diff --git a/core/src/main/groovy/com/muwire/core/files/FileHashedEvent.groovy b/core/src/main/groovy/com/muwire/core/files/FileHashedEvent.groovy
index 57d46237..8aea59a2 100644
--- a/core/src/main/groovy/com/muwire/core/files/FileHashedEvent.groovy
+++ b/core/src/main/groovy/com/muwire/core/files/FileHashedEvent.groovy
@@ -1,8 +1,10 @@
 package com.muwire.core.files
 
 import com.muwire.core.Event
+import com.muwire.core.SharedFile
 
 class FileHashedEvent extends Event {
 
-	def sharedFile
+	SharedFile sharedFile
+	String error
 }
diff --git a/core/src/main/groovy/com/muwire/core/files/HasherService.groovy b/core/src/main/groovy/com/muwire/core/files/HasherService.groovy
index 04fc9910..fd570d15 100644
--- a/core/src/main/groovy/com/muwire/core/files/HasherService.groovy
+++ b/core/src/main/groovy/com/muwire/core/files/HasherService.groovy
@@ -1,5 +1,42 @@
 package com.muwire.core.files
 
+import java.util.concurrent.Executor
+import java.util.concurrent.Executors
+
+import com.muwire.core.SharedFile
+
 class HasherService {
 
+	final FileHasher hasher
+	final def listener
+	Executor executor
+	
+	HasherService(FileHasher hasher, def listener) {
+		this.hasher = hasher
+		this.listener = listener
+	}
+	
+	void start() {
+		executor = Executors.newSingleThreadExecutor()
+	}
+	
+	void onFileSharedEvent(FileSharedEvent evt) {
+		executor.execute( { -> process(evt.file) } as Runnable)
+	}
+	
+	private void process(File f) {
+		f = f.getCanonicalFile()
+		if (f.isDirectory()) {
+			f.listFiles().each {onFileSharedEvent new FileSharedEvent(file: it) }
+		} else {
+			if (f.length() == 0) {
+				listener.publish new FileHashedEvent(error: "Not sharing empty file $f")
+			} else if (f.length() > FileHasher.MAX_SIZE) {
+				listener.publish new FileHashedEvent(error: "$f is too large to be shared ${f.length()}")
+			} else {
+				def hash = hasher.hashFile f
+				listener.publish new FileHashedEvent(sharedFile: new SharedFile(f, hash))
+			}
+		}
+	}
 }
diff --git a/core/src/test/groovy/com/muwire/core/files/HasherServiceTest.groovy b/core/src/test/groovy/com/muwire/core/files/HasherServiceTest.groovy
new file mode 100644
index 00000000..98da621d
--- /dev/null
+++ b/core/src/test/groovy/com/muwire/core/files/HasherServiceTest.groovy
@@ -0,0 +1,58 @@
+package com.muwire.core.files
+
+import java.util.concurrent.ArrayBlockingQueue
+import java.util.concurrent.TimeUnit
+
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+
+class HasherServiceTest {
+
+	HasherService service
+	FileHasher hasher
+	def listener = new ArrayBlockingQueue(100) {
+		void publish(def evt) {
+			offer evt
+		}
+	}
+	
+	@Before
+	void before() {
+		hasher = new FileHasher()
+		service = new HasherService(hasher, listener)
+		service.start()
+	}
+	
+	@After
+	void after() {
+		listener.clear()
+	}
+	
+	@Test
+	void testSingleFile() {
+		File f = new File("build.gradle")
+		service.onFileSharedEvent new FileSharedEvent(file: f)
+		Thread.sleep(100)
+		def hashed = listener.poll()
+		assert hashed instanceof FileHashedEvent
+		assert hashed.sharedFile.file == f.getCanonicalFile()
+		assert hashed.sharedFile.infoHash != null
+		assert listener.isEmpty()
+	}
+	
+	@Test
+	void testDirectory() {
+		File f = new File(".")
+		service.onFileSharedEvent new FileSharedEvent(file: f)
+		Set<String> fileNames = new HashSet<>()
+		while (true) {
+			def hashed = listener.poll(100, TimeUnit.MILLISECONDS)
+			if (hashed == null)
+				break
+			fileNames.add(hashed.sharedFile?.file?.getName())
+		}
+		assert fileNames.contains("build.gradle")
+		assert fileNames.contains("HasherServiceTest.groovy")
+	}
+}