Chore: Fix and improve coverage

Author: amotl

DEVELOP.rst

@@ -48,6 +48,14 @@ If the environment is outdated, you can upgrade it::
 
     composer update
 
+If you see messages like ``Warning: No code coverage driver available`` when running
+the tests, you will need to install the ``xdebug`` extension::
+
+    pecl install xdebug
+
+It may happen that you will have to re-install it, for example after your PHP
+version has been upgraded by your package manager.
+
 
 Running the Tests
 =================
@@ -62,6 +70,7 @@ You can run the tests like::
 
     # Output coverage report as HTML
     composer run -- test --coverage-html ./report
+    open report/index.html
 
     # Run specific tests
     composer run -- test --filter "testFetchColumn"

src/Crate/PDO/Http/ServerPool.php

@@ -94,47 +94,23 @@ public function __construct(array $servers, ClientInterface $client = null)
      */
     public function execute(string $query, array $parameters): CollectionInterface
     {
-        $numServers = count($this->availableServers) - 1;
-
-        for ($i = 0; $i <= $numServers; $i++) {
-            // always get the first available server
-            $server = $this->availableServers[0];
-
-            // Move the selected server to the end of the stack
-            $this->availableServers[] = array_shift($this->availableServers);
-
-            try {
-                return $this->sendRequest($server, $query, $parameters, false);
-            } catch (ConnectException $exception) {
-                // Catch it before the BadResponseException but do nothing.
-                continue;
-            } catch (BadResponseException $exception) {
-                $body = (string)$exception->getResponse()->getBody();
-                $json = json_decode($body, true);
-
-                if ($json === null && json_last_error() !== JSON_ERROR_NONE) {
-                    throw new RuntimeException(sprintf('Server returned non-JSON response: %s', $body), 0, $exception);
-                }
-
-                $errorCode    = $json['error']['code'];
-                $errorMessage = $json['error']['message'];
-
-                throw new RuntimeException($errorMessage, $errorCode, $exception);
-            }
-        }
-
-        throw new ConnectException(
-            sprintf('No more servers available, exception from last server: %s', $exception->getMessage()),
-            $exception->getRequest(),
-            $exception
-        );
+        return $this->executeGeneric($query, $parameters, false);
     }
 
     /**
      * {@Inheritdoc}
      * @throws \GuzzleHttp\Exception\ConnectException
      */
     public function executeBulk(string $query, array $parameters): BulkResponseInterface
+    {
+        return $this->executeGeneric($query, $parameters, true);
+    }
+
+    /**
+     * {@Inheritdoc}
+     * @throws \GuzzleHttp\Exception\ConnectException
+     */
+    private function executeGeneric(string $query, array $parameters, bool $bulk_mode = false)
     {
         $numServers = count($this->availableServers) - 1;
 
@@ -146,7 +122,7 @@ public function executeBulk(string $query, array $parameters): BulkResponseInter
             $this->availableServers[] = array_shift($this->availableServers);
 
             try {
-                return $this->sendRequest($server, $query, $parameters, true);
+                return $this->sendRequest($server, $query, $parameters, $bulk_mode);
             } catch (ConnectException $exception) {
                 // Catch it before the BadResponseException but do nothing.
                 continue;