psql: fix \connect with URIs and conninfo strings

psql was already accepting conninfo strings as the first parameter in
\connect, but the way it worked wasn't sane; some of the other
parameters would get the previous connection's values, causing it to
connect to a completely unexpected server or, more likely, not finding
any server at all because of completely wrong combinations of
parameters.

Fix by explicitely checking for a conninfo-looking parameter in the
dbname position; if one is found, use its complete specification rather
than mix with the other arguments.  Also, change tab-completion to not
try to complete conninfo/URI-looking "dbnames" and document that
conninfos are accepted as first argument.

There was a weak consensus to backpatch this, because while the behavior
of using the dbname as a conninfo is nowhere documented for \connect, it
is reasonable to expect that it works because it does work in many other
contexts.  Therefore this is backpatched all the way back to 9.0.

To implement this, routines previously private to libpq have been
duplicated so that psql can decide what looks like a conninfo/URI
string.  In back branches, just duplicate the same code all the way back
to 9.2, where URIs where introduced; 9.0 and 9.1 have a simpler version.
In master, the routines are moved to src/common and renamed.

Author: David Fetter, Andrew Dunstan.  Some editorialization by me
(probably earning a Gierth's "Sloppy" badge in the process.)
Reviewers: Andrew Gierth, Erik Rijkers, Pavel Stěhule, Stephen Frost,
Robert Haas, Andrew Dunstan.

Author: alvherre

doc/src/sgml/ref/psql-ref.sgml

@@ -778,23 +778,31 @@ testdb=>
       </varlistentry>
 
       <varlistentry>
-        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ]</literal></term>
+        <term><literal>\c</literal> or <literal>\connect</literal> <literal>[ <replaceable class="parameter">dbname</replaceable> [ <replaceable class="parameter">username</replaceable> ] [ <replaceable class="parameter">host</replaceable> ] [ <replaceable class="parameter">port</replaceable> ] ] | <replaceable class="parameter">conninfo</replaceable> </literal></term>
         <listitem>
         <para>
         Establishes a new connection to a <productname>PostgreSQL</>
-        server. If the new connection is successfully made, the
-        previous connection is closed. If any of <replaceable
-        class="parameter">dbname</replaceable>, <replaceable
-        class="parameter">username</replaceable>, <replaceable
-        class="parameter">host</replaceable> or <replaceable
-        class="parameter">port</replaceable> are omitted or specified
-        as <literal>-</literal>, the value of that parameter from the
-        previous connection is used. If there is no previous
-        connection, the <application>libpq</application> default for
-        the parameter's value is used.
+        server.  The connection parameters to use can be specified either
+        using a positional syntax, or using <literal>conninfo</> connection
+        strings as detailed in <xref linkend="libpq-connstring">.
         </para>
 
         <para>
+        When using positional parameters, if any of
+        <replaceable class="parameter">dbname</replaceable>,
+        <replaceable class="parameter">username</replaceable>,
+        <replaceable class="parameter">host</replaceable> or
+        <replaceable class="parameter">port</replaceable> are omitted or
+        specified as <literal>-</literal>, the value of that parameter from
+        the previous connection is used; if there is no previous connection,
+        the <application>libpq</application> default for the parameter's value
+        is used.  When using <literal>conninfo</> strings, no values from the
+        previous connection are used for the new connection.
+        </para>
+
+        <para>
+        If the new connection is successfully made, the previous
+        connection is closed.
         If the connection attempt failed (wrong user name, access
         denied, etc.), the previous connection will only be kept if
         <application>psql</application> is in interactive mode. When
@@ -804,6 +812,16 @@ testdb=&gt;
         mechanism that scripts are not accidentally acting on the
         wrong database on the other hand.
         </para>
+
+        <para>
+        Examples:
+        </para>
+<programlisting>
+=&gt; \c mydb myuser host.dom 6432
+=&gt; \c service=foo
+=&gt; \c "host=localhost port=5432 dbname=mydb connect_timeout=10 sslmode=disable"
+=&gt; \c postgresql://tom@localhost/mydb?application_name=myapp
+</programlisting>
         </listitem>
       </varlistentry>
 

