1 files changed, 527 insertions, 0 deletions
diff --git a/netwerk/base/TCPFastOpenLayer.cpp b/netwerk/base/TCPFastOpenLayer.cpp
new file mode 100644
index 0000000000..ea5e5f11d6
--- /dev/null
+++ b/netwerk/base/TCPFastOpenLayer.cpp
@@ -0,0 +1,527 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "TCPFastOpenLayer.h"
+#include "nsSocketTransportService2.h"
+#include "prmem.h"
+#include "prio.h"
+
+namespace mozilla {
+namespace net {
+
+static PRDescIdentity sTCPFastOpenLayerIdentity;
+static PRIOMethods sTCPFastOpenLayerMethods;
+static PRIOMethods* sTCPFastOpenLayerMethodsPtr = nullptr;
+
+#define TFO_MAX_PACKET_SIZE_IPV4 1460
+#define TFO_MAX_PACKET_SIZE_IPV6 1440
+#define TFO_TLS_RECORD_HEADER_SIZE 22
+
+/**
+ *  For the TCP Fast Open it is necessary to send all data that can fit into the
+ *  first packet on a single sendto function call. Consecutive calls will not
+ *  have an effect. Therefore  TCPFastOpenLayer will collect some data before
+ *  calling sendto. Necko and nss will call PR_Write multiple times with small
+ *  amount of  data.
+ *  TCPFastOpenLayer has 4 states:
+ *    WAITING_FOR_CONNECT:
+ *      This is before connect is call. A call of recv, send or getpeername will
+ *      return PR_NOT_CONNECTED_ERROR. After connect is call the state transfers
+ *      into COLLECT_DATA_FOR_FIRST_PACKET.
+ *
+ *    COLLECT_DATA_FOR_FIRST_PACKET:
+ *      In this state all data received by send function calls will be stored in
+ *      a buffer. If transaction do not have any more data ready to be sent or
+ *      the buffer is full, TCPFastOpenFinish is call. TCPFastOpenFinish sends
+ *      the collected data using sendto function and the state transfers to
+ *      WAITING_FOR_CONNECTCONTINUE. If an error occurs during sendto, the error
+ *      is reported by the TCPFastOpenFinish return values. nsSocketTransfer is
+ *      the only caller of TCPFastOpenFinish; it knows how to interpreter these
+ *      errors.
+ *    WAITING_FOR_CONNECTCONTINUE:
+ *      connectcontinue transfers from this state to CONNECTED. Any other
+ *      function (e.g. send, recv) returns PR_WOULD_BLOCK_ERROR.
+ *    CONNECTED:
+ *      The size of mFirstPacketBuf is 1440/1460 (RFC7413 recomends that packet
+ *      does exceeds these sizes). SendTo does not have to consume all buffered
+ *      data and some data can be still in mFirstPacketBuf. Before sending any
+ *      new data we need to send the remaining buffered data.
+ **/
+
+class TCPFastOpenSecret {
+ public:
+  TCPFastOpenSecret()
+      : mState(WAITING_FOR_CONNECT), mFirstPacketBufLen(0), mCondition(0) {
+    this->mAddr.raw.family = 0;
+    this->mAddr.inet.family = 0;
+    this->mAddr.inet.port = 0;
+    this->mAddr.inet.ip = 0;
+    this->mAddr.ipv6.family = 0;
+    this->mAddr.ipv6.port = 0;
+    this->mAddr.ipv6.flowinfo = 0;
+    this->mAddr.ipv6.scope_id = 0;
+    this->mAddr.local.family = 0;
+  }
+
+  enum {
+    CONNECTED,
+    WAITING_FOR_CONNECTCONTINUE,
+    COLLECT_DATA_FOR_FIRST_PACKET,
+    WAITING_FOR_CONNECT,
+    SOCKET_ERROR_STATE
+  } mState;
+  PRNetAddr mAddr;
+  char mFirstPacketBuf[1460];
+  uint16_t mFirstPacketBufLen;
+  PRErrorCode mCondition;
+};
+
+static PRStatus TCPFastOpenConnect(PRFileDesc* fd, const PRNetAddr* addr,
+                                   PRIntervalTime timeout) {
+  MOZ_RELEASE_ASSERT(fd->identity == sTCPFastOpenLayerIdentity);
+  MOZ_ASSERT(OnSocketThread(), "not on socket thread");
+
+  TCPFastOpenSecret* secret = reinterpret_cast<TCPFastOpenSecret*>(fd->secret);
+
+  SOCKET_LOG(("TCPFastOpenConnect state=%d.\n", secret->mState));
+
+  if (secret->mState != TCPFastOpenSecret::WAITING_FOR_CONNECT) {
+    PR_SetError(PR_IS_CONNECTED_ERROR, 0);
+    return PR_FAILURE;
+  }
+
+  // Remember the address. It will be used for sendto or connect later.
