no-std support for monero-serai (#311)

* Move monero-serai from std to std-shims, where possible

* no-std fixes

* Make the HttpRpc its own feature, thiserror only on std

* Drop monero-rs's epee for a homegrown one

We only need it for a single function. While I tried jeffro's, it didn't work
out of the box, had three unimplemented!s, and is no where near viable for
no_std.

Fixes #182, though should be further tested.

* no-std monero-serai

* Allow base58-monero via git

* cargo fmt

coins/monero/src/rpc/http.rs

@@ -0,0 +1,91 @@
+use async_trait::async_trait;
+
+use digest_auth::AuthContext;
+use reqwest::Client;
+
+use crate::rpc::{RpcError, RpcConnection, Rpc};
+
+#[derive(Clone, Debug)]
+pub struct HttpRpc {
+  client: Client,
+  userpass: Option<(String, String)>,
+  url: String,
+}
+
+impl HttpRpc {
+  /// Create a new HTTP(S) RPC connection.
+  ///
+  /// A daemon requiring authentication can be used via including the username and password in the
+  /// URL.
+  pub fn new(mut url: String) -> Result<Rpc<HttpRpc>, RpcError> {
+    // Parse out the username and password
+    let userpass = if url.contains('@') {
+      let url_clone = url;
+      let split_url = url_clone.split('@').collect::<Vec<_>>();
+      if split_url.len() != 2 {
+        Err(RpcError::InvalidNode)?;
+      }
+      let mut userpass = split_url[0];
+      url = split_url[1].to_string();
+
+      // If there was additionally a protocol string, restore that to the daemon URL
+      if userpass.contains("://") {
+        let split_userpass = userpass.split("://").collect::<Vec<_>>();
+        if split_userpass.len() != 2 {
+          Err(RpcError::InvalidNode)?;
+        }
+        url = split_userpass[0].to_string() + "://" + &url;
+        userpass = split_userpass[1];
+      }
+
+      let split_userpass = userpass.split(':').collect::<Vec<_>>();
+      if split_userpass.len() != 2 {
+        Err(RpcError::InvalidNode)?;
+      }
+      Some((split_userpass[0].to_string(), split_userpass[1].to_string()))
+    } else {
+      None
+    };
+
+    Ok(Rpc(HttpRpc { client: Client::new(), userpass, url }))
+  }
+}
+
+#[async_trait]
+impl RpcConnection for HttpRpc {
+  async fn post(&self, route: &str, body: Vec<u8>) -> Result<Vec<u8>, RpcError> {
+    let mut builder = self.client.post(self.url.clone() + "/" + route).body(body);
+
+    if let Some((user, pass)) = &self.userpass {
+      let req = self.client.post(&self.url).send().await.map_err(|_| RpcError::InvalidNode)?;
+      // Only provide authentication if this daemon actually expects it
+      if let Some(header) = req.headers().get("www-authenticate") {
+        builder = builder.header(
+          "Authorization",
+          digest_auth::parse(header.to_str().map_err(|_| RpcError::InvalidNode)?)
+            .map_err(|_| RpcError::InvalidNode)?
+            .respond(&AuthContext::new_post::<_, _, _, &[u8]>(
+              user,
+              pass,
+              "/".to_string() + route,
+              None,
+            ))
+            .map_err(|_| RpcError::InvalidNode)?
+            .to_header_string(),
+        );
+      }
+    }
+
+    Ok(
+      builder
+        .send()
+        .await
+        .map_err(|_| RpcError::ConnectionError)?
+        .bytes()
+        .await
+        .map_err(|_| RpcError::ConnectionError)?
+        .slice(..)
+        .to_vec(),
+    )
+  }
+}