Implement HttpBlock

In the future we might want to consider using the message port mechanism
to trigger the requests.

Fixes #236

CMakeLists.txt

@@ -84,6 +84,9 @@ if (EMSCRIPTEN)
             -fwasm-exceptions
             -pthread
             "SHELL:-s PTHREAD_POOL_SIZE=30"
+            "SHELL:-s FETCH=1"
+            "SHELL:-s ASSERTIONS=1"
+            "SHELL:-s USE_PTHREADS"
     )
 endif ()
 

blocks/CMakeLists.txt

@@ -1,4 +1,5 @@
 add_subdirectory(basic)
 add_subdirectory(filter)
 add_subdirectory(fourier)
+add_subdirectory(http)
 add_subdirectory(testing)

blocks/basic/include/gnuradio-4.0/basic/common_blocks.hpp

@@ -15,16 +15,16 @@
 template<typename T>
 class InspectSink : public gr::Block<InspectSink<T>> {
 public:
-    T             value{};
     gr::PortIn<T> in;
+    T             value{};
 
     constexpr void
     processOne(T val) {
         value = val;
     }
 };
 
-ENABLE_REFLECTION_FOR_TEMPLATE_FULL((typename T), (InspectSink<T>), value, in);
+ENABLE_REFLECTION_FOR_TEMPLATE(InspectSink, in, value);
 
 template<typename T>
 class builtin_multiply : public gr::Block<builtin_multiply<T>> {

blocks/http/CMakeLists.txt

@@ -0,0 +1,14 @@
+FetchContent_Declare(
+    httplib
+    GIT_REPOSITORY https://github.com/yhirose/cpp-httplib.git
+    GIT_TAG v0.15.1
+)
+FetchContent_MakeAvailable(httplib)
+
+add_library(gr-http INTERFACE)
+target_link_libraries(gr-http INTERFACE gnuradio-core gnuradio-algorithm httplib::httplib)
+target_include_directories(gr-http INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/> $<INSTALL_INTERFACE:include/>)
+
+if (ENABLE_TESTING)
+    add_subdirectory(test)
+endif ()

