web_service: follow-up fix to #4842 ...

* The web_service http request is now fixed on Windows (R) platform.
* The issue is due to a complicated race-condition in `httplib`, a detailed
  explanation is available at https://github.com/yhirose/cpp-httplib/pull/701
* A pending Pull Request on `httplib` has been applied to remedy the
  said race-condition.
* The socket availability check is removed due to a behavioral chice of
  `httplib` that a socket will not be created before any actual request
  is sent.

3 files changed, 441 insertions, 217 deletions

diff --git a/externals/httplib/README.md b/externals/httplib/README.md
index 73037d297..1940e446c 100644
--- a/externals/httplib/README.md
+++ b/externals/httplib/README.md
@@ -1,4 +1,4 @@
-From https://github.com/yhirose/cpp-httplib/tree/fce8e6fefdab4ad48bc5b25c98e5ebfda4f3cf53
+From https://github.com/yhirose/cpp-httplib/tree/ff5677ad197947177c158fe857caff4f0e242045 with https://github.com/yhirose/cpp-httplib/pull/701
 
 MIT License
 
diff --git a/externals/httplib/httplib.h b/externals/httplib/httplib.h
index 5139b7f05..8982054e2 100644
--- a/externals/httplib/httplib.h
+++ b/externals/httplib/httplib.h
@@ -173,6 +173,7 @@ using socket_t = int;
 #define INVALID_SOCKET (-1)
 #endif //_WIN32
 
+#include <algorithm>
 #include <array>
 #include <atomic>
 #include <cassert>
@@ -237,6 +238,27 @@ namespace httplib {
 
 namespace detail {
 
+/*
+ * Backport std::make_unique from C++14.
+ *
+ * NOTE: This code came up with the following stackoverflow post:
+ * https://stackoverflow.com/questions/10149840/c-arrays-and-make-unique
+ *
+ */
+
+template <class T, class... Args>
+typename std::enable_if<!std::is_array<T>::value, std::unique_ptr<T>>::type
+make_unique(Args &&... args) {
+  return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
+}
+
+template <class T>
+typename std::enable_if<std::is_array<T>::value, std::unique_ptr<T>>::type
+make_unique(std::size_t n) {
+  typedef typename std::remove_extent<T>::type RT;
+  return std::unique_ptr<T>(new RT[n]);
+}
+
 struct ci {
   bool operator()(const std::string &s1, const std::string &s2) const {
     return std::lexicographical_compare(
@@ -304,6 +326,10 @@ using ContentProvider =
 using ContentProviderWithoutLength =
     std::function<bool(size_t offset, DataSink &sink)>;
 
+using ContentReceiverWithProgress =
+    std::function<bool(const char *data, size_t data_length, uint64_t offset,
+                       uint64_t total_length)>;
+
 using ContentReceiver =
     std::function<bool(const char *data, size_t data_length)>;
 
@@ -317,14 +343,17 @@ public:
                                              ContentReceiver receiver)>;
 
   ContentReader(Reader reader, MultipartReader multipart_reader)
-      : reader_(reader), multipart_reader_(multipart_reader) {}
+      : reader_(std::move(reader)),
+        multipart_reader_(std::move(multipart_reader)) {}
 
   bool operator()(MultipartContentHeader header,
                   ContentReceiver receiver) const {
-    return multipart_reader_(header, receiver);
+    return multipart_reader_(std::move(header), std::move(receiver));
   }
 
-  bool operator()(ContentReceiver receiver) const { return reader_(receiver); }
+  bool operator()(ContentReceiver receiver) const {
+    return reader_(std::move(receiver));
+  }
 
   Reader reader_;
   MultipartReader multipart_reader_;
@@ -353,7 +382,7 @@ struct Request {
   // for client
   size_t redirect_count = CPPHTTPLIB_REDIRECT_MAX_COUNT;
   ResponseHandler response_handler;
-  ContentReceiver content_receiver;
+  ContentReceiverWithProgress content_receiver;
   size_t content_length = 0;
   ContentProvider content_provider;
   Progress progress;
@@ -475,7 +504,7 @@ public:
 
   void enqueue(std::function<void()> fn) override {
     std::unique_lock<std::mutex> lock(mutex_);
-    jobs_.push_back(fn);
+    jobs_.push_back(std::move(fn));
     cond_.notify_one();
   }
 
@@ -664,8 +693,8 @@ private:
                          ContentReceiver multipart_receiver);
 
   virtual bool process_and_close_socket(socket_t sock);
-  
-  struct MountPointEntry { 
+
+  struct MountPointEntry {
     std::string mount_point;
     std::string base_dir;
     Headers headers;
@@ -704,23 +733,27 @@ enum Error {
   Canceled,
   SSLConnection,
   SSLLoadingCerts,
-  SSLServerVerification
+  SSLServerVerification,
+  UnsupportedMultipartBoundaryChars
 };
 
 class Result {
 public:
-  Result(const std::shared_ptr<Response> &res, Error err)
-      : res_(res), err_(err) {}
+  Result(std::unique_ptr<Response> res, Error err)
+      : res_(std::move(res)), err_(err) {}
   operator bool() const { return res_ != nullptr; }
   bool operator==(std::nullptr_t) const { return res_ == nullptr; }
   bool operator!=(std::nullptr_t) const { return res_ != nullptr; }
   const Response &value() const { return *res_; }
+  Response &value() { return *res_; }
   const Response &operator*() const { return *res_; }
+  Response &operator*() { return *res_; }
   const Response *operator->() const { return res_.get(); }
+  Response *operator->() { return res_.get(); }
   Error error() const { return err_; }
 
 private:
-  std::shared_ptr<Response> res_;
+  std::unique_ptr<Response> res_;
   Error err_;
 };
 
@@ -777,6 +810,8 @@ public:
   Result Post(const char *path, const MultipartFormDataItems &items);
   Result Post(const char *path, const Headers &headers,
               const MultipartFormDataItems &items);
+  Result Post(const char *path, const Headers &headers,
+              const MultipartFormDataItems &items, const std::string &boundary);
 
