Changing shared strings cache path from Guid based to TempPath based (#897)

- Changing shared strings cache path from Guid based to TempPath based
- Adding an option to OpenXmlConfiguration for manually overriding the path

Author: michelebastione

src/MiniExcel.Core/OpenXml/OpenXmlConfiguration.cs

@@ -13,16 +13,24 @@ public class OpenXmlConfiguration : MiniExcelBaseConfiguration
     public int FreezeRowCount { get; set; } = 1;
     public int FreezeColumnCount { get; set; } = 0;
     public bool EnableConvertByteArray { get; set; } = true;
+    public bool EnableWriteFilePath{ get; set; } = true;
     public bool IgnoreTemplateParameterMissing { get; set; } = true;
     public bool EnableWriteNullValueCell { get; set; } = true;
     public bool WriteEmptyStringAsNull { get; set; } = false;
     public bool TrimColumnNames { get; set; } = true;
     public bool IgnoreEmptyRows { get; set; } = false;
+    
     public bool EnableSharedStringCache { get; set; } = true;
     public long SharedStringCacheSize { get; set; } = 5 * 1024 * 1024;
+        
+    /// <summary>
+    /// The directory where the shared strings cache files are stored.
+    /// It defaults to the system's temporary folder.
+    /// </summary>
+    public string SharedStringCachePath { get; set; } = Path.GetTempPath();
+
     public OpenXmlStyleOptions StyleOptions { get; set; } = new();
     public DynamicExcelSheetAttribute[]? DynamicSheets { get; set; }
-    public bool EnableWriteFilePath{ get; set; } = true;
 
     /// <summary>
     /// Calculate column widths automatically from each column value.

src/MiniExcel.Core/OpenXml/OpenXmlReader.cs

@@ -420,7 +420,7 @@ private async Task SetSharedStringsAsync(CancellationToken cancellationToken = d
 #endif
         if (_config.EnableSharedStringCache && sharedStringsEntry.Length >= _config.SharedStringCacheSize)
         {
-            SharedStrings = new SharedStringsDiskCache();
+            SharedStrings = new SharedStringsDiskCache(_config.SharedStringCachePath);
             await foreach (var sharedString in XmlReaderHelper.GetSharedStringsAsync(stream, cancellationToken, Ns).ConfigureAwait(false))
             {
                 SharedStrings[idx++] = sharedString;

src/MiniExcel.Core/OpenXml/Utils/SharedStringsDiskCache.cs

@@ -2,43 +2,45 @@
 
 internal class SharedStringsDiskCache : IDictionary<int, string>, IDisposable
 {
+    private const int ExcelCellMaxLength = 32767;
     private static readonly Encoding Encoding = new UTF8Encoding(true);
 
     private readonly FileStream _positionFs;
     private readonly FileStream _lengthFs;
     private readonly FileStream _valueFs;
 
-    private long _maxIndx = -1;
-        
+    private long _maxIndex = -1;
     private bool _disposedValue;
 
-    public int Count => checked((int)(_maxIndx + 1));
+    public int Count => checked((int)(_maxIndex + 1));
 
     public string this[int key]
     {
         get => GetValue(key);
         set => Add(key, value);
     }
 
-    public bool ContainsKey(int key) => key <= _maxIndx;
+    public bool ContainsKey(int key) => key <= _maxIndex;
 
-    public SharedStringsDiskCache()
+    public SharedStringsDiskCache(string sharedStringsCacheDir)
     {
-        var path = $"{Guid.NewGuid().ToString()}_miniexcelcache";
-        
-        _positionFs = new FileStream($"{path}_position", FileMode.OpenOrCreate);
-        _lengthFs = new FileStream($"{path}_length", FileMode.OpenOrCreate);
-        _valueFs = new FileStream($"{path}_data", FileMode.OpenOrCreate);
+        if (string.IsNullOrWhiteSpace(sharedStringsCacheDir) || !Directory.Exists(sharedStringsCacheDir))
+            throw new DirectoryNotFoundException($"\"{sharedStringsCacheDir}\" is not a valid directory for the shared strings cache.");
+
+        var prefix = $"{Path.GetRandomFileName()}_miniexcel";
+        _positionFs = new FileStream(Path.Combine(sharedStringsCacheDir, $"{prefix}_position"), FileMode.OpenOrCreate);
+        _lengthFs = new FileStream(Path.Combine(sharedStringsCacheDir, $"{prefix}_length"), FileMode.OpenOrCreate);
+        _valueFs = new FileStream(Path.Combine(sharedStringsCacheDir, $"{prefix}_data"), FileMode.OpenOrCreate);
     }
 
     // index must start with 0-N
-    internal void Add(int index, string value)
+    private void Add(int index, string value)
     {
-        if (index > _maxIndx)
-            _maxIndx = index;
+        if (index > _maxIndex)
+            _maxIndex = index;
 
         var valueBs = Encoding.GetBytes(value);
-        if (value.Length > 32767) //check info length, becasue cell string max length is 47483647
+        if (value.Length > ExcelCellMaxLength) //check info length, becasue cell string max length is 47483647
             throw new ArgumentOutOfRangeException("", "Excel one cell max length is 32,767 characters");
 
         _positionFs.Write(BitConverter.GetBytes(_valueFs.Position), 0, 4);
@@ -105,13 +107,13 @@ public bool Remove(KeyValuePair<int, string> item)
 
     public IEnumerator<KeyValuePair<int, string>> GetEnumerator()
     {
-        for (int i = 0; i < _maxIndx; i++)
+        for (int i = 0; i <= _maxIndex; i++)
             yield return new KeyValuePair<int, string>(i, this[i]);
     }
 
     IEnumerator IEnumerable.GetEnumerator()
     {
-        for (int i = 0; i < _maxIndx; i++)
+        for (int i = 0; i <= _maxIndex; i++)
             yield return this[i];
     }
 

tests/MiniExcel.Core.Tests/MiniExcelIssueTests.cs

@@ -303,22 +303,19 @@ public void TestIssue360()
     [Fact]
     public void TestIssue117()
     {
+        var cacheFull = new SharedStringsDiskCache(Path.GetTempPath());
+        for (int i = 0; i < 100; i++)
         {
-            var cache = new SharedStringsDiskCache();
-            for (int i = 0; i < 100; i++)
-            {
-                cache[i] = i.ToString();
-            }
-            for (int i = 0; i < 100; i++)
-            {
-                Assert.Equal(i.ToString(), cache[i]);
-            }
-            Assert.Equal(100, cache.Count);
+            cacheFull[i] = i.ToString();
         }
+        for (int i = 0; i < 100; i++)
         {
-            var cache = new SharedStringsDiskCache();
-            Assert.Empty(cache);
+            Assert.Equal(i.ToString(), cacheFull[i]);
         }
+        Assert.Equal(100, cacheFull.Count);
+
+        var cacheEmpty = new SharedStringsDiskCache(Path.GetTempPath());
+        Assert.Empty(cacheEmpty);
     }
 
     [Fact]