blocks/http/include/gnuradio-4.0/http/HttpBlock.hpp

@@ -0,0 +1,298 @@
+#ifndef GNURADIO_HTTP_BLOCK_HPP
+#define GNURADIO_HTTP_BLOCK_HPP
+
+#include <gnuradio-4.0/Block.hpp>
+#include <gnuradio-4.0/Graph.hpp>
+#include <gnuradio-4.0/reflection.hpp>
+#include <pmtv/pmt.hpp>
+#include <semaphore>
+
+#ifdef __EMSCRIPTEN__
+#include <emscripten/emscripten.h>
+#include <emscripten/fetch.h>
+#include <emscripten/threading.h>
+#else
+#include <httplib.h>
+#endif
+
+using namespace gr;
+using namespace std::chrono_literals;
+
+namespace gr::http {
+
+enum class RequestType {
+    GET,
+    SUBSCRIBE,
+    POST,
+};
+
+using HttpBlockDoc = Doc<R""(
+The HttpBlock allows to use the responses from HTTP APIs (e.g. REST APIs) as the value for this block's output port.
+The block can be used either on-demand to do single requests, or can use long polling to subscribe to an event stream.
+The result is provided on a single output port as a map with the following keys:
+- status: The HTTP status code, usually 200 on success
+- raw-data: The data of the response
+- mime-type: The mime-type of the response
+)"">;
+
+template<typename T>
+class HttpBlock : public gr::Block<HttpBlock<T>, BlockingIO<false>, HttpBlockDoc> {
+private:
+    // used for queuing GET responses for the consumer
+    std::queue<pmtv::map_t> _backlog;
+    std::mutex              _backlog_mutex;
+
+    std::shared_ptr<std::thread> _thread;
+    std::atomic_size_t           _pendingRequests = 0;
+    std::atomic_bool             _shutdownThread  = false;
+    std::binary_semaphore        _ready{ 0 };
+
+#ifndef __EMSCRIPTEN__
+    std::unique_ptr<httplib::Client> _client;
+#endif
+
+#ifdef __EMSCRIPTEN__
+    void
+    queueWorkEmscripten(emscripten_fetch_t *fetch) {
+        pmtv::map_t result;
+        result["mime-type"] = "text/plain";
+        result["status"]    = static_cast<int>(fetch->status);
+        result["raw-data"]  = std::string(fetch->data, static_cast<std::size_t>(fetch->numBytes));
+
+        queueWork(result);
+    }
+
+    void
+    onSuccess(emscripten_fetch_t *fetch) {
+        queueWorkEmscripten(fetch);
+        emscripten_fetch_close(fetch);
+    }
+
+    void
+    onError(emscripten_fetch_t *fetch) {
+        // we still want to queue the response, the statusCode will just not be 200
+        queueWorkEmscripten(fetch);
+        emscripten_fetch_close(fetch);
+    }
+
+    void
+    doRequestEmscripten() {
+        emscripten_fetch_attr_t attr;
+        emscripten_fetch_attr_init(&attr);
+        if (type == RequestType::POST) {
+            strcpy(attr.requestMethod, "POST");
+            if (!parameters.empty()) {
+                attr.requestData     = parameters.c_str();
+                attr.requestDataSize = parameters.size();
+            }
+        } else {
+            strcpy(attr.requestMethod, "GET");
+        }
+
+        // this is needed so that we can call into member functions again, when we receive the Fetch callback
+        attr.userData = this;
+
+        attr.attributes = EMSCRIPTEN_FETCH_LOAD_TO_MEMORY;
+        attr.onsuccess  = [](emscripten_fetch_t *fetch) {
+            auto src = static_cast<HttpBlock<T> *>(fetch->userData);
+            src->onSuccess(fetch);
+        };
+        attr.onerror = [](emscripten_fetch_t *fetch) {
+            auto src = static_cast<HttpBlock<T> *>(fetch->userData);
+            src->onError(fetch);
+        };
+        const auto target = url + endpoint;
+        std::ignore       = emscripten_fetch(&attr, target.c_str());
+    }
+
+    void
+    runThreadEmscripten() {
+        if (type == RequestType::SUBSCRIBE) {
+            while (!_shutdownThread) {
+                // long polling, just keep doing requests
+                std::thread thread{ &HttpBlock::doRequestEmscripten, this };
+                thread.join();
+            }
+        } else {
+            while (!_shutdownThread) {
+                while (_pendingRequests > 0) {
+                    _pendingRequests--;
+                    std::thread thread{ &HttpBlock::doRequestEmscripten, this };
+                    thread.join();
+                }
+                _ready.acquire();
+            }
+        }
+    }
+#else
+    void
+    runThreadNative() {
+        _client = std::make_unique<httplib::Client>(url);
+        _client->set_follow_location(true);
+        if (type == RequestType::SUBSCRIBE) {
+            // it's long polling, be generous with timeouts
+            _client->set_read_timeout(1h);
+            _client->Get(endpoint, [&](const char *data, size_t len) {
+                pmtv::map_t result;
+                result["mime-type"] = "text/plain";
+                result["status"]    = 200;
+                result["raw-data"]  = std::string(data, len);
+
+                queueWork(result);
+
+                return !_shutdownThread;
+            });
+        } else {
+            while (!_shutdownThread) {
