extension.c

/*-------------------------------------------------------------------------
 *
 * extension.c
 *	  Commands to manipulate extensions
 *
 * Extensions in PostgreSQL allow management of collections of SQL objects.
 *
 * All we need internally to manage an extension is an OID so that the
 * dependent objects can be associated with it.  An extension is created by
 * populating the pg_extension catalog from a "control" file.
 * The extension control file is parsed with the same parser we use for
 * postgresql.conf and recovery.conf.  An extension also has an installation
 * script file, containing SQL commands to create the extension's objects.
 *
 * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/commands/extension.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <dirent.h>
#include <limits.h>
#include <unistd.h>

#include "access/sysattr.h"
#include "access/xact.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/pg_depend.h"
#include "catalog/pg_extension.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_type.h"
#include "commands/alter.h"
#include "commands/comment.h"
#include "commands/extension.h"
#include "commands/trigger.h"
#include "executor/executor.h"
#include "funcapi.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "tcop/tcopprot.h"
#include "tcop/utility.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/snapmgr.h"
#include "utils/tqual.h"


/* Globally visible state variables */
bool			creating_extension = false;
Oid				CurrentExtensionObject = InvalidOid;

/*
 * Internal data structure to hold the results of parsing a control file
 */
typedef struct ExtensionControlFile
{
	char	   *name;			/* name of the extension */
	char	   *directory;		/* directory for script files */
	char	   *default_version; /* default install target version, if any */
	char	   *module_pathname; /* string to substitute for MODULE_PATHNAME */
	char	   *comment;		/* comment, if any */
	char	   *schema;			/* target schema (allowed if !relocatable) */
	bool		relocatable;	/* is ALTER EXTENSION SET SCHEMA supported? */
	int			encoding;		/* encoding of the script file, or -1 */
	List	   *requires;		/* names of prerequisite extensions */
} ExtensionControlFile;

/*
 * Internal data structure for update path information
 */
typedef struct ExtensionVersionInfo
{
	char	   *name;			/* name of the starting version */
	List	   *reachable;		/* List of ExtensionVersionInfo's */
	bool		installable;	/* does this version have an install script? */
	/* working state for Dijkstra's algorithm: */
	bool		distance_known;	/* is distance from start known yet? */
	int			distance;		/* current worst-case distance estimate */
	struct ExtensionVersionInfo *previous; /* current best predecessor */
} ExtensionVersionInfo;

/* Local functions */
static List *find_update_path(List *evi_list,
				 ExtensionVersionInfo *evi_start,
				 ExtensionVersionInfo *evi_target,
				 bool reinitialize);
static void get_available_versions_for_extension(ExtensionControlFile *pcontrol,
									 Tuplestorestate *tupstore,
									 TupleDesc tupdesc);
static void ApplyExtensionUpdates(Oid extensionOid,
					  ExtensionControlFile *pcontrol,
					  const char *initialVersion,
					  List *updateVersions);


/*
 * get_extension_oid - given an extension name, look up the OID
 *
 * If missing_ok is false, throw an error if extension name not found.  If
 * true, just return InvalidOid.
 */
Oid
get_extension_oid(const char *extname, bool missing_ok)
{
	Oid			result;
	Relation	rel;
	SysScanDesc scandesc;
	HeapTuple	tuple;
	ScanKeyData entry[1];

	rel = heap_open(ExtensionRelationId, AccessShareLock);

	ScanKeyInit(&entry[0],
				Anum_pg_extension_extname,
				BTEqualStrategyNumber, F_NAMEEQ,
				CStringGetDatum(extname));

	scandesc = systable_beginscan(rel, ExtensionNameIndexId, true,
								  SnapshotNow, 1, entry);

	tuple = systable_getnext(scandesc);

