paddle: Take any kind of `str` reference input, not just `&str`

Use `AsRef<str>` instead of `&str` to offer a more flexible interface.
We need this because `url::form_urlencoded::parse()` gives us an
iterator of `(Cow<_, str>, Cow<_, str>)`, and we want to pass that into
`verify_signature()`.

Also change `key.len()` and `value.len()` to `.chars().count()` because
I was having a hard time getting the `len()` method from a trait (`str`
doesn't implement `ExactSizeIterator`), and I learned this:

> This length is in bytes, not chars or graphemes. In other words, it
> may not be what a human considers the length of the string.

(https://doc.rust-lang.org/std/primitive.str.html#method.len)

Also:
https://stackoverflow.com/questions/46290655/get-the-string-length-in-characters-in-rust/46290728#46290728

I assume the PHP serializer uses character count instead of byte length.

1 files changed, 15 insertions, 6 deletions

diff --git a/license-generator/paddle/src/lib.rs b/license-generator/paddle/src/lib.rs
index 3ebc3f2..11fd87f 100644
--- a/license-generator/paddle/src/lib.rs
+++ b/license-generator/paddle/src/lib.rs
@@ -1,5 +1,8 @@
 extern crate openssl;
 
+use std::fmt::Display;
+use std::ops::Deref;
+
 use openssl::hash::MessageDigest;
 use openssl::pkey::PKey;
 use openssl::rsa::Rsa;
@@ -7,8 +10,11 @@ use openssl::sign::Verifier;
 
 
 // https://paddle.com/docs/reference-verifying-webhooks/
-fn verify_signature<'a, I>(pem: &[u8], signature: &str, params: I) -> bool
-where I: IntoIterator<Item = (&'a str, &'a str)> + PartialOrd {
+pub fn verify_signature<'a, S, I>(pem: &[u8], signature: &str, params: I) -> bool
+where
+    S: AsRef<str> + Deref<Target = str> + Display,
+    I: IntoIterator<Item = (S, S)> + PartialOrd,
+{
     let rsa = Rsa::public_key_from_pem(pem).unwrap();
     let pkey = PKey::from_rsa(rsa).unwrap();
     let mut verifier = Verifier::new(MessageDigest::sha1(), &pkey).unwrap();
@@ -19,8 +25,11 @@ where I: IntoIterator<Item = (&'a str, &'a str)> + PartialOrd {
     verifier.verify(signature.as_ref()).unwrap()
 }
 
-fn php_serialize<'a, I>(pairs: I) -> String
-where I: IntoIterator<Item = (&'a str, &'a str)> + PartialOrd {
+fn php_serialize<'a, S, I>(pairs: I) -> String
+where
+    S: AsRef<str> + Deref<Target = str> + Display,
+    I: IntoIterator<Item = (S, S)> + PartialOrd,
+{
     let mut serialized = String::with_capacity(500);
 
     let mut len = 0;
@@ -28,9 +37,9 @@ where I: IntoIterator<Item = (&'a str, &'a str)> + PartialOrd {
         serialized.push_str(
             &format!(
                 "s:{key_length}:\"{key}\";s:{value_length}:\"{value}\";",
-                key_length = key.len(),
+                key_length = key.chars().count(),
                 key = key,
-                value_length = value.len(),
+                value_length = value.chars().count(),
                 value = value
             )
         );