+                while (_pendingRequests > 0) {
+                    _pendingRequests--;
+                    httplib::Result resp;
+                    if (type == RequestType::POST) {
+                        resp = parameters.empty() ? _client->Post(endpoint) : _client->Post(endpoint, parameters, "application/x-www-form-urlencoded");
+                    } else {
+                        resp = _client->Get(endpoint);
+                    }
+                    pmtv::map_t result;
+                    if (resp) {
+                        result["mime-type"] = "text/plain";
+                        result["status"]    = resp->status;
+                        result["raw-data"]  = resp->body;
+                        queueWork(result);
+                    }
+                }
+
+                _ready.acquire();
+            }
+        }
+    }
+#endif
+
+    void
+    queueWork(const pmtv::map_t &item) {
+        {
+            std::lock_guard lg{ _backlog_mutex };
+            _backlog.push(item);
+        }
+        const auto work = this->invokeWork();
+        if (work == work::Status::DONE) {
+            std::atomic_store_explicit(&this->state, lifecycle::State::REQUESTED_STOP, std::memory_order_release);
+            this->state.notify_all();
+        }
+        this->ioLastWorkStatus.exchange(work, std::memory_order_relaxed);
+    }
+
+    void
+    runThread() {
+#ifdef __EMSCRIPTEN__
+        runThreadEmscripten();
+#else
+        runThreadNative();
+#endif
+    }
+
+    void
+    startThread() {
+        lifecycle::State expectedThreadState = lifecycle::State::INITIALISED;
+        if (!this->state.compare_exchange_strong(expectedThreadState, lifecycle::State::RUNNING, std::memory_order_acq_rel)) {
+            return;
+        }
+        this->state.notify_all();
+
+        _thread = std::shared_ptr<std::thread>(new std::thread([this]() { runThread(); }), [this](std::thread *t) {
+            _shutdownThread = true;
+            _ready.release();
+#ifndef __EMSCRIPTEN__
+            if (_client) {
+                _client->stop();
+            }
+#endif
+            if (t->joinable()) {
+                t->join();
+            }
+            _shutdownThread = false;
+            delete t;
+
+            std::atomic_store_explicit(&this->state, lifecycle::State::STOPPED, std::memory_order_release);
+            this->state.notify_all();
+        });
+    }
+
+    void
+    stopThread() {
+        _thread.reset();
+    }
+
+public:
+    PortIn<T>            in;
+    PortOut<pmtv::map_t> out;
+
+    std::string           url;
+    std::string           endpoint;
+    gr::http::RequestType type = gr::http::RequestType::GET;
+    std::string           parameters; // x-www-form-urlencoded encoded POST parameters
+
+    explicit HttpBlock(const std::string &_url, const std::string &_endpoint = "/", const RequestType _type = RequestType::GET, const std::string &_parameters = "")
+        : url(_url), endpoint(_endpoint), type(_type), parameters(_parameters) {}
+
+    ~HttpBlock() { stopThread(); }
+
+    void
+    settingsChanged(const property_map & /*oldSettings*/, property_map &newSettings) noexcept {
+        if (newSettings.contains("url") || newSettings.contains("type")) {
+            // other setting changes are hot-swappble without restarting the Client
+            startThread();
+        }
+    }
+
+    void
+    start() {
+        startThread();
+    }
+
+    void
+    stop() {
+        stopThread();
+    }
+
+    [[nodiscard]] constexpr auto
+    processOne(T value) noexcept {
+        if (type == RequestType::SUBSCRIBE) {
+            // for long polling, the subscription should stay active, if and only if the value on the input port is 1
+            if (value) {
+                if (!_thread) {
+                    startThread();
+                }
+            } else {
+                stopThread();
+            }
+        }
+
+        pmtv::map_t     result;
+        std::lock_guard lg{ _backlog_mutex };
+        if (!_backlog.empty()) {
+            result = _backlog.front();
+            _backlog.pop();
+        }
+        return result;
+    }
+
+    // TODO: Consider using message ports instead of a public function for triggering requests
+    void
+    trigger() {
+        if (!_thread) {
+            startThread();
+        }
+        if (type != RequestType::SUBSCRIBE) {
+            _pendingRequests++;
+            _ready.release();
+        }
+    }
+};
+
+static_assert(gr::BlockLike<http::HttpBlock<uint8_t>>);
+
+} // namespace gr::http
+
+ENABLE_REFLECTION_FOR_TEMPLATE_FULL((typename T), (gr::http::HttpBlock<T>), in, out, url, endpoint, type);
+
+#endif // GNURADIO_HTTP_BLOCK_HPP

blocks/http/test/CMakeLists.txt

@@ -0,0 +1,6 @@
+add_ut_test(qa_HttpBlock)
+target_link_libraries(qa_HttpBlock PRIVATE gr-http)
+
+if (EMSCRIPTEN)
+    target_link_options(qa_HttpBlock PRIVATE --pre-js=${CMAKE_CURRENT_SOURCE_DIR}/pre.js --emrun)
+endif ()