	/* We assume that there can be at most one matching tuple */
	if (HeapTupleIsValid(tuple))
		result = HeapTupleGetOid(tuple);
	else
		result = InvalidOid;

	systable_endscan(scandesc);

	heap_close(rel, AccessShareLock);

	if (!OidIsValid(result) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("extension \"%s\" does not exist",
                        extname)));

	return result;
}

/*
 * get_extension_name - given an extension OID, look up the name
 *
 * Returns a palloc'd string, or NULL if no such extension.
 */
char *
get_extension_name(Oid ext_oid)
{
	char	   *result;
	Relation	rel;
	SysScanDesc scandesc;
	HeapTuple	tuple;
	ScanKeyData entry[1];

	rel = heap_open(ExtensionRelationId, AccessShareLock);

	ScanKeyInit(&entry[0],
				ObjectIdAttributeNumber,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(ext_oid));

	scandesc = systable_beginscan(rel, ExtensionOidIndexId, true,
								  SnapshotNow, 1, entry);

	tuple = systable_getnext(scandesc);

	/* We assume that there can be at most one matching tuple */
	if (HeapTupleIsValid(tuple))
		result = pstrdup(NameStr(((Form_pg_extension) GETSTRUCT(tuple))->extname));
	else
		result = NULL;

	systable_endscan(scandesc);

	heap_close(rel, AccessShareLock);

	return result;
}

/*
 * get_extension_schema - given an extension OID, fetch its extnamespace
 *
 * Returns InvalidOid if no such extension.
 */
static Oid
get_extension_schema(Oid ext_oid)
{
	Oid			result;
	Relation	rel;
	SysScanDesc scandesc;
	HeapTuple	tuple;
	ScanKeyData entry[1];

	rel = heap_open(ExtensionRelationId, AccessShareLock);

	ScanKeyInit(&entry[0],
				ObjectIdAttributeNumber,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(ext_oid));

	scandesc = systable_beginscan(rel, ExtensionOidIndexId, true,
								  SnapshotNow, 1, entry);

	tuple = systable_getnext(scandesc);

	/* We assume that there can be at most one matching tuple */
	if (HeapTupleIsValid(tuple))
		result = ((Form_pg_extension) GETSTRUCT(tuple))->extnamespace;
	else
		result = InvalidOid;

	systable_endscan(scandesc);

	heap_close(rel, AccessShareLock);

	return result;
}

/*
 * Utility functions to check validity of extension and version names
 */
static void
check_valid_extension_name(const char *extensionname)
{
	int			namelen = strlen(extensionname);

	/*
	 * Disallow empty names (the parser rejects empty identifiers anyway,
	 * but let's check).
	 */
	if (namelen == 0)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid extension name: \"%s\"", extensionname),
				 errdetail("Extension names must not be empty.")));

	/*
	 * No double dashes, since that would make script filenames ambiguous.
	 */
	if (strstr(extensionname, "--"))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid extension name: \"%s\"", extensionname),
				 errdetail("Extension names must not contain \"--\".")));

	/*
	 * No leading or trailing dash either.  (We could probably allow this,
	 * but it would require much care in filename parsing and would make
	 * filenames visually if not formally ambiguous.  Since there's no
	 * real-world use case, let's just forbid it.)
	 */
	if (extensionname[0] == '-' || extensionname[namelen - 1] == '-')
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid extension name: \"%s\"", extensionname),
				 errdetail("Extension names must not begin or end with \"-\".")));

	/*
	 * No directory separators either (this is sufficient to prevent ".."
	 * style attacks).
	 */
	if (first_dir_separator(extensionname) != NULL)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid extension name: \"%s\"", extensionname),
				 errdetail("Extension names must not contain directory separator characters.")));
}

static void
check_valid_version_name(const char *versionname)
{
	int			namelen = strlen(versionname);

	/*
	 * Disallow empty names (we could possibly allow this, but there seems
	 * little point).
	 */
	if (namelen == 0)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid extension version name: \"%s\"", versionname),
				 errdetail("Version names must not be empty.")));

	/*
	 * No double dashes, since that would make script filenames ambiguous.
	 */
	if (strstr(versionname, "--"))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid extension version name: \"%s\"", versionname),
				 errdetail("Version names must not contain \"--\".")));

