diff --git a/ssl/ssl_buffer.c b/ssl/ssl_buffer.c
new file mode 100644
index 0000000..37f27be
--- /dev/null
+++ b/ssl/ssl_buffer.c
@@ -0,0 +1,309 @@
+/* Copyright (c) 2015, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+#include <openssl/ssl.h>
+
+#include <assert.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <openssl/bio.h>
+#include <openssl/err.h>
+#include <openssl/mem.h>
+#include <openssl/type_check.h>
+
+#include "internal.h"
+
+
+OPENSSL_COMPILE_ASSERT(0xffff <= INT_MAX, uint16_fits_in_int);
+
+OPENSSL_COMPILE_ASSERT((SSL3_ALIGN_PAYLOAD & (SSL3_ALIGN_PAYLOAD - 1)) == 0,
+                       align_to_a_power_of_two);
+
+/* setup_buffer initializes |buf| with capacity |cap|, aligned such that data
+ * written after |header_len| is aligned to a |SSL3_ALIGN_PAYLOAD|-byte
+ * boundary. It returns one on success and zero on error. */
+static int setup_buffer(SSL3_BUFFER *buf, size_t header_len, size_t cap) {
+  if (buf->buf != NULL || cap > 0xffff) {
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return 0;
+  }
+
+  /* Add up to |SSL3_ALIGN_PAYLOAD| - 1 bytes of slack for alignment. */
+  buf->buf = OPENSSL_malloc(cap + SSL3_ALIGN_PAYLOAD - 1);
+  if (buf->buf == NULL) {
+    OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
+    return 0;
+  }
+
+  /* Arrange the buffer such that the record body is aligned. */
+  buf->offset = (0 - header_len - (uintptr_t)buf->buf) &
+                (SSL3_ALIGN_PAYLOAD - 1);
+  buf->len = 0;
+  buf->cap = cap;
+  return 1;
+}
+
+static void consume_buffer(SSL3_BUFFER *buf, size_t len) {
+  if (len > buf->len) {
+    abort();
+  }
+  buf->offset += (uint16_t)len;
+  buf->len -= (uint16_t)len;
+  buf->cap -= (uint16_t)len;
+}
+
+static void clear_buffer(SSL3_BUFFER *buf) {
+  OPENSSL_free(buf->buf);
+  memset(buf, 0, sizeof(SSL3_BUFFER));
+}
+
+OPENSSL_COMPILE_ASSERT(DTLS1_RT_HEADER_LENGTH + SSL3_RT_MAX_ENCRYPTED_LENGTH +
+                           SSL3_RT_MAX_EXTRA <= 0xffff,
+                       maximum_read_buffer_too_large);
+
+/* setup_read_buffer initializes the read buffer if not already initialized. It
+ * returns one on success and zero on failure. */
+static int setup_read_buffer(SSL *ssl) {
+  SSL3_BUFFER *buf = &ssl->s3->read_buffer;
+
+  if (buf->buf != NULL) {
+    return 1;
+  }
+
+  size_t header_len = ssl_record_prefix_len(ssl);
+  size_t cap = SSL3_RT_HEADER_LENGTH + SSL3_RT_MAX_PLAIN_LENGTH;
+  if (ssl->options & SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER) {
+    cap += SSL3_RT_MAX_EXTRA;
+  }
+
+  return setup_buffer(buf, header_len, cap);
+}
+
+uint8_t *ssl_read_buffer(SSL *ssl) {
+  return ssl->s3->read_buffer.buf + ssl->s3->read_buffer.offset;
+}
+
+size_t ssl_read_buffer_len(const SSL *ssl) {
+  return ssl->s3->read_buffer.len;
+}
+
+static int dtls_read_buffer_next_packet(SSL *ssl) {
+  SSL3_BUFFER *buf = &ssl->s3->read_buffer;
+
+  if (buf->len > 0) {
+    /* It is an error to call |dtls_read_buffer_extend| when the read buffer is
