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[lldb] Support non-blocking reads in JSONRPCTransport #144610

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[lldb] Support non-blocking reads in JSONRPCTransport #144610

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19 changes: 15 additions & 4 deletions lldb/include/lldb/Host/JSONTransport.h
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Original file line number Diff line number Diff line change
Expand Up @@ -85,7 +85,8 @@ class JSONTransport {

/// Reads the next message from the input stream.
template <typename T>
llvm::Expected<T> Read(const std::chrono::microseconds &timeout) {
llvm::Expected<T>
Read(std::optional<std::chrono::microseconds> timeout = std::nullopt) {
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Since this type has moved into lldb_private now, should we use the Timeout helper? https://github.com/llvm/llvm-project/blob/main/lldb/include/lldb/Utility/Timeout.h#L28

llvm::Expected<std::string> message = ReadImpl(timeout);
if (!message)
return message.takeError();
Expand All @@ -97,10 +98,20 @@ class JSONTransport {

virtual llvm::Error WriteImpl(const std::string &message) = 0;
virtual llvm::Expected<std::string>
ReadImpl(const std::chrono::microseconds &timeout) = 0;
ReadImpl(std::optional<std::chrono::microseconds> timeout) = 0;

llvm::Expected<std::string>
ReadFull(IOObject &descriptor, size_t length,
std::optional<std::chrono::microseconds> timeout) const;

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And if these are members, then they probably don't need to take the IOObject arg.

llvm::Expected<std::string>
ReadUntil(IOObject &descriptor, llvm::StringRef delimiter,
std::optional<std::chrono::microseconds> timeout);

lldb::IOObjectSP m_input;
lldb::IOObjectSP m_output;

std::string m_buffer;
};

/// A transport class for JSON with a HTTP header.
Expand All @@ -113,7 +124,7 @@ class HTTPDelimitedJSONTransport : public JSONTransport {
protected:
virtual llvm::Error WriteImpl(const std::string &message) override;
virtual llvm::Expected<std::string>
ReadImpl(const std::chrono::microseconds &timeout) override;
ReadImpl(std::optional<std::chrono::microseconds> timeout) override;

// FIXME: Support any header.
static constexpr llvm::StringLiteral kHeaderContentLength =
Expand All @@ -131,7 +142,7 @@ class JSONRPCTransport : public JSONTransport {
protected:
virtual llvm::Error WriteImpl(const std::string &message) override;
virtual llvm::Expected<std::string>
ReadImpl(const std::chrono::microseconds &timeout) override;
ReadImpl(std::optional<std::chrono::microseconds> timeout) override;

static constexpr llvm::StringLiteral kMessageSeparator = "\n";
};
Expand Down
42 changes: 25 additions & 17 deletions lldb/source/Host/common/JSONTransport.cpp
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Expand Up @@ -27,9 +27,9 @@ using namespace lldb_private;

/// ReadFull attempts to read the specified number of bytes. If EOF is
/// encountered, an empty string is returned.
static Expected<std::string>
ReadFull(IOObject &descriptor, size_t length,
std::optional<std::chrono::microseconds> timeout = std::nullopt) {
Expected<std::string> JSONTransport::ReadFull(
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Could we keep this a static, so that it's clear it does not interact with m_buffer?

IOObject &descriptor, size_t length,
std::optional<std::chrono::microseconds> timeout) const {
if (!descriptor.IsValid())
return llvm::make_error<TransportInvalidError>();

Expand Down Expand Up @@ -67,19 +67,22 @@ ReadFull(IOObject &descriptor, size_t length,
return data.substr(0, length);
}

static Expected<std::string>
ReadUntil(IOObject &descriptor, StringRef delimiter,
std::optional<std::chrono::microseconds> timeout = std::nullopt) {
std::string buffer;
buffer.reserve(delimiter.size() + 1);
while (!llvm::StringRef(buffer).ends_with(delimiter)) {
Expected<std::string>
JSONTransport::ReadUntil(IOObject &descriptor, StringRef delimiter,
std::optional<std::chrono::microseconds> timeout) {
if (!timeout || *timeout != std::chrono::microseconds::zero()) {
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Why should this depend on the timeout value? If you previously timed out reading something (with a non-zero timeout) and you try to read again, who says the result is going to be better if you discard the data you've read so far?

m_buffer.clear();
m_buffer.reserve(delimiter.size() + 1);
}

while (!llvm::StringRef(m_buffer).ends_with(delimiter)) {
Expected<std::string> next =
ReadFull(descriptor, buffer.empty() ? delimiter.size() : 1, timeout);
ReadFull(descriptor, m_buffer.empty() ? delimiter.size() : 1, timeout);
Comment on lines +73 to +80
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If we have a buffer, we could adjust our approach to read in larger than 1 byte chunks when we're reading until a delimiter.

We could read chunks of say 1024 and then split the buffer on the delimited until we run out of data and then do a new read with the next chunk size.

I don't know if this approach would have issues on windows or anything though, so maybe someone with more platform specific knowledge may know how it handles blocking reads if _read is called with no data.

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https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/read The win32 _read API for reference.