   Result Put(const char *path);
   Result Put(const char *path, const std::string &body,
@@ -863,7 +898,21 @@ protected:
   };
 
   virtual bool create_and_connect_socket(Socket &socket);
-  virtual void close_socket(Socket &socket, bool process_socket_ret);
+
+  // All of:
+  //   shutdown_ssl
+  //   shutdown_socket
+  //   close_socket
+  // should ONLY be called when socket_mutex_ is locked.
+  // Also, shutdown_ssl and close_socket should also NOT be called concurrently
+  // with a DIFFERENT thread sending requests using that socket.
+  virtual void shutdown_ssl(Socket &socket, bool shutdown_gracefully);
+  void shutdown_socket(Socket &socket);
+  void close_socket(Socket &socket);
+
+  // Similar to shutdown_ssl and close_socket, this should NOT be called
+  // concurrently with a DIFFERENT thread sending requests from the socket
+  void lock_socket_and_shutdown_and_close();
 
   bool process_request(Stream &strm, const Request &req, Response &res,
                        bool close_connection);
@@ -873,7 +922,7 @@ protected:
   void copy_settings(const ClientImpl &rhs);
 
   // Error state
-  mutable Error error_ = Error::Success;
+  mutable std::atomic<Error> error_;
 
   // Socket endoint information
   const std::string host_;
@@ -885,6 +934,11 @@ protected:
   mutable std::mutex socket_mutex_;
   std::recursive_mutex request_mutex_;
 
+  // These are all protected under socket_mutex
+  int socket_requests_in_flight_ = 0;
+  std::thread::id socket_requests_are_from_thread_ = std::thread::id();
+  bool socket_should_be_closed_when_request_is_done_ = false;
+
   // Default headers
   Headers default_headers_;
 
@@ -942,13 +996,13 @@ private:
   bool redirect(const Request &req, Response &res);
   bool handle_request(Stream &strm, const Request &req, Response &res,
                       bool close_connection);
-  void stop_core();
-  std::shared_ptr<Response> send_with_content_provider(
+  std::unique_ptr<Response> send_with_content_provider(
       const char *method, const char *path, const Headers &headers,
       const std::string &body, size_t content_length,
       ContentProvider content_provider, const char *content_type);
 
-  virtual bool process_socket(Socket &socket,
+  // socket is const because this function is called when socket_mutex_ is not locked
+  virtual bool process_socket(const Socket &socket,
                               std::function<bool(Stream &strm)> callback);
   virtual bool is_ssl() const;
 };
@@ -1012,6 +1066,8 @@ public:
   Result Post(const char *path, const MultipartFormDataItems &items);
   Result Post(const char *path, const Headers &headers,
               const MultipartFormDataItems &items);
+  Result Post(const char *path, const Headers &headers,
+              const MultipartFormDataItems &items, const std::string &boundary);
   Result Put(const char *path);
   Result Put(const char *path, const std::string &body,
              const char *content_type);
@@ -1098,7 +1154,7 @@ public:
 #endif
 
 private:
-  std::shared_ptr<ClientImpl> cli_;
+  std::unique_ptr<ClientImpl> cli_;
 
 #ifdef CPPHTTPLIB_OPENSSL_SUPPORT
   bool is_ssl_ = false;
@@ -1154,9 +1210,9 @@ public:
 
 private:
   bool create_and_connect_socket(Socket &socket) override;
-  void close_socket(Socket &socket, bool process_socket_ret) override;
+  void shutdown_ssl(Socket &socket, bool shutdown_gracefully) override;
 
-  bool process_socket(Socket &socket,
+  bool process_socket(const Socket &socket,
                       std::function<bool(Stream &strm)> callback) override;
   bool is_ssl() const override;
 
@@ -1942,9 +1998,9 @@ inline socket_t create_client_socket(const char *host, int port,
                                      bool tcp_nodelay,
                                      SocketOptions socket_options,
                                      time_t timeout_sec, time_t timeout_usec,
-                                     const std::string &intf, Error &error) {
+                                     const std::string &intf, std::atomic<Error> &error) {
   auto sock = create_socket(
-      host, port, 0, tcp_nodelay, socket_options,
+      host, port, 0, tcp_nodelay, std::move(socket_options),
       [&](socket_t sock, struct addrinfo &ai) -> bool {
         if (!intf.empty()) {
 #ifdef USE_IF2IP
@@ -2478,7 +2534,8 @@ inline bool read_headers(Stream &strm, Headers &headers) {
 }
 
 inline bool read_content_with_length(Stream &strm, uint64_t len,
-                                     Progress progress, ContentReceiver out) {
+                                     Progress progress,
+                                     ContentReceiverWithProgress out) {
   char buf[CPPHTTPLIB_RECV_BUFSIZ];
 
   uint64_t r = 0;
@@ -2487,8 +2544,7 @@ inline bool read_content_with_length(Stream &strm, uint64_t len,
     auto n = strm.read(buf, (std::min)(read_len, CPPHTTPLIB_RECV_BUFSIZ));
     if (n <= 0) { return false; }
 
-    if (!out(buf, static_cast<size_t>(n))) { return false; }
-
+    if (!out(buf, static_cast<size_t>(n), r, len)) { return false; }
     r += static_cast<uint64_t>(n);
 
     if (progress) {
@@ -2510,8 +2566,10 @@ inline void skip_content_with_length(Stream &strm, uint64_t len) {
   }
 }
 
-inline bool read_content_without_length(Stream &strm, ContentReceiver out) {
+inline bool read_content_without_length(Stream &strm,
+                                        ContentReceiverWithProgress out) {
   char buf[CPPHTTPLIB_RECV_BUFSIZ];
+  uint64_t r = 0;
   for (;;) {
     auto n = strm.read(buf, CPPHTTPLIB_RECV_BUFSIZ);
     if (n < 0) {
@@ -2519,13 +2577,16 @@ inline bool read_content_without_length(Stream &strm, ContentReceiver out) {
     } else if (n == 0) {
       return true;
     }
-    if (!out(buf, static_cast<size_t>(n))) { return false; }
+
+    if (!out(buf, static_cast<size_t>(n), r, 0)) { return false; }
+    r += static_cast<uint64_t>(n);
   }
 
   return true;
 }
 
-inline bool read_content_chunked(Stream &strm, ContentReceiver out) {
+inline bool read_content_chunked(Stream &strm,
+                                 ContentReceiverWithProgress out) {
   const auto bufsiz = 16;
   char buf[bufsiz];
 