	/*
	 * No leading or trailing dash either.
	 */
	if (versionname[0] == '-' || versionname[namelen - 1] == '-')
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid extension version name: \"%s\"", versionname),
				 errdetail("Version names must not begin or end with \"-\".")));

	/*
	 * No directory separators either (this is sufficient to prevent ".."
	 * style attacks).
	 */
	if (first_dir_separator(versionname) != NULL)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid extension version name: \"%s\"", versionname),
				 errdetail("Version names must not contain directory separator characters.")));
}

/*
 * Utility functions to handle extension-related path names
 */
static bool
is_extension_control_filename(const char *filename)
{
	const char *extension = strrchr(filename, '.');

	return (extension != NULL) && (strcmp(extension, ".control") == 0);
}

static bool
is_extension_script_filename(const char *filename)
{
	const char *extension = strrchr(filename, '.');

	return (extension != NULL) && (strcmp(extension, ".sql") == 0);
}

static char *
get_extension_control_directory(void)
{
	char		sharepath[MAXPGPATH];
	char	   *result;

	get_share_path(my_exec_path, sharepath);
	result = (char *) palloc(MAXPGPATH);
	snprintf(result, MAXPGPATH, "%s/extension", sharepath);

	return result;
}

static char *
get_extension_control_filename(const char *extname)
{
	char		sharepath[MAXPGPATH];
	char	   *result;

	get_share_path(my_exec_path, sharepath);
	result = (char *) palloc(MAXPGPATH);
	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
			 sharepath, extname);

	return result;
}

static char *
get_extension_script_directory(ExtensionControlFile *control)
{
	char		sharepath[MAXPGPATH];
	char	   *result;

	/*
	 * The directory parameter can be omitted, absolute, or relative to the
	 * installation's share directory.
	 */
	if (!control->directory)
		return get_extension_control_directory();

	if (is_absolute_path(control->directory))
		return pstrdup(control->directory);

	get_share_path(my_exec_path, sharepath);
	result = (char *) palloc(MAXPGPATH);
    snprintf(result, MAXPGPATH, "%s/%s", sharepath, control->directory);

	return result;
}

static char *
get_extension_aux_control_filename(ExtensionControlFile *control,
								   const char *version)
{
	char	   *result;
	char	   *scriptdir;

	scriptdir = get_extension_script_directory(control);

	result = (char *) palloc(MAXPGPATH);
	snprintf(result, MAXPGPATH, "%s/%s--%s.control",
			 scriptdir, control->name, version);

	pfree(scriptdir);

	return result;
}

static char *
get_extension_script_filename(ExtensionControlFile *control,
							  const char *from_version, const char *version)
{
	char	   *result;
	char	   *scriptdir;

	scriptdir = get_extension_script_directory(control);

	result = (char *) palloc(MAXPGPATH);
	if (from_version)
		snprintf(result, MAXPGPATH, "%s/%s--%s--%s.sql",
				 scriptdir, control->name, from_version, version);
	else
		snprintf(result, MAXPGPATH, "%s/%s--%s.sql",
				 scriptdir, control->name, version);

	pfree(scriptdir);

	return result;
}


/*
 * Parse contents of primary or auxiliary control file, and fill in
 * fields of *control.  We parse primary file if version == NULL,
 * else the optional auxiliary file for that version.
 *
 * Control files are supposed to be very short, half a dozen lines,
 * so we don't worry about memory allocation risks here.  Also we don't
 * worry about what encoding it's in; all values are expected to be ASCII.
 */
static void
parse_extension_control_file(ExtensionControlFile *control,
							 const char *version)
{
	char	   *filename;
	FILE	   *file;
	ConfigVariable *item,
				   *head = NULL,
				   *tail = NULL;

	/*
	 * Locate the file to read.  Auxiliary files are optional.
	 */
	if (version)
		filename = get_extension_aux_control_filename(control, version);
	else
		filename = get_extension_control_filename(control->name);

	if ((file = AllocateFile(filename, "r")) == NULL)
	{
		if (version && errno == ENOENT)
		{
			/* no auxiliary file for this version */
			pfree(filename);
			return;
		}
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not open extension control file \"%s\": %m",
						filename)));
	}

