Refactor TEX and SVG temporary files to use stdin

CHANGELOG.md

@@ -22,6 +22,7 @@
 - Remove unused `getTimetableImage` function in `Export/GetImages.hs`
 - Refactored various backend text functions and tests to avoid `String` data in favour of `Text` when feasible
 - Removed unused files
+- Refactored `returnPDF`, `exportTimetablePDFResponse`, and `graphImageResponse` to use stdin instead of temporary `.tex` and `.svg` files
 
 ## [0.7.2] - 2025-12-10
 

app/Controllers/Graph.hs

@@ -3,12 +3,12 @@ module Controllers.Graph (graphResponse, index, getGraphJSON, graphImageResponse
 import Control.Monad.IO.Class (liftIO)
 import Data.Aeson (decode, object, (.=))
 import Data.Maybe (fromMaybe)
-import Export.ImageConversion (createImageFile)
+import Export.ImageConversion (withImageFile)
 import Happstack.Server (Response, ServerPart, look, lookBS, lookText', ok, toResponse)
 import MasterTemplate (masterTemplate)
 import Scripts (graphScripts)
-import System.IO (hClose)
-import System.IO.Temp (withSystemTempFile)
+import System.FilePath ((</>))
+import System.IO.Temp (withSystemTempDirectory)
 import Text.Blaze ((!))
 import qualified Text.Blaze.Html5 as H
 import qualified Text.Blaze.Html5.Attributes as A
@@ -54,13 +54,10 @@ getGraphJSON = do
 graphImageResponse :: ServerPart Response
 graphImageResponse = do
     graphInfo <- look "JsonLocalStorageObj"
-    liftIO $ withSystemTempFile "graph.svg" $ \svgPath svgHandle -> do
-        withSystemTempFile "graph.png" $ \pngPath pngHandle -> do
-            hClose pngHandle
-            writeActiveGraphImage graphInfo svgHandle
-            hClose svgHandle
-            createImageFile svgPath pngPath
-            readImageData pngPath
+    liftIO $ withSystemTempDirectory "graph-image" $ \tempDir -> do
+        let pngPath = tempDir </> "graph.png"
+        withImageFile pngPath (writeActiveGraphImage graphInfo)
+        readImageData pngPath
 
 -- | Inserts SVG graph data into Texts, Shapes, and Paths tables
 saveGraphJSON :: ServerPart Response

app/Controllers/Timetable.hs

@@ -15,15 +15,14 @@ import Data.Time.Calendar.OrdinalDate (fromMondayStartWeek, mondayStartWeek)
 import Database.Persist.Sqlite (entityKey, entityVal, selectList, (==.))
 import Database.Tables
 import Export.GetImages (getActiveTimetable, writeActiveGraphImage)
-import Export.ImageConversion (createImageFile)
+import Export.ImageConversion (withImageFile)
 import Export.LatexGenerator
 import Export.PdfGenerator
 import Happstack.Server
 import MasterTemplate
 import Models.Meeting (returnMeeting)
 import Scripts
 import System.FilePath ((</>))
-import System.IO (IOMode (WriteMode), withFile)
 import System.IO.Temp (withSystemTempDirectory)
 import Text.Blaze ((!))
 import qualified Text.Blaze.Html5 as H
@@ -60,12 +59,8 @@ exportTimetablePDFResponse = do
     graphInfo <- look "JsonLocalStorageObj"
 
     liftIO $ withSystemTempDirectory "timetable-pdf" $ \tempDir -> do
-        let graphSvgPath = tempDir </> "graph.svg"
-            graphPngPath = tempDir </> "graph.png"
-
-        withFile graphSvgPath WriteMode $ \graphSvgHandle ->
-            writeActiveGraphImage graphInfo graphSvgHandle
-        createImageFile graphSvgPath graphPngPath
+        let graphPngPath = tempDir </> "graph.png"
+        withImageFile graphPngPath (writeActiveGraphImage graphInfo)
         fallPngPath <- getActiveTimetable selectedCourses "Fall" tempDir
         springPngPath <- getActiveTimetable selectedCourses "Spring" tempDir
         pdfName <- returnPDF graphPngPath fallPngPath springPngPath tempDir
@@ -81,10 +76,10 @@ returnPdfBS pdfFilename = do
 -- and springTimetableImg generated in tempDir.
 returnPDF :: String -> String -> String -> FilePath -> IO String
 returnPDF graphImg fallTimetableImg springTimetableImg tempDir = do
-    let texName = tempDir </> "timetable.tex"
-        pdfName = tempDir </> "timetable.pdf"
-    generateTex [graphImg, fallTimetableImg, springTimetableImg] texName -- generate a temporary TEX file
-    createPDF texName                            -- create PDF using TEX
+    let timetableName = "timetable"
+        pdfName = tempDir </> (timetableName ++ ".pdf")
+    texText <- generateTex [graphImg, fallTimetableImg, springTimetableImg]
+    createPDF texText tempDir timetableName         -- create PDF using TEX
     return pdfName
 