@@ -2570,23 +2631,24 @@ inline bool is_chunked_transfer_encoding(const Headers &headers) {
 }
 
 template <typename T, typename U>
-bool prepare_content_receiver(T &x, int &status, ContentReceiver receiver,
+bool prepare_content_receiver(T &x, int &status,
+                              ContentReceiverWithProgress receiver,
                               bool decompress, U callback) {
   if (decompress) {
     std::string encoding = x.get_header_value("Content-Encoding");
-    std::shared_ptr<decompressor> decompressor;
+    std::unique_ptr<decompressor> decompressor;
 
     if (encoding.find("gzip") != std::string::npos ||
         encoding.find("deflate") != std::string::npos) {
 #ifdef CPPHTTPLIB_ZLIB_SUPPORT
-      decompressor = std::make_shared<gzip_decompressor>();
+      decompressor = detail::make_unique<gzip_decompressor>();
 #else
       status = 415;
       return false;
 #endif
     } else if (encoding.find("br") != std::string::npos) {
 #ifdef CPPHTTPLIB_BROTLI_SUPPORT
-      decompressor = std::make_shared<brotli_decompressor>();
+      decompressor = detail::make_unique<brotli_decompressor>();
 #else
       status = 415;
       return false;
@@ -2595,12 +2657,14 @@ bool prepare_content_receiver(T &x, int &status, ContentReceiver receiver,
 
     if (decompressor) {
       if (decompressor->is_valid()) {
-        ContentReceiver out = [&](const char *buf, size_t n) {
-          return decompressor->decompress(
-              buf, n,
-              [&](const char *buf, size_t n) { return receiver(buf, n); });
+        ContentReceiverWithProgress out = [&](const char *buf, size_t n,
+                                              uint64_t off, uint64_t len) {
+          return decompressor->decompress(buf, n,
+                                          [&](const char *buf, size_t n) {
+                                            return receiver(buf, n, off, len);
+                                          });
         };
-        return callback(out);
+        return callback(std::move(out));
       } else {
         status = 500;
         return false;
@@ -2608,18 +2672,20 @@ bool prepare_content_receiver(T &x, int &status, ContentReceiver receiver,
     }
   }
 
-  ContentReceiver out = [&](const char *buf, size_t n) {
-    return receiver(buf, n);
+  ContentReceiverWithProgress out = [&](const char *buf, size_t n, uint64_t off,
+                                        uint64_t len) {
+    return receiver(buf, n, off, len);
   };
-  return callback(out);
+  return callback(std::move(out));
 }
 
 template <typename T>
 bool read_content(Stream &strm, T &x, size_t payload_max_length, int &status,
-                  Progress progress, ContentReceiver receiver,
+                  Progress progress, ContentReceiverWithProgress receiver,
                   bool decompress) {
   return prepare_content_receiver(
-      x, status, receiver, decompress, [&](const ContentReceiver &out) {
+      x, status, std::move(receiver), decompress,
+      [&](const ContentReceiverWithProgress &out) {
         auto ret = true;
         auto exceed_payload_max_length = false;
 
@@ -2634,7 +2700,7 @@ bool read_content(Stream &strm, T &x, size_t payload_max_length, int &status,
             skip_content_with_length(strm, len);
             ret = false;
           } else if (len > 0) {
-            ret = read_content_with_length(strm, len, progress, out);
+            ret = read_content_with_length(strm, len, std::move(progress), out);
           }
         }
 
@@ -2875,7 +2941,7 @@ inline bool parse_multipart_boundary(const std::string &content_type,
   return !boundary.empty();
 }
 
-inline bool parse_range_header(const std::string &s, Ranges &ranges) {
+inline bool parse_range_header(const std::string &s, Ranges &ranges) try {
   static auto re_first_range = std::regex(R"(bytes=(\d*-\d*(?:,\s*\d*-\d*)*))");
   std::smatch m;
   if (std::regex_match(s, m, re_first_range)) {
@@ -2907,7 +2973,7 @@ inline bool parse_range_header(const std::string &s, Ranges &ranges) {
     return all_valid_ranges;
   }
   return false;
-}
+} catch (...) { return false; }
 
 class MultipartFormDataParser {
 public:
@@ -2918,7 +2984,8 @@ public:
   bool is_valid() const { return is_valid_; }
 
   template <typename T, typename U>
-  bool parse(const char *buf, size_t n, T content_callback, U header_callback) {
+  bool parse(const char *buf, size_t n, const T &content_callback,
+             const U &header_callback) {
 
     static const std::regex re_content_disposition(
         "^Content-Disposition:\\s*form-data;\\s*name=\"(.*?)\"(?:;\\s*filename="
@@ -3090,8 +3157,13 @@ inline std::string make_multipart_data_boundary() {
   static const char data[] =
       "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 
+  // std::random_device might actually be deterministic on some
+  // platforms, but due to lack of support in the c++ standard library,
+  // doing better requires either some ugly hacks or breaking portability.
   std::random_device seed_gen;
-  std::mt19937 engine(seed_gen());
+  // Request 128 bits of entropy for initialization
+  std::seed_seq seed_sequence{seed_gen(), seed_gen(), seed_gen(), seed_gen()};
+  std::mt19937 engine(seed_sequence);
 
   std::string result = "--cpp-httplib-multipart-data-";
 
@@ -3114,7 +3186,7 @@ get_range_offset_and_length(const Request &req, size_t content_length,
   auto slen = static_cast<ssize_t>(content_length);
 
   if (r.first == -1) {
-    r.first = slen - r.second;
+    r.first = (std::max)(static_cast<ssize_t>(0), slen - r.second);
     r.second = slen - 1;
   }
 