	/*
	 * Parse the file content, using GUC's file parsing code
	 */
	ParseConfigFp(file, filename, 0, ERROR, &head, &tail);

	FreeFile(file);

	/*
	 * Convert the ConfigVariable list into ExtensionControlFile entries.
	 */
	for (item = head; item != NULL; item = item->next)
	{
		if (strcmp(item->name, "directory") == 0)
		{
			if (version)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("parameter \"%s\" cannot be set in a secondary extension control file",
								item->name)));

			control->directory = pstrdup(item->value);
		}
		else if (strcmp(item->name, "default_version") == 0)
		{
			if (version)
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("parameter \"%s\" cannot be set in a secondary extension control file",
								item->name)));

			control->default_version = pstrdup(item->value);
		}
		else if (strcmp(item->name, "module_pathname") == 0)
		{
			control->module_pathname = pstrdup(item->value);
		}
		else if (strcmp(item->name, "comment") == 0)
		{
			control->comment = pstrdup(item->value);
		}
		else if (strcmp(item->name, "schema") == 0)
		{
			control->schema = pstrdup(item->value);
		}
		else if (strcmp(item->name, "relocatable") == 0)
		{
			if (!parse_bool(item->value, &control->relocatable))
				ereport(ERROR,
						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
						 errmsg("parameter \"%s\" requires a Boolean value",
								item->name)));
		}
		else if (strcmp(item->name, "encoding") == 0)
		{
			control->encoding = pg_valid_server_encoding(item->value);
			if (control->encoding < 0)
				ereport(ERROR,
						(errcode(ERRCODE_UNDEFINED_OBJECT),
						 errmsg("\"%s\" is not a valid encoding name",
								item->value)));
		}
		else if (strcmp(item->name, "requires") == 0)
		{
			/* Need a modifiable copy of string */
			char	   *rawnames = pstrdup(item->value);

			/* Parse string into list of identifiers */
			if (!SplitIdentifierString(rawnames, ',', &control->requires))
			{
				/* syntax error in name list */
				ereport(ERROR,
						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
						 errmsg("parameter \"%s\" must be a list of extension names",
								item->name)));
			}
		}
		else
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("unrecognized parameter \"%s\" in file \"%s\"",
							item->name, filename)));
	}

	FreeConfigVariables(head);

	if (control->relocatable && control->schema != NULL)
		ereport(ERROR,
				(errcode(ERRCODE_SYNTAX_ERROR),
				 errmsg("parameter \"schema\" cannot be specified when \"relocatable\" is true")));

	pfree(filename);
}

/*
 * Read the primary control file for the specified extension.
 */
static ExtensionControlFile *
read_extension_control_file(const char *extname)
{
	ExtensionControlFile *control;

	/*
	 * Set up default values.  Pointer fields are initially null.
	 */
	control = (ExtensionControlFile *) palloc0(sizeof(ExtensionControlFile));
	control->name = pstrdup(extname);
	control->relocatable = false;
	control->encoding = -1;

	/*
	 * Parse the primary control file.
	 */
	parse_extension_control_file(control, NULL);

	return control;
}

/*
 * Read the auxiliary control file for the specified extension and version.
 *
 * Returns a new modified ExtensionControlFile struct; the original struct
 * (reflecting just the primary control file) is not modified.
 */
static ExtensionControlFile *
read_extension_aux_control_file(const ExtensionControlFile *pcontrol,
								const char *version)
{
	ExtensionControlFile *acontrol;

	/*
	 * Flat-copy the struct.  Pointer fields share values with original.
	 */
	acontrol = (ExtensionControlFile *) palloc(sizeof(ExtensionControlFile));
	memcpy(acontrol, pcontrol, sizeof(ExtensionControlFile));

