From dfd76f4dbcf3834371442d593d315797762bbd11 Mon Sep 17 00:00:00 2001
From: Jacob Champion <jchampion@timescale.com>
Date: Tue, 19 Jul 2022 10:48:58 -0700
Subject: [PATCH v3 1/2] pg_clean_ascii(): escape bytes rather than lose them

Rather than replace each unprintable byte with a '?' character, replace
it with a hex escape instead. The API now allocates a copy rather than
modifying the input in place.
---
 src/backend/postmaster/postmaster.c |  6 +-----
 src/backend/utils/misc/guc.c        |  4 ++--
 src/common/string.c                 | 26 +++++++++++++++++---------
 src/include/common/string.h         |  2 +-
 4 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 1c25457526..5e8cd770c0 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -2284,11 +2284,7 @@ retry1:
 				 */
 				if (strcmp(nameptr, "application_name") == 0)
 				{
-					char	   *tmp_app_name = pstrdup(valptr);
-
-					pg_clean_ascii(tmp_app_name);
-
-					port->application_name = tmp_app_name;
+					port->application_name = pg_clean_ascii(valptr);
 				}
 			}
 			offset = valoffset + strlen(valptr) + 1;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 0328029d43..60400752e5 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -12480,7 +12480,7 @@ static bool
 check_application_name(char **newval, void **extra, GucSource source)
 {
 	/* Only allow clean ASCII chars in the application name */
-	pg_clean_ascii(*newval);
+	*newval = guc_strdup(ERROR, pg_clean_ascii(*newval));
 
 	return true;
 }
@@ -12496,7 +12496,7 @@ static bool
 check_cluster_name(char **newval, void **extra, GucSource source)
 {
 	/* Only allow clean ASCII chars in the cluster name */
-	pg_clean_ascii(*newval);
+	*newval = guc_strdup(ERROR, pg_clean_ascii(*newval));
 
 	return true;
 }
diff --git a/src/common/string.c b/src/common/string.c
index 16940d1fa7..db15324c62 100644
--- a/src/common/string.c
+++ b/src/common/string.c
@@ -22,6 +22,7 @@
 #endif
 
 #include "common/string.h"
+#include "lib/stringinfo.h"
 
 
 /*
@@ -59,9 +60,9 @@ strtoint(const char *pg_restrict str, char **pg_restrict endptr, int base)
 
 
 /*
- * pg_clean_ascii -- Replace any non-ASCII chars with a '?' char
+ * pg_clean_ascii -- Replace any non-ASCII chars with a "\xXX" string
  *
- * Modifies the string passed in which must be '\0'-terminated.
+ * Makes a palloc'd copy of the string passed in, which must be '\0'-terminated.
  *
  * This function exists specifically to deal with filtering out
  * non-ASCII characters in a few places where the client can provide an almost
@@ -73,22 +74,29 @@ strtoint(const char *pg_restrict str, char **pg_restrict endptr, int base)
  * In general, this function should NOT be used- instead, consider how to handle
  * the string without needing to filter out the non-ASCII characters.
  *
- * Ultimately, we'd like to improve the situation to not require stripping out
- * all non-ASCII but perform more intelligent filtering which would allow UTF or
+ * Ultimately, we'd like to improve the situation to not require replacing all
+ * non-ASCII but perform more intelligent filtering which would allow UTF or
  * similar, but it's unclear exactly what we should allow, so stick to ASCII only
  * for now.
  */
-void
-pg_clean_ascii(char *str)
+char *
+pg_clean_ascii(const char *str)
 {
-	/* Only allow clean ASCII chars in the string */
-	char	   *p;
+	StringInfoData buf;
+	const char   *p;
+
+	initStringInfo(&buf);
 
 	for (p = str; *p != '\0'; p++)
 	{
+		/* Only allow clean ASCII chars in the string */
 		if (*p < 32 || *p > 126)
-			*p = '?';
+			appendStringInfo(&buf, "\\x%02x", (unsigned char) *p);
+		else
+			appendStringInfoChar(&buf, *p);
 	}
+
+	return buf.data;
 }
 
 
diff --git a/src/include/common/string.h b/src/include/common/string.h
index cf00fb53cd..d10d0c9cbf 100644
--- a/src/include/common/string.h
+++ b/src/include/common/string.h
@@ -24,7 +24,7 @@ typedef struct PromptInterruptContext
 extern bool pg_str_endswith(const char *str, const char *end);
 extern int	strtoint(const char *pg_restrict str, char **pg_restrict endptr,
 					 int base);
-extern void pg_clean_ascii(char *str);
+extern char *pg_clean_ascii(const char *str);
 extern int	pg_strip_crlf(char *str);
 extern bool pg_is_ascii(const char *str);
 
-- 
2.25.1