@@ -3451,7 +3523,7 @@ inline std::pair<std::string, std::string> make_range_header(Ranges ranges) {
     if (r.second != -1) { field += std::to_string(r.second); }
     i++;
   }
-  return std::make_pair("Range", field);
+  return std::make_pair("Range", std::move(field));
 }
 
 inline std::pair<std::string, std::string>
@@ -3460,7 +3532,7 @@ make_basic_authentication_header(const std::string &username,
                                  bool is_proxy = false) {
   auto field = "Basic " + detail::base64_encode(username + ":" + password);
   auto key = is_proxy ? "Proxy-Authorization" : "Authorization";
-  return std::make_pair(key, field);
+  return std::make_pair(key, std::move(field));
 }
 
 inline std::pair<std::string, std::string>
@@ -3468,7 +3540,7 @@ make_bearer_token_authentication_header(const std::string &token,
                                         bool is_proxy = false) {
   auto field = "Bearer " + token;
   auto key = is_proxy ? "Proxy-Authorization" : "Authorization";
-  return std::make_pair(key, field);
+  return std::make_pair(key, std::move(field));
 }
 
 // Request implementation
@@ -3761,60 +3833,66 @@ inline Server::Server()
 inline Server::~Server() {}
 
 inline Server &Server::Get(const char *pattern, Handler handler) {
-  get_handlers_.push_back(std::make_pair(std::regex(pattern), handler));
+  get_handlers_.push_back(
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
 inline Server &Server::Post(const char *pattern, Handler handler) {
-  post_handlers_.push_back(std::make_pair(std::regex(pattern), handler));
+  post_handlers_.push_back(
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
 inline Server &Server::Post(const char *pattern,
                             HandlerWithContentReader handler) {
   post_handlers_for_content_reader_.push_back(
-      std::make_pair(std::regex(pattern), handler));
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
 inline Server &Server::Put(const char *pattern, Handler handler) {
-  put_handlers_.push_back(std::make_pair(std::regex(pattern), handler));
+  put_handlers_.push_back(
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
 inline Server &Server::Put(const char *pattern,
                            HandlerWithContentReader handler) {
   put_handlers_for_content_reader_.push_back(
-      std::make_pair(std::regex(pattern), handler));
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
 inline Server &Server::Patch(const char *pattern, Handler handler) {
-  patch_handlers_.push_back(std::make_pair(std::regex(pattern), handler));
+  patch_handlers_.push_back(
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
 inline Server &Server::Patch(const char *pattern,
                              HandlerWithContentReader handler) {
   patch_handlers_for_content_reader_.push_back(
-      std::make_pair(std::regex(pattern), handler));
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
 inline Server &Server::Delete(const char *pattern, Handler handler) {
-  delete_handlers_.push_back(std::make_pair(std::regex(pattern), handler));
+  delete_handlers_.push_back(
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
 inline Server &Server::Delete(const char *pattern,
                               HandlerWithContentReader handler) {
   delete_handlers_for_content_reader_.push_back(
-      std::make_pair(std::regex(pattern), handler));
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
 inline Server &Server::Options(const char *pattern, Handler handler) {
-  options_handlers_.push_back(std::make_pair(std::regex(pattern), handler));
+  options_handlers_.push_back(
+      std::make_pair(std::regex(pattern), std::move(handler)));
   return *this;
 }
 
@@ -3860,7 +3938,7 @@ inline void Server::set_error_handler(Handler handler) {
 inline void Server::set_tcp_nodelay(bool on) { tcp_nodelay_ = on; }
 
 inline void Server::set_socket_options(SocketOptions socket_options) {
-  socket_options_ = socket_options;
+  socket_options_ = std::move(socket_options);
 }
 
 inline void Server::set_logger(Logger logger) { logger_ = std::move(logger); }
@@ -4045,16 +4123,16 @@ inline bool Server::write_response(Stream &strm, bool close_connection,
     }
 
     if (type != detail::EncodingType::None) {
-      std::shared_ptr<detail::compressor> compressor;
+      std::unique_ptr<detail::compressor> compressor;
 
       if (type == detail::EncodingType::Gzip) {
 #ifdef CPPHTTPLIB_ZLIB_SUPPORT
-        compressor = std::make_shared<detail::gzip_compressor>();
+        compressor = detail::make_unique<detail::gzip_compressor>();
         res.set_header("Content-Encoding", "gzip");
 #endif
       } else if (type == detail::EncodingType::Brotli) {
 #ifdef CPPHTTPLIB_BROTLI_SUPPORT
-        compressor = std::make_shared<detail::brotli_compressor>();
+        compressor = detail::make_unique<detail::brotli_compressor>();
         res.set_header("Content-Encoding", "brotli");
 #endif
       }
@@ -4136,17 +4214,17 @@ Server::write_content_with_provider(Stream &strm, const Request &req,
     if (res.is_chunked_content_provider) {
       auto type = detail::encoding_type(req, res);
 
-      std::shared_ptr<detail::compressor> compressor;
+      std::unique_ptr<detail::compressor> compressor;
       if (type == detail::EncodingType::Gzip) {
 #ifdef CPPHTTPLIB_ZLIB_SUPPORT
-        compressor = std::make_shared<detail::gzip_compressor>();
+        compressor = detail::make_unique<detail::gzip_compressor>();
 #endif
       } else if (type == detail::EncodingType::Brotli) {
 #ifdef CPPHTTPLIB_BROTLI_SUPPORT
-        compressor = std::make_shared<detail::brotli_compressor>();
+        compressor = detail::make_unique<detail::brotli_compressor>();
 #endif
       } else {
-        compressor = std::make_shared<detail::nocompressor>();
+        compressor = detail::make_unique<detail::nocompressor>();
       }
       assert(compressor != nullptr);
 
