Pass supported_versions from calling module

This finally allows v1, v2 features to be additive. However, it does
complicate the UnknownVersion variant (used only by v1 as far as I can
tell).

I'm inclined to leave this as an open issue until we separate the
receive::{v1,v2} errors from each other.

payjoin/src/receive/error.rs

@@ -123,16 +123,15 @@ impl fmt::Display for RequestError {
                 format!("Content length too large: {}.", length),
             ),
             InternalRequestError::SenderParams(e) => match e {
-                super::optional_parameters::Error::UnknownVersion => {
+                super::optional_parameters::Error::UnknownVersion { supported_versions } => {
                     write!(
                         f,
                         r#"{{
                             "errorCode": "version-unsupported",
                             "supported": "{}",
                             "message": "This version of payjoin is not supported."
                         }}"#,
-                        serde_json::to_string(&super::optional_parameters::SUPPORTED_VERSIONS)
-                            .map_err(|_| fmt::Error)?
+                        serde_json::to_string(supported_versions).map_err(|_| fmt::Error)?
                     )
                 }
                 _ => write_error(f, "sender-params-error", e),

payjoin/src/receive/optional_parameters.rs

@@ -4,11 +4,6 @@ use std::fmt;
 use bitcoin::FeeRate;
 use log::warn;
 
-#[cfg(feature = "v2")]
-pub(crate) const SUPPORTED_VERSIONS: [usize; 2] = [1, 2];
-#[cfg(not(feature = "v2"))]
-pub(crate) const SUPPORTED_VERSIONS: [usize; 1] = [1];
-
 #[derive(Debug, Clone)]
 pub(crate) struct Params {
     // version
@@ -33,8 +28,10 @@ impl Default for Params {
 }
 
 impl Params {
-    #[cfg(feature = "receive")]
-    pub fn from_query_pairs<K, V, I>(pairs: I) -> Result<Self, Error>
+    pub fn from_query_pairs<K, V, I>(
+        pairs: I,
+        supported_versions: &'static [usize],
+    ) -> Result<Self, Error>
     where
         I: Iterator<Item = (K, V)>,
         K: Borrow<str> + Into<String>,
@@ -49,8 +46,8 @@ impl Params {
             match (key.borrow(), v.borrow()) {
                 ("v", version) =>
                     params.v = match version.parse::<usize>() {
-                        Ok(version) if SUPPORTED_VERSIONS.contains(&version) => version,
-                        _ => return Err(Error::UnknownVersion),
+                        Ok(version) if supported_versions.contains(&version) => version,
+                        _ => return Err(Error::UnknownVersion { supported_versions }),
                     },
                 ("additionalfeeoutputindex", index) =>
                     additional_fee_output_index = match index.parse::<usize>() {
@@ -107,14 +104,14 @@ impl Params {
 
 #[derive(Debug)]
 pub(crate) enum Error {
-    UnknownVersion,
+    UnknownVersion { supported_versions: &'static [usize] },
     FeeRate,
 }
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
-            Error::UnknownVersion => write!(f, "unknown version"),
+            Error::UnknownVersion { .. } => write!(f, "unknown version"),
             Error::FeeRate => write!(f, "could not parse feerate"),
         }
     }

payjoin/src/receive/v1.rs

@@ -43,6 +43,8 @@ use super::{
 };
 use crate::psbt::PsbtExt;
 
+const SUPPORTED_VERSIONS: &[usize] = &[1];
+
 pub trait Headers {
     fn get_header(&self, key: &str) -> Option<&str>;
 }
@@ -104,7 +106,8 @@ impl UncheckedProposal {
         log::debug!("Received original psbt: {:?}", psbt);
 
         let pairs = url::form_urlencoded::parse(query.as_bytes());
-        let params = Params::from_query_pairs(pairs).map_err(InternalRequestError::SenderParams)?;
+        let params = Params::from_query_pairs(pairs, SUPPORTED_VERSIONS)
+            .map_err(InternalRequestError::SenderParams)?;
         log::debug!("Received request with params: {:?}", params);
 
         // TODO check that params are valid for the request's Original PSBT

payjoin/src/receive/v2/mod.rs

@@ -23,6 +23,8 @@ use crate::Request;
 
 pub(crate) mod error;
 
+const SUPPORTED_VERSIONS: &[usize] = &[1, 2];
+
 static TWENTY_FOUR_HOURS_DEFAULT_EXPIRY: Duration = Duration::from_secs(60 * 60 * 24);
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -165,8 +167,11 @@ impl Receiver {
         let unchecked_psbt = Psbt::from_str(base64).map_err(InternalRequestError::ParsePsbt)?;
         let psbt = unchecked_psbt.validate().map_err(InternalRequestError::InconsistentPsbt)?;
         log::debug!("Received original psbt: {:?}", psbt);
-        let mut params = Params::from_query_pairs(url::form_urlencoded::parse(query.as_bytes()))
-            .map_err(InternalRequestError::SenderParams)?;
+        let mut params = Params::from_query_pairs(
+            url::form_urlencoded::parse(query.as_bytes()),
+            SUPPORTED_VERSIONS,
+        )
+        .map_err(InternalRequestError::SenderParams)?;
 
         // Output substitution must be disabled for V1 sessions in V2 contexts.
         //