+        Assert.Equal(title, call.Stock.Title);
+        Assert.Equal(file, call.Stock.FileName);
+        Assert.Equal("2024-10-24", call.Start);
+        Assert.Equal("2024-10-27", call.End);
 
         var content = Assert.IsType<ContentHttpResult>(result);
-        Assert.Equal($"{ticker}|{file}|2024-10-24|2024-10-27", content.ResponseContent);
         Assert.Equal("text/html", content.ContentType);
-        Assert.Equal(title, MinimalApiExtension.Tickers[id].Title);
+        Assert.Contains($"/dynamic-plots/{call.PlotName}.png", content.ResponseContent);
     }
 
     [Theory]
@@ -33,47 +47,108 @@ public void KnownTicker_RendersWithResolvedStock(int id, string ticker, string t
     [InlineData(99)]
     public void UnknownTicker_IsRejectedWithoutCallingPython(int id)
     {
-        var called = false;
+        var recorder = new Recorder();
 
-        var result = MinimalApiExtension.StockPlot(id, Start, End, (_, _, _) =>
-        {
-            called = true;
-            return "should not happen";
-        });
+        var result = MinimalApiExtension.StockPlot(id, Start, End, recorder.Save);
 
         var bad = Assert.IsType<BadRequest<string>>(result);
         Assert.Contains($"Unknown ticker '{id}'", bad.Value);
-        Assert.False(called);
+        Assert.Empty(recorder.Calls);
     }
 
     [Fact]
-    public void StartAfterEnd_IsRejected()
+    public void StartAfterEnd_IsRejectedWithoutCallingPython()
     {
-        var result = MinimalApiExtension.StockPlot(1, End, Start, Marker);
+        var recorder = new Recorder();
+
+        var result = MinimalApiExtension.StockPlot(1, End, Start, recorder.Save);
 
         var bad = Assert.IsType<BadRequest<string>>(result);
         Assert.Contains("startDate must be on or before endDate", bad.Value);
+        Assert.Empty(recorder.Calls);
     }
 
     [Fact]
     public void SameStartAndEnd_IsAllowed()
     {
-        var result = MinimalApiExtension.StockPlot(1, Start, Start, Marker);
+        var result = MinimalApiExtension.StockPlot(1, Start, Start, new Recorder().Save);
 
         Assert.IsType<ContentHttpResult>(result);
     }
 
     [Fact]
-    public void RenderFailure_BecomesProblemResponse()
+    public void SaveFailure_BecomesProblemResponse()
     {
         var result = MinimalApiExtension.StockPlot(1, Start, End,
-            (_, _, _) => throw new FileNotFoundException("Data/aapl_27.10.24-24.10.24.csv"));
+            (_, _, _, _) => throw new FileNotFoundException("Data/aapl_27.10.24-24.10.24.csv"));
 
         var problem = Assert.IsType<ProblemHttpResult>(result);
         Assert.Equal(StatusCodes.Status500InternalServerError, problem.StatusCode);
         Assert.Contains("Could not plot AAPL", problem.ProblemDetails.Detail);
     }
 
