diff --git a/osi/include/socket.h b/osi/include/socket.h
new file mode 100644
index 0000000..ba36291
--- /dev/null
+++ b/osi/include/socket.h
@@ -0,0 +1,78 @@
+/******************************************************************************
+ *
+ *  Copyright (C) 2014 Google, Inc.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at:
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ ******************************************************************************/
+
+#pragma once
+
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct reactor_t reactor_t;
+typedef struct socket_t socket_t;
+typedef uint16_t port_t;
+
+typedef void (*socket_cb)(socket_t *socket, void *context);
+
+// Returns a new socket object. The socket is in an idle, disconnected state when
+// it is returned by this function. The returned object must be freed by calling
+// |socket_free|. Returns NULL on failure.
+socket_t *socket_new(void);
+
+// Frees a socket object created by |socket_new| or |socket_accept|. |socket| may
+// be NULL. If the socket was connected, it will be disconnected.
+void socket_free(socket_t *socket);
+
+// Puts |socket| in listening mode for incoming TCP connections on the specified
+// |port|. Returns true on success, false on failure (e.g. |port| is bound by
+// another socket). |socket| may not be NULL.
+bool socket_listen(const socket_t *socket, port_t port);
+
+// Blocks on a listening socket, |socket|, until a client connects to it. Returns
+// a connected socket on success, NULL on failure. The returned object must be
+// freed by calling |socket_free|. |socket| may not be NULL.
+socket_t *socket_accept(const socket_t *socket);
+
+// Reads up to |count| bytes from |socket| into |buf|. This function will not
+// block. This function returns a positive integer representing the number
+// of bytes copied into |buf| on success, 0 if the socket has disconnected,
+// and -1 on error. This function may return a value less than |count| if not
+// enough data is currently available. If this function returns -1, errno will also
+// be set (see recv(2) for possible errno values). If there were no bytes available
+// to be read, this function returns -1 and sets errno to EWOULDBLOCK. Neither
+// |socket| nor |buf| may be NULL.
+ssize_t socket_read(const socket_t *socket, void *buf, size_t count);
+
+// Writes up to |count| bytes from |buf| into |socket|. This function will not
+// block. Returns a positive integer representing the number of bytes written
+// to |socket| on success, 0 if the socket has disconnected, and -1 on error. This
+// function may return a value less than |count| if writing more bytes would result
+// in blocking. If this function returns -1, errno will also be set (see send(2) for
+// possible errno values). If no bytes could be written without blocking, this
+// function will return -1 and set errno to EWOULDBLOCK. Neither |socket| nor |buf|
+// may be NULL.
+ssize_t socket_write(const socket_t *socket, const void *buf, size_t count);
+
+// Registers |socket| with the |reactor|. When the socket becomes readable, |read_cb|
+// will be called. When the socket becomes writeable, |write_cb| will be called. The
+// |context| parameter is passed, untouched, to each of the callback routines. Neither
+// |socket| nor |reactor| may be NULL. |read_cb| or |write_cb|, but not both, may be NULL.
+// |context| may be NULL.
+void socket_register(socket_t *socket, reactor_t *reactor, socket_cb read_cb, socket_cb write_cb, void *context);
+
+// Unregisters |socket| from whichever reactor it is registered with, if any. This
+// function is idempotent.
+void socket_unregister(socket_t *socket);