diff --git a/src/python/oftest/pcap_writer.py b/src/python/oftest/pcap_writer.py
new file mode 100644
index 0000000..33918c0
--- /dev/null
+++ b/src/python/oftest/pcap_writer.py
@@ -0,0 +1,43 @@
+"""
+Pcap file writer
+"""
+
+import struct
+
+PcapHeader = struct.Struct("<LHHLLLL")
+PcapPktHeader = struct.Struct("<LLLL")
+
+class PcapWriter(object):
+    def __init__(self, filename):
+        """
+        Open a pcap file
+        """
+        self.stream = file(filename, 'w')
+
+        self.stream.write(PcapHeader.pack(
+            0xa1b2c3d4, # magic
+            2, # major
+            4, # minor
+            0, # timezone offset
+            0, # timezone accuracy
+            65535, # snapshot length
+            1 # ethernet linktype
+        ))
+
+    def write(self, data, timestamp):
+        """
+        Write a packet to a pcap file
+
+        'data' should be a string containing the packet data.
+        'timestamp' should be a float.
+        """
+        self.stream.write(PcapPktHeader.pack(
+            int(timestamp), # timestamp seconds
+            int((timestamp - int(timestamp)) * 10**6), # timestamp microseconds
+            len(data), # truncated length
+            len(data) # un-truncated length
+        ))
+        self.stream.write(data)
+
+    def close(self):
+        self.stream.close()