[PHP] handle properly multiple accept headers

modules/openapi-generator/src/main/resources/php/HeaderSelector.mustache

@@ -42,31 +42,195 @@ class HeaderSelector
         if ($accept !== null) {
             $headers['Accept'] = $accept;
         }
-        if(!$isMultipart) {
+
+        if (!$isMultipart) {
             if($contentType === '') {
                 $contentType = 'application/json';
             }
+
             $headers['Content-Type'] = $contentType;
         }
 
         return $headers;
     }
 
     /**
-     * Return the header 'Accept' based on an array of Accept provided
+     * Return the header 'Accept' based on an array of Accept provided.
      *
      * @param string[] $accept Array of header
      *
      * @return null|string Accept (e.g. application/json)
      */
-    private function selectAcceptHeader($accept)
+    private function selectAcceptHeader(array $accept): ?string
     {
-        if (count($accept) === 0 || (count($accept) === 1 && $accept[0] === '')) {
+        # filter out empty entries
+        $accept = array_filter($accept);
+
+        if (count($accept) === 0) {
             return null;
-        } elseif ($jsonAccept = preg_grep('~(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$~', $accept)) {
-            return implode(',', $jsonAccept);
-        } else {
+        }
+
+        # If there's only one Accept header, just use it
+        if (count($accept) === 1) {
+            return reset($accept);
+        }
+
+        # If none of the available Accept headers is of type "json", then just use all them
+        $headersWithJson = preg_grep('~(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$~', $accept);
+        if (count($headersWithJson) === 0) {
             return implode(',', $accept);
         }
+
+        # If we got here, then we need add quality values (weight), as described in IETF RFC 9110, Items 12.4.2/12.5.1,
+        # to give the highest priority to json-like headers - recalculating the existing ones, if needed
+        return $this->getAcceptHeaderWithAdjustedWeight($accept, $headersWithJson);
+    }
+
+    /**
+    * Create an Accept header string from the given "Accept" headers array, recalculating all weights
+    *
+    * @param string[] $accept            Array of Accept Headers
+    * @param string[] $headersWithJson   Array of Accept Headers of type "json"
+    *
+    * @return string "Accept" Header (e.g. "application/json, text/html; q=0.9")
+    */
+    private function getAcceptHeaderWithAdjustedWeight(array $accept, array $headersWithJson): string
+    {
+        $processedHeaders = [
+            'withApplicationJson' => [],
+            'withJson' => [],
+            'withoutJson' => [],
+        ];
+
+        foreach ($accept as $header) {
+
+            $headerData = $this->getHeaderAndWeight($header);
+
+            if (stripos($headerData['header'], 'application/json') === 0) {
+                $processedHeaders['withApplicationJson'][] = $headerData;
+            } elseif (in_array($header, $headersWithJson, true)) {
+                $processedHeaders['withJson'][] = $headerData;
+            } else {
+                $processedHeaders['withoutJson'][] = $headerData;
+            }
+        }
+
+        $acceptHeaders = [];
+        $currentWeight = 1000;
+
+        $hasMoreThan28Headers = count($accept) > 28;
+
+        foreach($processedHeaders as $headers) {
+            if (count($headers) > 0) {
+                $acceptHeaders[] = $this->adjustWeight($headers, $currentWeight, $hasMoreThan28Headers);
+            }
+        }
+
+        $acceptHeaders = array_merge(...$acceptHeaders);
+
+        return implode(',', $acceptHeaders);
+    }
+
+    /**
+     * Given an Accept header, returns an associative array splitting the header and its weight
+     *
+     * @param string $header "Accept" Header
+     *
+     * @return array with the header and its weight
+     */
+    private function getHeaderAndWeight(string $header): array
+    {
+        # matches headers with weight, splitting the header and the weight in $outputArray
+        if (preg_match('/(.*);\s*q=(1(?:\.0+)?|0\.\d+)$/', $header, $outputArray) === 1) {
+            $headerData = [
+                'header' => $outputArray[1],
+                'weight' => (int)($outputArray[2] * 1000),
+            ];
+        } else {
+            $headerData = [
+                'header' => trim($header),
+                'weight' => 1000,
+            ];
+        }
+
+        return $headerData;
+    }
+
+    /**
+     * @param array[] $headers
+     * @param float   $currentWeight
+     * @param bool    $hasMoreThan28Headers
+     * @return string[] array of adjusted "Accept" headers
+     */
+    private function adjustWeight(array $headers, float &$currentWeight, bool $hasMoreThan28Headers): array
+    {
+        usort($headers, function (array $a, array $b) {
+            return $b['weight'] - $a['weight'];
+        });
+
+        $acceptHeaders = [];
+        foreach ($headers as $index => $header) {
+            if($index > 0 && $headers[$index - 1]['weight'] > $header['weight'])
+            {
+                $currentWeight = $this->getNextWeight($currentWeight, $hasMoreThan28Headers);
+            }
+
+            $weight = $currentWeight;
+
+            $acceptHeaders[] = $this->buildAcceptHeader($header['header'], $weight);
+        }
+
+        $currentWeight = $this->getNextWeight($currentWeight, $hasMoreThan28Headers);
+
+        return $acceptHeaders;
+    }
+
+    /**
+     * @param string $header
+     * @param int    $weight
+     * @return string
+     */
+    private function buildAcceptHeader(string $header, int $weight): string
+    {
+        if($weight === 1000) {
+            return $header;
+        }
+
+        return trim($header, '; ') . ';q=' . rtrim(sprintf('%0.3f', $weight / 1000), '0');
+    }
+
+    /**
+     * Calculate the next weight, based on the current one.
+     *
+     * If there are less than 28 "Accept" headers, the weights will be decreased by 1 on its highest significant digit, using the
+     * following formula:
+     *
+     *    next weight = current weight - 10 ^ (floor(log(current weight - 1)))
+     *
+     *    ( current weight minus ( 10 raised to the power of ( floor of (log to the base 10 of ( current weight minus 1 ) ) ) ) )
+     *
+     * Starting from 1000, this generates the following series:
+     *
+     * 1000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1
+     *
+     * The resulting quality codes are closer to the average "normal" usage of them (like "q=0.9", "q=0.8" and so on), but it only works
+     * if there is a maximum of 28 "Accept" headers. If we have more than that (which is extremely unlikely), then we fall back to a 1-by-1
+     * decrement rule, which will result in quality codes like "q=0.999", "q=0.998" etc.
+     *
+     * @param int  $currentWeight varying from 1 to 1000 (will be divided by 1000 to build the quality value)
+     * @param bool $hasMoreThan28Headers
+     * @return int
+     */
+    public function getNextWeight(int $currentWeight, bool $hasMoreThan28Headers): int
+    {
+        if ($currentWeight <= 1) {
+            return 1;
+        }
+
+        if ($hasMoreThan28Headers) {
+            return $currentWeight - 1;
+        }
+
+        return $currentWeight - 10 ** floor( log10($currentWeight - 1) );
     }
 }