JSONTransport.cpp

//===--- JSONTransport.cpp - sending and receiving LSP messages over JSON -===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "Protocol.h" // For LSPError
#include "Transport.h"
#include "support/Cancellation.h"
#include "support/Logger.h"
#include "support/Shutdown.h"
#include "support/ThreadCrashReporter.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/Error.h"
#include <optional>
#include <system_error>

namespace clang {
namespace clangd {
namespace {

llvm::json::Object encodeError(llvm::Error E) {
  std::string Message;
  ErrorCode Code = ErrorCode::UnknownErrorCode;
  // FIXME: encode cancellation errors using RequestCancelled or ContentModified
  // as appropriate.
  if (llvm::Error Unhandled = llvm::handleErrors(
          std::move(E),
          [&](const CancelledError &C) -> llvm::Error {
            switch (C.Reason) {
            case static_cast<int>(ErrorCode::ContentModified):
              Code = ErrorCode::ContentModified;
              Message = "Request cancelled because the document was modified";
              break;
            default:
              Code = ErrorCode::RequestCancelled;
              Message = "Request cancelled";
              break;
            }
            return llvm::Error::success();
          },
          [&](const LSPError &L) -> llvm::Error {
            Message = L.Message;
            Code = L.Code;
            return llvm::Error::success();
          }))
    Message = llvm::toString(std::move(Unhandled));

  return llvm::json::Object{
      {"message", std::move(Message)},
      {"code", int64_t(Code)},
  };
}

llvm::Error decodeError(const llvm::json::Object &O) {
  llvm::StringRef Msg = O.getString("message").value_or("Unspecified error");
  if (auto Code = O.getInteger("code"))
    return llvm::make_error<LSPError>(Msg.str(), ErrorCode(*Code));
  return error(Msg.str());
}

class JSONTransport : public Transport {
public:
  JSONTransport(std::FILE *In, llvm::raw_ostream &Out,
                llvm::raw_ostream *InMirror, bool Pretty, JSONStreamStyle Style)
      : In(In), Out(Out), InMirror(InMirror ? *InMirror : llvm::nulls()),
        Pretty(Pretty), Style(Style) {}

  void notify(llvm::StringRef Method, llvm::json::Value Params) override {
    sendMessage(llvm::json::Object{
        {"jsonrpc", "2.0"},
        {"method", Method},
        {"params", std::move(Params)},
    });
  }
  void call(llvm::StringRef Method, llvm::json::Value Params,
            llvm::json::Value ID) override {
    sendMessage(llvm::json::Object{
        {"jsonrpc", "2.0"},
        {"id", std::move(ID)},
        {"method", Method},
        {"params", std::move(Params)},
    });
  }
  void reply(llvm::json::Value ID,
             llvm::Expected<llvm::json::Value> Result) override {
    if (Result) {
      sendMessage(llvm::json::Object{
          {"jsonrpc", "2.0"},
          {"id", std::move(ID)},
          {"result", std::move(*Result)},
      });
    } else {
      sendMessage(llvm::json::Object{
          {"jsonrpc", "2.0"},
          {"id", std::move(ID)},
          {"error", encodeError(Result.takeError())},
      });
    }
  }

  llvm::Error loop(MessageHandler &Handler) override {
    std::string JSON; // Messages may be large, reuse same big buffer.
    while (!feof(In)) {
      if (shutdownRequested())
        return error(std::make_error_code(std::errc::operation_canceled),
                     "Got signal, shutting down");
      if (ferror(In))
        return llvm::errorCodeToError(llvm::errnoAsErrorCode());
      if (readRawMessage(JSON)) {
        ThreadCrashReporter ScopedReporter([&JSON]() {
          auto &OS = llvm::errs();
          OS << "Signalled while processing message:\n";
          OS << JSON << "\n";
        });
        if (auto Doc = llvm::json::parse(JSON)) {
          vlog(Pretty ? "<<< {0:2}\n" : "<<< {0}\n", *Doc);
          if (!handleMessage(std::move(*Doc), Handler))
            return llvm::Error::success(); // we saw the "exit" notification.
        } else {
          // Parse error. Log the raw message.
          vlog("<<< {0}\n", JSON);
          elog("JSON parse error: {0}", llvm::toString(Doc.takeError()));
        }
      }
    }
    return llvm::errorCodeToError(std::make_error_code(std::errc::io_error));
  }