+  memcpy(&secret->mAddr, addr, sizeof(secret->mAddr));
+  secret->mState = TCPFastOpenSecret::COLLECT_DATA_FOR_FIRST_PACKET;
+
+  return PR_SUCCESS;
+}
+
+static PRInt32 TCPFastOpenSend(PRFileDesc* fd, const void* buf, PRInt32 amount,
+                               PRIntn flags, PRIntervalTime timeout) {
+  MOZ_RELEASE_ASSERT(fd->identity == sTCPFastOpenLayerIdentity);
+  MOZ_ASSERT(OnSocketThread(), "not on socket thread");
+
+  TCPFastOpenSecret* secret = reinterpret_cast<TCPFastOpenSecret*>(fd->secret);
+
+  SOCKET_LOG(("TCPFastOpenSend state=%d.\n", secret->mState));
+
+  switch (secret->mState) {
+    case TCPFastOpenSecret::CONNECTED:
+      // Before sending new data we need to drain the data collected during tfo.
+      if (secret->mFirstPacketBufLen) {
+        SOCKET_LOG(
+            ("TCPFastOpenSend - %d bytes to drain from "
+             "mFirstPacketBufLen.\n",
+             secret->mFirstPacketBufLen));
+        PRInt32 rv = (fd->lower->methods->send)(
+            fd->lower, secret->mFirstPacketBuf, secret->mFirstPacketBufLen,
+            0,  // flags
+            PR_INTERVAL_NO_WAIT);
+        if (rv <= 0) {
+          return rv;
+        }
+        secret->mFirstPacketBufLen -= rv;
+        if (secret->mFirstPacketBufLen) {
+          memmove(secret->mFirstPacketBuf, secret->mFirstPacketBuf + rv,
+                  secret->mFirstPacketBufLen);
+
+          PR_SetError(PR_WOULD_BLOCK_ERROR, 0);
+          return PR_FAILURE;
+        }  // if we drained the buffer we can fall through this checks and call
+           // send for the new data
+      }
+      SOCKET_LOG(("TCPFastOpenSend sending new data.\n"));
+      return (fd->lower->methods->send)(fd->lower, buf, amount, flags, timeout);
+    case TCPFastOpenSecret::WAITING_FOR_CONNECTCONTINUE:
+      PR_SetError(PR_WOULD_BLOCK_ERROR, 0);
+      return -1;
+    case TCPFastOpenSecret::COLLECT_DATA_FOR_FIRST_PACKET: {
+      int32_t toSend = (secret->mAddr.raw.family == PR_AF_INET)
+                           ? TFO_MAX_PACKET_SIZE_IPV4
+                           : TFO_MAX_PACKET_SIZE_IPV6;
+      MOZ_ASSERT(secret->mFirstPacketBufLen <= toSend);
+      toSend -= secret->mFirstPacketBufLen;
+
+      SOCKET_LOG(
+          ("TCPFastOpenSend: amount of data in the buffer=%d; the amount"
+           " of additional data that can be stored=%d.\n",
+           secret->mFirstPacketBufLen, toSend));
+
+      if (!toSend) {
+        PR_SetError(PR_WOULD_BLOCK_ERROR, 0);
+        return -1;
+      }
+
+      toSend = (toSend > amount) ? amount : toSend;
+      memcpy(secret->mFirstPacketBuf + secret->mFirstPacketBufLen, buf, toSend);
+      secret->mFirstPacketBufLen += toSend;
+      return toSend;
+    }
+    case TCPFastOpenSecret::WAITING_FOR_CONNECT:
+      PR_SetError(PR_NOT_CONNECTED_ERROR, 0);
+      return -1;
+    case TCPFastOpenSecret::SOCKET_ERROR_STATE:
+      PR_SetError(secret->mCondition, 0);
+      return -1;
+  }
+  PR_SetError(PR_WOULD_BLOCK_ERROR, 0);
+  return PR_FAILURE;
+}
+
+static PRInt32 TCPFastOpenWrite(PRFileDesc* fd, const void* buf,
+                                PRInt32 amount) {
+  return TCPFastOpenSend(fd, buf, amount, 0, PR_INTERVAL_NO_WAIT);
+}
+
+static PRInt32 TCPFastOpenRecv(PRFileDesc* fd, void* buf, PRInt32 amount,
+                               PRIntn flags, PRIntervalTime timeout) {
+  MOZ_RELEASE_ASSERT(fd->identity == sTCPFastOpenLayerIdentity);
+
+  TCPFastOpenSecret* secret = reinterpret_cast<TCPFastOpenSecret*>(fd->secret);
+
+  PRInt32 rv = -1;
+  switch (secret->mState) {
+    case TCPFastOpenSecret::CONNECTED:
+
+      if (secret->mFirstPacketBufLen) {
+        // TLS will not call write before receiving data from a server,
+        // therefore we need to force sending buffered data even during recv
+        // call. Otherwise It can come to a deadlock (clients waits for
+        // response, but the request is sitting in mFirstPacketBufLen).
