iemejia commented on code in PR #3857:
URL: https://github.com/apache/avro/pull/3857#discussion_r3564494980


##########
lang/csharp/src/apache/main/File/Codec.cs:
##########
@@ -29,6 +29,71 @@ namespace Avro.File
     /// </summary>
     public abstract class Codec
     {
+        /// <summary>
+        /// Default upper bound, in bytes, on the size a single data-file 
block may
+        /// decompress to. A block with a very high compression ratio (or a 
malformed
+        /// block) can otherwise expand to far more memory than its compressed 
size.
+        /// Mirrors the Java SDK's decompression limit (AVRO-4247). 
Overridable with
+        /// the AVRO_MAX_DECOMPRESS_LENGTH environment variable.
+        /// </summary>
+        public const long DefaultMaxDecompressLength = 200L * 1024 * 1024; // 
200 MiB
+
+        /// <summary>
+        /// Name of the environment variable used to override the default 
maximum
+        /// decompressed size of a single block.
+        /// </summary>
+        public const string MaxDecompressLengthEnvVar = 
"AVRO_MAX_DECOMPRESS_LENGTH";
+
+        /// <summary>
+        /// The maximum number of bytes a single block is allowed to 
decompress to.
+        /// </summary>
+        /// <returns>The configured limit, honoring the environment 
override.</returns>
+        public static long GetMaxDecompressLength()
+        {
+            var value = 
Environment.GetEnvironmentVariable(MaxDecompressLengthEnvVar);
+            if (value != null && long.TryParse(value, out var parsed) && 
parsed > 0)
+            {
+                return parsed;
+            }
+
+            return DefaultMaxDecompressLength;
+        }
+
+        /// <summary>
+        /// Throws if the given decompressed length exceeds the maximum 
allowed.
+        /// </summary>
+        /// <param name="length">The number of decompressed bytes.</param>
+        /// <param name="maxLength">The maximum number of decompressed bytes 
allowed.</param>
+        public static void CheckDecompressLength(long length, long maxLength)
+        {
+            if (length > maxLength)
+            {
+                throw new AvroRuntimeException(
+                    $"Decompressed block size exceeds the maximum allowed of 
{maxLength} bytes");
+            }

Review Comment:
   Fixed in 15737e5942 — the exception now reports the observed decompressed 
size and names the AVRO_MAX_DECOMPRESS_LENGTH environment variable to raise the 
limit.



##########
lang/csharp/src/apache/main/File/Codec.cs:
##########
@@ -29,6 +29,71 @@ namespace Avro.File
     /// </summary>
     public abstract class Codec
     {
+        /// <summary>
+        /// Default upper bound, in bytes, on the size a single data-file 
block may
+        /// decompress to. A block with a very high compression ratio (or a 
malformed
+        /// block) can otherwise expand to far more memory than its compressed 
size.
+        /// Mirrors the Java SDK's decompression limit (AVRO-4247). 
Overridable with
+        /// the AVRO_MAX_DECOMPRESS_LENGTH environment variable.
+        /// </summary>
+        public const long DefaultMaxDecompressLength = 200L * 1024 * 1024; // 
200 MiB
+
+        /// <summary>
+        /// Name of the environment variable used to override the default 
maximum
+        /// decompressed size of a single block.
+        /// </summary>
+        public const string MaxDecompressLengthEnvVar = 
"AVRO_MAX_DECOMPRESS_LENGTH";
+
+        /// <summary>
+        /// The maximum number of bytes a single block is allowed to 
decompress to.
+        /// </summary>
+        /// <returns>The configured limit, honoring the environment 
override.</returns>
+        public static long GetMaxDecompressLength()
+        {
+            var value = 
Environment.GetEnvironmentVariable(MaxDecompressLengthEnvVar);
+            if (value != null && long.TryParse(value, out var parsed) && 
parsed > 0)
+            {
+                return parsed;
+            }
+
+            return DefaultMaxDecompressLength;
+        }
+
+        /// <summary>
+        /// Throws if the given decompressed length exceeds the maximum 
allowed.
+        /// </summary>
+        /// <param name="length">The number of decompressed bytes.</param>
+        /// <param name="maxLength">The maximum number of decompressed bytes 
allowed.</param>
+        public static void CheckDecompressLength(long length, long maxLength)
+        {
+            if (length > maxLength)
+            {
+                throw new AvroRuntimeException(
+                    $"Decompressed block size exceeds the maximum allowed of 
{maxLength} bytes");
+            }
+        }
+
+        /// <summary>
+        /// Copies a decompression stream to the destination, rejecting the 
block as
+        /// soon as its decompressed size would exceed <paramref 
name="maxLength"/> so
+        /// an over-large (or malicious) block is not fully materialized in 
memory.
+        /// </summary>
+        /// <param name="source">The decompression stream to read from.</param>
+        /// <param name="destination">The stream to write the decompressed 
data to.</param>
+        /// <param name="maxLength">The maximum number of decompressed bytes 
allowed.</param>
+        public static void CopyBounded(Stream source, Stream destination, long 
maxLength)
+        {
+            byte[] buffer = new byte[81920];
+            long total = 0;
+            int read;
+            while ((read = source.Read(buffer, 0, buffer.Length)) > 0)

Review Comment:
   Fixed in 15737e5942 — CopyBounded now validates its arguments 
(ArgumentNullException for null streams, ArgumentOutOfRangeException for a 
negative maxLength), with a test.



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