	/*
	 * Parse the auxiliary control file, overwriting struct fields
	 */
	parse_extension_control_file(acontrol, version);

	return acontrol;
}

/*
 * Read a SQL script file into a string, and convert to database encoding
 */
static char *
read_extension_script_file(const ExtensionControlFile *control,
						   const char *filename)
{
	int         src_encoding;
	int         dest_encoding = GetDatabaseEncoding();
	bytea      *content;
	char	   *src_str;
	char       *dest_str;
	int         len;

	content = read_binary_file(filename, 0, -1);

	/* use database encoding if not given */
	if (control->encoding < 0)
		src_encoding = dest_encoding;
	else
		src_encoding = control->encoding;

	/* make sure that source string is valid in the expected encoding */
	len = VARSIZE_ANY_EXHDR(content);
	src_str = VARDATA_ANY(content);
	pg_verify_mbstr_len(src_encoding, src_str, len, false);

	/* convert the encoding to the database encoding */
	dest_str = (char *) pg_do_encoding_conversion((unsigned char *) src_str,
												  len,
												  src_encoding,
												  dest_encoding);

	/* if no conversion happened, we have to arrange for null termination */
	if (dest_str == src_str)
	{
		dest_str = (char *) palloc(len + 1);
		memcpy(dest_str, src_str, len);
		dest_str[len] = '\0';
	}

	return dest_str;
}

/*
 * Execute given SQL string.
 *
 * filename is used only to report errors.
 *
 * Note: it's tempting to just use SPI to execute the string, but that does
 * not work very well.  The really serious problem is that SPI will parse,
 * analyze, and plan the whole string before executing any of it; of course
 * this fails if there are any plannable statements referring to objects
 * created earlier in the script.  A lesser annoyance is that SPI insists
 * on printing the whole string as errcontext in case of any error, and that
 * could be very long.
 */
static void
execute_sql_string(const char *sql, const char *filename)
{
	List	   *raw_parsetree_list;
	DestReceiver *dest;
	ListCell   *lc1;

	/*
	 * Parse the SQL string into a list of raw parse trees.
	 */
	raw_parsetree_list = pg_parse_query(sql);

	/* All output from SELECTs goes to the bit bucket */
	dest = CreateDestReceiver(DestNone);

	/*
	 * Do parse analysis, rule rewrite, planning, and execution for each raw
	 * parsetree.  We must fully execute each query before beginning parse
	 * analysis on the next one, since there may be interdependencies.
	 */
	foreach(lc1, raw_parsetree_list)
	{
		Node	   *parsetree = (Node *) lfirst(lc1);
		List	   *stmt_list;
		ListCell   *lc2;

		stmt_list = pg_analyze_and_rewrite(parsetree,
										   sql,
										   NULL,
										   0);
		stmt_list = pg_plan_queries(stmt_list, 0, NULL);

		foreach(lc2, stmt_list)
		{
			Node	   *stmt = (Node *) lfirst(lc2);

			if (IsA(stmt, TransactionStmt))
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						 errmsg("transaction control statements are not allowed within an extension script")));

			CommandCounterIncrement();

			PushActiveSnapshot(GetTransactionSnapshot());

			if (IsA(stmt, PlannedStmt) &&
				((PlannedStmt *) stmt)->utilityStmt == NULL)
			{
				QueryDesc  *qdesc;

				qdesc = CreateQueryDesc((PlannedStmt *) stmt,
										sql,
										GetActiveSnapshot(), NULL,
										dest, NULL, 0);

				AfterTriggerBeginQuery();
				ExecutorStart(qdesc, 0);
				ExecutorRun(qdesc, ForwardScanDirection, 0);
				AfterTriggerEndQuery(qdesc->estate);
				ExecutorEnd(qdesc);

				FreeQueryDesc(qdesc);
			}
			else
			{
				ProcessUtility(stmt,
							   sql,
							   NULL,
							   false,	/* not top level */
							   dest,
							   NULL);
			}

			PopActiveSnapshot();
		}
	}

	/* Be sure to advance the command counter after the last script command */
	CommandCounterIncrement();
}

