uri: uri.format encapsulate IPv6 address in []

This patch adds encapsulation for IPv6 addresses in brackets when
calling uri.format (as per RFC 2732).

Closes #9556

NO_DOC=bugfix

(cherry picked from commit a49ec23b85edb684744eb525427465dfa4f660e1)

changelogs/unreleased/gh-9556-fix-uri-ipv6.md

 ## bugfix/lua/uri
 
 * Fixed a bug that caused characters A-F to be unsupported in IPv6
-  addresses (gh-9556).
+  addresses. Changed the `uri.format` output for IPv6 to be
+  encapsulated in brackets `[]` (gh-9556).

src/lib/uri/uri.c

@@ -309,7 +309,10 @@ uri_format(char *str, int len, const struct uri *uri, bool write_password)
 		SNPRINT(total, snprintf, str, len, "@");
 	}
 	if (uri->host != NULL) {
-		SNPRINT(total, snprintf, str, len, "%s", uri->host);
+		if (uri->host_hint == 2)
+			SNPRINT(total, snprintf, str, len, "[%s]", uri->host);
+		else
+			SNPRINT(total, snprintf, str, len, "%s", uri->host);
 	}
 	if (uri->service != NULL) {
 		if (uri->host != NULL) {

src/lua/uri.lua

@@ -231,6 +231,16 @@ local function format(uri, write_password)
     uribuf.path = uri.path
     uribuf.query = uri.query
     uribuf.fragment = uri.fragment
+    -- The `uri_format` function needs the hint to enclose an IPv6
+    -- address into square brackets. So we must set the `host_hint`
+    -- to determine the type of `uri.host`.
+    if uri.ipv4 ~= nil then
+        uribuf.host_hint = 1
+    elseif uri.ipv6 ~= nil then
+        uribuf.host_hint = 2
+    else
+        uribuf.host_hint = 3
+    end
     fill_uribuf_params(uribuf, uri)
     local ibuf = cord_ibuf_take()
     local str = ibuf:alloc(1024)

test/app-luatest/gh_9556_uri_parse_format_ipv6_test.lua

@@ -55,3 +55,15 @@ g1.test_parse_urls_with_ipv6_addresses = function(cg)
         t.assert_equals(value, res[key], msg)
     end
 end
+
+
+g1.test_format_urls_with_ipv6_addresses = function(cg)
+    -- This test checks the correct formatting URIs containing IPv6 addresses.
+    local url = join_url(cg.params)
+    local res = uri.parse(url)
+    t.assert_not_equals(res, nil, string.format('Error while parsing %q', url))
+    t.assert_equals(type(res), 'table',
+                    string.format('uri.parse(%q) is not a table', url))
+    local u = uri.format(res)
+    t.assert_equals(url, u)
+end