#89: Add SnappyIOException to distinguish empty input, incompatible format version, etc.

src/main/java/org/xerial/snappy/SnappyErrorCode.java

@@ -38,7 +38,11 @@ public enum SnappyErrorCode {
     PARSING_ERROR(2),
     NOT_A_DIRECT_BUFFER(3),
     OUT_OF_MEMORY(4),
-    FAILED_TO_UNCOMPRESS(5);
+    FAILED_TO_UNCOMPRESS(5),
+    EMPTY_INPUT(6),
+    INCOMPATIBLE_VERSION(7),
+    INVALID_CHUNK_SIZE(8)
+    ;
 
     public final int id;
 

src/main/java/org/xerial/snappy/SnappyIOException.java

@@ -0,0 +1,23 @@
+package org.xerial.snappy;
+
+import java.io.IOException;
+
+/**
+ * Enhanced IOException with SnappyErrorCode
+ */
+public class SnappyIOException extends IOException {
+    private final SnappyErrorCode errorCode;
+
+    public SnappyIOException(SnappyErrorCode errorCode, String message) {
+        super(message);
+        this.errorCode = errorCode;
+    }
+
+    @Override
+    public String getMessage() {
+        return String.format("[%s] %s", errorCode.name(), super.getMessage());
+    }
+
+    public SnappyErrorCode getErrorCode() { return errorCode; }
+
+}

src/main/java/org/xerial/snappy/SnappyInputStream.java

@@ -83,6 +83,10 @@ public class SnappyInputStream extends InputStream
         }
 
         // Quick test of the header
+        if(readBytes == 0) {
+            // Snappy produces at least 1-byte result. So the empty input is not a valid input
+            throw new SnappyIOException(SnappyErrorCode.EMPTY_INPUT, "Cannot decompress empty stream");
+        }
         if (readBytes < header.length || header[0] != SnappyCodec.MAGIC_HEADER[0]) {
             // do the default uncompression
             readFully(header, readBytes);
@@ -93,8 +97,8 @@ public class SnappyInputStream extends InputStream
         if (codec.isValidMagicHeader()) {
             // The input data is compressed by SnappyOutputStream
             if (codec.version < SnappyCodec.MINIMUM_COMPATIBLE_VERSION) {
-                throw new IOException(String.format(
-                        "compressed with imcompatible codec version %d. At least version %d is required",
+                throw new SnappyIOException(SnappyErrorCode.INCOMPATIBLE_VERSION, String.format(
+                        "Compressed with an incompatible codec version %d. At least version %d is required",
                         codec.version, SnappyCodec.MINIMUM_COMPATIBLE_VERSION));
             }
         }
@@ -351,20 +355,15 @@ public class SnappyInputStream extends InputStream
         if (readBytes < chunkSize) {
             throw new IOException("failed to read chunk");
         }
-        try {
         int uncompressedLength = Snappy.uncompressedLength(compressed, 0, chunkSize);
         if (uncompressed == null || uncompressedLength > uncompressed.length) {
             uncompressed = new byte[uncompressedLength];
         }
         int actualUncompressedLength = Snappy.uncompress(compressed, 0, chunkSize, uncompressed, 0);
         if (uncompressedLength != actualUncompressedLength) {
-                throw new IOException("invalid uncompressed byte size");
+            throw new SnappyIOException(SnappyErrorCode.INVALID_CHUNK_SIZE, String.format("expected %,d bytes, but decompressed chunk has %,d bytes", uncompressedLength, actualUncompressedLength));
         }
         uncompressedLimit = actualUncompressedLength;
-        }
-        catch (IOException e) {
-            throw new IOException("failed to uncompress the chunk: " + e.getMessage());
-        }
 
         return true;
     }

src/test/java/org/xerial/snappy/SnappyInputStreamTest.java

@@ -135,11 +135,11 @@ public class SnappyInputStreamTest
             SnappyInputStream in = new SnappyInputStream(new ByteArrayInputStream(new byte[0]));
             byte[] uncompressed = readFully(in);
             assertEquals(0, uncompressed.length);
-        }
-        catch(Exception e) {
             fail("should not reach here");
         }
-
+        catch(SnappyIOException e) {
+            assertEquals(SnappyErrorCode.EMPTY_INPUT, e.getErrorCode());
+        }
     }
 
 }