add Host(String) wrapper type

we can use this to handle rocket Requests (from_request)
but we still have to figure out how to automatically assign the type to
custom_domain: Optional<Host>, and public_domain: Host.

plume-models/src/blogs.rs

@@ -7,6 +7,10 @@ use openssl::{
     rsa::Rsa,
     sign::{Signer, Verifier},
 };
+use rocket::{
+    outcome::IntoOutcome,
+    request::{self, FromRequest, Request},
+};
 use serde_json;
 use url::Url;
 use webfinger::*;
@@ -21,11 +25,45 @@ use posts::Post;
 use safe_string::SafeString;
 use schema::blogs;
 use search::Searcher;
+use std::fmt;
 use users::User;
 use {Connection, Error, PlumeRocket, Result};
 
 pub type CustomGroup = CustomObject<ApSignature, Group>;
 
+#[derive(Queryable, Clone)]
+pub struct Host(String);
+
+impl Host {
+    pub fn new<T: Into<String>>(host: T) -> Host {
+        Host(host.into())
+    }
+}
+
+impl Into<String> for Host {
+    fn into(self) -> String {
+        self.0.clone()
+    }
+}
+
+impl From<String> for Host {
+    fn from(s: String) -> Host {
+        Host::new(s)
+    }
+}
+
+impl AsRef<str> for Host {
+    fn as_ref(&self) -> &str {
+        &self.0
+    }
+}
+
+impl std::fmt::Display for Host {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
 #[derive(Queryable, Identifiable, Clone, AsChangeset)]
 #[changeset_options(treat_none_as_null = "true")]
 pub struct Blog {
@@ -294,6 +332,24 @@ impl Blog {
     }
 }
 
+impl<'a, 'r> FromRequest<'a, 'r> for Host {
+    type Error = ();
+
+    fn from_request(request: &'a Request<'r>) -> request::Outcome<Host, ()> {
+        request
+            .headers()
+            .get_one("Host")
+            .and_then(|x| {
+                if x != Instance::get_local().ok()?.public_domain {
+                    Some(Host(x.to_string()))
+                } else {
+                    None
+                }
+            })
+            .or_forward(())
+    }
+}
+
 impl IntoId for Blog {
     fn into_id(self) -> Id {
         Id::new(self.ap_url)