Extend integration test to test sequence of FUSE operation

Original FUSE integration test has limited capabilities. To test more
situations, the new integration test framework introduces a protocol
to communicate between testing thread and the FUSE server. In summary,
this change includes:

1. Remove CompareResult() and break SetExpected() into
   SetServerResponse() and GetServerActualRequest(). We no longer set
   up an expected request because we want to retrieve the actual FUSE
   request made to the FUSE server and check in the testing thread.

2. Declare a serial buffer data structure to save the received requests
   and expected responses sequentially. The data structure contains a
   cursor to indicate the progress of accessing. This change makes
   sequential SetServerResponse() and GetServerActualRequest() possible.

3. Replace 2 single directional pipes with 1 bi-directional socketpair.
   A protocol which starts with FuseTestCmd is used between the testing
   thread and the FUSE server to provide various functionality.

Fixes #3405

1 files changed, 131 insertions, 41 deletions

diff --git a/test/fuse/linux/fuse_base.h b/test/fuse/linux/fuse_base.h
index 3a2f255a9..b610d0f54 100644
--- a/test/fuse/linux/fuse_base.h
+++ b/test/fuse/linux/fuse_base.h
@@ -16,8 +16,10 @@
 #define GVISOR_TEST_FUSE_FUSE_BASE_H_
 
 #include <linux/fuse.h>
+#include <string.h>
 #include <sys/uio.h>
 
+#include <iostream>
 #include <vector>
 
 #include "gtest/gtest.h"
@@ -29,68 +31,156 @@ namespace testing {
 
 constexpr char kMountOpts[] = "rootmode=755,user_id=0,group_id=0";
 
-class FuseTest : public ::testing::Test {
+// Internal commands used to communicate between testing thread and the FUSE
+// server. See test/fuse/README.md for further detail.
+enum class FuseTestCmd {
+  kSetResponse = 0,
+  kGetRequest,
+};
+
+// Holds the information of a memory block in a serial buffer.
+struct FuseMemBlock {
+  uint32_t opcode;
+  size_t offset;
+  size_t len;
+};
+
+// A wrapper of a simple serial buffer that can be used with read(2) and
+// write(2). Contains a cursor to indicate accessing. This class is not thread-
+// safe and can only be used in single-thread version.
+class FuseMemBuffer {
  public:
-  FuseTest() {
-    buf_.resize(FUSE_MIN_READ_BUFFER);
-    mem_in_.resize(FUSE_MIN_READ_BUFFER);
-    mem_out_.resize(FUSE_MIN_READ_BUFFER);
+  FuseMemBuffer() : cursor_(0) {
+    // To read from /dev/fuse, a buffer needs at least FUSE_MIN_READ_BUFFER
+    // bytes to avoid EINVAL. FuseMemBuffer holds memory that can accommodate
+    // a sequence of FUSE request/response, so it is initiated with double
+    // minimal requirement.
+    mem_.resize(FUSE_MIN_READ_BUFFER * 2);
   }
+
+  // Returns whether there is no memory block.
+  bool Empty() { return blocks_.empty(); }
+
+  // Returns if there is no more remaining memory blocks.
+  bool End() { return cursor_ == blocks_.size(); }
+
+  // Returns how many bytes that have been received.
+  size_t UsedBytes() {
+    return Empty() ? 0 : blocks_.back().offset + blocks_.back().len;
+  }
+
+  // Returns the available bytes remains in the serial buffer.
+  size_t AvailBytes() { return mem_.size() - UsedBytes(); }
+
+  // Appends a memory block information that starts at the tail of the serial
+  // buffer. /dev/fuse requires at least FUSE_MIN_READ_BUFFER bytes to read, or
+  // it will issue EINVAL. If it is not enough, just double the buffer length.
+  void AddMemBlock(uint32_t opcode, void* data, size_t len) {
+    if (AvailBytes() < FUSE_MIN_READ_BUFFER) {
+      mem_.resize(mem_.size() << 1);
+    }
+    size_t offset = UsedBytes();
+    memcpy(mem_.data() + offset, data, len);
+    blocks_.push_back(FuseMemBlock{opcode, offset, len});
+  }
+
+  // Returns the memory address at a specific offset. Used with read(2) or
+  // write(2).
+  char* DataAtOffset(size_t offset) { return mem_.data() + offset; }
+
+  // Returns current memory block pointed by the cursor and increase by 1.
+  FuseMemBlock Next() {
+    if (End()) {
+      std::cerr << "Buffer is already exhausted." << std::endl;
+      return FuseMemBlock{};
+    }
+    return blocks_[cursor_++];
+  }
+
+  // Returns the number of the blocks that has not been requested.
+  size_t RemainingBlocks() { return blocks_.size() - cursor_; }
+
+ private:
+  size_t cursor_;
+  std::vector<FuseMemBlock> blocks_;
+  std::vector<char> mem_;
+};
+
+// FuseTest base class is useful in FUSE integration test. Inherit this class
+// to automatically set up a fake FUSE server and use the member functions
+// to manipulate with it. Refer to test/fuse/README.md for detailed explanation.
+class FuseTest : public ::testing::Test {
+ public:
   void SetUp() override;
   void TearDown() override;
 
