libpq: Trace responses to SSLRequest and GSSENCRequest

Since these are single bytes instead of v2 or v3 messages they need
custom tracing logic.  These "messages" don't even have official names
in the protocol specification, so I (Jelte) called them SSLResponse and
GSSENCResponse here.

Author: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/CAGECzQSoPHtZ4xe0raJ6FYSEiPPS+YWXBhOGo+Y1YecLgknF3g@mail.gmail.com

src/interfaces/libpq/fe-connect.c

@@ -3493,11 +3493,17 @@ keep_going:						/* We will come back to here until there is
 					}
 					if (SSLok == 'S')
 					{
+						if (conn->Pfdebug)
+							pqTraceOutputCharResponse(conn, "SSLResponse",
+													  SSLok);
 						/* mark byte consumed */
 						conn->inStart = conn->inCursor;
 					}
 					else if (SSLok == 'N')
 					{
+						if (conn->Pfdebug)
+							pqTraceOutputCharResponse(conn, "SSLResponse",
+													  SSLok);
 						/* mark byte consumed */
 						conn->inStart = conn->inCursor;
 
@@ -3635,6 +3641,10 @@ keep_going:						/* We will come back to here until there is
 
 					if (gss_ok == 'N')
 					{
+						if (conn->Pfdebug)
+							pqTraceOutputCharResponse(conn, "GSSENCResponse",
+													  gss_ok);
+
 						/*
 						 * The connection is still valid, so if it's OK to
 						 * continue without GSS, we can proceed using this
@@ -3648,6 +3658,10 @@ keep_going:						/* We will come back to here until there is
 												gss_ok);
 						goto error_return;
 					}
+
+					if (conn->Pfdebug)
+						pqTraceOutputCharResponse(conn, "GSSENCResponse",
+												  gss_ok);
 				}
 
 				/* Begin or continue GSSAPI negotiation */

src/interfaces/libpq/fe-trace.c

@@ -840,3 +840,23 @@ pqTraceOutputNoTypeByteMessage(PGconn *conn, const char *message)
 
 	fputc('\n', conn->Pfdebug);
 }
+
+/*
+ * Trace a single-byte backend response received for a known request
+ * type the frontend previously sent.  Only useful for the simplest of
+ * FE/BE interaction workflows such as SSL/GSS encryption requests.
+ */
+void
+pqTraceOutputCharResponse(PGconn *conn, const char *responseType,
+						  char response)
+{
+	if ((conn->traceFlags & PQTRACE_SUPPRESS_TIMESTAMPS) == 0)
+	{
+		char		timestr[128];
+
+		pqTraceFormatTimestamp(timestr, sizeof(timestr));
+		fprintf(conn->Pfdebug, "%s\t", timestr);
+	}
+
+	fprintf(conn->Pfdebug, "B\t1\t%s\t %c\n", responseType, response);
+}

src/interfaces/libpq/libpq-int.h

@@ -889,6 +889,8 @@ extern ssize_t pg_GSS_read(PGconn *conn, void *ptr, size_t len);
 extern void pqTraceOutputMessage(PGconn *conn, const char *message,
 								 bool toServer);
 extern void pqTraceOutputNoTypeByteMessage(PGconn *conn, const char *message);
+extern void pqTraceOutputCharResponse(PGconn *conn, const char *responseType,
+									  char response);
 
 /* === miscellaneous macros === */