[WIP] API requester abstraction

Authentication, etc. is shuffled into Requester. Implementators
(currently OAuth and Bearer) should prepare proper requests.

4 files changed, 202 insertions, 0 deletions

diff --git a/src/mining/AbstractRequester.java b/src/mining/AbstractRequester.java
new file mode 100644
index 0000000..a42eb80
--- /dev/null
+++ b/src/mining/AbstractRequester.java
@@ -0,0 +1,72 @@
+package mining;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.net.HttpURLConnection;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLConnection;
+import org.apache.commons.io.Charsets;
+import org.apache.commons.io.IOUtils;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+/**
+ * Performs an API Request.
+ *
+ * @author Peter Wu
+ */
+public abstract class AbstractRequester implements Requester {
+
+    @Override
+    public JSONObject getJSON(String resource) throws IOException {
+        HttpURLConnection conn = open(buildUrl(resource));
+        preconnect(conn);
+        if (conn.getResponseCode() != 200) {
+            // TODO: print more helpful details
+            throw new IOException("Unexpected response code");
+        }
+        return getResponseAsJson(conn);
+    }
+
+    protected final URL buildUrl(String resource) throws IOException {
+        String spec = "https://api.twitter.com/1.1/";
+        // TODO: detect API version? For example, drop 1.1 for oauth2/token
+        spec += resource;
+        return new URL(spec);
+    }
+
+    /**
+     * Opens a connection to the URL.
+     */
+    protected final HttpURLConnection open(URL url) throws IOException {
+        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
+        // set default param: fail if no response within 5 seconds
+        conn.setReadTimeout(5000);
+        return conn;
+    }
+
+    /**
+     * Reads the response body from a connection (in JSON format).
+     */
+    protected final JSONObject getResponseAsJson(URLConnection conn)
+            throws IOException {
+        StringWriter writer = new StringWriter();
+        IOUtils.copy(conn.getInputStream(), writer, Charsets.UTF_8);
+        try {
+            return new JSONObject(writer.toString());
+        } catch (JSONException ex) {
+            // treat JSON errors as if an I/O error occurred
+            throw new IOException(ex);
+        }
+    }
+
+    /**
+     * Prepare the request before it gets send.
+     *
+     * @param conn A connection for the request.
+     * @throws java.io.IOException on failing to prepare the request.
+     */
+    protected abstract void preconnect(URLConnection conn)
+            throws IOException;
+}
diff --git a/src/mining/BearerRequester.java b/src/mining/BearerRequester.java
new file mode 100644
index 0000000..94c5314
--- /dev/null
+++ b/src/mining/BearerRequester.java
@@ -0,0 +1,72 @@
+package mining;
+
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URL;
+import java.net.URLConnection;
+import org.apache.commons.codec.binary.Base64;
+import org.apache.commons.io.Charsets;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+/**
+ * An API requester used for application-only requests. Not all requests are
+ * allowed, see https://dev.twitter.com/docs/auth/application-only-auth for
+ * details.
+ *
+ * @author Peter Wu
+ */
+public class BearerRequester extends AbstractRequester {
+
+    private final String access_token;
+
+    /**
+     *
+     * @param access_token The bearer token that authenticates a request.
+     */
+    public BearerRequester(String access_token) {
+        this.access_token = access_token;
+    }
+
+    public BearerRequester(String consumerKey, String consumerSecret)
+            throws IOException {
+        String creds = encodeToken(consumerKey, consumerSecret);
+        String postData = "grant_type=client_credentials";
+        URL url = buildUrl("oauth2/token");
+        HttpURLConnection conn = open(url);
+        conn.setRequestMethod("POST");
+        // set request headers
+        conn.addRequestProperty("Authorization", "Basic " + creds);
+        conn.addRequestProperty("Content-Type",
+                "application/x-www-form-urlencoded; charset=UTF-8");
+        conn.setFixedLengthStreamingMode(postData.length());
+        // connect and send request
+        conn.getOutputStream().write(postData.getBytes(Charsets.UTF_8));
+
+        try {
+            JSONObject resp = getResponseAsJson(conn);
+            // TODO: parse resp.errors
+            if (!resp.getString("token_type").equals("bearer")) {
+                throw new IOException("Expected bearer token type");
+            }
+            access_token = resp.getString("access_token");
+        } catch (JSONException ex) {
+            // treat JSON errors as if an I/O error occurred
+            throw new IOException(ex);
+        }
+    }
+
+    @Override
+    protected void preconnect(URLConnection conn) throws IOException {
+        // requests do not have to be signed, instead rely on the Bearer token
+        conn.addRequestProperty("Authorization", "Bearer " + access_token);
+    }
+
+    private String encodeToken(String consumerKey, String consumerSecret) {
+        StringBuilder sb = new StringBuilder();
+        sb.append(consumerKey);
+        sb.append(":");
+        sb.append(consumerSecret);
+        return Base64.encodeBase64String(sb.toString().getBytes(Charsets.UTF_8));
+    }
+}
diff --git a/src/mining/OAuthRequester.java b/src/mining/OAuthRequester.java
new file mode 100644
index 0000000..e72360e
--- /dev/null
+++ b/src/mining/OAuthRequester.java
@@ -0,0 +1,35 @@
+package mining;
+
+import java.io.IOException;
+import java.net.URLConnection;
+import oauth.signpost.OAuthConsumer;
+import oauth.signpost.basic.DefaultOAuthConsumer;
+import oauth.signpost.exception.OAuthException;
+
+/**
+ * An API requester that uses OAuth to sign its requests.
+ *
+ * @author Peter Wu
+ */
+public class OAuthRequester extends AbstractRequester {
+
+    /**
+     * Instance that signs signs HTTP requests with an OAuth token and secret.
+     */
+    private final OAuthConsumer consumer;
+
+    public OAuthRequester(String consumerKey, String consumerSecret) {
+        // create a new application-specific OAuth consumer
+        consumer = new DefaultOAuthConsumer(consumerKey, consumerSecret);
+        // TODO: access tokens?
+    }
+
+    @Override
+    protected void preconnect(URLConnection conn) throws IOException {
+        try {
+            consumer.sign(conn);
+        } catch (OAuthException ex) {
+            throw new IOException(ex);
+        }
+    }
+}
diff --git a/src/mining/Requester.java b/src/mining/Requester.java
new file mode 100644
index 0000000..931b0ac
--- /dev/null
+++ b/src/mining/Requester.java
@@ -0,0 +1,23 @@
+package mining;
+
+import java.io.IOException;
+import org.json.JSONObject;
+
+/**
+ * Performs an API request.
+ *
+ * @author Peter Wu
+ */
+public interface Requester {
+
+    /**
+     * Performs an API request for a resource, for example
+     * "statuses/mentions_timeline" (note that there is no version or leading
+     * slash).
+     *
+     * @param resource The REST resource.
+     * @return A JSON object resulting from the request.
+     * @throws java.io.IOException on error fetching the resource.
+     */
+    public JSONObject getJSON(String resource) throws IOException;
+}