fix: update stale Twitter URLs, extract error message constant, improve HMAC perf and code style

src/main/java/com/stripe/exception/ApiConnectionException.java

@@ -10,4 +10,23 @@ public ApiConnectionException(String message) {
   public ApiConnectionException(String message, Throwable e) {
     super(message, null, null, 0, e);
   }
+
+  /**
+   * Creates an {@link ApiConnectionException} with a standard message for IO errors during API
+   * requests.
+   *
+   * @param url the base URL that the request was made to
+   * @param cause the underlying IOException
+   * @return the exception
+   */
+  public static ApiConnectionException create(String url, Throwable cause) {
+    String message =
+        String.format(
+            "IOException during API request to Stripe (%s): %s "
+                + "Please check your internet connection and try again. If this problem persists,"
+                + " you should check Stripe's service status at https://status.stripe.com,"
+                + " or let us know at support@stripe.com.",
+            url, cause.getMessage());
+    return new ApiConnectionException(message, cause);
+  }
 }

src/main/java/com/stripe/net/HttpURLConnectionClient.java

@@ -45,14 +45,7 @@ public StripeResponseStream requestStream(StripeRequest request) throws ApiConne
       return new StripeResponseStream(responseCode, headers, responseStream);
 
     } catch (IOException e) {
-      throw new ApiConnectionException(
-          String.format(
-              "IOException during API request to Stripe (%s): %s "
-                  + "Please check your internet connection and try again. If this problem persists,"
-                  + "you should check Stripe's service status at https://twitter.com/stripestatus,"
-                  + " or let us know at support@stripe.com.",
-              Stripe.getApiBase(), e.getMessage()),
-          e);
+      throw ApiConnectionException.create(Stripe.getApiBase(), e);
     }
   }
 
@@ -69,14 +62,7 @@ public StripeResponse request(StripeRequest request) throws ApiConnectionExcepti
     try {
       return responseStream.unstream();
     } catch (IOException e) {
-      throw new ApiConnectionException(
-          String.format(
-              "IOException during API request to Stripe (%s): %s "
-                  + "Please check your internet connection and try again. If this problem persists,"
-                  + "you should check Stripe's service status at https://twitter.com/stripestatus,"
-                  + " or let us know at support@stripe.com.",
-              Stripe.getApiBase(), e.getMessage()),
-          e);
+      throw ApiConnectionException.create(Stripe.getApiBase(), e);
     }
   }
 

src/main/java/com/stripe/net/LiveStripeResponseGetter.java

@@ -181,14 +181,7 @@ public InputStream requestStream(ApiRequest apiRequest) throws StripeException {
       try {
         response = responseStream.unstream();
       } catch (IOException e) {
-        throw new ApiConnectionException(
-            String.format(
-                "IOException during API request to Stripe (%s): %s "
-                    + "Please check your internet connection and try again. If this problem persists,"
-                    + "you should check Stripe's service status at https://twitter.com/stripestatus,"
-                    + " or let us know at support@stripe.com.",
-                Stripe.getApiBase(), e.getMessage()),
-            e);
+        throw ApiConnectionException.create(Stripe.getApiBase(), e);
       }
       handleError(response, apiRequest.getApiMode());
     }

src/main/java/com/stripe/net/RequestTelemetry.java

@@ -74,7 +74,7 @@ public void maybeEnqueueMetrics(
       return;
     }
 
-    if (usage != null && usage.size() == 0) {
+    if (usage != null && usage.isEmpty()) {
       usage = null;
     }
 

src/main/java/com/stripe/net/StripeRequest.java

@@ -75,14 +75,7 @@ private StripeRequest(
       this.headers = buildHeaders(method, this.options, this.content, apiMode);
       this.apiMode = apiMode;
     } catch (IOException e) {
-      throw new ApiConnectionException(
-          String.format(
-              "IOException during API request to Stripe (%s): %s "
-                  + "Please check your internet connection and try again. If this problem persists,"
-                  + "you should check Stripe's service status at https://twitter.com/stripestatus,"
-                  + " or let us know at support@stripe.com.",
-              Stripe.getApiBase(), e.getMessage()),
-          e);
+      throw ApiConnectionException.create(Stripe.getApiBase(), e);
     }
   }
 
@@ -112,14 +105,7 @@ private StripeRequest(
       this.headers = buildHeaders(method, this.options, this.content, apiMode);
       this.apiMode = apiMode;
     } catch (IOException e) {
-      throw new ApiConnectionException(
-          String.format(
-              "IOException during API request to Stripe (%s): %s "
-                  + "Please check your internet connection and try again. If this problem persists,"
-                  + "you should check Stripe's service status at https://twitter.com/stripestatus,"
-                  + " or let us know at support@stripe.com.",
-              Stripe.getApiBase(), e.getMessage()),
-          e);
+      throw ApiConnectionException.create(Stripe.getApiBase(), e);
     }
   }
 
@@ -279,14 +265,7 @@ private static HttpContent buildContentFromString(
   }
 
   private static void handleIOException(IOException e) throws ApiConnectionException {
-    throw new ApiConnectionException(
-        String.format(
-            "IOException during API request to Stripe (%s): %s "
-                + "Please check your internet connection and try again. If this problem persists,"
-                + "you should check Stripe's service status at https://twitter.com/stripestatus,"
-                + " or let us know at support@stripe.com.",
-            Stripe.getApiBase(), e.getMessage()),
-        e);
+    throw ApiConnectionException.create(Stripe.getApiBase(), e);
   }
 
   private static HttpHeaders buildHeaders(

src/main/java/com/stripe/net/Webhook.java

@@ -133,7 +133,7 @@ public static boolean verifyHeader(
         throw new SignatureVerificationException(
             "Unable to extract timestamp and signatures from header", sigHeader);
       }
-      if (signatures.size() == 0) {
+      if (signatures.isEmpty()) {
         throw new SignatureVerificationException(
             "No signatures found with expected scheme", sigHeader);
       }
@@ -239,11 +239,11 @@ public static String computeHmacSha256(String key, String message)
       Mac hasher = Mac.getInstance("HmacSHA256");
       hasher.init(new SecretKeySpec(key.getBytes(StandardCharsets.UTF_8), "HmacSHA256"));
       byte[] hash = hasher.doFinal(message.getBytes(StandardCharsets.UTF_8));
-      String result = "";
+      StringBuilder result = new StringBuilder(hash.length * 2);
       for (byte b : hash) {
-        result += Integer.toString((b & 0xff) + 0x100, 16).substring(1);
+        result.append(Integer.toString((b & 0xff) + 0x100, 16).substring(1));
       }
-      return result;
+      return result.toString();
     }
 
     /**