feat: implement download

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

lib/Client/Protocol/CommandExecutor.php

@@ -6,9 +6,11 @@ namespace KTXM\ProviderImap\Client\Protocol;
 
 use Generator;
 use KTXM\ProviderImap\Client\Command\CommandInterface;
+use KTXM\ProviderImap\Client\FetchTarget;
 use KTXM\ProviderImap\Client\ImapException;
 use KTXM\ProviderImap\Client\Protocol\Response\TaggedResponse;
 use KTXM\ProviderImap\Client\Protocol\Response\UntaggedResponse;
+use KTXM\ProviderImap\Client\Protocol\RequestFrame;
 use KTXM\ProviderImap\Client\SessionContext;
 use KTXM\ProviderImap\Client\SessionState;
 use Psr\Log\LoggerInterface;
@@ -41,10 +43,42 @@ final class CommandExecutor
         $this->writer->write($tag, $frame);
 
         return $command->handle(new ResponseStream(function () use ($tag, $context): Generator {
-            yield from $this->responsesUntilCompletion($tag, $context);
+            yield from $this->processPerform($tag, $context);
         }), $context);
     }
 
+    /**
+     * Stream the raw bytes of a single IMAP BODY section without buffering.
+     *
+     * Sends a UID FETCH for the given section and yields the literal bytes
+     * directly from the socket in chunks, never assembling a full string.
+     * The caller MUST fully exhaust the returned Generator before issuing
+     * any further IMAP commands.
+     *
+     * @return \Generator<string>  raw (transfer-encoded) bytes from the socket
+     */
+    public function download(FetchTarget $target, string $section, int $chunkSize, SessionContext $context): \Generator
+    {
+        $this->assertState([SessionState::Selected], $context->state(), 'FETCH (download)');
+
+        $tag = $this->tags->next();
+        $this->writer->write($tag, new RequestFrame(sprintf(
+            'UID FETCH %s (UID BODY[%s])',
+            $target->sequenceSet()->toCommand(),
+            $section,
+        )));
+
+        $result = $this->reader->readUntilFetchLiteral($tag);
+
+        if ($result === null) {
+            return; // UID not found or empty FETCH result
+        }
+
+        yield from $this->reader->streamLiteral($result['literalLength'], $chunkSize);
+
+        $this->reader->readToEnd($tag);
+    }
+
     /**
      * @param list<SessionState> $allowedStates
      */
@@ -63,7 +97,7 @@ final class CommandExecutor
         ));
     }
 
-    private function responsesUntilCompletion(string $tag, SessionContext $context): Generator
+    private function processPerform(string $tag, SessionContext $context): Generator
     {
         while (true) {
             $response = $this->reader->readResponse();

lib/Client/Protocol/ProtocolReader.php

@@ -42,7 +42,14 @@ final class ProtocolReader
 
     public function readResponse(): ResponseInterface
     {
-        $raw = $this->readRawResponse();
+        $raw = $this->connection->readLine();
+
+        while (($literalLength = $this->trailingLiteralLength($raw)) !== null) {
+            $raw .= $this->connection->readBytes($literalLength);
+            $raw .= $this->connection->readLine();
+        }
+
+        $raw = $this->trimTrailingLineEnding($raw);
 
         if ($raw === '') {
             throw new ImapException('Received empty IMAP response line.');
@@ -85,16 +92,72 @@ final class ProtocolReader
         return new TaggedResponse($parts[0], $status, $parts[2] ?? '', $raw);
     }
 
-    private function readRawResponse(): string
+    /**
+     * Read responses until an untagged FETCH response containing a literal marker is found,
+     * returning the literal byte count WITHOUT consuming the literal bytes from the socket.
+     * Returns null if the tagged OK/NO/BAD for $tag arrives before any literal is detected.
+     *
+     * ⚠️ After a non-null return the literal bytes MUST be consumed (via streamLiteral())
+     * before any further reads are made on this reader.
+     *
+     * @return array{literalLength: int, prefixLine: string}|null
+     */
+    public function readUntilFetchLiteral(string $tag): ?array
     {
-        $raw = $this->connection->readLine();
+        while (true) {
+            $line = $this->connection->readLine();
+            $trimmed = $this->trimTrailingLineEnding($line);
 
-        while (($literalLength = $this->trailingLiteralLength($raw)) !== null) {
-            $raw .= $this->connection->readBytes($literalLength);
-            $raw .= $this->connection->readLine();
+            // Literal marker at the end of the line — stop before consuming the bytes
+            $literalLength = $this->trailingLiteralLength($line);
+            if ($literalLength !== null) {
+                return ['literalLength' => $literalLength, 'prefixLine' => $trimmed];
+            }
+
+            // Tagged completion for our command
+            if (str_starts_with($trimmed, $tag . ' ')) {
+                $parts = preg_split('/\s+/', $trimmed, 3) ?: [];
+                $status = strtoupper($parts[1] ?? '');
+                if ($status === 'NO' || $status === 'BAD') {
+                    throw new ImapException(sprintf('FETCH command failed: %s', $trimmed));
+                }
+                return null; // Tagged OK without ever finding a literal → UID not found
+            }
+
+            // Any other untagged response — discard and continue
         }
+    }
 
-        return $this->trimTrailingLineEnding($raw);
+    public function readToEnd(string $tag): TaggedResponse
+    {
+        while (true) {
+            $response = $this->readResponse();
+
+            if ($response instanceof TaggedResponse && $response->tag() === $tag) {
+                if (!$response->isOk()) {
+                    throw new ImapException(sprintf('FETCH failed: %s', $response->text()));
+                }
+                return $response;
+            }
+        }
+    }
+
+    /**
+     * Yield the literal bytes already waiting in the socket as chunks.
+     * After the generator is fully exhausted this method reads the one trailing
+     * line that closes the FETCH parenthesised response (e.g. ")\r\n").
+     *
+     * Contract: the caller MUST exhaust this generator before issuing any further
+     * reads on this reader.
+     *
+     * @return \Generator<string>
+     */
+    public function streamLiteral(int $length, int $chunkSize = 8192): \Generator
+    {
+        yield from $this->connection->readBytesChunked($length, $chunkSize);
+
+        // Consume the closing portion of the FETCH parenthesised list (e.g. ")\r\n")
+        $this->connection->readLine();
     }
 
     private function trailingLiteralLength(string $raw): ?int