 

app/Export/ImageConversion.hs

@@ -3,10 +3,22 @@
     Description : Includes functions for converting SVG files to PNG.
 -}
 module Export.ImageConversion
-    (createImageFile) where
+    (createImageFile, withImageFile) where
 
 import GHC.IO.Handle.Types
-import System.Process (ProcessHandle, createProcess, shell, waitForProcess)
+import System.IO (hClose)
+import System.Process (ProcessHandle, StdStream (CreatePipe), createProcess, proc, shell, std_in,
+                       waitForProcess)
+
+-- | Opens a new process to convert an SVG read from stdin to a PNG (outName)
+withImageFile :: String -> (Handle -> IO ()) -> IO ()
+withImageFile outName writeAction = do
+    (Just hin, _, _, pid) <- createProcess (proc "magick" ["svg:-", outName]) { std_in = CreatePipe }
+    writeAction hin
+    hClose hin
+    putStrLn "Waiting for process..."
+    _ <- waitForProcess pid
+    putStrLn "Process Complete"
 
 -- | Opens a new process to convert an SVG (inName) to a PNG (outName)
 -- Note: hGetContents can be used to read Handles. Useful when trying to read from

app/Export/LatexGenerator.hs

@@ -10,10 +10,11 @@ import Text.LaTeX.Packages.Fancyhdr
 import Text.LaTeX.Packages.Geometry
 import Text.LaTeX.Packages.Graphicx
 
--- | Create a TEX file named texName that includes all of the images in
--- imageNames
-generateTex :: [String] -> String -> IO ()
-generateTex imageNames texName = execLaTeXT (buildTex imageNames) >>= renderFile texName
+-- | Generates a TEX text that includes all of the images in imageNames
+generateTex :: [String] -> IO Text
+generateTex imageNames = do
+    texText <- execLaTeXT (buildTex imageNames)
+    return $ render texText
 
 -- | Combine the preamble and the document text into a single block of latex
 -- code. The document text contains code to insert all of the images in

app/Export/PdfGenerator.hs

@@ -5,30 +5,34 @@
 module Export.PdfGenerator
     (createPDF) where
 
-import Data.List.Utils (replace)
+import Data.Text (Text)
+import qualified Data.Text.IO as TIO
 import GHC.IO.Handle.Types
-import System.Directory (removeFile)
-import System.Process (ProcessHandle, createProcess, shell, waitForProcess)
+import System.IO (hClose)
+import System.Process (ProcessHandle, StdStream (CreatePipe), createProcess, proc, std_in,
+                       waitForProcess)
 
--- | Opens a new process to create a PDF from a TEX (texName) and deletes
--- the tex file and extra files created by pdflatex
-createPDF :: String -> IO ()
-createPDF texName  = do
-  (_, _, _, pid) <- convertTexToPDF texName
-  putStrLn "Waiting for a process..."
-  _ <- waitForProcess pid
-  let auxFile = replace ".tex" ".aux" texName
-      logFile = replace ".tex" ".log" texName
-  mapM_ removeFile [auxFile, logFile, texName]
-  putStrLn "Process Complete"
+-- | Opens a new process to create a PDF from a TEX
+createPDF :: Text -> FilePath -> String -> IO ()
+createPDF texText outDir jobName = do
+    (Just hin, _, _, pid) <- convertTexToPDF outDir jobName
+    TIO.hPutStr hin texText
+    hClose hin
+    putStrLn "Waiting for a process..."
+    _ <- waitForProcess pid
+    putStrLn "Process Complete"
 
 -- | Create a process to use the pdflatex program to create a PDF from a TEX
--- file (texName). The process is run in nonstop mode and so it will not block
--- if an error occurs. The resulting PDF will have the same filename as texName.
-convertTexToPDF :: String -> IO
-                            (Maybe Handle,
-                             Maybe Handle,
-                             Maybe Handle,
-                             ProcessHandle)
-convertTexToPDF texName =
-    createProcess $ shell $ "pdflatex -interaction=nonstopmode " ++ texName
+-- read from stdin. The process is run in nonstop mode and so it will not block
+-- if an error occurs. The resulting PDF will have the same filename as jobName.
+convertTexToPDF :: FilePath -> String -> IO
+                                        (Maybe Handle,
+                                         Maybe Handle,
+                                         Maybe Handle,
+                                         ProcessHandle)
+convertTexToPDF outDir jobName =
+    createProcess (proc "pdflatex"
+      [ "-interaction=nonstopmode"
+      , "-output-directory=" ++ outDir
+      , "-jobname=" ++ jobName
+      ]) { std_in = CreatePipe }