credential_format(): also encode <host>[:<port>]

An upcoming change wants to sanitize the credential password prompt
where a URL is displayed that may potentially come from a `.gitmodules`
file. To this end, the `credential_format()` function is employed.

To sanitize the host name (and optional port) part of the URL, we need a
new mode of the `strbuf_add_percentencode()` function because the
current mode is both too strict and too lenient: too strict because it
encodes `:`, `[` and `]` (which should be left unencoded in
`<host>:<port>` and in IPv6 addresses), and too lenient because it does
not encode invalid host name characters `/`, `_` and `~`.

So let's introduce and use a new mode specifically to encode the host
name and optional port part of a URI, leaving alpha-numerical
characters, periods, colons and brackets alone and encoding all others.

This only leads to a change of behavior for URLs that contain invalid
host names.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

credential.c

@@ -164,7 +164,8 @@ static void credential_format(struct credential *c, struct strbuf *out)
 		strbuf_addch(out, '@');
 	}
 	if (c->host)
-		strbuf_addstr(out, c->host);
+		strbuf_add_percentencode(out, c->host,
+					 STRBUF_ENCODE_HOST_AND_PORT);
 	if (c->path) {
 		strbuf_addch(out, '/');
 		strbuf_add_percentencode(out, c->path, 0);

strbuf.c

@@ -492,7 +492,9 @@ void strbuf_add_percentencode(struct strbuf *dst, const char *src, int flags)
 		unsigned char ch = src[i];
 		if (ch <= 0x1F || ch >= 0x7F ||
 		    (ch == '/' && (flags & STRBUF_ENCODE_SLASH)) ||
-		    strchr(URL_UNSAFE_CHARS, ch))
+		    ((flags & STRBUF_ENCODE_HOST_AND_PORT) ?
+		     !isalnum(ch) && !strchr("-.:[]", ch) :
+		     !!strchr(URL_UNSAFE_CHARS, ch)))
 			strbuf_addf(dst, "%%%02X", (unsigned char)ch);
 		else
 			strbuf_addch(dst, ch);

strbuf.h

@@ -380,6 +380,7 @@ size_t strbuf_expand_dict_cb(struct strbuf *sb,
 void strbuf_addbuf_percentquote(struct strbuf *dst, const struct strbuf *src);
 
 #define STRBUF_ENCODE_SLASH 1
+#define STRBUF_ENCODE_HOST_AND_PORT 2
 
 /**
  * Append the contents of a string to a strbuf, percent-encoding any characters

t/t0300-credentials.sh

@@ -514,6 +514,19 @@ test_expect_success 'match percent-encoded values in username' '
 	EOF
 '
 
+test_expect_success 'match percent-encoded values in hostname' '
+	test_config "credential.https://a%20b%20c/.helper" "$HELPER" &&
+	check fill <<-\EOF
+	url=https://a b c/
+	--
+	protocol=https
+	host=a b c
+	username=foo
+	password=bar
+	--
+	EOF
+'
+
 test_expect_success 'fetch with multiple path components' '
 	test_unconfig credential.helper &&
 	test_config credential.https://example.com/foo/repo.git.helper "verbatim foo bar" &&