Handle OHTTP key rejection responses

Clients with bad OHTTP key configurations should not retry requests to
the directory with the same key configuration, so they must be able to
switch on that error variant.

Author: spacebear21

payjoin/src/ohttp.rs

@@ -3,6 +3,7 @@ use std::{error, fmt};
 
 use bitcoin::bech32::{self, EncodeError};
 use bitcoin::key::constants::UNCOMPRESSED_PUBLIC_KEY_SIZE;
+use http::HeaderValue;
 
 use crate::directory::ENCAPSULATED_MESSAGE_BYTES;
 
@@ -53,6 +54,7 @@ pub fn ohttp_encapsulate(
 pub enum DirectoryResponseError {
     InvalidSize(usize),
     OhttpDecapsulation(OhttpEncapsulationError),
+    OhttpKeyRejected,
     UnexpectedStatusCode(http::StatusCode),
 }
 
@@ -64,6 +66,11 @@ pub fn process_get_res(
     let body = match response.status() {
         http::StatusCode::OK => response.body().to_vec(),
         http::StatusCode::ACCEPTED => return Ok(None),
+        http::StatusCode::BAD_REQUEST => match response.headers().get("content-type") {
+            Some(t) if t == HeaderValue::from_static("application/problem+json") =>
+                return Err(DirectoryResponseError::OhttpKeyRejected),
+            _ => return Err(DirectoryResponseError::UnexpectedStatusCode(response.status())),
+        },
         _ => return Err(DirectoryResponseError::UnexpectedStatusCode(response.status())),
     };
     Ok(Some(body))
@@ -76,6 +83,11 @@ pub fn process_post_res(
     let response = process_ohttp_res(res, ohttp_context)?;
     match response.status() {
         http::StatusCode::OK => return Ok(()),
+        http::StatusCode::BAD_REQUEST => match response.headers().get("content-type") {
+            Some(t) if t == HeaderValue::from_static("application/problem+json") =>
+                return Err(DirectoryResponseError::OhttpKeyRejected),
+            _ => return Err(DirectoryResponseError::UnexpectedStatusCode(response.status())),
+        },
         _ => return Err(DirectoryResponseError::UnexpectedStatusCode(response.status())),
     };
 }

payjoin/src/receive/v2/error.rs

@@ -30,6 +30,7 @@ impl From<DirectoryResponseError> for SessionError {
                 InternalSessionError::OhttpEncapsulation(e),
             DirectoryResponseError::UnexpectedStatusCode(e) =>
                 InternalSessionError::UnexpectedStatusCode(e),
+            DirectoryResponseError::OhttpKeyRejected => todo!(),
         }
         .into()
     }

payjoin/src/send/v2/error.rs

@@ -131,6 +131,7 @@ impl From<DirectoryResponseError> for EncapsulationError {
             DirectoryResponseError::OhttpDecapsulation(e) => InternalEncapsulationError::Ohttp(e),
             DirectoryResponseError::UnexpectedStatusCode(e) =>
                 InternalEncapsulationError::UnexpectedStatusCode(e),
+            DirectoryResponseError::OhttpKeyRejected => todo!(),
         }
         .into()
     }