src/bin/psql/command.c

@@ -1595,6 +1595,8 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	PGconn	   *o_conn = pset.db,
 			   *n_conn;
 	char	   *password = NULL;
+	bool		keep_password;
+	bool		has_connection_string;
 
 	if (!o_conn && (!dbname || !user || !host || !port))
 	{
@@ -1608,15 +1610,35 @@ do_connect(char *dbname, char *user, char *host, char *port)
 		return false;
 	}
 
-	if (!dbname)
-		dbname = PQdb(o_conn);
+	/* grab values from the old connection, unless supplied by caller */
 	if (!user)
 		user = PQuser(o_conn);
 	if (!host)
 		host = PQhost(o_conn);
 	if (!port)
 		port = PQport(o_conn);
 
+	has_connection_string =
+		dbname ? recognized_connection_string(dbname) : false;
+
+	/*
+	 * Any change in the parameters read above makes us discard the password.
+	 * We also discard it if we're to use a conninfo rather than the positional
+	 * syntax.
+	 */
+	keep_password =
+		((strcmp(user, PQuser(o_conn)) == 0) &&
+		 (!host || strcmp(host, PQhost(o_conn)) == 0) &&
+		 (strcmp(port, PQport(o_conn)) == 0) &&
+		 !has_connection_string);
+
+	/*
+	 * Grab dbname from old connection unless supplied by caller.  No password
+	 * discard if this changes: passwords aren't (usually) database-specific.
+	 */
+	if (!dbname)
+		dbname = PQdb(o_conn);
+
 	/*
 	 * If the user asked to be prompted for a password, ask for one now. If
 	 * not, use the password from the old connection, provided the username
@@ -1631,42 +1653,53 @@ do_connect(char *dbname, char *user, char *host, char *port)
 	{
 		password = prompt_for_password(user);
 	}
-	else if (o_conn && user && strcmp(PQuser(o_conn), user) == 0)
+	else if (o_conn && keep_password)
 	{
-		password = pg_strdup(PQpass(o_conn));
+		password = PQpass(o_conn);
+		if (password && *password)
+			password = pg_strdup(password);
+		else
+			password = NULL;
 	}
 
 	while (true)
 	{
 #define PARAMS_ARRAY_SIZE	8
 		const char **keywords = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*keywords));
 		const char **values = pg_malloc(PARAMS_ARRAY_SIZE * sizeof(*values));
+		int			paramnum = 0;
+
+		keywords[0] = "dbname";
+		values[0] = dbname;
+
+		if (!has_connection_string)
+		{
+			keywords[++paramnum] = "host";
+			values[paramnum] = host;
+			keywords[++paramnum] = "port";
+			values[paramnum] = port;
+			keywords[++paramnum] = "user";
+			values[paramnum] = user;
+		}
+		keywords[++paramnum] = "password";
+		values[paramnum] = password;
+		keywords[++paramnum] = "fallback_application_name";
+		values[paramnum] = pset.progname;
+		keywords[++paramnum] = "client_encoding";
+		values[paramnum] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
 
-		keywords[0] = "host";
-		values[0] = host;
-		keywords[1] = "port";
-		values[1] = port;
-		keywords[2] = "user";
-		values[2] = user;
-		keywords[3] = "password";
-		values[3] = password;
-		keywords[4] = "dbname";
-		values[4] = dbname;
-		keywords[5] = "fallback_application_name";
-		values[5] = pset.progname;
-		keywords[6] = "client_encoding";
-		values[6] = (pset.notty || getenv("PGCLIENTENCODING")) ? NULL : "auto";
-		keywords[7] = NULL;
-		values[7] = NULL;
+		/* add array terminator */
+		keywords[++paramnum] = NULL;
+		values[paramnum] = NULL;
 
 		n_conn = PQconnectdbParams(keywords, values, true);
 