@@ -4198,8 +4276,9 @@ inline bool Server::read_content_with_content_receiver(
     Stream &strm, Request &req, Response &res, ContentReceiver receiver,
     MultipartContentHeader multipart_header,
     ContentReceiver multipart_receiver) {
-  return read_content_core(strm, req, res, receiver, multipart_header,
-                           multipart_receiver);
+  return read_content_core(strm, req, res, std::move(receiver),
+                           std::move(multipart_header),
+                           std::move(multipart_receiver));
 }
 
 inline bool Server::read_content_core(Stream &strm, Request &req, Response &res,
@@ -4207,7 +4286,7 @@ inline bool Server::read_content_core(Stream &strm, Request &req, Response &res,
                                       MultipartContentHeader mulitpart_header,
                                       ContentReceiver multipart_receiver) {
   detail::MultipartFormDataParser multipart_form_data_parser;
-  ContentReceiver out;
+  ContentReceiverWithProgress out;
 
   if (req.is_multipart_form_data()) {
     const auto &content_type = req.get_header_value("Content-Type");
@@ -4218,7 +4297,7 @@ inline bool Server::read_content_core(Stream &strm, Request &req, Response &res,
     }
 
     multipart_form_data_parser.set_boundary(std::move(boundary));
-    out = [&](const char *buf, size_t n) {
+    out = [&](const char *buf, size_t n, uint64_t /*off*/, uint64_t /*len*/) {
       /* For debug
       size_t pos = 0;
       while (pos < n) {
@@ -4234,7 +4313,8 @@ inline bool Server::read_content_core(Stream &strm, Request &req, Response &res,
                                               mulitpart_header);
     };
   } else {
-    out = receiver;
+    out = [receiver](const char *buf, size_t n, uint64_t /*off*/,
+                     uint64_t /*len*/) { return receiver(buf, n); };
   }
 
   if (req.method == "DELETE" && !req.has_header("Content-Length")) {
@@ -4271,7 +4351,7 @@ inline bool Server::handle_file_request(Request &req, Response &res,
           auto type =
               detail::find_content_type(path, file_extension_and_mimetype_map_);
           if (type) { res.set_header("Content-Type", type); }
-          for (const auto& kv : entry.headers) {
+          for (const auto &kv : entry.headers) {
             res.set_header(kv.first.c_str(), kv.second);
           }
           res.status = 200;
@@ -4290,7 +4370,7 @@ inline socket_t
 Server::create_server_socket(const char *host, int port, int socket_flags,
                              SocketOptions socket_options) const {
   return detail::create_socket(
-      host, port, socket_flags, tcp_nodelay_, socket_options,
+      host, port, socket_flags, tcp_nodelay_, std::move(socket_options),
       [](socket_t sock, struct addrinfo &ai) -> bool {
         if (::bind(sock, ai.ai_addr, static_cast<socklen_t>(ai.ai_addrlen))) {
           return false;
@@ -4392,32 +4472,37 @@ inline bool Server::routing(Request &req, Response &res, Stream &strm) {
     {
       ContentReader reader(
           [&](ContentReceiver receiver) {
-            return read_content_with_content_receiver(strm, req, res, receiver,
-                                                      nullptr, nullptr);
+            return read_content_with_content_receiver(
+                strm, req, res, std::move(receiver), nullptr, nullptr);
           },
           [&](MultipartContentHeader header, ContentReceiver receiver) {
             return read_content_with_content_receiver(strm, req, res, nullptr,
-                                                      header, receiver);
+                                                      std::move(header),
+                                                      std::move(receiver));
           });
 
       if (req.method == "POST") {
         if (dispatch_request_for_content_reader(
-                req, res, reader, post_handlers_for_content_reader_)) {
+                req, res, std::move(reader),
+                post_handlers_for_content_reader_)) {
           return true;
         }
       } else if (req.method == "PUT") {
         if (dispatch_request_for_content_reader(
-                req, res, reader, put_handlers_for_content_reader_)) {
+                req, res, std::move(reader),
+                put_handlers_for_content_reader_)) {
           return true;
         }
       } else if (req.method == "PATCH") {
         if (dispatch_request_for_content_reader(
-                req, res, reader, patch_handlers_for_content_reader_)) {
+                req, res, std::move(reader),
+                patch_handlers_for_content_reader_)) {
           return true;
         }
       } else if (req.method == "DELETE") {
         if (dispatch_request_for_content_reader(
-                req, res, reader, delete_handlers_for_content_reader_)) {
+                req, res, std::move(reader),
+                delete_handlers_for_content_reader_)) {
           return true;
         }
       }
@@ -4448,7 +4533,6 @@ inline bool Server::routing(Request &req, Response &res, Stream &strm) {
 
 inline bool Server::dispatch_request(Request &req, Response &res,
                                      const Handlers &handlers) {
-
   try {
     for (const auto &x : handlers) {
       const auto &pattern = x.first;
@@ -4531,7 +4615,8 @@ Server::process_request(Stream &strm, bool close_connection,
   if (req.has_header("Range")) {
     const auto &range_header_value = req.get_header_value("Range");
     if (!detail::parse_range_header(range_header_value, req.ranges)) {
-      // TODO: error
+      res.status = 416;
+      return write_response(strm, close_connection, req, res);
     }
   }
 
@@ -4588,11 +4673,11 @@ inline ClientImpl::ClientImpl(const std::string &host, int port)
 inline ClientImpl::ClientImpl(const std::string &host, int port,
                               const std::string &client_cert_path,
                               const std::string &client_key_path)
-    : host_(host), port_(port),
+    : error_(Error::Success), host_(host), port_(port),
       host_and_port_(host_ + ":" + std::to_string(port_)),
       client_cert_path_(client_cert_path), client_key_path_(client_key_path) {}
 
-inline ClientImpl::~ClientImpl() { stop_core(); }
+inline ClientImpl::~ClientImpl() { lock_socket_and_shutdown_and_close(); }
 
 inline bool ClientImpl::is_valid() const { return true; }
 
@@ -4653,15 +4738,47 @@ inline bool ClientImpl::create_and_connect_socket(Socket &socket) {
   return true;
 }
 