+        SOCKET_LOG(
+            ("TCPFastOpenRevc - %d bytes to drain from mFirstPacketBuf.\n",
+             secret->mFirstPacketBufLen));
+        PRInt32 rv = (fd->lower->methods->send)(
+            fd->lower, secret->mFirstPacketBuf, secret->mFirstPacketBufLen,
+            0,  // flags
+            PR_INTERVAL_NO_WAIT);
+        if (rv <= 0) {
+          return rv;
+        }
+        secret->mFirstPacketBufLen -= rv;
+        if (secret->mFirstPacketBufLen) {
+          memmove(secret->mFirstPacketBuf, secret->mFirstPacketBuf + rv,
+                  secret->mFirstPacketBufLen);
+        }
+      }
+      rv = (fd->lower->methods->recv)(fd->lower, buf, amount, flags, timeout);
+      break;
+    case TCPFastOpenSecret::WAITING_FOR_CONNECTCONTINUE:
+    case TCPFastOpenSecret::COLLECT_DATA_FOR_FIRST_PACKET:
+      PR_SetError(PR_WOULD_BLOCK_ERROR, 0);
+      break;
+    case TCPFastOpenSecret::WAITING_FOR_CONNECT:
+      PR_SetError(PR_NOT_CONNECTED_ERROR, 0);
+      break;
+    case TCPFastOpenSecret::SOCKET_ERROR_STATE:
+      PR_SetError(secret->mCondition, 0);
+  }
+  return rv;
+}
+
+static PRInt32 TCPFastOpenRead(PRFileDesc* fd, void* buf, PRInt32 amount) {
+  return TCPFastOpenRecv(fd, buf, amount, 0, PR_INTERVAL_NO_WAIT);
+}
+
+static PRStatus TCPFastOpenConnectContinue(PRFileDesc* fd, PRInt16 out_flags) {
+  MOZ_RELEASE_ASSERT(fd->identity == sTCPFastOpenLayerIdentity);
+
+  TCPFastOpenSecret* secret = reinterpret_cast<TCPFastOpenSecret*>(fd->secret);
+
+  PRStatus rv = PR_FAILURE;
+  switch (secret->mState) {
+    case TCPFastOpenSecret::CONNECTED:
+      rv = PR_SUCCESS;
+      break;
+    case TCPFastOpenSecret::WAITING_FOR_CONNECT:
+    case TCPFastOpenSecret::COLLECT_DATA_FOR_FIRST_PACKET:
+      PR_SetError(PR_NOT_CONNECTED_ERROR, 0);
+      rv = PR_FAILURE;
+      break;
+    case TCPFastOpenSecret::WAITING_FOR_CONNECTCONTINUE:
+      rv = (fd->lower->methods->connectcontinue)(fd->lower, out_flags);
+
+      SOCKET_LOG(("TCPFastOpenConnectContinue result=%d.\n", rv));
+      secret->mState = TCPFastOpenSecret::CONNECTED;
+      break;
+    case TCPFastOpenSecret::SOCKET_ERROR_STATE:
+      PR_SetError(secret->mCondition, 0);
+      rv = PR_FAILURE;
+  }
+  return rv;
+}
+
+static PRStatus TCPFastOpenClose(PRFileDesc* fd) {
+  if (!fd) {
+    return PR_FAILURE;
+  }
+
+  PRFileDesc* layer = PR_PopIOLayer(fd, PR_TOP_IO_LAYER);
+
+  MOZ_RELEASE_ASSERT(layer && layer->identity == sTCPFastOpenLayerIdentity,
+                     "TCP Fast Open Layer not on top of stack");
+
