set up schema submodule with local resolver

src/request/mod.rs

+pub mod message;
+pub mod schema;
\ No newline at end of file

src/request/schema.rs

+use std::fs;
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+
+use anyhow::anyhow;
+use jsonschema::{JSONSchema, SchemaResolver, SchemaResolverError};
+use log::warn;
+use serde_json::{json, Value};
+use url::Url;
+
+pub fn load_schema(schema_dir: &Path) -> JSONSchema {
+    let schema_json = read_schema(schema_dir);
+    compile_schema(&schema_json, schema_dir)
+}
+
+fn read_schema(schema_dir: &Path) -> Value {
+    let schema_path = schema_dir.join("api.json");
+    read_json_from_path(schema_path.as_path())
+}
+
+fn read_json_from_path(path: &Path) -> Value {
+    let json_string = fs::read_to_string(path).expect("Valid path");
+    serde_json::from_str(&json_string).expect("Valid JSON")
+}
+
+fn compile_schema(schema: &Value, schema_dir: &Path) -> JSONSchema {
+    let resolver = LocalResolver { schema_dir: PathBuf::from(schema_dir) };
+    JSONSchema::options()
+        .with_resolver(resolver)
+        .compile(schema)
+        .expect("Valid schema")
+}
+
+/*
+Set up a resolver that will work with local JSON schema
+The local schema contain relative references to local files in the same directory
+In the future we should change to online schemas with absolute references
+*/
+struct LocalResolver {
+    schema_dir: PathBuf,
+}
+
+impl SchemaResolver for LocalResolver {
+    fn resolve(&self, _root_schema: &Value, url: &Url, _original_reference: &str) -> Result<Arc<Value>, SchemaResolverError> {
+        match url.scheme() {
+            "json-schema" => {
+                let local_schema_path: PathBuf = self.schema_dir.join(_original_reference);
+                Ok(Arc::new(read_json_from_path(local_schema_path.as_path())))
+            }
+            _ => Err(anyhow!("scheme is not supported"))
+        }
+    }
+}
+