Add a function to read an API from a file.

examples/hello-world/main.rs

@@ -2,7 +2,6 @@ use async_std::sync::RwLock;
 use futures::FutureExt;
 use serde::{Deserialize, Serialize};
 use snafu::Snafu;
-use std::fs;
 use std::io;
 use tide_disco::{http::StatusCode, Api, App, Error, RequestError};
 use tracing::info;
@@ -37,10 +36,8 @@ async fn serve(port: u16) -> io::Result<()> {
     let mut app = App::<_, HelloError>::with_state(RwLock::new("Hello".to_string()));
     app.with_version(env!("CARGO_PKG_VERSION").parse().unwrap());
 
-    let mut api = Api::<RwLock<String>, HelloError>::new(toml::from_slice(&fs::read(
-        "examples/hello-world/api.toml",
-    )?)?)
-    .unwrap();
+    let mut api =
+        Api::<RwLock<String>, HelloError>::from_file("examples/hello-world/api.toml").unwrap();
     api.with_version(env!("CARGO_PKG_VERSION").parse().unwrap());
 
     // Can invoke by browsing

src/api.rs

@@ -30,7 +30,9 @@ use serde_with::{serde_as, DisplayFromStr};
 use snafu::{OptionExt, ResultExt, Snafu};
 use std::collections::hash_map::{Entry, HashMap, IntoValues, Values};
 use std::fmt::Display;
+use std::fs;
 use std::ops::Index;
+use std::path::Path;
 use tide::http::content::Accept;
 
 /// An error encountered when parsing or constructing an [Api].
@@ -47,6 +49,7 @@ pub enum ApiError {
     MissingFormatVersion,
     InvalidFormatVersion,
     AmbiguousRoutes { route1: String, route2: String },
+    CannotReadToml { reason: String },
 }
 
 /// Version information about an API.
@@ -178,6 +181,18 @@ impl<State, Error> Api<State, Error> {
         })
     }
 
+    /// Create an [Api] by reading a TOML specification from a file.
+    pub fn from_file<P: AsRef<Path>>(path: P) -> Result<Self, ApiError> {
+        Self::new(
+            toml::from_slice(&fs::read(path).map_err(|err| ApiError::CannotReadToml {
+                reason: err.to_string(),
+            })?)
+            .map_err(|err| ApiError::CannotReadToml {
+                reason: err.to_string(),
+            })?,
+        )
+    }
+
     /// Iterate over groups of routes with the same path.
     pub fn routes_by_path(&self) -> impl Iterator<Item = (&str, RoutesWithPath<'_, State, Error>)> {
         self.routes_by_path.iter().map(|(path, routes)| {