Making it possible to specify different compresion algorithms in both directions

Author: knizhnik

doc/src/sgml/libpq.sgml

@@ -1232,7 +1232,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
         Request compression of libpq traffic. The client sends a request with a list of compression algorithms.
         Compression can be requested by a client by including the "compression" option in its connection string.
         This can either be a boolean value to enable or disable compression
-        ("true"/"false", "on"/"off", "yes"/"no", "1"/"0"), "auto", or an explicit list of comma-separated compression algorithms
+        ("true"/"false", "on"/"off", "yes"/"no", "1"/"0"), "any", or an explicit list of comma-separated compression algorithms
         which can optionally include compression level ("zlib,zstd:5").
         If compression is enabled but an algorithm is not explicitly specified, the client library sends its full list of
         supported algorithms and the server chooses a preferred algorithm.

src/interfaces/libpq/fe-connect.c

@@ -3268,6 +3268,14 @@ PQconnectPoll(PGconn *conn)
 											  conn->compression);
 							goto error_return;
 						}
+						if ((unsigned)index >= conn->n_compressors)
+						{
+							appendPQExpBuffer(&conn->errorMessage,
+											  libpq_gettext(
+												  "server returns incorrect compression aslogirhm  index: %d\n"),
+											  index);
+							goto error_return;
+						}
 						Assert(!conn->zstream);
 						conn->zstream = zpq_create(conn->compressors[index].impl,
 												   conn->compressors[index].level,
@@ -3286,6 +3294,13 @@ PQconnectPoll(PGconn *conn)
 						}
 						/* reset buffer */
 						conn->inStart = conn->inCursor = conn->inEnd = 0;
+					}
+					else if (conn->n_compressors != 0 && beresp == 'v') /* negotiate protocol version */
+					{
+						appendPQExpBuffer(&conn->errorMessage,
+										  libpq_gettext(
+											  "server is not supporting libpq compression\n"));
+						goto error_return;
 					} else
 						break;
 				}

src/interfaces/libpq/fe-protocol3.c

@@ -2172,6 +2172,7 @@ build_compressors_list(PGconn *conn, char** client_compressors, bool build_descr
 		{
 			*client_compressors = NULL; /* no compressors are available */
 			conn->compressors = NULL;
+			conn->n_compressors = 0;
 			return true;
 		}
 		*client_compressors = p = malloc(total_len);
@@ -2200,6 +2201,7 @@ build_compressors_list(PGconn *conn, char** client_compressors, bool build_descr
 		/* Compression is disabled */
 		*client_compressors = NULL;
 		conn->compressors = NULL;
+		conn->n_compressors = 0;
 		return true;
 	}
 	else
@@ -2258,6 +2260,7 @@ build_compressors_list(PGconn *conn, char** client_compressors, bool build_descr
 				break;
 		}
 		free(suggested_algorithms);
+		conn->n_compressors = n_suggested_algorithms;
 		if (n_suggested_algorithms == 0)
 		{
 			if (!build_descriptors)
@@ -2268,6 +2271,7 @@ build_compressors_list(PGconn *conn, char** client_compressors, bool build_descr
 			{
 				free(conn->compressors);
 				conn->compressors = NULL;
+				conn->n_compressors = 0;
 			}
 			free(*client_compressors);
 			*client_compressors = NULL;

src/interfaces/libpq/libpq-int.h

@@ -386,6 +386,7 @@ struct pg_conn
 								 * comma) */
 	pg_conn_compressor *compressors;	/* descriptors of compression
 										 * algorithms chosen by client */
+	unsigned			n_compressors;  /* size of compressors array  */
 
 	/* Type of connection to make.  Possible values: any, read-write. */
 	char	   *target_session_attrs;