binder: Refactor: move FdTrigger to its own file / class.

Also move interruptable*Fully functions to RpcTransport so that we no
longer need pending() and pollSocket().

This also allows us to hide send() / recv(); callers should use
interruptableWriteFully / interruptableReadFully instead, because
those repsect the shutdown trigger.
- Fix one place to use interruptableWriteFully() instead of send() when
  sending header.

interruptable*Fully are marked as virtual functions because TLS will
need to poll with events dynamically adjusted. See follow-up CLs for
TLS implementation.

Test: TH
Bug: 190868302
Change-Id: I131eed3a637b3a30280b320966e466bbfac0fc45
diff --git a/libs/binder/FdTrigger.cpp b/libs/binder/FdTrigger.cpp
new file mode 100644
index 0000000..e38ac63
--- /dev/null
+++ b/libs/binder/FdTrigger.cpp
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#define LOG_TAG "FdTrigger"
+#include <log/log.h>
+
+#include <poll.h>
+
+#include <android-base/macros.h>
+
+#include "FdTrigger.h"
+namespace android {
+
+std::unique_ptr<FdTrigger> FdTrigger::make() {
+    auto ret = std::make_unique<FdTrigger>();
+    if (!android::base::Pipe(&ret->mRead, &ret->mWrite)) {
+        ALOGE("Could not create pipe %s", strerror(errno));
+        return nullptr;
+    }
+    return ret;
+}
+
+void FdTrigger::trigger() {
+    mWrite.reset();
+}
+
+bool FdTrigger::isTriggered() {
+    return mWrite == -1;
+}
+
+status_t FdTrigger::triggerablePoll(base::borrowed_fd fd, int16_t event) {
+    while (true) {
+        pollfd pfd[]{{.fd = fd.get(), .events = static_cast<int16_t>(event), .revents = 0},
+                     {.fd = mRead.get(), .events = POLLHUP, .revents = 0}};
+        int ret = TEMP_FAILURE_RETRY(poll(pfd, arraysize(pfd), -1));
+        if (ret < 0) {
+            return -errno;
+        }
+        if (ret == 0) {
+            continue;
+        }
+        if (pfd[1].revents & POLLHUP) {
+            return -ECANCELED;
+        }
+        return pfd[0].revents & event ? OK : DEAD_OBJECT;
+    }
+}
+
+} // namespace android