private:
  // Dispatches incoming message to Handler onNotify/onCall/onReply.
  bool handleMessage(llvm::json::Value Message, MessageHandler &Handler);
  // Writes outgoing message to Out stream.
  void sendMessage(llvm::json::Value Message) {
    OutputBuffer.clear();
    llvm::raw_svector_ostream OS(OutputBuffer);
    OS << llvm::formatv(Pretty ? "{0:2}" : "{0}", Message);
    Out << "Content-Length: " << OutputBuffer.size() << "\r\n\r\n"
        << OutputBuffer;
    Out.flush();
    vlog(">>> {0}\n", OutputBuffer);
  }

  // Read raw string messages from input stream.
  bool readRawMessage(std::string &JSON) {
    return Style == JSONStreamStyle::Delimited ? readDelimitedMessage(JSON)
                                               : readStandardMessage(JSON);
  }
  bool readDelimitedMessage(std::string &JSON);
  bool readStandardMessage(std::string &JSON);

  llvm::SmallVector<char, 0> OutputBuffer;
  std::FILE *In;
  llvm::raw_ostream &Out;
  llvm::raw_ostream &InMirror;
  bool Pretty;
  JSONStreamStyle Style;
};

bool JSONTransport::handleMessage(llvm::json::Value Message,
                                  MessageHandler &Handler) {
  // Message must be an object with "jsonrpc":"2.0".
  auto *Object = Message.getAsObject();
  if (!Object ||
      Object->getString("jsonrpc") != std::optional<llvm::StringRef>("2.0")) {
    elog("Not a JSON-RPC 2.0 message: {0:2}", Message);
    return false;
  }
  // ID may be any JSON value. If absent, this is a notification.
  std::optional<llvm::json::Value> ID;
  if (auto *I = Object->get("id"))
    ID = std::move(*I);
  auto Method = Object->getString("method");
  if (!Method) { // This is a response.
    if (!ID) {
      elog("No method and no response ID: {0:2}", Message);
      return false;
    }
    if (auto *Err = Object->getObject("error"))
      return Handler.onReply(std::move(*ID), decodeError(*Err));
    // Result should be given, use null if not.
    llvm::json::Value Result = nullptr;
    if (auto *R = Object->get("result"))
      Result = std::move(*R);
    return Handler.onReply(std::move(*ID), std::move(Result));
  }
  // Params should be given, use null if not.
  llvm::json::Value Params = nullptr;
  if (auto *P = Object->get("params"))
    Params = std::move(*P);

  if (ID)
    return Handler.onCall(*Method, std::move(Params), std::move(*ID));
  return Handler.onNotify(*Method, std::move(Params));
}

// Tries to read a line up to and including \n.
// If failing, feof(), ferror(), or shutdownRequested() will be set.
bool readLine(std::FILE *In, llvm::SmallVectorImpl<char> &Out) {
  // Big enough to hold any reasonable header line. May not fit content lines
  // in delimited mode, but performance doesn't matter for that mode.
  static constexpr int BufSize = 128;
  size_t Size = 0;
  Out.clear();
  for (;;) {
    Out.resize_for_overwrite(Size + BufSize);
    // Handle EINTR which is sent when a debugger attaches on some platforms.
    if (!retryAfterSignalUnlessShutdown(
            nullptr, [&] { return std::fgets(&Out[Size], BufSize, In); }))
      return false;
    clearerr(In);
    // If the line contained null bytes, anything after it (including \n) will
    // be ignored. Fortunately this is not a legal header or JSON.
    size_t Read = std::strlen(&Out[Size]);
    if (Read > 0 && Out[Size + Read - 1] == '\n') {
      Out.resize(Size + Read);
      return true;
    }
    Size += Read;
  }
}