/*
 * Execute the appropriate script file for installing or updating the extension
 *
 * If from_version isn't NULL, it's an update
 */
static void
execute_extension_script(Oid extensionOid, ExtensionControlFile *control,
						 const char *from_version,
						 const char *version,
						 List *requiredSchemas,
						 const char *schemaName, Oid schemaOid)
{
	char       *filename;
	char	   *save_client_min_messages,
			   *save_log_min_messages,
			   *save_search_path;
	StringInfoData pathbuf;
	ListCell   *lc;

	filename = get_extension_script_filename(control, from_version, version);

	/*
	 * Force client_min_messages and log_min_messages to be at least WARNING,
	 * so that we won't spam the user with useless NOTICE messages from common
	 * script actions like creating shell types.
	 *
	 * We use the equivalent of SET LOCAL to ensure the setting is undone
	 * upon error.
	 */
	save_client_min_messages =
		pstrdup(GetConfigOption("client_min_messages", false));
	if (client_min_messages < WARNING)
		(void) set_config_option("client_min_messages", "warning",
								 PGC_USERSET, PGC_S_SESSION,
								 GUC_ACTION_LOCAL, true);

	save_log_min_messages =
		pstrdup(GetConfigOption("log_min_messages", false));
	if (log_min_messages < WARNING)
		(void) set_config_option("log_min_messages", "warning",
								 PGC_SUSET, PGC_S_SESSION,
								 GUC_ACTION_LOCAL, true);

	/*
	 * Set up the search path to contain the target schema, then the schemas
	 * of any prerequisite extensions, and nothing else.  In particular this
	 * makes the target schema be the default creation target namespace.
	 *
	 * Note: it might look tempting to use PushOverrideSearchPath for this,
	 * but we cannot do that.  We have to actually set the search_path GUC
	 * in case the extension script examines or changes it.
	 */
	save_search_path = pstrdup(GetConfigOption("search_path", false));

	initStringInfo(&pathbuf);
	appendStringInfoString(&pathbuf, quote_identifier(schemaName));
	foreach(lc, requiredSchemas)
	{
		Oid			reqschema = lfirst_oid(lc);
		char	   *reqname = get_namespace_name(reqschema);

		if (reqname)
			appendStringInfo(&pathbuf, ", %s", quote_identifier(reqname));
	}

	(void) set_config_option("search_path", pathbuf.data,
							 PGC_USERSET, PGC_S_SESSION,
							 GUC_ACTION_LOCAL, true);

	/*
	 * Set creating_extension and related variables so that
	 * recordDependencyOnCurrentExtension and other functions do the right
	 * things.  On failure, ensure we reset these variables.
	 */
	creating_extension = true;
	CurrentExtensionObject = extensionOid;
	PG_TRY();
	{
		char *sql = read_extension_script_file(control, filename);

		/*
		 * If it's not relocatable, substitute the target schema name for
		 * occcurrences of @extschema@.
		 *
		 * For a relocatable extension, we just run the script as-is.
		 * There cannot be any need for @extschema@, else it wouldn't
		 * be relocatable.
		 */
		if (!control->relocatable)
		{
			const char   *qSchemaName = quote_identifier(schemaName);

			sql = text_to_cstring(
				DatumGetTextPP(
					DirectFunctionCall3(replace_text,
										CStringGetTextDatum(sql),
										CStringGetTextDatum("@extschema@"),
										CStringGetTextDatum(qSchemaName))));
		}

		/*
		 * If module_pathname was set in the control file, substitute its
		 * value for occurrences of MODULE_PATHNAME.
		 */
		if (control->module_pathname)
		{
			sql = text_to_cstring(
				DatumGetTextPP(
					DirectFunctionCall3(replace_text,
										CStringGetTextDatum(sql),
										CStringGetTextDatum("MODULE_PATHNAME"),
										CStringGetTextDatum(control->module_pathname))));
		}

		execute_sql_string(sql, filename);
	}
	PG_CATCH();
	{
		creating_extension = false;
		CurrentExtensionObject = InvalidOid;
		PG_RE_THROW();
	}
	PG_END_TRY();

	creating_extension = false;
	CurrentExtensionObject = InvalidOid;