+    [Fact]
+    public void ConcurrentRequestsForOneTicker_GetDistinctPlotNames()
+    {
+        var recorder = new Recorder();
+
+        var htmlA = (ContentHttpResult)MinimalApiExtension.StockPlot(1, Start, End, recorder.Save);
+        var htmlB = (ContentHttpResult)MinimalApiExtension.StockPlot(1, Start, End, recorder.Save);
+
+        var (first, second) = (recorder.Calls[0].PlotName, recorder.Calls[1].PlotName);
+        Assert.StartsWith("plot_AAPL_", first);
+        Assert.StartsWith("plot_AAPL_", second);
+        Assert.NotEqual(first, second);
+        Assert.NotEqual(htmlA.ResponseContent, htmlB.ResponseContent);
+    }
+
+    [Fact]
+    public void SweepStalePlots_DeletesOnlyPlotsPastTheirAge()
+    {
+        var cwd = Directory.GetCurrentDirectory();
+        var scratch = Directory.CreateTempSubdirectory().FullName;
+        try
+        {
+            Directory.SetCurrentDirectory(scratch);
+            var plots = Directory.CreateDirectory(MinimalApiExtension.PlotDirectory).FullName;
+
+            var stale = Path.Combine(plots, "plot_AAPL_old.png");
+            var fresh = Path.Combine(plots, "plot_AAPL_new.png");
+            var other = Path.Combine(plots, "keep-me.txt");
+            foreach (var f in new[] { stale, fresh, other }) File.WriteAllText(f, "x");
+            File.SetLastWriteTimeUtc(stale, DateTime.UtcNow.AddMinutes(-30));
+
+            MinimalApiExtension.SweepStalePlots(TimeSpan.FromMinutes(5));
+
+            Assert.False(File.Exists(stale));
+            Assert.True(File.Exists(fresh));
+            Assert.True(File.Exists(other));
+        }
+        finally
+        {
+            Directory.SetCurrentDirectory(cwd);
+            Directory.Delete(scratch, recursive: true);
+        }
+    }
+
+    [Fact]
+    public void SweepStalePlots_IsANoOpWhenThereIsNoPlotDirectory()
+    {
+        var cwd = Directory.GetCurrentDirectory();
+        var scratch = Directory.CreateTempSubdirectory().FullName;
+        try
+        {
+            Directory.SetCurrentDirectory(scratch);
+            MinimalApiExtension.SweepStalePlots();
+            Assert.False(Directory.Exists(MinimalApiExtension.PlotDirectory));
+        }
+        finally
+        {
+            Directory.SetCurrentDirectory(cwd);
+            Directory.Delete(scratch, recursive: true);
+        }
+    }
+
     [Fact]
     public void EveryTickerMapsToAShippedCsv()
     {
diff --git a/PythonNet.App.Web/MinimalApiExtension.cs b/PythonNet.App.Web/MinimalApiExtension.cs
@@ -7,66 +7,23 @@ public static class MinimalApiExtension
     public static void MinimalApi(this WebApplication app)
     {
         app.MapGet("/api/dashboard/stock", (IUtil util, IPlot plotter, int tickerDd, DateTime startDate, DateTime endDate, string? openCb, string? closeCb, string? theme) =>
-            StockPlot(tickerDd, startDate, endDate, (stock, start, end) =>
+            StockPlot(tickerDd, startDate, endDate, (stock, start, end, plotName) =>
             {
                 var data = util.ReadCsv(stock.FileName);
                 var filtered = util.DateFilter(data, start, end);
                 var sorted = util.SortData(filtered, "Date", true);
                 var plot = plotter.Plot(sorted, stock.Ticker, stock.Title, openCb!, closeCb!, start, end,
                     theme == "dark" ? "dark" : "light");
 
-                // ponytail: one PNG per ticker, overwritten in place. Concurrent requests for the same
-                // ticker race on this file; switch to a per-request name if this ever serves >1 user.
-                util.SavePlot(plot, "wwwroot/plots/", $"plot_{stock.Ticker}", "png");
-
-                return $"<img class='img-fluid' src='/dynamic-plots/plot_{stock.Ticker}.png' alt='PNG Image'>";
+                util.SavePlot(plot, PlotDirectory + Path.DirectorySeparatorChar, plotName, "png");
             }));
 
