Don't use Asserts to check for violations of replication protocol.

Using an Assert to check the validity of incoming messages is an
extremely poor decision.  In a debug build, it should not be that easy
for a broken or malicious remote client to crash the logrep worker.
The consequences could be even worse in non-debug builds, which will
fail to make such checks at all, leading to who-knows-what misbehavior.
Hence, promote every Assert that could possibly be triggered by wrong
or out-of-order replication messages to a full test-and-ereport.

To avoid bloating the set of messages the translation team has to cope
with, establish a policy that replication protocol violation error
reports don't need to be translated.  Hence, all the new messages here
use errmsg_internal().  A couple of old messages are changed likewise
for consistency.

Along the way, fix some non-idiomatic or outright wrong uses of
hash_search().

Most of these mistakes are new with the "streaming replication"
patch (commit 464824323), but a couple go back a long way.
Back-patch as appropriate.

Discussion: https://postgr.es/m/1719083.1623351052@sss.pgh.pa.us

src/backend/replication/logical/reorderbuffer.c

@@ -1703,7 +1703,7 @@ ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
 		ent = (ReorderBufferTupleCidEnt *)
 			hash_search(txn->tuplecid_hash,
 						(void *) &key,
-						HASH_ENTER | HASH_FIND,
+						HASH_ENTER,
 						&found);
 		if (!found)
 		{

src/backend/replication/logical/worker.c

@@ -177,7 +177,7 @@ bool		in_remote_transaction = false;
 static XLogRecPtr remote_final_lsn = InvalidXLogRecPtr;
 
 /* fields valid only when processing streamed transaction */
-bool		in_streamed_transaction = false;
+static bool in_streamed_transaction = false;
 
 static TransactionId stream_xid = InvalidTransactionId;
 
@@ -345,7 +345,10 @@ handle_streamed_transaction(LogicalRepMsgType action, StringInfo s)
 	 */
 	xid = pq_getmsgint(s, 4);
 
-	Assert(TransactionIdIsValid(xid));
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid transaction ID in streamed replication transaction")));
 
 	/* Add the new subxact to the array (unless already there). */
 	subxact_info_add(xid);
@@ -785,7 +788,12 @@ apply_handle_commit(StringInfo s)
 
 	logicalrep_read_commit(s, &commit_data);
 
-	Assert(commit_data.commit_lsn == remote_final_lsn);
+	if (commit_data.commit_lsn != remote_final_lsn)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("incorrect commit LSN %X/%X in commit message (expected %X/%X)",
+								 LSN_FORMAT_ARGS(commit_data.commit_lsn),
+								 LSN_FORMAT_ARGS(remote_final_lsn))));
 
 	apply_handle_commit_internal(s, &commit_data);
 
@@ -812,7 +820,7 @@ apply_handle_origin(StringInfo s)
 		 (IsTransactionState() && !am_tablesync_worker())))
 		ereport(ERROR,
 				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg("ORIGIN message sent out of order")));
+				 errmsg_internal("ORIGIN message sent out of order")));
 }
 
 /*
@@ -824,7 +832,10 @@ apply_handle_stream_start(StringInfo s)
 	bool		first_segment;
 	HASHCTL		hash_ctl;
 
-	Assert(!in_streamed_transaction);
+	if (in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("duplicate STREAM START message")));
 
 	/*
 	 * Start a transaction on stream start, this transaction will be committed
@@ -841,6 +852,11 @@ apply_handle_stream_start(StringInfo s)
 	/* extract XID of the top-level transaction */
 	stream_xid = logicalrep_read_stream_start(s, &first_segment);
 
+	if (!TransactionIdIsValid(stream_xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid transaction ID in streamed replication transaction")));
+
 	/*
 	 * Initialize the xidhash table if we haven't yet. This will be used for
 	 * the entire duration of the apply worker so create it in permanent
@@ -873,7 +889,10 @@ apply_handle_stream_start(StringInfo s)
 static void
 apply_handle_stream_stop(StringInfo s)
 {
-	Assert(in_streamed_transaction);
+	if (!in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("STREAM STOP message without STREAM START")));
 