	/*
	 * Restore GUC variables for the remainder of the current transaction.
	 * Again use SET LOCAL, so we won't affect the session value.
	 */
	(void) set_config_option("search_path", save_search_path,
							 PGC_USERSET, PGC_S_SESSION,
							 GUC_ACTION_LOCAL, true);
	(void) set_config_option("client_min_messages", save_client_min_messages,
							 PGC_USERSET, PGC_S_SESSION,
							 GUC_ACTION_LOCAL, true);
	(void) set_config_option("log_min_messages", save_log_min_messages,
							 PGC_SUSET, PGC_S_SESSION,
							 GUC_ACTION_LOCAL, true);
}

/*
 * Find or create an ExtensionVersionInfo for the specified version name
 *
 * Currently, we just use a List of the ExtensionVersionInfo's.  Searching
 * for them therefore uses about O(N^2) time when there are N versions of
 * the extension.  We could change the data structure to a hash table if
 * this ever becomes a bottleneck.
 */
static ExtensionVersionInfo *
get_ext_ver_info(const char *versionname, List **evi_list)
{
	ExtensionVersionInfo *evi;
	ListCell   *lc;

	foreach(lc, *evi_list)
	{
		evi = (ExtensionVersionInfo *) lfirst(lc);
		if (strcmp(evi->name, versionname) == 0)
			return evi;
	}

	evi = (ExtensionVersionInfo *) palloc(sizeof(ExtensionVersionInfo));
	evi->name = pstrdup(versionname);
	evi->reachable = NIL;
	evi->installable = false;
	/* initialize for later application of Dijkstra's algorithm */
	evi->distance_known = false;
	evi->distance = INT_MAX;
	evi->previous = NULL;

	*evi_list = lappend(*evi_list, evi);

	return evi;
}

/*
 * Locate the nearest unprocessed ExtensionVersionInfo
 *
 * This part of the algorithm is also about O(N^2).  A priority queue would
 * make it much faster, but for now there's no need.
 */
static ExtensionVersionInfo *
get_nearest_unprocessed_vertex(List *evi_list)
{
	ExtensionVersionInfo *evi = NULL;
	ListCell   *lc;

	foreach(lc, evi_list)
	{
		ExtensionVersionInfo *evi2 = (ExtensionVersionInfo *) lfirst(lc);

		/* only vertices whose distance is still uncertain are candidates */
		if (evi2->distance_known)
			continue;
		/* remember the closest such vertex */
		if (evi == NULL ||
			evi->distance > evi2->distance)
			evi = evi2;
	}

	return evi;
}

/*
 * Obtain information about the set of update scripts available for the
 * specified extension.  The result is a List of ExtensionVersionInfo
 * structs, each with a subsidiary list of the ExtensionVersionInfos for
 * the versions that can be reached in one step from that version.
 */
static List *
get_ext_ver_list(ExtensionControlFile *control)
{
	List	   *evi_list = NIL;
	int			extnamelen = strlen(control->name);
	char	   *location;
	DIR		   *dir;
	struct dirent *de;

	location = get_extension_script_directory(control);
	dir  = AllocateDir(location);
	while ((de = ReadDir(dir, location)) != NULL)
	{
		char	   *vername;
		char	   *vername2;
		ExtensionVersionInfo *evi;
		ExtensionVersionInfo *evi2;

		/* must be a .sql file ... */
		if (!is_extension_script_filename(de->d_name))
			continue;

		/* ... matching extension name followed by separator */
		if (strncmp(de->d_name, control->name, extnamelen) != 0 ||
			de->d_name[extnamelen] != '-' ||
			de->d_name[extnamelen + 1] != '-')
			continue;

		/* extract version name(s) from 'extname--something.sql' filename */
		vername = pstrdup(de->d_name + extnamelen + 2);
		*strrchr(vername, '.') = '\0';
		vername2 = strstr(vername, "--");
		if (!vername2)
		{
			/* It's an install, not update, script; record its version name */