[2.14]: Fix: Fold long lines during SMTP communication

src/Protocol/Smtp.php

@@ -8,6 +8,9 @@
 
 namespace Laminas\Mail\Protocol;
 
+use Generator;
+use Laminas\Mail\Headers;
+
 /**
  * SMTP implementation of Laminas\Mail\Protocol\AbstractProtocol
  *
@@ -18,6 +21,13 @@ class Smtp extends AbstractProtocol
 {
     use ProtocolTrait;
 
+    /**
+     * RFC 5322 section-2.2.3 specifies maximum of 998 bytes per line.
+     * This may not be exceeded.
+     * @see https://tools.ietf.org/html/rfc5322#section-2.2.3
+     */
+    public const SMTP_LINE_LIMIT = 998;
+
     /**
      * The transport method for the socket
      *
@@ -170,6 +180,61 @@ public function setUseCompleteQuit($useCompleteQuit)
         return $this->useCompleteQuit = (bool) $useCompleteQuit;
     }
 
+    /**
+     * Read $data as lines terminated by "\n"
+     *
+     * @param string $data
+     * @param int $chunkSize
+     * @return Generator|string[]
+     * @author Elan Ruusamäe <[email protected]>
+     */
+    private static function chunkedReader(string $data, int $chunkSize = 4096): Generator
+    {
+        if (($fp = fopen("php://temp", "r+")) === false) {
+            throw new Exception\RuntimeException('cannot fopen');
+        }
+        if (fwrite($fp, $data) === false) {
+            throw new Exception\RuntimeException('cannot fwrite');
+        }
+        rewind($fp);
+
+        $line = null;
+        while (($buffer = fgets($fp, $chunkSize)) !== false) {
+            $line .= $buffer;
+
+            // This is optimization to avoid calling length() in a loop.
+            // We need to match a condition that is when:
+            // 1. maximum was read from fgets, which is $chunkSize-1
+            // 2. last byte of the buffer is not \n
+            //
+            // to access last byte of buffer, we can do
+            // - $buffer[strlen($buffer)-1]
+            // and when maximum is read from fgets, then:
+            // - strlen($buffer) === $chunkSize-1
+            // - strlen($buffer)-1 === $chunkSize-2
+            // which means this is also true:
+            // - $buffer[strlen($buffer)-1] === $buffer[$chunkSize-2]
+            //
+            // the null coalesce works, as string offset can never be null
+            $lastByte = $buffer[$chunkSize - 2] ?? null;
+
+            // partial read, continue loop to read again to complete the line
+            // compare \n first as that's usually false
+            if ($lastByte !== "\n" && $lastByte !== null) {
+                continue;
+            }
+
+            yield $line;
+            $line = null;
+        }
+
+        if ($line !== null) {
+            yield $line;
+        }
+
+        fclose($fp);
+    }
+
     /**
      * Whether or not send QUIT command
      *
@@ -315,25 +380,25 @@ public function data($data)
         $this->_send('DATA');
         $this->_expect(354, 120); // Timeout set for 2 minutes as per RFC 2821 4.5.3.2
 
-        if (($fp = fopen("php://temp", "r+")) === false) {
-            throw new Exception\RuntimeException('cannot fopen');
-        }
-        if (fwrite($fp, $data) === false) {
-            throw new Exception\RuntimeException('cannot fwrite');
-        }
-        unset($data);
-        rewind($fp);
-
-        // max line length is 998 char + \r\n = 1000
-        while (($line = stream_get_line($fp, 1000, "\n")) !== false) {
-            $line = rtrim($line, "\r");
+        $reader = self::chunkedReader($data);
+        foreach ($reader as $line) {
+            $line = rtrim($line, "\r\n");
             if (isset($line[0]) && $line[0] === '.') {
                 // Escape lines prefixed with a '.'
                 $line = '.' . $line;
             }
+
+            if (strlen($line) > self::SMTP_LINE_LIMIT) {
+                // Long lines are "folded" by inserting "<CR><LF><SPACE>"
+                // https://tools.ietf.org/html/rfc5322#section-2.2.3
+                // Add "-1" to stay within limits,
+                // because Headers::FOLDING includes a byte for space character after \r\n
+                $chunks = chunk_split($line, self::SMTP_LINE_LIMIT - 1, Headers::FOLDING);
+                $line = substr($chunks, 0, -strlen(Headers::FOLDING));
+            }
+
             $this->_send($line);
         }
-        fclose($fp);
 
         $this->_send('.');
         $this->_expect(250, 600); // Timeout set for 10 minutes as per RFC 2821 4.5.3.2

test/Transport/SmtpTest.php

@@ -199,6 +199,51 @@ public function testReceivesMailArtifacts(): void
         $this->assertStringContainsString("\r\n\r\nThis is only a test.", $data, $data);
     }
 
+    /**
+     * Fold long lines during smtp communication in Protocol\Smtp class.
+     * Test folding of long lines following RFC 5322 section-2.2.3
+     *
+     * @see https://github.com/laminas/laminas-mail/pull/140
+     */
+    public function testLongLinesFoldingRFC5322(): void
+    {
+        $message = 'The folding logic expects exactly 1 byte after \r\n in folding';
+        $this->assertEquals("\r\n ", Headers::FOLDING, $message);
+
+        $message = $this->getMessage();
+        // Create buffer of 8192 bytes (PHP_SOCK_CHUNK_SIZE)
+        $buffer = str_repeat('0123456789abcdef', 512);
+
+        $maxLen = SmtpProtocol::SMTP_LINE_LIMIT;
+        $headerWithLargeValue = $buffer;
+        $headerWithExactlyMaxLineLength = substr($buffer, 0, $maxLen - strlen('X-Exact-Length: '));
+        $message->getHeaders()->addHeaders([
+            'X-Ms-Exchange-Antispam-Messagedata' => $headerWithLargeValue,
+            'X-Exact-Length' => $headerWithExactlyMaxLineLength,
+        ]);
+
+        $this->transport->send($message);
+        $data = $this->connection->getLog();
+
+        $lines = explode("\r\n", $data);
+        $this->assertCount(28, $lines);
+
+        foreach ($lines as $line) {
+            $this->assertLessThanOrEqual($maxLen, strlen($line), sprintf('Line is too long: ' . $line));
+        }
+
+        $this->assertStringNotContainsString(
+            $headerWithLargeValue,
+            $data,
+            "The original header can't be present if it's wrapped"
+        );
+        $this->assertStringContainsString(
+            $headerWithExactlyMaxLineLength,
+            $data,
+            "Header with exact length is not wrapped"
+        );
+    }
+
     public function testCanUseAuthenticationExtensionsViaPluginManager(): void
     {
         $options    = new SmtpOptions([