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I think I don't understand the question. A blocking read with no data... blocks, sort of by definition.

if (auto Err = next.takeError())
return std::move(Err);
buffer += *next;
m_buffer += *next;
}
return buffer.substr(0, buffer.size() - delimiter.size());
return m_buffer.substr(0, m_buffer.size() - delimiter.size());
}

JSONTransport::JSONTransport(IOObjectSP input, IOObjectSP output)
Expand All @@ -89,11 +92,15 @@ void JSONTransport::Log(llvm::StringRef message) {
LLDB_LOG(GetLog(LLDBLog::Host), "{0}", message);
}

Expected<std::string>
HTTPDelimitedJSONTransport::ReadImpl(const std::chrono::microseconds &timeout) {
Expected<std::string> HTTPDelimitedJSONTransport::ReadImpl(
std::optional<std::chrono::microseconds> timeout) {
if (!m_input || !m_input->IsValid())
return llvm::make_error<TransportInvalidError>();

if (timeout && *timeout == std::chrono::microseconds::zero())
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Suggested change
if (timeout && *timeout == std::chrono::microseconds::zero())
if (timeout == std::chrono::microseconds::zero())

this should also work

return llvm::createStringError(
"HTTPDelimitedJSONTransport does not support non-blocking reads");

IOObject *input = m_input.get();
Expected<std::string> message_header =
ReadFull(*input, kHeaderContentLength.size(), timeout);
Expand All @@ -104,7 +111,8 @@ HTTPDelimitedJSONTransport::ReadImpl(const std::chrono::microseconds &timeout) {
kHeaderContentLength, *message_header)
.str());

Expected<std::string> raw_length = ReadUntil(*input, kHeaderSeparator);
Expected<std::string> raw_length =
ReadUntil(*input, kHeaderSeparator, timeout);
if (!raw_length)
return handleErrors(raw_length.takeError(),
[&](const TransportEOFError &E) -> llvm::Error {
Expand All @@ -117,7 +125,7 @@ HTTPDelimitedJSONTransport::ReadImpl(const std::chrono::microseconds &timeout) {
return createStringError(
formatv("invalid content length {0}", *raw_length).str());

Expected<std::string> raw_json = ReadFull(*input, length);
Expected<std::string> raw_json = ReadFull(*input, length, timeout);
if (!raw_json)
return handleErrors(
raw_json.takeError(), [&](const TransportEOFError &E) -> llvm::Error {
Expand All @@ -143,7 +151,7 @@ Error HTTPDelimitedJSONTransport::WriteImpl(const std::string &message) {
}

Expected<std::string>
JSONRPCTransport::ReadImpl(const std::chrono::microseconds &timeout) {
JSONRPCTransport::ReadImpl(std::optional<std::chrono::microseconds> timeout) {
if (!m_input || !m_input->IsValid())
return make_error<TransportInvalidError>();

Expand Down
43 changes: 39 additions & 4 deletions lldb/unittests/Host/JSONTransportTest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ using namespace lldb_private;
namespace {
template <typename T> class JSONTransportTest : public PipeTest {
protected:
std::unique_ptr<JSONTransport> transport;
std::unique_ptr<T> transport;

void SetUp() override {
PipeTest::SetUp();
Expand All @@ -36,7 +36,13 @@ class HTTPDelimitedJSONTransportTest
using JSONTransportTest::JSONTransportTest;
};

class JSONRPCTransportTest : public JSONTransportTest<JSONRPCTransport> {
class TestJSONRPCTransport : public JSONRPCTransport {
public:
using JSONRPCTransport::JSONRPCTransport;
using JSONRPCTransport::WriteImpl; // For partial writes.
};

class JSONRPCTransportTest : public JSONTransportTest<TestJSONRPCTransport> {
public:
using JSONTransportTest::JSONTransportTest;
};
Expand Down Expand Up @@ -84,7 +90,6 @@ TEST_F(HTTPDelimitedJSONTransportTest, ReadWithEOF) {
Failed<TransportEOFError>());
}


TEST_F(HTTPDelimitedJSONTransportTest, InvalidTransport) {
transport = std::make_unique<HTTPDelimitedJSONTransport>(nullptr, nullptr);
ASSERT_THAT_EXPECTED(
Expand Down Expand Up @@ -142,13 +147,43 @@ TEST_F(JSONRPCTransportTest, Write) {
}

TEST_F(JSONRPCTransportTest, InvalidTransport) {
transport = std::make_unique<JSONRPCTransport>(nullptr, nullptr);
transport = std::make_unique<TestJSONRPCTransport>(nullptr, nullptr);
ASSERT_THAT_EXPECTED(
transport->Read<JSONTestType>(std::chrono::milliseconds(1)),
Failed<TransportInvalidError>());
}

#ifndef _WIN32
TEST_F(HTTPDelimitedJSONTransportTest, NonBlockingRead) {
ASSERT_THAT_EXPECTED(
transport->Read<JSONTestType>(std::chrono::microseconds::zero()),
llvm::FailedWithMessage(
"HTTPDelimitedJSONTransport does not support non-blocking reads"));
}

TEST_F(JSONRPCTransportTest, NonBlockingRead) {
llvm::StringRef head = R"({"str")";
llvm::StringRef tail = R"(: "foo"})"
"\n";

ASSERT_THAT_EXPECTED(input.Write(head.data(), head.size()), Succeeded());
ASSERT_THAT_EXPECTED(
transport->Read<JSONTestType>(std::chrono::microseconds::zero()),
Failed<TransportTimeoutError>());

ASSERT_THAT_EXPECTED(input.Write(tail.data(), tail.size()), Succeeded());
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Can we also test a chunk with the delimiter in the middle of the data?

while (true) {
llvm::Expected<JSONTestType> result =
transport->Read<JSONTestType>(std::chrono::microseconds::zero());
if (result.errorIsA<TransportTimeoutError>()) {
llvm::consumeError(result.takeError());
continue;
}
ASSERT_THAT_EXPECTED(result, HasValue(testing::FieldsAre(/*str=*/"foo")));
break;
}
}

TEST_F(HTTPDelimitedJSONTransportTest, ReadWithTimeout) {
ASSERT_THAT_EXPECTED(
transport->Read<JSONTestType>(std::chrono::milliseconds(1)),
Expand Down
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