libbinder: replace RpcTransport::peek() with pollRead()

peek uses MSG_PEEK internally which only works with sockets.
This refactors that function into a more specific pollRead()
which works for e.g. pipes and other files.

Bug: 224644083
Test: atest binderRpcTest
Change-Id: I340fa7ee7a7bb2077115fc28835bcadf67db03d9

4 files changed, 21 insertions, 15 deletions

diff --git a/libs/binder/RpcState.cpp b/libs/binder/RpcState.cpp
index 6d89064a5d..4ef9cd859d 100644
--- a/libs/binder/RpcState.cpp
+++ b/libs/binder/RpcState.cpp
@@ -661,13 +661,10 @@ status_t RpcState::getAndExecuteCommand(const sp<RpcSession::RpcConnection>& con
 
 status_t RpcState::drainCommands(const sp<RpcSession::RpcConnection>& connection,
                                  const sp<RpcSession>& session, CommandType type) {
-    uint8_t buf;
     while (true) {
-        size_t num_bytes;
-        status_t status = connection->rpcTransport->peek(&buf, sizeof(buf), &num_bytes);
+        status_t status = connection->rpcTransport->pollRead();
         if (status == WOULD_BLOCK) break;
         if (status != OK) return status;
-        if (!num_bytes) break;
 
         status = getAndExecuteCommand(connection, session, type);
         if (status != OK) return status;
diff --git a/libs/binder/RpcTransportRaw.cpp b/libs/binder/RpcTransportRaw.cpp
index 7cfc78082e..f5cc41332e 100644
--- a/libs/binder/RpcTransportRaw.cpp
+++ b/libs/binder/RpcTransportRaw.cpp
@@ -32,19 +32,22 @@ namespace {
 class RpcTransportRaw : public RpcTransport {
 public:
     explicit RpcTransportRaw(android::base::unique_fd socket) : mSocket(std::move(socket)) {}
-    status_t peek(void* buf, size_t size, size_t* out_size) override {
-        ssize_t ret = TEMP_FAILURE_RETRY(::recv(mSocket.get(), buf, size, MSG_PEEK));
+    status_t pollRead(void) override {
+        uint8_t buf;
+        ssize_t ret = TEMP_FAILURE_RETRY(
+                ::recv(mSocket.get(), &buf, sizeof(buf), MSG_PEEK | MSG_DONTWAIT));
         if (ret < 0) {
             int savedErrno = errno;
             if (savedErrno == EAGAIN || savedErrno == EWOULDBLOCK) {
                 return WOULD_BLOCK;
             }
 
-            LOG_RPC_DETAIL("RpcTransport peek(): %s", strerror(savedErrno));
+            LOG_RPC_DETAIL("RpcTransport poll(): %s", strerror(savedErrno));
             return -savedErrno;
+        } else if (ret == 0) {
+            return DEAD_OBJECT;
         }
 
-        *out_size = static_cast<size_t>(ret);
         return OK;
     }
 
diff --git a/libs/binder/RpcTransportTls.cpp b/libs/binder/RpcTransportTls.cpp
index bc68c379ce..85c7655727 100644
--- a/libs/binder/RpcTransportTls.cpp
+++ b/libs/binder/RpcTransportTls.cpp
@@ -277,7 +277,7 @@ class RpcTransportTls : public RpcTransport {
 public:
     RpcTransportTls(android::base::unique_fd socket, Ssl ssl)
           : mSocket(std::move(socket)), mSsl(std::move(ssl)) {}
-    status_t peek(void* buf, size_t size, size_t* out_size) override;
+    status_t pollRead(void) override;
     status_t interruptableWriteFully(FdTrigger* fdTrigger, iovec* iovs, int niovs,
                                      const std::function<status_t()>& altPoll) override;
     status_t interruptableReadFully(FdTrigger* fdTrigger, iovec* iovs, int niovs,
@@ -289,9 +289,9 @@ private:
 };
 
 // Error code is errno.
-status_t RpcTransportTls::peek(void* buf, size_t size, size_t* out_size) {
-    size_t todo = std::min<size_t>(size, std::numeric_limits<int>::max());
-    auto [ret, errorQueue] = mSsl.call(SSL_peek, buf, static_cast<int>(todo));
+status_t RpcTransportTls::pollRead(void) {
+    uint8_t buf;
+    auto [ret, errorQueue] = mSsl.call(SSL_peek, &buf, sizeof(buf));
     if (ret < 0) {
         int err = mSsl.getError(ret);
         if (err == SSL_ERROR_WANT_WRITE || err == SSL_ERROR_WANT_READ) {
@@ -304,7 +304,6 @@ status_t RpcTransportTls::peek(void* buf, size_t size, size_t* out_size) {
     }
     errorQueue.clear();
     LOG_TLS_DETAIL("TLS: Peeked %d bytes!", ret);
-    *out_size = static_cast<size_t>(ret);
     return OK;
 }
 
diff --git a/libs/binder/include/binder/RpcTransport.h b/libs/binder/include/binder/RpcTransport.h
index 751c4f905d..2c864f82f5 100644
--- a/libs/binder/include/binder/RpcTransport.h
+++ b/libs/binder/include/binder/RpcTransport.h
@@ -39,8 +39,15 @@ class RpcTransport {
 public:
     virtual ~RpcTransport() = default;
 
-    // replacement of ::recv(MSG_PEEK). Error code may not be set if TLS is enabled.
-    [[nodiscard]] virtual status_t peek(void *buf, size_t size, size_t *out_size) = 0;
+    /**
+     * Poll the transport to check whether there is any data ready to read.
+     *
+     * Return:
+     *   OK - There is data available on this transport
+     *   WOULDBLOCK - No data is available
+     *   error - any other error
+     */
+    [[nodiscard]] virtual status_t pollRead(void) = 0;
 
     /**
      * Read (or write), but allow to be interrupted by a trigger.