// Returns None when:
//  - ferror(), feof(), or shutdownRequested() are set.
//  - Content-Length is missing or empty (protocol error)
bool JSONTransport::readStandardMessage(std::string &JSON) {
  // A Language Server Protocol message starts with a set of HTTP headers,
  // delimited  by \r\n, and terminated by an empty line (\r\n).
  unsigned long long ContentLength = 0;
  llvm::SmallString<128> Line;
  while (true) {
    if (feof(In) || ferror(In) || !readLine(In, Line))
      return false;
    InMirror << Line;

    llvm::StringRef LineRef = Line;

    // We allow comments in headers. Technically this isn't part

    // of the LSP specification, but makes writing tests easier.
    if (LineRef.starts_with("#"))
      continue;

    // Content-Length is a mandatory header, and the only one we handle.
    if (LineRef.consume_front("Content-Length: ")) {
      if (ContentLength != 0) {
        elog("Warning: Duplicate Content-Length header received. "
             "The previous value for this message ({0}) was ignored.",
             ContentLength);
      }
      llvm::getAsUnsignedInteger(LineRef.trim(), 0, ContentLength);
      continue;
    }

    // An empty line indicates the end of headers.
    // Go ahead and read the JSON.
    if (LineRef.trim().empty())
      break;

    // It's another header, ignore it.
  }

  // The fuzzer likes crashing us by sending "Content-Length: 9999999999999999"
  if (ContentLength > 1 << 30) { // 1024M
    elog("Refusing to read message with long Content-Length: {0}. "
         "Expect protocol errors",
         ContentLength);
    return false;
  }
  if (ContentLength == 0) {
    log("Warning: Missing Content-Length header, or zero-length message.");
    return false;
  }

  JSON.resize(ContentLength);
  for (size_t Pos = 0, Read; Pos < ContentLength; Pos += Read) {
    // Handle EINTR which is sent when a debugger attaches on some platforms.
    Read = retryAfterSignalUnlessShutdown(0, [&]{
      return std::fread(&JSON[Pos], 1, ContentLength - Pos, In);
    });
    if (Read == 0) {
      elog("Input was aborted. Read only {0} bytes of expected {1}.", Pos,
           ContentLength);
      return false;
    }
    InMirror << llvm::StringRef(&JSON[Pos], Read);
    clearerr(In); // If we're done, the error was transient. If we're not done,
                  // either it was transient or we'll see it again on retry.
    Pos += Read;
  }
  return true;
}

// For lit tests we support a simplified syntax:
// - messages are delimited by '---' on a line by itself
// - lines starting with # are ignored.
// This is a testing path, so favor simplicity over performance here.
// When returning false: feof(), ferror(), or shutdownRequested() will be set.
bool JSONTransport::readDelimitedMessage(std::string &JSON) {
  JSON.clear();
  llvm::SmallString<128> Line;
  while (readLine(In, Line)) {
    InMirror << Line;
    auto LineRef = Line.str().trim();
    if (LineRef.starts_with("#")) // comment
      continue;

    // found a delimiter
    if (LineRef.rtrim() == "---")
      break;

    JSON += Line;
  }

  if (shutdownRequested())
    return false;
  if (ferror(In)) {
    elog("Input error while reading message!");
    return false;
  }
  return true; // Including at EOF
}

} // namespace

std::unique_ptr<Transport> newJSONTransport(std::FILE *In,
                                            llvm::raw_ostream &Out,
                                            llvm::raw_ostream *InMirror,
                                            bool Pretty,
                                            JSONStreamStyle Style) {
  return std::make_unique<JSONTransport>(In, Out, InMirror, Pretty, Style);
}

} // namespace clangd
} // namespace clang