-        app.MapGet("/api/dashboard/backtest", (IUtil util/*, IPlot plotter, int tickerDd, DateTime startDate, DateTime endDate, string? openCb, string? closeCb, string theme*/) =>
+        // TODO: work in progress - fetches live data but does not plot it yet.
+        app.MapGet("/api/dashboard/backtest", (IUtil util) =>
         {
-            //Stock stock = new();
-            //switch (tickerDd)
-            //{
-            //    case 1:
-            //        {
-            //            stock.Ticker = "AAPL";
-            //            stock.Title = "Apple";
-            //            stock.FileName = "aapl_27.10.24-24.10.24.csv";
-            //        }
-            //        break;
-            //    case 2:
-            //        {
-            //            stock.Ticker = "MSFT";
-            //            stock.Title = "Microsoft";
-            //            stock.FileName = "msft_27.10.24-24.10.24.csv";
-            //        }
-            //        break;
-            //    case 3:
-            //        {
-            //            stock.Ticker = "IBM";
-            //            stock.Title = "IBM";
-            //            stock.FileName = "ibm_27.10.24-24.10.24.csv";
-            //        }
-            //        break;
-            //}
-
-            //var start = startDate.ToString("yyyy-MM-dd");
-            //var end = endDate.ToString("yyyy-MM-dd");
-
-            //var data = util.ReadCsv(stock.FileName!);
-            //var filtered = util.DateFilter(data, start, end);
-            //var sorted = util.SortData(filtered, "Date", true);
-            //var plot = plotter.Plot(sorted, stock.Ticker!, stock.Title!, openCb!, closeCb!, start, end, theme);
-
-            //util.SavePlot(plot, "wwwroot/plots/", $"plot_{stock.Ticker}", "png");
-
-            var data =  util.DownloadData("AAPL", "2024-10-20", "2024-10-30");
-
-            //var html = $"<img class='img-fluid' src='/dynamic-plots/plot_{stock.Ticker}.png' alt='PNG Image'>";
-            var html = $"<img class='img-fluid' src='/dynamic-plots/plot_.png' alt='PNG Image'>";
-
-
-            return Content(html);
+            var data = util.DownloadData("AAPL", "2024-10-20", "2024-10-30");
+
+            return Content("<img class='img-fluid' src='/dynamic-plots/plot_.png' alt='PNG Image'>");
         });
     }
 
@@ -77,25 +34,62 @@ public static void MinimalApi(this WebApplication app)
         [3] = new("IBM", "IBM", "ibm_27.10.24-24.10.24.csv"),
     };
 
-    // ponytail: `render` is the only seam here - it lets the validation and failure branches be tested
-    // without booting a Python runtime. Split into a service class if this grows past one call chain.
+    internal const string PlotDirectory = "wwwroot/plots";
+
+    /// <summary>
+    /// Validates the request, hands a unique output name to <paramref name="savePlot"/>, and returns the
+    /// HTMX fragment pointing at it. <paramref name="savePlot"/> is the only seam - it lets the validation,
+    /// naming and failure branches be tested without booting a Python runtime.
+    /// </summary>
     internal static IResult StockPlot(int tickerDd, DateTime startDate, DateTime endDate,
-        Func<Stock, string, string, string> render)
+        Action<Stock, string, string, string> savePlot)
     {
         if (!Tickers.TryGetValue(tickerDd, out var stock))
             return Results.BadRequest($"Unknown ticker '{tickerDd}'. Expected one of: {string.Join(", ", Tickers.Keys)}.");
 
         if (startDate > endDate)
             return Results.BadRequest("startDate must be on or before endDate.");
 
+        // Unique per request: a fixed plot_{ticker}.png let concurrent callers overwrite each other's
+        // chart between SavePlot and the browser's follow-up GET.
+        var plotName = $"plot_{stock.Ticker}_{Guid.NewGuid():N}";
+
         try
         {
-            return Content(render(stock, startDate.ToString("yyyy-MM-dd"), endDate.ToString("yyyy-MM-dd")));
+            savePlot(stock, startDate.ToString("yyyy-MM-dd"), endDate.ToString("yyyy-MM-dd"), plotName);
         }
         catch (Exception ex)
         {
             return Results.Problem($"Could not plot {stock.Ticker}: {ex.Message}", statusCode: 500);
         }
+
+        SweepStalePlots();
+
+        return Content($"<img class='img-fluid' src='/dynamic-plots/{plotName}.png' alt='PNG Image'>");
+    }
+
+    /// <summary>
+    /// Each PNG is fetched once, right after the response. Drop anything the browser has long since had.
+    /// </summary>
+    // ponytail: swept inline on the next request rather than by a background service - it is a handful
+    // of File.Delete calls. Move it to a hosted service if the plots directory ever gets big enough to stat.
+    internal static void SweepStalePlots(TimeSpan? maxAge = null)
+    {
+        if (!Directory.Exists(PlotDirectory)) return;
+
+        var cutoff = DateTime.UtcNow - (maxAge ?? TimeSpan.FromMinutes(5));
+
+        foreach (var file in Directory.EnumerateFiles(PlotDirectory, "plot_*.png"))
+        {
+            try
+            {
+                if (File.GetLastWriteTimeUtc(file) < cutoff) File.Delete(file);
+            }
+            catch (IOException)
+            {
+                // Raced with another request still serving it; the next sweep gets it.
+            }
+        }
     }
 