 	/*
 	 * Close the file with serialized changes, and serialize information about
@@ -905,7 +924,10 @@ apply_handle_stream_abort(StringInfo s)
 	TransactionId xid;
 	TransactionId subxid;
 
-	Assert(!in_streamed_transaction);
+	if (in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("STREAM ABORT message without STREAM STOP")));
 
 	logicalrep_read_stream_abort(s, &xid, &subxid);
 
@@ -932,7 +954,6 @@ apply_handle_stream_abort(StringInfo s)
 		 * performed rollback to savepoint for one of the earlier
 		 * sub-transaction.
 		 */
-
 		int64		i;
 		int64		subidx;
 		BufFile    *fd;
@@ -967,13 +988,15 @@ apply_handle_stream_abort(StringInfo s)
 			return;
 		}
 
-		Assert((subidx >= 0) && (subidx < subxact_data.nsubxacts));
-
 		ent = (StreamXidHash *) hash_search(xidhash,
 											(void *) &xid,
 											HASH_FIND,
-											&found);
+											NULL);
-		Assert(found);
+		if (!ent)
+			ereport(ERROR,
+					(errcode(ERRCODE_PROTOCOL_VIOLATION),
+					 errmsg_internal("transaction %u not found in stream XID hash table",
+									 xid)));
 
 		/* open the changes file */
 		changes_filename(path, MyLogicalRepWorker->subid, xid);
@@ -1006,13 +1029,15 @@ apply_handle_stream_commit(StringInfo s)
 	int			nchanges;
 	char		path[MAXPGPATH];
 	char	   *buffer = NULL;
-	bool		found;
 	LogicalRepCommitData commit_data;
 	StreamXidHash *ent;
 	MemoryContext oldcxt;
 	BufFile    *fd;
 
-	Assert(!in_streamed_transaction);
+	if (in_streamed_transaction)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("STREAM COMMIT message without STREAM STOP")));
 
 	xid = logicalrep_read_stream_commit(s, &commit_data);
 
@@ -1031,11 +1056,17 @@ apply_handle_stream_commit(StringInfo s)
 	/* open the spool file for the committed transaction */
 	changes_filename(path, MyLogicalRepWorker->subid, xid);
 	elog(DEBUG1, "replaying changes from file \"%s\"", path);
+
 	ent = (StreamXidHash *) hash_search(xidhash,
 										(void *) &xid,
 										HASH_FIND,
-										&found);
+										NULL);
-	Assert(found);
+	if (!ent)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("transaction %u not found in stream XID hash table",
+								 xid)));
+
 	fd = BufFileOpenShared(ent->stream_fileset, path, O_RDONLY);
 
 	buffer = palloc(BLCKSZ);
@@ -1080,7 +1111,9 @@ apply_handle_stream_commit(StringInfo s)
 					 errmsg("could not read from streaming transaction's changes file \"%s\": %m",
 							path)));
 
-		Assert(len > 0);
+		if (len <= 0)
+			elog(ERROR, "incorrect length %d in streaming transaction's changes file \"%s\"",
+				 len, path);
 
 		/* make sure we have sufficiently large buffer */
 		buffer = repalloc(buffer, len);
@@ -1108,7 +1141,7 @@ apply_handle_stream_commit(StringInfo s)
 		nchanges++;
 
 		if (nchanges % 1000 == 0)
-			elog(DEBUG1, "replayed %d changes from file '%s'",
+			elog(DEBUG1, "replayed %d changes from file \"%s\"",
 				 nchanges, path);
 	}
 
@@ -2053,7 +2086,8 @@ apply_dispatch(StringInfo s)
 
 	ereport(ERROR,
 			(errcode(ERRCODE_PROTOCOL_VIOLATION),
-			 errmsg("invalid logical replication message type \"%c\"", action)));
+			 errmsg_internal("invalid logical replication message type \"%c\"",
+							 action)));
 }
 
 /*
@@ -2589,20 +2623,19 @@ static void
 subxact_info_write(Oid subid, TransactionId xid)
 {
 	char		path[MAXPGPATH];
-	bool		found;
 	Size		len;
 	StreamXidHash *ent;
 	BufFile    *fd;
 
