Add support for conditional get

Fixes #77.

src/main/java/org/gaul/s3proxy/S3ProxyHandler.java

@@ -244,6 +244,10 @@ final class S3ProxyHandler extends AbstractHandler {
                     ImmutableMap.<String, String>of());
             baseRequest.setHandled(true);
             return;
+        } catch (HttpResponseException hre) {
+            response.sendError(hre.getResponse().getStatusCode());
+            baseRequest.setHandled(true);
+            return;
         } catch (S3Exception se) {
             sendSimpleErrorResponse(request, response, se.getError(),
                     se.getMessage(), se.getElements());
@@ -1116,6 +1120,29 @@ final class S3ProxyHandler extends AbstractHandler {
             throws IOException, S3Exception {
         int status = HttpServletResponse.SC_OK;
         GetOptions options = new GetOptions();
+
+        String ifMatch = request.getHeader(HttpHeaders.IF_MATCH);
+        if (ifMatch != null) {
+            options.ifETagMatches(ifMatch);
+        }
+
+        String ifNoneMatch = request.getHeader(HttpHeaders.IF_NONE_MATCH);
+        if (ifNoneMatch != null) {
+            options.ifETagDoesntMatch(ifNoneMatch);
+        }
+
+        long ifModifiedSince = request.getDateHeader(
+                HttpHeaders.IF_MODIFIED_SINCE);
+        if (ifModifiedSince != -1) {
+            options.ifModifiedSince(new Date(ifModifiedSince));
+        }
+
+        long ifUnmodifiedSince = request.getDateHeader(
+                HttpHeaders.IF_UNMODIFIED_SINCE);
+        if (ifUnmodifiedSince != -1) {
+            options.ifUnmodifiedSince(new Date(ifUnmodifiedSince));
+        }
+
         String range = request.getHeader(HttpHeaders.RANGE);
         if (range != null && range.startsWith("bytes=") &&
                 // ignore multiple ranges

src/test/java/org/gaul/s3proxy/S3ProxyTest.java

@@ -49,9 +49,11 @@ import org.jclouds.blobstore.domain.MultipartUpload;
 import org.jclouds.blobstore.domain.PageSet;
 import org.jclouds.blobstore.domain.StorageMetadata;
 import org.jclouds.blobstore.options.CopyOptions;
+import org.jclouds.blobstore.options.GetOptions;
 import org.jclouds.blobstore.options.ListContainerOptions;
 import org.jclouds.http.HttpRequest;
 import org.jclouds.http.HttpResponse;
+import org.jclouds.http.HttpResponseException;
 import org.jclouds.io.ContentMetadata;
 import org.jclouds.io.ContentMetadataBuilder;
 import org.jclouds.io.Payload;
@@ -610,6 +612,29 @@ public final class S3ProxyTest {
                 userMetadata);
     }
 
+    @Test
+    public void testConditionalGet() throws Exception {
+        String blobName = "blob-name";
+        Blob putBlob = s3BlobStore.blobBuilder(blobName)
+                .payload(BYTE_SOURCE)
+                .contentLength(BYTE_SOURCE.size())
+                .build();
+        String eTag = s3BlobStore.putBlob(containerName, putBlob);
+
+        Blob getBlob = s3BlobStore.getBlob(containerName, blobName,
+                new GetOptions().ifETagMatches(eTag));
+        assertThat(getBlob.getPayload()).isNotNull();
+
+        try {
+            s3BlobStore.getBlob(containerName, blobName,
+                    new GetOptions().ifETagDoesntMatch(eTag));
+            Fail.failBecauseExceptionWasNotThrown(HttpResponseException.class);
+        } catch (HttpResponseException hre) {
+            assertThat(hre.getResponse().getStatusCode()).isEqualTo(
+                    HttpServletResponse.SC_NOT_MODIFIED);
+        }
+    }
+
     @Test
     public void testUnknownParameter() throws Exception {
         final S3Client s3Client = s3Context.unwrapApi(S3Client.class);