Add limits overriding with system properties (#112)

lib/src/main/java/de/siegmar/fastcsv/util/Limits.java

@@ -2,6 +2,16 @@
 
 /**
  * The {@code Limits} class defines the maximum limits for various fields and records in a CSV file.
+ * <p>
+ * Example use:
+ * <pre>{@code
+ * System.setProperty("fastcsv.max.field.size", "1024");
+ * }</pre>
+ * <p>
+ * Or using VM options:
+ * <pre>{@code
+ * -Dfastcsv.max.field.count=1024
+ * }</pre>
  */
 public final class Limits {
 
@@ -10,13 +20,13 @@ public final class Limits {
      * The value is set to 16,777,216 characters (16 to 64 MiB depending on the circumstance of multibyte character
      * utilization).
      */
-    public static final int MAX_FIELD_SIZE = 16 * 1024 * 1024;
+    public static final int MAX_FIELD_SIZE = getIntProperty("fastcsv.max.field.size", 16 * 1024 * 1024);
 
     /**
      * The {@code MAX_FIELDS_SIZE} constant defines the maximum number of fields per record.
      * The value is set to 16,384.
      */
-    public static final int MAX_FIELD_COUNT = 16 * 1024;
+    public static final int MAX_FIELD_COUNT = getIntProperty("fastcsv.max.field.count", 16 * 1024);
 
     /**
      * The {@code MAX_RECORD_SIZE} constant defines the maximum size for all fields combined in a CSV record.
@@ -27,4 +37,26 @@ public final class Limits {
     private Limits() {
     }
 
+    /**
+     * Retrieves the system property value if presented, otherwise default value is returned.
+     * If the property cannot be parsed as an integer, an {@code IllegalArgumentException} is thrown.
+     *
+     * @param key The system property key.
+     * @param defaultValue The default value to use if the system property is not set or is invalid.
+     * @return The system property value as an integer or the default value if the property is not set or is invalid.
+     * @throws IllegalArgumentException If the system property value cannot be parsed as an integer.
+     */
+    static int getIntProperty(final String key, final int defaultValue) {
+        final String value = System.getProperty(key);
+
+        if (value == null) {
+            return defaultValue;
+        }
+
+        try {
+            return Integer.parseInt(value);
+        } catch (final NumberFormatException e) {
+            throw new IllegalArgumentException("Invalid format for system property " + key, e);
+        }
+    }
 }

lib/src/test/java/de/siegmar/fastcsv/util/LimitsTest.java

@@ -0,0 +1,69 @@
+package de.siegmar.fastcsv.util;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+class LimitsTest {
+
+    public static final String FASTCSV_MAX_FIELD_SIZE = "fastcsv.max.field.size";
+    public static final String FASTCSV_MAX_FIELD_COUNT = "fastcsv.max.field.count";
+
+    @AfterEach
+    void cleanup() {
+        System.clearProperty(FASTCSV_MAX_FIELD_SIZE);
+        System.clearProperty(FASTCSV_MAX_FIELD_COUNT);
+    }
+
+    @Test
+    void defaultMaxFieldSize() {
+        assertThat(Limits.MAX_FIELD_SIZE)
+            .as("Default max field size should be correct")
+            .isEqualTo(16 * 1024 * 1024);
+    }
+
+    @Test
+    void customMaxFieldSize() {
+        System.setProperty(FASTCSV_MAX_FIELD_SIZE, "100000");
+
+        assertThat(Limits.getIntProperty(FASTCSV_MAX_FIELD_SIZE, 16 * 1024 * 1024))
+            .as("Custom max field size should be respected")
+            .isEqualTo(100000);
+    }
+
+    @Test
+    void defaultMaxFieldCount() {
+        assertThat(Limits.MAX_FIELD_COUNT)
+            .as("Default max field count should be correct")
+            .isEqualTo(16 * 1024);
+    }
+
+    @Test
+    void customMaxFieldCount() {
+        System.setProperty(FASTCSV_MAX_FIELD_COUNT, "200");
+
+        assertThat(Limits.getIntProperty(FASTCSV_MAX_FIELD_COUNT, 16 * 1024))
+            .as("Custom max field count should be respected")
+            .isEqualTo(200);
+    }
+
+    @Test
+    void invalidMaxFieldSizeThrowsException() {
+        System.setProperty(FASTCSV_MAX_FIELD_SIZE, "invalid");
+
+        assertThatExceptionOfType(IllegalArgumentException.class)
+            .isThrownBy(() -> Limits.getIntProperty(FASTCSV_MAX_FIELD_SIZE, 16 * 1024 * 1024))
+            .withMessageContaining("Invalid format for system property " + FASTCSV_MAX_FIELD_SIZE);
+    }
+
+    @Test
+    void maxRecordSizeBasedOnMaxFieldSize() {
+        System.setProperty(FASTCSV_MAX_FIELD_SIZE, "4000000");
+
+        assertThat(4 * Limits.getIntProperty(FASTCSV_MAX_FIELD_SIZE, 16 * 1024 * 1024))
+            .as("MAX_RECORD_SIZE should be four times MAX_FIELD_SIZE")
+            .isEqualTo(4 * 4000000);
+    }
+}