 	Assert(TransactionIdIsValid(xid));
 
-	/* find the xid entry in the xidhash */
+	/* Find the xid entry in the xidhash */
 	ent = (StreamXidHash *) hash_search(xidhash,
 										(void *) &xid,
 										HASH_FIND,
-										&found);
+										NULL);
-	/* we must found the entry for its top transaction by this time */
+	/* By this time we must have created the transaction entry */
-	Assert(found);
+	Assert(ent);
 
 	/*
 	 * If there is no subtransaction then nothing to do, but if already have
@@ -2667,13 +2700,11 @@ static void
 subxact_info_read(Oid subid, TransactionId xid)
 {
 	char		path[MAXPGPATH];
-	bool		found;
 	Size		len;
 	BufFile    *fd;
 	StreamXidHash *ent;
 	MemoryContext oldctx;
 
-	Assert(TransactionIdIsValid(xid));
 	Assert(!subxact_data.subxacts);
 	Assert(subxact_data.nsubxacts == 0);
 	Assert(subxact_data.nsubxacts_max == 0);
@@ -2682,7 +2713,12 @@ subxact_info_read(Oid subid, TransactionId xid)
 	ent = (StreamXidHash *) hash_search(xidhash,
 										(void *) &xid,
 										HASH_FIND,
-										&found);
+										NULL);
+	if (!ent)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("transaction %u not found in stream XID hash table",
+								 xid)));
 
 	/*
 	 * If subxact_fileset is not valid that mean we don't have any subxact
@@ -2836,14 +2872,17 @@ stream_cleanup_files(Oid subid, TransactionId xid)
 {
 	char		path[MAXPGPATH];
 	StreamXidHash *ent;
-	bool		found = false;
 
-	/* By this time we must have created the transaction entry */
+	/* Find the xid entry in the xidhash */
 	ent = (StreamXidHash *) hash_search(xidhash,
 										(void *) &xid,
 										HASH_FIND,
-										&found);
+										NULL);
-	Assert(found);
+	if (!ent)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("transaction %u not found in stream XID hash table",
+								 xid)));
 
 	/* Delete the change file and release the stream fileset memory */
 	changes_filename(path, subid, xid);
@@ -2893,9 +2932,9 @@ stream_open_file(Oid subid, TransactionId xid, bool first_segment)
 	/* create or find the xid entry in the xidhash */
 	ent = (StreamXidHash *) hash_search(xidhash,
 										(void *) &xid,
-										HASH_ENTER | HASH_FIND,
+										HASH_ENTER,
 										&found);
-	Assert(first_segment || found);
+
 	changes_filename(path, subid, xid);
 	elog(DEBUG1, "opening file \"%s\" for streamed changes", path);
 
@@ -2915,6 +2954,11 @@ stream_open_file(Oid subid, TransactionId xid, bool first_segment)
 		MemoryContext savectx;
 		SharedFileSet *fileset;
 
+		if (found)
+			ereport(ERROR,
+					(errcode(ERRCODE_PROTOCOL_VIOLATION),
+					 errmsg_internal("incorrect first-segment flag for streamed replication transaction")));
+
 		/*
 		 * We need to maintain shared fileset across multiple stream
 		 * start/stop calls. So, need to allocate it in a persistent context.
@@ -2934,6 +2978,11 @@ stream_open_file(Oid subid, TransactionId xid, bool first_segment)
 	}
 	else
 	{
+		if (!found)
+			ereport(ERROR,
+					(errcode(ERRCODE_PROTOCOL_VIOLATION),
+					 errmsg_internal("incorrect first-segment flag for streamed replication transaction")));
+
 		/*
 		 * Open the file and seek to the end of the file because we always
 		 * append the changes file.
@@ -3140,7 +3189,8 @@ ApplyWorkerMain(Datum main_arg)
 		 */
 		if (!myslotname)
 			ereport(ERROR,
-					(errmsg("subscription has no replication slot set")));
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("subscription has no replication slot set")));
 
 		/* Setup replication origin tracking. */
 		StartTransactionCommand();