1 files changed, 52 insertions, 0 deletions
diff --git a/src/morfologik/fsa/FSAHeader.java b/src/morfologik/fsa/FSAHeader.java
new file mode 100644
index 0000000..76fd6ff
--- /dev/null
+++ b/src/morfologik/fsa/FSAHeader.java
@@ -0,0 +1,52 @@
+package morfologik.fsa;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import morfologik.util.FileUtils;
+import static morfologik.util.FileUtils.*;
+
+/**
+ * Standard FSA file header, as described in <code>fsa</code> package documentation. 
+ */
+final class FSAHeader {
+	/**
+	 * FSA magic (4 bytes).
+	 */
+	public final static int FSA_MAGIC = ('\\' << 24) | ('f' << 16) | ('s' << 8) | ('a');
+
+	/**
+	 * Maximum length of the header block.
+	 */
+	public static final int MAX_HEADER_LENGTH = 4 + 8;
+	
+	/** FSA version number. */
+	public byte version;
+
+	/** Filler character. */
+	public byte filler;
+	
+	/** Annotation character. */
+	public byte annotation;
+	
+	/** Goto field (may be a compound, depending on the automaton version). */
+	public byte gtl;
+
+	/**
+	 * Read FSA header from a stream, consuming its bytes.
+	 * 
+	 * @throws IOException If the stream ends prematurely or if it contains invalid data.
+	 */
+	public static FSAHeader read(InputStream in) throws IOException {
+		if (FSA_MAGIC != FileUtils.readInt(in))
+			throw new IOException("Invalid file header magic bytes.");
+
+		final FSAHeader h = new FSAHeader();
+		h.version = readByte(in);
+		h.filler = readByte(in);
+		h.annotation = readByte(in);
+		h.gtl = readByte(in);
+
+	    return h;
+    }
+}