Fix relative URI serialisation

4 files changed, 30 insertions, 6 deletions

diff --git a/NEWS b/NEWS
index b54e8bd4..3752c90f 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,7 @@ serd (0.29.3) unstable;
   * Clarify errors returned by serd_env_expand()
   * Fix reported error when reading statements with only a blank node
   * Fix parsing local names that end with escaped dots
+  * Improve relative URI serialisation
   * Add serdi option to write ASCII output
   * Make serdi guess input syntax from extension if unspecified
   * Make serdi syntax options case-insensitive
diff --git a/src/serd_internal.h b/src/serd_internal.h
index cfcdc82c..52dd31ed 100644
--- a/src/serd_internal.h
+++ b/src/serd_internal.h
@@ -431,9 +431,9 @@ uri_path_at(const SerdURI* uri, size_t i)
 	}
 }
 
-/** Return true iff `uri` is within the base of `root` */
+/** Return true iff `uri` shares path components with `root` */
 static inline bool
-uri_is_under(const SerdURI* uri, const SerdURI* root)
+uri_is_related(const SerdURI* uri, const SerdURI* root)
 {
 	if (!root || !root->scheme.len ||
 	    !chunk_equals(&root->scheme, &uri->scheme) ||
@@ -456,6 +456,13 @@ uri_is_under(const SerdURI* uri, const SerdURI* root)
 	return true;
 }
 
+/** Return true iff `uri` is within the base of `root` */
+static inline bool
+uri_is_under(const SerdURI* uri, const SerdURI* root)
+{
+	return uri->path.len >= root->path.len && uri_is_related(uri, root);
+}
+
 static inline bool
 is_uri_scheme_char(const uint8_t c)
 {
diff --git a/src/uri.c b/src/uri.c
index 7b172e42..e6f03547 100644
--- a/src/uri.c
+++ b/src/uri.c
@@ -433,8 +433,6 @@ write_rel_path(SerdSink       sink,
 
 	if (i == path_len && i == base_len) {  // Paths are identical
 		return 0;
-	} else if (last_shared_sep == 0) {  // No common components
-		return write_path_tail(sink, stream, uri, 0);
 	}
 
 	// Find the number of up references ("..") required
@@ -451,6 +449,10 @@ write_rel_path(SerdSink       sink,
 		len += sink("../", 3, stream);
 	}
 
+	if (last_shared_sep == 0 && up == 0) {
+		len += sink("/", 1, stream);
+	}
+
 	// Write suffix
 	return len += write_path_tail(sink, stream, uri, last_shared_sep + 1);
 }
@@ -464,8 +466,10 @@ serd_uri_serialise_relative(const SerdURI* uri,
                             SerdSink       sink,
                             void*          stream)
 {
-	size_t     len      = 0;
-	const bool relative = uri_is_under(uri, root ? root : base);
+	size_t     len = 0;
+	const bool relative =
+		root ? uri_is_under(uri, root) : uri_is_related(uri, base);
+
 	if (relative) {
 		len = write_rel_path(sink, stream, uri, base);
 	}
diff --git a/tests/serd_test.c b/tests/serd_test.c
index b80c8b82..945fefe3 100644
--- a/tests/serd_test.c
+++ b/tests/serd_test.c
@@ -408,6 +408,18 @@ main(void)
 		FAILF("Bad relative URI %s (expected '/foo/bar')\n", rel.buf);
 	}
 
+	SerdNode up = serd_node_new_relative_uri(&base_uri, &abs_uri, NULL, NULL);
+	if (strcmp((const char*)up.buf, "../")) {
+		FAILF("Bad relative URI %s (expected '../')\n", up.buf);
+	}
+
+	SerdNode noup = serd_node_new_relative_uri(&base_uri, &abs_uri, &abs_uri, NULL);
+	if (strcmp((const char*)noup.buf, "http://example.org/")) {
+		FAILF("Bad relative URI %s (expected 'http://example.org/')\n", noup.buf);
+	}
+
+	serd_node_free(&noup);
+	serd_node_free(&up);
 	serd_node_free(&rel);
 	serd_node_free(&base);