Split out recovery confing-writing code from pg_basebackup

... into a new file, fe_utils/recovery_gen.c.

This can later be used by pg_rewind.

Authors: Paul Guo, Jimmy Yih, Ashwin Agrawal.  A few tweaks by Álvaro Herrera
Reviewed-by: Michaël Paquier
Discussion: https://postgr.es/m/CAEET0ZEffUkXc48pg2iqARQgGRYDiiVxDu+yYek_bTwJF+q=Uw@mail.gmail.com

src/fe_utils/Makefile

@@ -19,7 +19,8 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -DFRONTEND -I$(libpq_srcdir) $(CPPFLAGS)
 
-OBJS = mbprint.o print.o psqlscan.o simple_list.o string_utils.o conditional.o
+OBJS = conditional.o mbprint.o print.o psqlscan.o recovery_gen.o \
+       simple_list.o string_utils.o
 
 all: libpgfeutils.a
 

src/fe_utils/recovery_gen.c

@@ -0,0 +1,176 @@
+/*-------------------------------------------------------------------------
+ *
+ * recovery_gen.c
+ *		Generator for recovery configuration
+ *
+ * Portions Copyright (c) 2011-2019, PostgreSQL Global Development Group
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres_fe.h"
+
+#include "common/logging.h"
+#include "fe_utils/string_utils.h"
+#include "fe_utils/recovery_gen.h"
+
+
+static char *escape_quotes(const char *src);
+
+/*
+ * Write recovery configuration contents into a fresh PQExpBuffer, and
+ * return it.
+ */
+PQExpBuffer
+GenerateRecoveryConfig(PGconn *pgconn, char *replication_slot)
+{
+	PQconninfoOption *connOptions;
+	PQExpBufferData conninfo_buf;
+	char	   *escaped;
+	PQExpBuffer contents;
+
+	Assert(pgconn != NULL);
+
+	contents = createPQExpBuffer();
+	if (!contents)
+	{
+		pg_log_error("out of memory");
+		exit(1);
+	}
+
+	/*
+	 * In PostgreSQL 12 and newer versions, standby_mode is gone, replaced by
+	 * standby.signal to trigger a standby state at recovery.
+	 */
+	if (PQserverVersion(pgconn) < MINIMUM_VERSION_FOR_RECOVERY_GUC)
+		appendPQExpBufferStr(contents, "standby_mode = 'on'\n");
+
+	connOptions = PQconninfo(pgconn);
+	if (connOptions == NULL)
+	{
+		pg_log_error("out of memory");
+		exit(1);
+	}
+
+	initPQExpBuffer(&conninfo_buf);
+	for (PQconninfoOption *opt = connOptions; opt && opt->keyword; opt++)
+	{
+		/* Omit empty settings and those libpqwalreceiver overrides. */
+		if (strcmp(opt->keyword, "replication") == 0 ||
+			strcmp(opt->keyword, "dbname") == 0 ||
+			strcmp(opt->keyword, "fallback_application_name") == 0 ||
+			(opt->val == NULL) ||
+			(opt->val != NULL && opt->val[0] == '\0'))
+			continue;
+
+		/* Separate key-value pairs with spaces */
+		if (conninfo_buf.len != 0)
+			appendPQExpBufferChar(&conninfo_buf, ' ');
+
+		/*
+		 * Write "keyword=value" pieces, the value string is escaped and/or
+		 * quoted if necessary.
+		 */
+		appendPQExpBuffer(&conninfo_buf, "%s=", opt->keyword);
+		appendConnStrVal(&conninfo_buf, opt->val);
+	}
+	if (PQExpBufferDataBroken(conninfo_buf))
+	{
+		pg_log_error("out of memory");
+		exit(1);
+	}
+
+	/*
+	 * Escape the connection string, so that it can be put in the config file.
+	 * Note that this is different from the escaping of individual connection
+	 * options above!
+	 */
+	escaped = escape_quotes(conninfo_buf.data);
+	termPQExpBuffer(&conninfo_buf);
+	appendPQExpBuffer(contents, "primary_conninfo = '%s'\n", escaped);
+	free(escaped);
+
+	if (replication_slot)
+	{
+		/* unescaped: ReplicationSlotValidateName allows [a-z0-9_] only */
+		appendPQExpBuffer(contents, "primary_slot_name = '%s'\n",
+						  replication_slot);
+	}
+
+	if (PQExpBufferBroken(contents))
+	{
+		pg_log_error("out of memory");
+		exit(1);
+	}
+
+	PQconninfoFree(connOptions);
+
+	return contents;
+}
+
+/*
+ * Write the configuration file in the directory specified in target_dir,
+ * with the contents already collected in memory appended.  Then write
+ * the signal file into the target_dir.  If the server does not support
+ * recovery parameters as GUCs, the signal file is not necessary, and
+ * configuration is written to recovery.conf.
+ */
+void
+WriteRecoveryConfig(PGconn *pgconn, char *target_dir, PQExpBuffer contents)
+{
+	char		filename[MAXPGPATH];
+	FILE	   *cf;
+	bool		use_recovery_conf;
+
+	Assert(pgconn != NULL);
+
+	use_recovery_conf =
+		PQserverVersion(pgconn) < MINIMUM_VERSION_FOR_RECOVERY_GUC;
+
+	snprintf(filename, MAXPGPATH, "%s/%s", target_dir,
+			 use_recovery_conf ? "recovery.conf" : "postgresql.auto.conf");
+
+	cf = fopen(filename, use_recovery_conf ? "a" : "w");
+	if (cf == NULL)
+	{
+		pg_log_error("could not open file \"%s\": %m", filename);
+		exit(1);
+	}
+
+	if (fwrite(contents->data, contents->len, 1, cf) != 1)
+	{
+		pg_log_error("could not write to file \"%s\": %m", filename);
+		exit(1);
+	}
+
+	fclose(cf);
+
+	if (!use_recovery_conf)
+	{
+		snprintf(filename, MAXPGPATH, "%s/%s", target_dir, "standby.signal");
+		cf = fopen(filename, "w");
+		if (cf == NULL)
+		{
+			pg_log_error("could not create file \"%s\": %m", filename);
+			exit(1);
+		}
+
+		fclose(cf);
+	}
+}
+
+/*
+ * Escape a string so that it can be used as a value in a key-value pair
+ * a configuration file.
+ */
+static char *
+escape_quotes(const char *src)
+{
+	char	   *result = escape_single_quotes_ascii(src);
+
+	if (!result)
+	{
+		pg_log_error("out of memory");
+		exit(1);
+	}
+	return result;
+}