+  TCPFastOpenSecret* secret =
+      reinterpret_cast<TCPFastOpenSecret*>(layer->secret);
+  layer->secret = nullptr;
+  layer->dtor(layer);
+  delete secret;
+  return fd->methods->close(fd);
+}
+
+static PRStatus TCPFastOpenGetpeername(PRFileDesc* fd, PRNetAddr* addr) {
+  MOZ_RELEASE_ASSERT(fd);
+  MOZ_RELEASE_ASSERT(addr);
+
+  MOZ_RELEASE_ASSERT(fd->identity == sTCPFastOpenLayerIdentity);
+
+  TCPFastOpenSecret* secret = reinterpret_cast<TCPFastOpenSecret*>(fd->secret);
+  if (secret->mState == TCPFastOpenSecret::WAITING_FOR_CONNECT) {
+    PR_SetError(PR_NOT_CONNECTED_ERROR, 0);
+    return PR_FAILURE;
+  }
+
+  memcpy(addr, &secret->mAddr, sizeof(secret->mAddr));
+  return PR_SUCCESS;
+}
+
+static PRInt16 TCPFastOpenPoll(PRFileDesc* fd, PRInt16 how_flags,
+                               PRInt16* p_out_flags) {
+  MOZ_RELEASE_ASSERT(fd);
+  MOZ_RELEASE_ASSERT(fd->identity == sTCPFastOpenLayerIdentity);
+
+  TCPFastOpenSecret* secret = reinterpret_cast<TCPFastOpenSecret*>(fd->secret);
+  if (secret->mFirstPacketBufLen) {
+    how_flags |= PR_POLL_WRITE;
+  }
+
+  return fd->lower->methods->poll(fd->lower, how_flags, p_out_flags);
+}
+
+nsresult AttachTCPFastOpenIOLayer(PRFileDesc* fd) {
+  MOZ_ASSERT(OnSocketThread(), "not on socket thread");
+
+  if (!sTCPFastOpenLayerMethodsPtr) {
+    sTCPFastOpenLayerIdentity = PR_GetUniqueIdentity("TCPFastOpen Layer");
+    sTCPFastOpenLayerMethods = *PR_GetDefaultIOMethods();
+    sTCPFastOpenLayerMethods.connect = TCPFastOpenConnect;
+    sTCPFastOpenLayerMethods.send = TCPFastOpenSend;
+    sTCPFastOpenLayerMethods.write = TCPFastOpenWrite;
+    sTCPFastOpenLayerMethods.recv = TCPFastOpenRecv;
+    sTCPFastOpenLayerMethods.read = TCPFastOpenRead;
+    sTCPFastOpenLayerMethods.connectcontinue = TCPFastOpenConnectContinue;
+    sTCPFastOpenLayerMethods.close = TCPFastOpenClose;
+    sTCPFastOpenLayerMethods.getpeername = TCPFastOpenGetpeername;
+    sTCPFastOpenLayerMethods.poll = TCPFastOpenPoll;
+    sTCPFastOpenLayerMethodsPtr = &sTCPFastOpenLayerMethods;
+  }
+
+  PRFileDesc* layer = PR_CreateIOLayerStub(sTCPFastOpenLayerIdentity,
+                                           sTCPFastOpenLayerMethodsPtr);
+
+  if (!layer) {
+    return NS_ERROR_FAILURE;
+  }
+
+  TCPFastOpenSecret* secret = new TCPFastOpenSecret();
+
+  layer->secret = reinterpret_cast<PRFilePrivate*>(secret);
+
+  PRStatus status = PR_PushIOLayer(fd, PR_NSPR_IO_LAYER, layer);
+
+  if (status == PR_FAILURE) {
+    delete secret;
+    PR_Free(layer);  // PR_CreateIOLayerStub() uses PR_Malloc().