+     * not empty. */
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return -1;
+  }
+
+  /* Read a single packet from |ssl->rbio|. |buf->cap| must fit in an int. */
+  ssl->rwstate = SSL_READING;
+  int ret = BIO_read(ssl->rbio, buf->buf + buf->offset, (int)buf->cap);
+  if (ret <= 0) {
+    return ret;
+  }
+  ssl->rwstate = SSL_NOTHING;
+  /* |BIO_read| was bound by |buf->cap|, so this cannot overflow. */
+  buf->len = (uint16_t)ret;
+  return 1;
+}
+
+static int tls_read_buffer_extend_to(SSL *ssl, size_t len) {
+  SSL3_BUFFER *buf = &ssl->s3->read_buffer;
+
+  if (len > buf->cap) {
+    /* This may occur if |SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER| was toggled after
+     * |setup_read_buffer| was called. Stay within bounds, but do not attempt to
+     * recover. */
+    OPENSSL_PUT_ERROR(SSL, SSL_R_BUFFER_TOO_SMALL);
+    return -1;
+  }
+
+  /* Read until the target length is reached. */
+  while (buf->len < len) {
+    /* The amount of data to read is bounded by |buf->cap|, which must fit in an
+     * int. */
+    ssl->rwstate = SSL_READING;
+    int ret = BIO_read(ssl->rbio, buf->buf + buf->offset + buf->len,
+                       (int)(len - buf->len));
+    if (ret <= 0) {
+      return ret;
+    }
+    ssl->rwstate = SSL_NOTHING;
+    /* |BIO_read| was bound by |buf->cap - buf->len|, so this cannot
+     * overflow. */
+    buf->len += (uint16_t)ret;
+  }
+
+  return 1;
+}
+
+int ssl_read_buffer_extend_to(SSL *ssl, size_t len) {
+  /* |ssl_read_buffer_extend_to| implicitly discards any consumed data. */
+  ssl_read_buffer_discard(ssl);
+
+  if (!setup_read_buffer(ssl)) {
+    return -1;
+  }
+
+  if (ssl->rbio == NULL) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_BIO_NOT_SET);
+    return -1;
+  }
+
+  ERR_clear_system_error();
+
+  int ret;
+  if (SSL_IS_DTLS(ssl)) {
+    /* |len| is ignored for a datagram transport. */
+    ret = dtls_read_buffer_next_packet(ssl);
+  } else {
+    ret = tls_read_buffer_extend_to(ssl, len);
+  }
+
+  if (ret <= 0) {
+    /* If the buffer was empty originally and remained empty after attempting to
+     * extend it, release the buffer until the next attempt. */
+    ssl_read_buffer_discard(ssl);
+  }
+  return ret;
+}
+
+void ssl_read_buffer_consume(SSL *ssl, size_t len) {
+  SSL3_BUFFER *buf = &ssl->s3->read_buffer;
+
+  consume_buffer(buf, len);
+  if (!SSL_IS_DTLS(ssl)) {
+    /* The TLS stack never reads beyond the current record, so there will never
+     * be unconsumed data. If read-ahead is ever reimplemented,
+     * |ssl_read_buffer_discard| will require a |memcpy| to shift the excess
+     * back to the front of the buffer, to ensure there is enough space for the
+     * next record. */
+     assert(buf->len == 0);
+  }
+}
+
+void ssl_read_buffer_discard(SSL *ssl) {
+  if (ssl->s3->read_buffer.len == 0) {
+    ssl_read_buffer_clear(ssl);
+  }
+}
+
+void ssl_read_buffer_clear(SSL *ssl) {