     private static IResult Content(string content)
diff --git a/PythonNet.App.Web/Program.cs b/PythonNet.App.Web/Program.cs
@@ -5,8 +5,12 @@
 var builder = WebApplication.CreateBuilder(args);
 
 var pythonBuilder = builder.Services.WithPython();
-var home = Path.Join(Environment.CurrentDirectory, "..", "PythonNet.Python");
-var venv = Path.Join(home, ".venv");
+
+// Overridable via appsettings or Python__Home / Python__VirtualEnvironment env vars, so the app can run
+// from a published layout where the sources are not a sibling directory of the working directory.
+var home = builder.Configuration["Python:Home"]
+           ?? Path.Join(Environment.CurrentDirectory, "..", "PythonNet.Python");
+var venv = builder.Configuration["Python:VirtualEnvironment"] ?? Path.Join(home, ".venv");
 pythonBuilder
     .WithHome(home)
     .WithVirtualEnvironment(venv)
@@ -22,8 +26,12 @@
 
 var app = builder.Build();
 
+// Generated charts land here at runtime, so the directory may not exist on a fresh checkout.
+var plots = Path.Combine(Directory.GetCurrentDirectory(), MinimalApiExtension.PlotDirectory);
+Directory.CreateDirectory(plots);
+
 app.UseStaticFiles(new StaticFileOptions{
-    FileProvider = new PhysicalFileProvider(Path.Combine(Directory.GetCurrentDirectory(), "wwwroot", "plots")), 
+    FileProvider = new PhysicalFileProvider(plots),
     RequestPath = "/dynamic-plots",
     OnPrepareResponse = r => {
         r.Context.Response.Headers["Cache-Control"] = "no-store, no-cache, must-revalidate, max-age=0";
diff --git a/README.md b/README.md
@@ -29,10 +29,17 @@ On first start CSnakes creates `PythonNet.Python/.venv` and pip-installs
 `PythonNet.Python/requirements.txt` into it. This takes a minute or two; progress
 is visible in the console output. Subsequent starts reuse the venv.
 
-> Run from `PythonNet.App.Web`, not the solution root — `Program.cs` resolves the
-> Python home as `<cwd>/../PythonNet.Python`, and `util.read_csv` resolves data
+> Run from `PythonNet.App.Web`, not the solution root — `Program.cs` defaults the
+> Python home to `<cwd>/../PythonNet.Python`, and `util.read_csv` resolves data
 > files as `Data/<file>` relative to the working directory.
 
+To point at a Python home elsewhere (a published layout, a shared venv), override
+either setting via `appsettings.json` or the environment:
+
+```bash
+Python__Home=/srv/pythonnet Python__VirtualEnvironment=/srv/venv dotnet run
+```
+
 ## Running the tests
 
 ```bash
@@ -56,8 +63,10 @@ Both are run by `.github/workflows/build.yml` on every push and pull request.
 4. **`MinimalApiExtension.cs`** injects them into `GET /api/dashboard/stock`, which
    validates its query parameters, then chains
    `read_csv → date_filter → sort_data → plot → save_plot` and returns an `<img>`
-   fragment for HTMX to swap into the page. Rendered PNGs are written to
-   `wwwroot/plots/` and served from `/dynamic-plots` with caching disabled.
+   fragment for HTMX to swap into the page. Each request renders to its own
+   `wwwroot/plots/plot_{ticker}_{guid}.png` — served from `/dynamic-plots` with
+   caching disabled — so concurrent callers cannot overwrite each other's chart.
+   Files older than five minutes are swept on the next request.
 
 Adding a Python function is therefore: annotate it, rebuild, call the generated
 C# method. Adding a *new* `.py` file also needs an `<AdditionalFiles>` entry.