-inline void ClientImpl::close_socket(Socket &socket,
-                                     bool /*process_socket_ret*/) {
-  detail::close_socket(socket.sock);
-  socket_.sock = INVALID_SOCKET;
+inline void ClientImpl::shutdown_ssl(Socket &socket, bool shutdown_gracefully) {
+  (void)socket;
+  (void)shutdown_gracefully;
+  //If there are any requests in flight from threads other than us, then it's
+  //a thread-unsafe race because individual ssl* objects are not thread-safe. 
+  assert(socket_requests_in_flight_ == 0 ||
+         socket_requests_are_from_thread_ == std::this_thread::get_id());
+}
+
+inline void ClientImpl::shutdown_socket(Socket &socket) {
+  if (socket.sock == INVALID_SOCKET)
+    return;  
+  detail::shutdown_socket(socket.sock);
+}
+ 
+inline void ClientImpl::close_socket(Socket &socket) {
+  // If there are requests in flight in another thread, usually closing
+  // the socket will be fine and they will simply receive an error when
+  // using the closed socket, but it is still a bug since rarely the OS
+  // may reassign the socket id to be used for a new socket, and then
+  // suddenly they will be operating on a live socket that is different
+  // than the one they intended!
+  assert(socket_requests_in_flight_ == 0 ||
+         socket_requests_are_from_thread_ == std::this_thread::get_id());
+  // It is also a bug if this happens while SSL is still active
 #ifdef CPPHTTPLIB_OPENSSL_SUPPORT
-  socket_.ssl = nullptr;
+  assert(socket.ssl == nullptr);
 #endif
+  if (socket.sock == INVALID_SOCKET)
+    return;
+  detail::close_socket(socket.sock);
+  socket.sock = INVALID_SOCKET;
 }
 
+inline void ClientImpl::lock_socket_and_shutdown_and_close() {
+  std::lock_guard<std::mutex> guard(socket_mutex_);
+  shutdown_ssl(socket_, true);
+  shutdown_socket(socket_);
+  close_socket(socket_);
+}
+ 
 inline bool ClientImpl::read_response_line(Stream &strm, Response &res) {
   std::array<char, 2048> buf;
 
@@ -4696,11 +4813,23 @@ inline bool ClientImpl::send(const Request &req, Response &res) {
 
   {
     std::lock_guard<std::mutex> guard(socket_mutex_);
+    // Set this to false immediately - if it ever gets set to true by the end of the
+    // request, we know another thread instructed us to close the socket.
+    socket_should_be_closed_when_request_is_done_ = false;
 
     auto is_alive = false;
     if (socket_.is_open()) {
       is_alive = detail::select_write(socket_.sock, 0, 0) > 0;
-      if (!is_alive) { close_socket(socket_, false); }
+      if (!is_alive) {
+        // Attempt to avoid sigpipe by shutting down nongracefully if it seems like
+        // the other side has already closed the connection
+        // Also, there cannot be any requests in flight from other threads since we locked
+        // request_mutex_, so safe to close everything immediately
+        const bool shutdown_gracefully = false;
+        shutdown_ssl(socket_, shutdown_gracefully);
+        shutdown_socket(socket_);
+        close_socket(socket_);
+      }
     }
 
     if (!is_alive) {
@@ -4721,15 +4850,38 @@ inline bool ClientImpl::send(const Request &req, Response &res) {
       }
 #endif
     }
+
+    // Mark the current socket as being in use so that it cannot be closed by anyone
+    // else while this request is ongoing, even though we will be releasing the mutex.
+    if (socket_requests_in_flight_ > 1) {
+      assert(socket_requests_are_from_thread_ == std::this_thread::get_id());
+    }
+    socket_requests_in_flight_ += 1;
+    socket_requests_are_from_thread_ = std::this_thread::get_id();
   }
 
   auto close_connection = !keep_alive_;
-
   auto ret = process_socket(socket_, [&](Stream &strm) {
     return handle_request(strm, req, res, close_connection);
   });
 
-  if (close_connection || !ret) { stop_core(); }
+  //Briefly lock mutex in order to mark that a request is no longer ongoing
+  {
+    std::lock_guard<std::mutex> guard(socket_mutex_);
+    socket_requests_in_flight_ -= 1;
+    if (socket_requests_in_flight_ <= 0) {
+      assert(socket_requests_in_flight_ == 0);
+      socket_requests_are_from_thread_ = std::thread::id();
+    }
+
+    if (socket_should_be_closed_when_request_is_done_ ||
+        close_connection ||
+        !ret ) {
+      shutdown_ssl(socket_, true);
+      shutdown_socket(socket_);
+      close_socket(socket_);
+    }
+  }
 
   if (!ret) {
     if (error_ == Error::Success) { error_ = Error::Unknown; }
@@ -4973,7 +5125,7 @@ inline bool ClientImpl::write_request(Stream &strm, const Request &req,
   return true;
 }
 
-inline std::shared_ptr<Response> ClientImpl::send_with_content_provider(
+inline std::unique_ptr<Response> ClientImpl::send_with_content_provider(
     const char *method, const char *path, const Headers &headers,
     const std::string &body, size_t content_length,
     ContentProvider content_provider, const char *content_type) {
@@ -5036,15 +5188,15 @@ inline std::shared_ptr<Response> ClientImpl::send_with_content_provider(
   {
     if (content_provider) {
       req.content_length = content_length;
-      req.content_provider = content_provider;
+      req.content_provider = std::move(content_provider);
     } else {
       req.body = body;
     }
   }
 
-  auto res = std::make_shared<Response>();
+  auto res = detail::make_unique<Response>();
 
-  return send(req, *res) ? res : nullptr;
+  return send(req, *res) ? std::move(res) : nullptr;
 }
 
 inline bool ClientImpl::process_request(Stream &strm, const Request &req,
@@ -5070,16 +5222,21 @@ inline bool ClientImpl::process_request(Stream &strm, const Request &req,
   if (req.method != "HEAD" && req.method != "CONNECT") {
     auto out =
         req.content_receiver
-            ? static_cast<ContentReceiver>([&](const char *buf, size_t n) {
-                auto ret = req.content_receiver(buf, n);
-                if (!ret) { error_ = Error::Canceled; }
-                return ret;
-              })
-            : static_cast<ContentReceiver>([&](const char *buf, size_t n) {
-                if (res.body.size() + n > res.body.max_size()) { return false; }
-                res.body.append(buf, n);
-                return true;
-              });
+            ? static_cast<ContentReceiverWithProgress>(
+                  [&](const char *buf, size_t n, uint64_t off, uint64_t len) {
+                    auto ret = req.content_receiver(buf, n, off, len);
+                    if (!ret) { error_ = Error::Canceled; }
+                    return ret;
+                  })
+            : static_cast<ContentReceiverWithProgress>(
+                  [&](const char *buf, size_t n, uint64_t /*off*/,
+                      uint64_t /*len*/) {
+                    if (res.body.size() + n > res.body.max_size()) {
+                      return false;
+                    }
+                    res.body.append(buf, n);
+                    return true;
+                  });
 