+  clear_buffer(&ssl->s3->read_buffer);
+}
+
+
+int ssl_write_buffer_is_pending(const SSL *ssl) {
+  return ssl->s3->write_buffer.len > 0;
+}
+
+OPENSSL_COMPILE_ASSERT(SSL3_RT_HEADER_LENGTH * 2 +
+                           SSL3_RT_SEND_MAX_ENCRYPTED_OVERHEAD * 2 +
+                           SSL3_RT_MAX_PLAIN_LENGTH <= 0xffff,
+                       maximum_tls_write_buffer_too_large);
+
+OPENSSL_COMPILE_ASSERT(DTLS1_RT_HEADER_LENGTH +
+                           SSL3_RT_SEND_MAX_ENCRYPTED_OVERHEAD +
+                           SSL3_RT_MAX_PLAIN_LENGTH <= 0xffff,
+                       maximum_dtls_write_buffer_too_large);
+
+int ssl_write_buffer_init(SSL *ssl, uint8_t **out_ptr, size_t max_len) {
+  SSL3_BUFFER *buf = &ssl->s3->write_buffer;
+
+  if (buf->buf != NULL) {
+    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
+    return 0;
+  }
+
+  size_t header_len = ssl_seal_prefix_len(ssl);
+
+  /* TODO(davidben): This matches the original behavior in keeping the malloc
+   * size consistent. Does this matter? |cap| could just be |max_len|. */
+  size_t cap = SSL3_RT_HEADER_LENGTH + SSL3_RT_MAX_PLAIN_LENGTH +
+               SSL3_RT_SEND_MAX_ENCRYPTED_OVERHEAD;
+  if (!SSL_IS_DTLS(ssl) && (ssl->mode & SSL_MODE_CBC_RECORD_SPLITTING)) {
+    cap += SSL3_RT_HEADER_LENGTH + SSL3_RT_SEND_MAX_ENCRYPTED_OVERHEAD;
+  }
+
+  if (max_len > cap) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_BUFFER_TOO_SMALL);
+    return 0;
+  }
+
+  if (!setup_buffer(buf, header_len, cap)) {
+    return 0;
+  }
+  *out_ptr = buf->buf + buf->offset;
+  return 1;
+}
+
+void ssl_write_buffer_set_len(SSL *ssl, size_t len) {
+  SSL3_BUFFER *buf = &ssl->s3->write_buffer;
+
+  if (len > buf->cap) {
+    abort();
+  }
+  buf->len = len;
+}
+
+static int tls_write_buffer_flush(SSL *ssl) {
+  SSL3_BUFFER *buf = &ssl->s3->write_buffer;
+
+  while (buf->len > 0) {
+    ssl->rwstate = SSL_WRITING;
+    int ret = BIO_write(ssl->wbio, buf->buf + buf->offset, buf->len);
+    if (ret <= 0) {
+      return ret;
+    }
+    ssl->rwstate = SSL_NOTHING;
+    consume_buffer(buf, (size_t)ret);
+  }
+  ssl_write_buffer_clear(ssl);
+  return 1;
+}
+
+static int dtls_write_buffer_flush(SSL *ssl) {
+  SSL3_BUFFER *buf = &ssl->s3->write_buffer;
+  if (buf->len == 0) {
+    return 1;
+  }
+
+  int ret = BIO_write(ssl->wbio, buf->buf + buf->offset, buf->len);
+  /* Drop the write buffer whether or not the write succeeded synchronously.
+   * TODO(davidben): How does this interact with the retry flag? */
+  ssl_write_buffer_clear(ssl);
+  return (ret <= 0) ? ret : 1;
+}
+
+int ssl_write_buffer_flush(SSL *ssl) {
+  if (ssl->wbio == NULL) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_BIO_NOT_SET);
+    return -1;
+  }
+  ERR_clear_system_error();
+
+  if (SSL_IS_DTLS(ssl)) {
+    return dtls_write_buffer_flush(ssl);
+  } else {
+    return tls_write_buffer_flush(ssl);
+  }
+}
+
+void ssl_write_buffer_clear(SSL *ssl) {
+  clear_buffer(&ssl->s3->write_buffer);
+}