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Bound STDIO server reads

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Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>
This commit is contained in:
Daniel Garnier-Moiroux 2026-07-02 18:48:58 +02:00 • committed by Daniel Garnier-Moiroux
commit 3b72eec0b8
1 changed files with 101 additions and 3 deletions
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56
mcp-core/src/main/java/io/modelcontextprotocol/server/transport/StdioServerTransportProvider.java
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@ -41,6 +41,8 @@ import reactor.core.scheduler.Schedulers;
*/
public class StdioServerTransportProvider implements McpServerTransportProvider {
private static final int DEFAULT_INPUT_MAX_SIZE = 16 * 1024 * 1024; // 16MB
private static final Logger logger = LoggerFactory.getLogger(StdioServerTransportProvider.class);
private final McpJsonMapper jsonMapper;
@ -49,6 +51,8 @@ public class StdioServerTransportProvider implements McpServerTransportProvider
private final OutputStream outputStream;
private final int inputMaxSize;
private McpServerSession session;
private final AtomicBoolean isClosing = new AtomicBoolean(false);
@ -72,13 +76,29 @@ public class StdioServerTransportProvider implements McpServerTransportProvider
* @param outputStream The output stream to write to
*/
public StdioServerTransportProvider(McpJsonMapper jsonMapper, InputStream inputStream, OutputStream outputStream) {
this(jsonMapper, inputStream, outputStream, DEFAULT_INPUT_MAX_SIZE);
}
/**
* Creates a new StdioServerTransportProvider.
* @param jsonMapper The JsonMapper to use for JSON serialization/deserialization
* @param inputStream The input stream to read from
* @param outputStream The output stream to write to
* @param inputMaxSize The maximum number of characters read for a single inbound
* message. A peer that sends a longer message (or never terminates a line) has its
* message rejected instead of forcing the transport to buffer it in memory.
*/
public StdioServerTransportProvider(McpJsonMapper jsonMapper, InputStream inputStream, OutputStream outputStream,
int inputMaxSize) {
Assert.notNull(jsonMapper, "The JsonMapper can not be null");
Assert.notNull(inputStream, "The InputStream can not be null");
Assert.notNull(outputStream, "The OutputStream can not be null");
Assert.isTrue(inputMaxSize > 0, "inputMaxSize must be positive");
this.jsonMapper = jsonMapper;
this.inputStream = inputStream;
this.outputStream = outputStream;
this.inputMaxSize = inputMaxSize;
}
@Override
@ -211,7 +231,7 @@ public class StdioServerTransportProvider implements McpServerTransportProvider
reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
while (!isClosing.get()) {
try {
String line = reader.readLine();
String line = readLine(reader, inputMaxSize);
if (line == null || isClosing.get()) {
break;
}
@ -232,6 +252,10 @@ public class StdioServerTransportProvider implements McpServerTransportProvider
break;
}
}
catch (MaxSizeExceededException e) {
logIfNotClosing("Inbound message exceeds the maximum allowed size", e);
break;
}
catch (IOException e) {
logIfNotClosing("Error reading from stdin", e);
break;
@ -304,6 +328,36 @@ public class StdioServerTransportProvider implements McpServerTransportProvider
outboundConsumer.apply(outboundSink.asFlux()).subscribe();
} // @formatter:on
/**
* Read line with a max size.
*/
private static String readLine(BufferedReader reader, int maxSize)
throws IOException, MaxSizeExceededException {
StringBuilder sb = new StringBuilder();
int c;
while ((c = reader.read()) != -1) {
if (c == '\n') {
return sb.toString();
}
if (c == '\r') {
// Consume an optional trailing '\n' so that "\r\n" is treated as a
// single terminator, mirroring BufferedReader#readLine().
reader.mark(1);
int next = reader.read();
if (next != '\n' && next != -1) {
reader.reset();
}
return sb.toString();
}
if (sb.length() >= maxSize) {
throw new MaxSizeExceededException(
"Inbound message exceeds the maximum allowed size of " + maxSize + " characters");
}
sb.append((char) c);
}
return sb.isEmpty() ? null : sb.toString();
}
private void logIfNotClosing(String message, Exception e) {
if (!isClosing.get()) {
logger.error(message, e);