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
+
+void TCPFastOpenFinish(PRFileDesc* fd, PRErrorCode& err,
+                       bool& fastOpenNotSupported, uint8_t& tfoStatus) {
+  PRFileDesc* tfoFd = PR_GetIdentitiesLayer(fd, sTCPFastOpenLayerIdentity);
+  MOZ_RELEASE_ASSERT(tfoFd);
+  MOZ_ASSERT(OnSocketThread(), "not on socket thread");
+
+  TCPFastOpenSecret* secret =
+      reinterpret_cast<TCPFastOpenSecret*>(tfoFd->secret);
+
+  MOZ_ASSERT(secret->mState ==
+             TCPFastOpenSecret::COLLECT_DATA_FOR_FIRST_PACKET);
+
+  fastOpenNotSupported = false;
+  tfoStatus = TFO_NOT_TRIED;
+  PRErrorCode result = 0;
+
+  // If we do not have data to send with syn packet or nspr version does not
+  // have sendto implemented we will call normal connect.
+  // If sendto is not implemented it points to _PR_InvalidInt, therefore we
+  // check if sendto != _PR_InvalidInt. _PR_InvalidInt is exposed so we use
+  // reserved_fn_0 which also points to _PR_InvalidInt.
+  if (!secret->mFirstPacketBufLen ||
+      (tfoFd->lower->methods->sendto ==
+       (PRSendtoFN)tfoFd->lower->methods->reserved_fn_0)) {
+    // Because of the way our nsHttpTransaction dispatch work, it can happened
+    // that data has not been written into the socket.
+    // In this case we can just call connect.
+    PRInt32 rv = (tfoFd->lower->methods->connect)(tfoFd->lower, &secret->mAddr,
+                                                  PR_INTERVAL_NO_WAIT);
+    if (rv == PR_SUCCESS) {
+      result = PR_IS_CONNECTED_ERROR;
+    } else {
+      result = PR_GetError();
+    }
+    if (tfoFd->lower->methods->sendto ==
+        (PRSendtoFN)tfoFd->lower->methods->reserved_fn_0) {
+      // sendto is not implemented, it is equal to _PR_InvalidInt!
+      // We will disable Fast Open.
+      SOCKET_LOG(("TCPFastOpenFinish - sendto not implemented.\n"));
+      fastOpenNotSupported = true;
+      tfoStatus = TFO_DISABLED;
+    }
+  } else {
+    // We have some data ready in the buffer we will send it with the syn
+    // packet.
+    PRInt32 rv = (tfoFd->lower->methods->sendto)(
+        tfoFd->lower, secret->mFirstPacketBuf, secret->mFirstPacketBufLen,
+        0,  // flags
+        &secret->mAddr, PR_INTERVAL_NO_WAIT);
+
+    SOCKET_LOG(("TCPFastOpenFinish - sendto result=%d.\n", rv));
+    if (rv > 0) {
+      result = PR_IN_PROGRESS_ERROR;
+      secret->mFirstPacketBufLen -= rv;
+      if (secret->mFirstPacketBufLen) {
+        memmove(secret->mFirstPacketBuf, secret->mFirstPacketBuf + rv,
+                secret->mFirstPacketBufLen);
+      }
+      tfoStatus = TFO_DATA_SENT;
+    } else {
+      result = PR_GetError();
+      SOCKET_LOG(("TCPFastOpenFinish - sendto error=%d.\n", result));
+
+      if (result ==
+          PR_NOT_TCP_SOCKET_ERROR) {  // SendTo will return
+                                      // PR_NOT_TCP_SOCKET_ERROR if TCP Fast
+                                      // Open is turned off on Linux.
+        // We can call connect again.
+        fastOpenNotSupported = true;
+        rv = (tfoFd->lower->methods->connect)(tfoFd->lower, &secret->mAddr,
+                                              PR_INTERVAL_NO_WAIT);
+
+        if (rv == PR_SUCCESS) {
+          result = PR_IS_CONNECTED_ERROR;
+        } else {
+          result = PR_GetError();
+        }
+        tfoStatus = TFO_DISABLED;
+      } else {
+        tfoStatus = TFO_TRIED;
+      }
+    }
+  }
+
+  if (result == PR_IN_PROGRESS_ERROR) {
+    secret->mState = TCPFastOpenSecret::WAITING_FOR_CONNECTCONTINUE;
+  } else {
+    // If the error is not PR_IN_PROGRESS_ERROR, change the state to CONNECT so
+    // that recv/send can perform recv/send on the next lower layer and pick up
+    // the real error. This is really important!
+    // The result can also be PR_IS_CONNECTED_ERROR, that should change the
+    // state to CONNECT anyway.