     auto progress = [&](uint64_t current, uint64_t total) {
       if (!req.progress) { return true; }
@@ -5090,7 +5247,8 @@ inline bool ClientImpl::process_request(Stream &strm, const Request &req,
 
     int dummy_status;
     if (!detail::read_content(strm, res, (std::numeric_limits<size_t>::max)(),
-                              dummy_status, progress, out, decompress_)) {
+                              dummy_status, std::move(progress), std::move(out),
+                              decompress_)) {
       if (error_ != Error::Canceled) { error_ = Error::Read; }
       return false;
     }
@@ -5098,7 +5256,16 @@ inline bool ClientImpl::process_request(Stream &strm, const Request &req,
 
   if (res.get_header_value("Connection") == "close" ||
       (res.version == "HTTP/1.0" && res.reason != "Connection established")) {
-    stop_core();
+    // TODO this requires a not-entirely-obvious chain of calls to be correct
+    // for this to be safe. Maybe a code refactor (such as moving this out to
+    // the send function and getting rid of the recursiveness of the mutex)
+    // could make this more obvious.
+    
+    // This is safe to call because process_request is only called by handle_request
+    // which is only called by send, which locks the request mutex during the process.
+    // It would be a bug to call it from a different thread since it's a thread-safety
+    // issue to do these things to the socket if another thread is using the socket.
+    lock_socket_and_shutdown_and_close();
   }
 
   // Log
@@ -5108,11 +5275,11 @@ inline bool ClientImpl::process_request(Stream &strm, const Request &req,
 }
 
 inline bool
-ClientImpl::process_socket(Socket &socket,
+ClientImpl::process_socket(const Socket &socket,
                            std::function<bool(Stream &strm)> callback) {
-  return detail::process_client_socket(socket.sock, read_timeout_sec_,
-                                       read_timeout_usec_, write_timeout_sec_,
-                                       write_timeout_usec_, callback);
+  return detail::process_client_socket(
+      socket.sock, read_timeout_sec_, read_timeout_usec_, write_timeout_sec_,
+      write_timeout_usec_, std::move(callback));
 }
 
 inline bool ClientImpl::is_ssl() const { return false; }
@@ -5138,9 +5305,9 @@ inline Result ClientImpl::Get(const char *path, const Headers &headers,
   req.headers.insert(headers.begin(), headers.end());
   req.progress = std::move(progress);
 
-  auto res = std::make_shared<Response>();
+  auto res = detail::make_unique<Response>();
   auto ret = send(req, *res);
-  return Result{ret ? res : nullptr, get_last_error()};
+  return Result{ret ? std::move(res) : nullptr, get_last_error()};
 }
 
 inline Result ClientImpl::Get(const char *path,
@@ -5170,23 +5337,23 @@ inline Result ClientImpl::Get(const char *path, const Headers &headers,
 inline Result ClientImpl::Get(const char *path,
                               ResponseHandler response_handler,
                               ContentReceiver content_receiver) {
-  return Get(path, Headers(), std::move(response_handler), content_receiver,
-             nullptr);
+  return Get(path, Headers(), std::move(response_handler),
+             std::move(content_receiver), nullptr);
 }
 
 inline Result ClientImpl::Get(const char *path, const Headers &headers,
                               ResponseHandler response_handler,
                               ContentReceiver content_receiver) {
-  return Get(path, headers, std::move(response_handler), content_receiver,
-             nullptr);
+  return Get(path, headers, std::move(response_handler),
+             std::move(content_receiver), nullptr);
 }
 
 inline Result ClientImpl::Get(const char *path,
                               ResponseHandler response_handler,
                               ContentReceiver content_receiver,
                               Progress progress) {
-  return Get(path, Headers(), std::move(response_handler), content_receiver,
-             progress);
+  return Get(path, Headers(), std::move(response_handler),
+             std::move(content_receiver), std::move(progress));
 }
 
 inline Result ClientImpl::Get(const char *path, const Headers &headers,
@@ -5199,12 +5366,16 @@ inline Result ClientImpl::Get(const char *path, const Headers &headers,
   req.headers = default_headers_;
   req.headers.insert(headers.begin(), headers.end());
   req.response_handler = std::move(response_handler);
-  req.content_receiver = std::move(content_receiver);
+  req.content_receiver =
+      [content_receiver](const char *data, size_t data_length,
+                         uint64_t /*offset*/, uint64_t /*total_length*/) {
+        return content_receiver(data, data_length);
+      };
   req.progress = std::move(progress);
 
-  auto res = std::make_shared<Response>();
+  auto res = detail::make_unique<Response>();
   auto ret = send(req, *res);
-  return Result{ret ? res : nullptr, get_last_error()};
+  return Result{ret ? std::move(res) : nullptr, get_last_error()};
 }
 
 inline Result ClientImpl::Head(const char *path) {
@@ -5218,9 +5389,9 @@ inline Result ClientImpl::Head(const char *path, const Headers &headers) {
   req.headers.insert(headers.begin(), headers.end());
   req.path = path;
 
