encode space to '%20' as per url standard

Previously the space character was exclusively encoded to '+'. This is
wrong, as the URL Standard [0] specifies that the default is '%20'.
Another function has been introduced as well, which replicates the old
behavior and converts spaces to '+'.
Notice that this breaks the default behavior and could lead to bugs.

[0]: https://url.spec.whatwg.org/#string-percent-encode-after-encoding

Fixes: servo#927
Fixes: servo#888

Signed-off-by: Gabriel Goller <g.goller@proxmox.com>

form_urlencoded/src/lib.rs

@@ -116,16 +116,33 @@ impl<'a> Iterator for ParseIntoOwned<'a> {
 
 /// The [`application/x-www-form-urlencoded` byte serializer](
 /// https://url.spec.whatwg.org/#concept-urlencoded-byte-serializer).
+/// Converts spaces (b' ') to the percent-encoded equivalent ("%20").
 ///
 /// Return an iterator of `&str` slices.
 pub fn byte_serialize(input: &[u8]) -> ByteSerialize<'_> {
-    ByteSerialize { bytes: input }
+    ByteSerialize {
+        bytes: input,
+        space_as_plus: false,
+    }
+}
+
+/// The [`application/x-www-form-urlencoded` byte serializer](
+/// https://url.spec.whatwg.org/#concept-urlencoded-byte-serializer).
+/// Converts spaces (b' ') to plus signs (b'+').
+///
+/// Return an iterator of `&str` slices.
+pub fn byte_serialize_space_as_plus(input: &[u8]) -> ByteSerialize<'_> {
+    ByteSerialize {
+        bytes: input,
+        space_as_plus: true,
+    }
 }
 
 /// Return value of `byte_serialize()`.
 #[derive(Debug)]
 pub struct ByteSerialize<'a> {
     bytes: &'a [u8],
+    space_as_plus: bool,
 }
 
 fn byte_serialized_unchanged(byte: u8) -> bool {
@@ -139,7 +156,7 @@ impl<'a> Iterator for ByteSerialize<'a> {
         if let Some((&first, tail)) = self.bytes.split_first() {
             if !byte_serialized_unchanged(first) {
                 self.bytes = tail;
-                return Some(if first == b' ' {
+                return Some(if first == b' ' && self.space_as_plus {
                     "+"
                 } else {
                     percent_encode_byte(first)
@@ -337,7 +354,7 @@ impl<'a, T: Target> Serializer<'a, T> {
     ///     .append_pair("foo", "bar & baz")
     ///     .append_pair("saison", "Été+hiver")
     ///     .finish();
-    /// assert_eq!(encoded, "foo=bar+%26+baz&saison=%C3%89t%C3%A9%2Bhiver");
+    /// assert_eq!(encoded, "foo=bar%20%26%20baz&saison=%C3%89t%C3%A9%2Bhiver");
     /// ```
     ///
     /// Panics if called more than once.
@@ -428,3 +445,34 @@ pub(crate) fn decode_utf8_lossy(input: Cow<'_, [u8]>) -> Cow<'_, str> {
 }
 
 pub type EncodingOverride<'a> = Option<&'a dyn Fn(&str) -> Cow<'_, [u8]>>;
+
+#[cfg(test)]
+mod tests {
+    use alloc::string::String;
+
+    use crate::{byte_serialize, byte_serialize_space_as_plus};
+
+    #[test]
+    fn byte_serializer() {
+        let in_1 = "c ool/org";
+        let out_1 = "c%20ool%2Forg";
+
+        let in_2 = "a🔒nother&bu=ck?et";
+        let out_2 = "a%F0%9F%94%92nother%26bu%3Dck%3Fet";
+
+        assert_eq!(byte_serialize(in_1.as_bytes()).collect::<String>(), out_1);
+        assert_eq!(byte_serialize(in_2.as_bytes()).collect::<String>(), out_2);
+    }
+
+    #[test]
+    fn byte_serializer_space_as_plus() {
+        let in_1 = "c ool/org";
+        let out_1 = "c+ool%2Forg";
+
+        let in_2 = "a🔒nother&bu=ck?et ";
+        let out_2 = "a%F0%9F%94%92nother%26bu%3Dck%3Fet+";
+
+        assert_eq!(byte_serialize_space_as_plus(in_1.as_bytes()).collect::<String>(), out_1);
+        assert_eq!(byte_serialize_space_as_plus(in_2.as_bytes()).collect::<String>(), out_2);
+    }
+}

url/src/lib.rs

@@ -1623,9 +1623,9 @@ impl Url {
     ///     .clear()
     ///     .append_pair("foo", "bar & baz")
     ///     .append_pair("saisons", "\u{00C9}t\u{00E9}+hiver");
-    /// assert_eq!(url.query(), Some("foo=bar+%26+baz&saisons=%C3%89t%C3%A9%2Bhiver"));
+    /// assert_eq!(url.query(), Some("foo=bar%20%26%20baz&saisons=%C3%89t%C3%A9%2Bhiver"));
     /// assert_eq!(url.as_str(),
-    ///            "https://example.net/?foo=bar+%26+baz&saisons=%C3%89t%C3%A9%2Bhiver#nav");
+    ///            "https://example.net/?foo=bar%20%26%20baz&saisons=%C3%89t%C3%A9%2Bhiver#nav");
     /// # Ok(())
     /// # }
     /// # run().unwrap();