LibIPC: Prepend each message with its size

This makes it much simpler to determine when we've read a complete message, and
will make it possible to integrate recvfd() in the future commit.

1 files changed, 30 insertions, 17 deletions

diff --git a/Libraries/LibIPC/Connection.h b/Libraries/LibIPC/Connection.h
index 4db21a6dc7..781a2d4c4f 100644
--- a/Libraries/LibIPC/Connection.h
+++ b/Libraries/LibIPC/Connection.h
@@ -35,6 +35,7 @@
 #include <LibCore/SyscallUtils.h>
 #include <LibCore/Timer.h>
 #include <LibIPC/Message.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/select.h>
@@ -75,10 +76,13 @@ public:
             return;
 
         auto buffer = message.encode();
+        // Prepend the message size.
+        uint32_t message_size = buffer.size();
+        buffer.prepend(reinterpret_cast<const u8*>(&message_size), sizeof(message_size));
 
-        auto bytes_remaining = buffer.size();
-        while (bytes_remaining) {
-            auto nwritten = write(m_socket->fd(), buffer.data(), buffer.size());
+        size_t total_nwritten = 0;
+        while (total_nwritten < buffer.size()) {
+            auto nwritten = write(m_socket->fd(), buffer.data() + total_nwritten, buffer.size() - total_nwritten);
             if (nwritten < 0) {
                 switch (errno) {
                 case EPIPE:
@@ -95,7 +99,7 @@ public:
                     return;
                 }
             }
-            bytes_remaining -= nwritten;
+            total_nwritten += nwritten;
         }
 
         m_responsiveness_timer->start();
@@ -190,25 +194,34 @@ protected:
             did_become_responsive();
         }
 
-        size_t decoded_bytes = 0;
-        for (size_t index = 0; index < bytes.size(); index += decoded_bytes) {
+        size_t index = 0;
+        uint32_t message_size = 0;
+        for (; index + sizeof(message_size) < bytes.size(); index += message_size) {
+            message_size = *reinterpret_cast<uint32_t*>(bytes.data() + index);
+            if (message_size == 0 || bytes.size() - index - sizeof(uint32_t) < message_size)
+                break;
+            index += sizeof(message_size);
             auto remaining_bytes = ByteBuffer::wrap(bytes.data() + index, bytes.size() - index);
-            if (auto message = LocalEndpoint::decode_message(remaining_bytes, decoded_bytes)) {
+            if (auto message = LocalEndpoint::decode_message(remaining_bytes)) {
                 m_unprocessed_messages.append(message.release_nonnull());
-            } else if (auto message = PeerEndpoint::decode_message(remaining_bytes, decoded_bytes)) {
+            } else if (auto message = PeerEndpoint::decode_message(remaining_bytes)) {
                 m_unprocessed_messages.append(message.release_nonnull());
             } else {
-                // Sometimes we might receive a partial message. That's okay, just stash away
-                // the unprocessed bytes and we'll prepend them to the next incoming message
-                // in the next run of this function.
-                if (!m_unprocessed_bytes.is_empty()) {
-                    dbg() << *this << "::drain_messages_from_peer: Already have unprocessed bytes";
-                    shutdown();
-                }
-                m_unprocessed_bytes = remaining_bytes.isolated_copy();
+                dbgln("Failed to parse a message");
                 break;
             }
-            ASSERT(decoded_bytes);
+        }
+
+        if (index < bytes.size()) {
+            // Sometimes we might receive a partial message. That's okay, just stash away
+            // the unprocessed bytes and we'll prepend them to the next incoming message
+            // in the next run of this function.
+            auto remaining_bytes = ByteBuffer::wrap(bytes.data() + index, bytes.size() - index);
+            if (!m_unprocessed_bytes.is_empty()) {
+                dbg() << *this << "::drain_messages_from_peer: Already have unprocessed bytes";
+                shutdown();
+            }
+            m_unprocessed_bytes = remaining_bytes.isolated_copy();
         }
 
         if (!m_unprocessed_messages.is_empty()) {