Log error message

CHANGELOG.md

@@ -8,3 +8,6 @@ Change Log
 ### Changes
 
 - Change to return just empty NSData instead nil if given data is empty
+- Log error message if compression/decompression is failed.
+    - [Note] This is a temporaly improvement.
+      I'll migrate functions to throw NSError when Swift 2.0 becomes stable.

Project/Tests/NSData_GZIPTests.swift

@@ -54,4 +54,12 @@ class NSData_GZIPTests: XCTestCase
         XCTAssertEqual(zeroLengthData.gzippedData()!, zeroLengthData)
         XCTAssertEqual(zeroLengthData.gunzippedData()!, zeroLengthData)
     }
+
+    func testWrongUngzip()
+    {
+        // data not compressed
+        let data = ("testString" as NSString).dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: true)!
+
+        XCTAssertNil(data.gunzippedData())
+    }
 }

Sources/NSData+GZIP.swift

@@ -43,8 +43,15 @@ public extension NSData
         }
 
         var stream = self.createZStream()
+        var status : Int32
 
-        if deflateInit2_(&stream, Z_DEFAULT_COMPRESSION, Z_DEFLATED, 31, 8, Z_DEFAULT_STRATEGY, ZLIB_VERSION, STREAM_SIZE) != Z_OK {
+        status = deflateInit2_(&stream, Z_DEFAULT_COMPRESSION, Z_DEFLATED, 31, 8, Z_DEFAULT_STRATEGY, ZLIB_VERSION, STREAM_SIZE)
+
+        if status != Z_OK {
+            if let errorMessage = String.fromCString(stream.msg) {
+                println(String(format: "Compression failed: %@", errorMessage))
+            }
+
             return nil
         }
 
@@ -75,13 +82,18 @@ public extension NSData
         }
 
         var stream = self.createZStream()
+        var status : Int32
 
-        if inflateInit2_(&stream, 47, ZLIB_VERSION, STREAM_SIZE) != Z_OK {
+        status = inflateInit2_(&stream, 47, ZLIB_VERSION, STREAM_SIZE)
+
+        if status != Z_OK {
+            if let errorMessage = String.fromCString(stream.msg) {
+                println(String(format: "Decompression failed: %@", errorMessage))
+            }
             return nil
         }
 
         var data = NSMutableData(length: self.length * 2)!
-        var status : Int32
         do {
             if Int(stream.total_out) >= data.length {
                 data.length += self.length / 2;
@@ -94,6 +106,9 @@ public extension NSData
         } while status == Z_OK
 
         if inflateEnd(&stream) != Z_OK || status != Z_STREAM_END {
+            if let errorMessage = String.fromCString(stream.msg) {
+                println(String(format: "Decompression failed: %@", errorMessage))
+            }
             return nil
         }