sd-bus: introduce new match type "arg0has=" for matching arrays of strings

Previously, sd-bus inofficially already supported bus matches that
tested a string against an array of strings ("as"). This was done via an
enhanced way to interpret "arg0=" matches. This is problematic however,
since clients have no way to determine if their respective
implementation understood strv matches or not, thus allowing invalid
matches to be installed without a way to detect that.

This patch changes the logic to only allow such matches with a new
"arg0has=" syntax. This has the benefit that non-conforming
implementations will return a parse error and a client application may
thus efficiently detect support for the match type.

Matches of this type are useful for "udev"-like systems that "tag" objects
with a number of strings, and clients need to be able to match against
any of these "tags".

The name "has" takes inspiration from Python's ".has_key()" construct.

1 files changed, 48 insertions, 21 deletions

diff --git a/src/libsystemd/sd-bus/bus-message.c b/src/libsystemd/sd-bus/bus-message.c
index a212f0b398..970aaabdc2 100644
--- a/src/libsystemd/sd-bus/bus-message.c
+++ b/src/libsystemd/sd-bus/bus-message.c
@@ -5611,21 +5611,23 @@ _public_ int sd_bus_message_read_strv(sd_bus_message *m, char ***l) {
         return 1;
 }
 
-int bus_message_get_arg(sd_bus_message *m, unsigned i, const char **str, char ***strv) {
-        const char *contents;
+static int bus_message_get_arg_skip(
+                sd_bus_message *m,
+                unsigned i,
+                char *_type,
+                const char **_contents) {
+
         unsigned j;
-        char type;
         int r;
 
-        assert(m);
-        assert(str);
-        assert(strv);
-
         r = sd_bus_message_rewind(m, true);
         if (r < 0)
                 return r;
 
         for (j = 0;; j++) {
+                const char *contents;
+                char type;
+
                 r = sd_bus_message_peek_type(m, &type, &contents);
                 if (r < 0)
                         return r;
@@ -5637,31 +5639,56 @@ int bus_message_get_arg(sd_bus_message *m, unsigned i, const char **str, char **
                     !(type == SD_BUS_TYPE_ARRAY && STR_IN_SET(contents, "s", "o", "g")))
                         return -ENXIO;
 
-                if (j >= i)
-                        break;
+                if (j >= i) {
+                        if (_contents)
+                                *_contents = contents;
+                        if (_type)
+                                *_type = type;
+                        return 0;
+                }
 
                 r = sd_bus_message_skip(m, NULL);
                 if (r < 0)
                         return r;
         }
 
-        if (type == SD_BUS_TYPE_ARRAY) {
+}
 
-                r = sd_bus_message_read_strv(m, strv);
-                if (r < 0)
-                        return r;
+int bus_message_get_arg(sd_bus_message *m, unsigned i, const char **str) {
+        char type;
+        int r;
 
-                *str = NULL;
+        assert(m);
+        assert(str);
 
-        } else {
-                r = sd_bus_message_read_basic(m, type, str);
-                if (r < 0)
-                        return r;
+        r = bus_message_get_arg_skip(m, i, &type, NULL);
+        if (r < 0)
+                return r;
 
-                *strv = NULL;
-        }
+        if (!IN_SET(type, SD_BUS_TYPE_STRING, SD_BUS_TYPE_OBJECT_PATH, SD_BUS_TYPE_SIGNATURE))
+                return -ENXIO;
 
-        return 0;
+        return sd_bus_message_read_basic(m, type, str);
+}
+
+int bus_message_get_arg_strv(sd_bus_message *m, unsigned i, char ***strv) {
+        const char *contents;
+        char type;
+        int r;
+
+        assert(m);
+        assert(strv);
+
+        r = bus_message_get_arg_skip(m, i, &type, &contents);
+        if (r < 0)
+                return r;
+
+        if (type != SD_BUS_TYPE_ARRAY)
+                return -ENXIO;
+        if (!STR_IN_SET(contents, "s", "o", "g"))
+                return -ENXIO;
+
+        return sd_bus_message_read_strv(m, strv);
 }
 
 _public_ int sd_bus_message_get_errno(sd_bus_message *m) {