-  // CompareRequest is used by the FUSE server and should be implemented to
-  // compare different FUSE operations. It compares the actual FUSE input
-  // request with the expected one set by `SetExpected()`.
-  virtual bool CompareRequest(void* expected_mem, size_t expected_len,
-                              void* real_mem, size_t real_len);
-
-  // SetExpected is called by the testing main thread. Writes a request-
-  // response pair into FUSE server's member variables via pipe.
-  void SetExpected(struct iovec* iov_in, int iov_in_cnt, struct iovec* iov_out,
-                   int iov_out_cnt);
+  // Called by the testing thread to set up a fake response for an expected
+  // opcode via socket. This can be used multiple times to define a sequence of
+  // expected FUSE reactions.
+  void SetServerResponse(uint32_t opcode, std::vector<struct iovec>& iovecs);
 
-  // WaitCompleted waits for FUSE server to complete its processing. It
-  // complains if the FUSE server responds failure during tests.
-  void WaitCompleted();
+  // Called by the testing thread to ask the FUSE server for its next received
+  // FUSE request. Be sure to use the corresponding struct of iovec to receive
+  // data from server.
+  void GetServerActualRequest(std::vector<struct iovec>& iovecs);
 
  protected:
   TempPath mount_point_;
 
  private:
+  // Opens /dev/fuse and inherit the file descriptor for the FUSE server.
   void MountFuse();
+
+  // Unmounts the mountpoint of the FUSE server.
   void UnmountFuse();
 
-  // ConsumeFuseInit is only used during FUSE server setup.
-  PosixError ConsumeFuseInit();
+  // Creates a socketpair for communication and forks FUSE server.
+  void SetUpFuseServer();
 
-  // ReceiveExpected is the FUSE server side's corresponding code of
-  // `SetExpected()`. Save the request-response pair into its memory.
-  void ReceiveExpected();
+  // Waits for FUSE server to complete its processing. Complains if the FUSE
+  // server responds any failure during tests.
+  void WaitServerComplete();
 
-  // MarkDone is used by the FUSE server to tell testing main if it's OK to
-  // proceed next command.
-  void MarkDone(bool success);
+  // The FUSE server stays here and waits next command or FUSE request until it
+  // is terminated.
+  void ServerFuseLoop();
 
-  // FuseLoop is where the FUSE server stay until it is terminated.
-  void FuseLoop();
+  // Used by the FUSE server to tell testing thread if it is OK to proceed next
+  // command. Will be issued after processing each FuseTestCmd.
+  void ServerCompleteWith(bool success);
 
-  // SetUpFuseServer creates 2 pipes for communication and forks FUSE server.
-  void SetUpFuseServer();
+  // Consumes the first FUSE request when mounting FUSE. Replies with a
+  // response with empty payload.
+  PosixError ServerConsumeFuseInit();
+
+  // A command switch that dispatch different FuseTestCmd to its handler.
+  void ServerHandleCommand();
+
+  // The FUSE server side's corresponding code of `SetServerResponse()`.
+  // Handles `kSetResponse` command. Saves the fake response into its output
+  // memory queue.
+  void ServerReceiveResponse();
+
+  // The FUSE server side's corresponding code of `GetServerActualRequest()`.
+  // Handles `kGetRequest` command. Sends the next received request pointed by
+  // the cursor.
+  void ServerSendReceivedRequest();
 
-  // GetPayloadSize is a helper function to get the number of bytes of a
-  // specific FUSE operation struct.
-  size_t GetPayloadSize(uint32_t opcode, bool in);
+  // Handles FUSE request sent to /dev/fuse by its saved responses.
+  void ServerProcessFuseRequest();
+
+  // Responds to FUSE request with a saved data.
+  void ServerRespondFuseSuccess(FuseMemBuffer& mem_buf,
+                                const FuseMemBlock& block, uint64_t unique);
+
+  // Responds an error header to /dev/fuse when bad thing happens.
+  void ServerRespondFuseError(uint64_t unique);
 
   int dev_fd_;
-  int set_expected_[2];
-  int done_[2];
-
-  std::vector<char> buf_;
-  std::vector<char> mem_in_;
-  std::vector<char> mem_out_;
-  ssize_t len_in_;
-  ssize_t len_out_;
+  int sock_[2];
+
+  FuseMemBuffer requests_;
+  FuseMemBuffer responses_;
 };
 
 }  // namespace testing