Add support for abstract Unix-domain sockets

This is a variant of the normal Unix-domain sockets that don't use the
file system but a separate "abstract" namespace.  At the user
interface, such sockets are represented by names starting with "@".
Supported on Linux and Windows right now.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/6dee8574-b0ad-fc49-9c8c-2edc796f0033@2ndquadrant.com

1 files changed, 23 insertions, 1 deletions

diff --git a/src/common/ip.c b/src/common/ip.c
index 69fcca8479..bcc779e00c 100644
--- a/src/common/ip.c
+++ b/src/common/ip.c
@@ -217,6 +217,21 @@ getaddrinfo_unix(const char *path, const struct addrinfo *hintsp,
 
 	strcpy(unp->sun_path, path);
 
+	/*
+	 * If the supplied path starts with @, replace that with a zero byte for
+	 * the internal representation.  In that mode, the entire sun_path is the
+	 * address, including trailing zero bytes.  But we set the address length
+	 * to only include the length of the original string.  That way the
+	 * trailing zero bytes won't show up in any network or socket lists of the
+	 * operating system.  This is just a convention, also followed by other
+	 * packages.
+	 */
+	if (path[0] == '@')
+	{
+		unp->sun_path[0] = '\0';
+		aip->ai_addrlen = offsetof(struct sockaddr_un, sun_path) + strlen(path);
+	}
+
 #ifdef HAVE_STRUCT_SOCKADDR_STORAGE_SS_LEN
 	unp->sun_len = sizeof(struct sockaddr_un);
 #endif
@@ -249,7 +264,14 @@ getnameinfo_unix(const struct sockaddr_un *sa, int salen,
 
 	if (service)
 	{
-		ret = snprintf(service, servicelen, "%s", sa->sun_path);
+		/*
+		 * Check whether it looks like an abstract socket, but it could also
+		 * just be an empty string.
+		 */
+		if (sa->sun_path[0] == '\0' && sa->sun_path[1] != '\0')
+			ret = snprintf(service, servicelen, "@%s", sa->sun_path + 1);
+		else
+			ret = snprintf(service, servicelen, "%s", sa->sun_path);
 		if (ret < 0 || ret >= servicelen)
 			return EAI_MEMORY;
 	}