binder: libbinder_tls ensure to check trigger at least once.

If the SSL_write / SSL_read finishes in one round, we might have
never checked the fdTrigger. Ensure to check it at least once
before SSL_write / SSL_read.

Test: binderRpcTest
Bug: 190868302
Change-Id: I4588475354025f8f02d3eb998e9390d5babbc860
diff --git a/libs/binder/RpcTransportTls.cpp b/libs/binder/RpcTransportTls.cpp
index 6d39890..a102913 100644
--- a/libs/binder/RpcTransportTls.cpp
+++ b/libs/binder/RpcTransportTls.cpp
@@ -304,6 +304,8 @@
 private:
     android::base::unique_fd mSocket;
     Ssl mSsl;
+
+    static status_t isTriggered(FdTrigger* fdTrigger);
 };
 
 // Error code is errno.
@@ -324,6 +326,15 @@
     return ret;
 }
 
+status_t RpcTransportTls::isTriggered(FdTrigger* fdTrigger) {
+    auto ret = fdTrigger->isTriggeredPolled();
+    if (!ret.ok()) {
+        ALOGE("%s: %s", __PRETTY_FUNCTION__, ret.error().message().c_str());
+        return ret.error().code() == 0 ? UNKNOWN_ERROR : -ret.error().code();
+    }
+    return OK;
+}
+
 status_t RpcTransportTls::interruptableWriteFully(FdTrigger* fdTrigger, const void* data,
                                                   size_t size) {
     auto buffer = reinterpret_cast<const uint8_t*>(data);
@@ -331,6 +342,10 @@
 
     MAYBE_WAIT_IN_FLAKE_MODE;
 
+    // Before doing any I/O, check trigger once. This ensures the trigger is checked at least
+    // once. The trigger is also checked via triggerablePoll() after every SSL_write().
+    if (status_t status = isTriggered(fdTrigger); status != OK) return status;
+
     while (buffer < end) {
         size_t todo = std::min<size_t>(end - buffer, std::numeric_limits<int>::max());
         auto [writeSize, errorQueue] = mSsl.call(SSL_write, buffer, todo);
@@ -358,6 +373,10 @@
 
     MAYBE_WAIT_IN_FLAKE_MODE;
 
+    // Before doing any I/O, check trigger once. This ensures the trigger is checked at least
+    // once. The trigger is also checked via triggerablePoll() after every SSL_write().
+    if (status_t status = isTriggered(fdTrigger); status != OK) return status;
+
     while (buffer < end) {
         size_t todo = std::min<size_t>(end - buffer, std::numeric_limits<int>::max());
         auto [readSize, errorQueue] = mSsl.call(SSL_read, buffer, todo);