+    secret->mState = TCPFastOpenSecret::CONNECTED;
+  }
+  err = result;
+}
+
+/* This function returns the size of the remaining free space in the
+ * first_packet_buffer. This will be used by transactions with a tls layer. For
+ * other transactions it is not necessary. The tls transactions make a tls
+ * record before writing to this layer and if the record is too big the part
+ * that does not have place in the mFirstPacketBuf will be saved on the tls
+ * layer. During TFO we cannot send more than TFO_MAX_PACKET_SIZE_IPV4/6 bytes,
+ * so if we have a big tls record, this record is encrypted with 0RTT key,
+ * tls-early-data can be rejected and than we still need to send the rest of the
+ * record.
+ */
+int32_t TCPFastOpenGetBufferSizeLeft(PRFileDesc* fd) {
+  PRFileDesc* tfoFd = PR_GetIdentitiesLayer(fd, sTCPFastOpenLayerIdentity);
+  MOZ_RELEASE_ASSERT(tfoFd);
+  MOZ_ASSERT(OnSocketThread(), "not on socket thread");
+
+  TCPFastOpenSecret* secret =
+      reinterpret_cast<TCPFastOpenSecret*>(tfoFd->secret);
+
+  if (secret->mState != TCPFastOpenSecret::COLLECT_DATA_FOR_FIRST_PACKET) {
+    return 0;
+  }
+
+  int32_t sizeLeft = (secret->mAddr.raw.family == PR_AF_INET)
+                         ? TFO_MAX_PACKET_SIZE_IPV4
+                         : TFO_MAX_PACKET_SIZE_IPV6;
+  MOZ_ASSERT(secret->mFirstPacketBufLen <= sizeLeft);
+  sizeLeft -= secret->mFirstPacketBufLen;
+
+  SOCKET_LOG(("TCPFastOpenGetBufferSizeLeft=%d.\n", sizeLeft));
+
+  return (sizeLeft > TFO_TLS_RECORD_HEADER_SIZE)
+             ? sizeLeft - TFO_TLS_RECORD_HEADER_SIZE
+             : 0;
+}
+
+bool TCPFastOpenGetCurrentBufferSize(PRFileDesc* fd) {
+  PRFileDesc* tfoFd = PR_GetIdentitiesLayer(fd, sTCPFastOpenLayerIdentity);
+  MOZ_RELEASE_ASSERT(tfoFd);
+  MOZ_ASSERT(OnSocketThread(), "not on socket thread");
+
+  TCPFastOpenSecret* secret =
+      reinterpret_cast<TCPFastOpenSecret*>(tfoFd->secret);
+
+  return secret->mFirstPacketBufLen;
+}
+
+bool TCPFastOpenFlushBuffer(PRFileDesc* fd) {
+  PRFileDesc* tfoFd = PR_GetIdentitiesLayer(fd, sTCPFastOpenLayerIdentity);
+  MOZ_RELEASE_ASSERT(tfoFd);
+  MOZ_ASSERT(OnSocketThread(), "not on socket thread");
+
+  TCPFastOpenSecret* secret =
+      reinterpret_cast<TCPFastOpenSecret*>(tfoFd->secret);
+  MOZ_ASSERT(secret->mState == TCPFastOpenSecret::CONNECTED);
+
+  if (secret->mFirstPacketBufLen) {
+    SOCKET_LOG(
+        ("TCPFastOpenFlushBuffer - %d bytes to drain from "
+         "mFirstPacketBufLen.\n",
+         secret->mFirstPacketBufLen));
+    PRInt32 rv = (tfoFd->lower->methods->send)(
+        tfoFd->lower, secret->mFirstPacketBuf, secret->mFirstPacketBufLen,
+        0,  // flags
+        PR_INTERVAL_NO_WAIT);
+    if (rv <= 0) {
+      PRErrorCode err = PR_GetError();
+      if (err == PR_WOULD_BLOCK_ERROR) {
+        // We still need to send this data.
+        return true;
+      }
+      // There is an error, let nsSocketTransport pick it up properly.
+      secret->mCondition = err;
+      secret->mState = TCPFastOpenSecret::SOCKET_ERROR_STATE;
+      return false;
+    }
+
+    secret->mFirstPacketBufLen -= rv;
+    if (secret->mFirstPacketBufLen) {
+      memmove(secret->mFirstPacketBuf, secret->mFirstPacketBuf + rv,
+              secret->mFirstPacketBufLen);
+    }
+  }
+  return secret->mFirstPacketBufLen;
+}
+
+}  // namespace net
+}  // namespace mozilla