-		free(keywords);
-		free(values);
+		pg_free(keywords);
+		pg_free(values);
 
 		/* We can immediately discard the password -- no longer needed */
 		if (password)
-			free(password);
+			pg_free(password);
 
 		if (PQstatus(n_conn) == CONNECTION_OK)
 			break;

src/bin/psql/common.c

@@ -1748,3 +1748,44 @@ expand_tilde(char **filename)
 
 	return;
 }
+
+/*
+ * Checks if connection string starts with either of the valid URI prefix
+ * designators.
+ *
+ * Returns the URI prefix length, 0 if the string doesn't contain a URI prefix.
+ *
+ * XXX This is a duplicate of the eponymous libpq function.
+ */
+static int
+uri_prefix_length(const char *connstr)
+{
+	/* The connection URI must start with either of the following designators: */
+	static const char uri_designator[] = "postgresql://";
+	static const char short_uri_designator[] = "postgres://";
+
+	if (strncmp(connstr, uri_designator,
+				sizeof(uri_designator) - 1) == 0)
+		return sizeof(uri_designator) - 1;
+
+	if (strncmp(connstr, short_uri_designator,
+				sizeof(short_uri_designator) - 1) == 0)
+		return sizeof(short_uri_designator) - 1;
+
+	return 0;
+}
+
+/*
+ * Recognized connection string either starts with a valid URI prefix or
+ * contains a "=" in it.
+ *
+ * Must be consistent with parse_connection_string: anything for which this
+ * returns true should at least look like it's parseable by that routine.
+ *
+ * XXX This is a duplicate of the eponymous libpq function.
+ */
+bool
+recognized_connection_string(const char *connstr)
+{
+	return uri_prefix_length(connstr) != 0 || strchr(connstr, '=') != NULL;
+}

src/bin/psql/common.h

@@ -46,4 +46,6 @@ extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
 
+extern bool recognized_connection_string(const char *connstr);
+
 #endif   /* COMMON_H */

src/bin/psql/help.c

@@ -244,11 +244,11 @@ slashUsage(unsigned short int pager)
 
 	fprintf(output, _("Connection\n"));
 	if (currdb)
-		fprintf(output, _("  \\c[onnect] [DBNAME|- USER|- HOST|- PORT|-]\n"
+		fprintf(output, _("  \\c[onnect] {[DBNAME|- USER|- HOST|- PORT|-] | conninfo}\n"
 						  "                         connect to new database (currently \"%s\")\n"),
 				currdb);
 	else
-		fprintf(output, _("  \\c[onnect] [DBNAME|- USER|- HOST|- PORT|-]\n"
+		fprintf(output, _("  \\c[onnect] {[DBNAME|- USER|- HOST|- PORT|-] | conninfo}\n"
 						  "                         connect to new database (currently no connection)\n"));
 	fprintf(output, _("  \\encoding [ENCODING]   show or set client encoding\n"));
 	fprintf(output, _("  \\password [USERNAME]   securely change the password for a user\n"));

src/bin/psql/tab-complete.c

@@ -3413,7 +3413,10 @@ psql_completion(const char *text, int start, int end)
 /* Backslash commands */
 /* TODO:  \dc \dd \dl */
 	else if (strcmp(prev_wd, "\\connect") == 0 || strcmp(prev_wd, "\\c") == 0)
-		COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	{
+		if (!recognized_connection_string(text))
+			COMPLETE_WITH_QUERY(Query_for_list_of_databases);
+	}
 
 	else if (strncmp(prev_wd, "\\da", strlen("\\da")) == 0)
 		COMPLETE_WITH_SCHEMA_QUERY(Query_for_list_of_aggregates, NULL);