Add basic infrastructure for API calls, GSON, and GSON request class

app/build.gradle

@@ -45,4 +45,5 @@ dependencies {
     implementation "androidx.camera:camera-view:1.0.0-alpha14"
     implementation 'com.google.zxing:core:3.3.0'
     implementation 'com.android.volley:volley:1.2.0'
+    implementation 'com.google.code.gson:gson:2.8.6'
 }

app/src/main/java/dev/garrettmills/starship/hyperlink/util/APIv1.java

@@ -0,0 +1,25 @@
+package dev.garrettmills.starship.hyperlink.util;
+
+import dev.garrettmills.starship.hyperlink.Hyperlink;
+
+public class APIv1 {
+    /**
+     * Given an API endpoint, resolve the fully qualified URL using the stored server address.
+     * Example:
+     * resolveEndpoint("/auth/redeem")  // => "https://hyperlink.url/api/v1/auth/redeem"
+     * @param endpoint un-qualified api endpoint
+     * @return The resolved string.
+     */
+    public static String resolveEndpoint(String endpoint) {
+        if ( !endpoint.startsWith("/") ) {
+            endpoint = "/" + endpoint;
+        }
+
+        String server = Hyperlink.preferences.getString(Hyperlink.SERVER_ADDR, "");
+        if ( server.endsWith("/") ) {
+            server = server.substring(0, server.length() - 1);
+        }
+
+        return server + "/api/v1" + endpoint;
+    }
+}

app/src/main/java/dev/garrettmills/starship/hyperlink/util/GsonRequest.java

@@ -0,0 +1,61 @@
+package dev.garrettmills.starship.hyperlink.util;
+
+import com.android.volley.AuthFailureError;
+import com.android.volley.NetworkResponse;
+import com.android.volley.ParseError;
+import com.android.volley.Request;
+import com.android.volley.Response;
+import com.android.volley.toolbox.HttpHeaderParser;
+import com.google.gson.Gson;
+import com.google.gson.JsonSyntaxException;
+
+import java.io.UnsupportedEncodingException;
+import java.util.Map;
+
+public class GsonRequest<T> extends Request<T> {
+    private final Gson gson = new Gson();
+    private final Class<T> clazz;
+    private final Map<String, String> headers;
+    private final Response.Listener<T> listener;
+
+    /**
+     * Make a GET request and return a parsed object from JSON.
+     *
+     * @param url URL of the request to make
+     * @param clazz Relevant class object, for Gson's reflection
+     * @param headers Map of request headers
+     */
+    public GsonRequest(String url, Class<T> clazz, Map<String, String> headers,
+                       Response.Listener<T> listener, Response.ErrorListener errorListener) {
+        super(Method.GET, url, errorListener);
+        this.clazz = clazz;
+        this.headers = headers;
+        this.listener = listener;
+    }
+
+    @Override
+    public Map<String, String> getHeaders() throws AuthFailureError {
+        return headers != null ? headers : super.getHeaders();
+    }
+
+    @Override
+    protected void deliverResponse(T response) {
+        listener.onResponse(response);
+    }
+
+    @Override
+    protected Response<T> parseNetworkResponse(NetworkResponse response) {
+        try {
+            String json = new String(
+                    response.data,
+                    HttpHeaderParser.parseCharset(response.headers));
+            return Response.success(
+                    gson.fromJson(json, clazz),
+                    HttpHeaderParser.parseCacheHeaders(response));
+        } catch (UnsupportedEncodingException e) {
+            return Response.error(new ParseError(e));
+        } catch (JsonSyntaxException e) {
+            return Response.error(new ParseError(e));
+        }
+    }
+}