-  auto res = std::make_shared<Response>();
+  auto res = detail::make_unique<Response>();
   auto ret = send(req, *res);
-  return Result{ret ? res : nullptr, get_last_error()};
+  return Result{ret ? std::move(res) : nullptr, get_last_error()};
 }
 
 inline Result ClientImpl::Post(const char *path) {
@@ -5237,7 +5408,7 @@ inline Result ClientImpl::Post(const char *path, const Headers &headers,
                                const char *content_type) {
   auto ret = send_with_content_provider("POST", path, headers, body, 0, nullptr,
                                         content_type);
-  return Result{ret, get_last_error()};
+  return Result{std::move(ret), get_last_error()};
 }
 
 inline Result ClientImpl::Post(const char *path, const Params &params) {
@@ -5247,17 +5418,18 @@ inline Result ClientImpl::Post(const char *path, const Params &params) {
 inline Result ClientImpl::Post(const char *path, size_t content_length,
                                ContentProvider content_provider,
                                const char *content_type) {
-  return Post(path, Headers(), content_length, content_provider, content_type);
+  return Post(path, Headers(), content_length, std::move(content_provider),
+              content_type);
 }
 
 inline Result ClientImpl::Post(const char *path, const Headers &headers,
                                size_t content_length,
                                ContentProvider content_provider,
                                const char *content_type) {
-  auto ret = send_with_content_provider("POST", path, headers, std::string(),
-                                        content_length, content_provider,
-                                        content_type);
-  return Result{ret, get_last_error()};
+  auto ret = send_with_content_provider(
+      "POST", path, headers, std::string(), content_length,
+      std::move(content_provider), content_type);
+  return Result{std::move(ret), get_last_error()};
 }
 
 inline Result ClientImpl::Post(const char *path, const Headers &headers,
@@ -5273,7 +5445,18 @@ inline Result ClientImpl::Post(const char *path,
 
 inline Result ClientImpl::Post(const char *path, const Headers &headers,
                                const MultipartFormDataItems &items) {
-  auto boundary = detail::make_multipart_data_boundary();
+  return Post(path, headers, items, detail::make_multipart_data_boundary());
+}
+inline Result ClientImpl::Post(const char *path, const Headers &headers,
+                               const MultipartFormDataItems &items,
+                               const std::string &boundary) {
+  for (size_t i = 0; i < boundary.size(); i++) {
+    char c = boundary[i];
+    if (!std::isalnum(c) && c != '-' && c != '_') {
+      error_ = Error::UnsupportedMultipartBoundaryChars;
+      return Result{nullptr, error_};
+    }
+  }
 
   std::string body;
 
@@ -5311,23 +5494,24 @@ inline Result ClientImpl::Put(const char *path, const Headers &headers,
                               const char *content_type) {
   auto ret = send_with_content_provider("PUT", path, headers, body, 0, nullptr,
                                         content_type);
-  return Result{ret, get_last_error()};
+  return Result{std::move(ret), get_last_error()};
 }
 
 inline Result ClientImpl::Put(const char *path, size_t content_length,
                               ContentProvider content_provider,
                               const char *content_type) {
-  return Put(path, Headers(), content_length, content_provider, content_type);
+  return Put(path, Headers(), content_length, std::move(content_provider),
+             content_type);
 }
 
 inline Result ClientImpl::Put(const char *path, const Headers &headers,
                               size_t content_length,
                               ContentProvider content_provider,
                               const char *content_type) {
-  auto ret = send_with_content_provider("PUT", path, headers, std::string(),
-                                        content_length, content_provider,
-                                        content_type);
-  return Result{ret, get_last_error()};
+  auto ret = send_with_content_provider(
+      "PUT", path, headers, std::string(), content_length,
+      std::move(content_provider), content_type);
+  return Result{std::move(ret), get_last_error()};
 }
 
 inline Result ClientImpl::Put(const char *path, const Params &params) {
@@ -5350,23 +5534,24 @@ inline Result ClientImpl::Patch(const char *path, const Headers &headers,
                                 const char *content_type) {
   auto ret = send_with_content_provider("PATCH", path, headers, body, 0,
                                         nullptr, content_type);
-  return Result{ret, get_last_error()};
+  return Result{std::move(ret), get_last_error()};
 }
 
 inline Result ClientImpl::Patch(const char *path, size_t content_length,
                                 ContentProvider content_provider,
                                 const char *content_type) {
-  return Patch(path, Headers(), content_length, content_provider, content_type);
+  return Patch(path, Headers(), content_length, std::move(content_provider),
+               content_type);
 }
 
 inline Result ClientImpl::Patch(const char *path, const Headers &headers,
                                 size_t content_length,
                                 ContentProvider content_provider,
                                 const char *content_type) {
-  auto ret = send_with_content_provider("PATCH", path, headers, std::string(),
-                                        content_length, content_provider,
-                                        content_type);
-  return Result{ret, get_last_error()};
+  auto ret = send_with_content_provider(
+      "PATCH", path, headers, std::string(), content_length,
+      std::move(content_provider), content_type);
+  return Result{std::move(ret), get_last_error()};
 }
 
 inline Result ClientImpl::Delete(const char *path) {
@@ -5394,9 +5579,9 @@ inline Result ClientImpl::Delete(const char *path, const Headers &headers,
   if (content_type) { req.headers.emplace("Content-Type", content_type); }
   req.body = body;
 
-  auto res = std::make_shared<Response>();
+  auto res = detail::make_unique<Response>();
   auto ret = send(req, *res);
-  return Result{ret ? res : nullptr, get_last_error()};
+  return Result{ret ? std::move(res) : nullptr, get_last_error()};
 }
 
 inline Result ClientImpl::Options(const char *path) {
@@ -5410,9 +5595,9 @@ inline Result ClientImpl::Options(const char *path, const Headers &headers) {
   req.headers.insert(headers.begin(), headers.end());
   req.path = path;
 
-  auto res = std::make_shared<Response>();
+  auto res = detail::make_unique<Response>();
   auto ret = send(req, *res);
-  return Result{ret ? res : nullptr, get_last_error()};
+  return Result{ret ? std::move(res) : nullptr, get_last_error()};
 }
 
 inline size_t ClientImpl::is_socket_open() const {
@@ -5421,18 +5606,27 @@ inline size_t ClientImpl::is_socket_open() const {
 }
 
 inline void ClientImpl::stop() {
-  stop_core();
-  error_ = Error::Canceled;
-}
-
-inline void ClientImpl::stop_core() {
   std::lock_guard<std::mutex> guard(socket_mutex_);
-  if (socket_.is_open()) {
-    detail::shutdown_socket(socket_.sock);
-    std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    close_socket(socket_, true);
-    std::this_thread::sleep_for(std::chrono::milliseconds(1));
+  // There is no guarantee that this doesn't get overwritten later, but set it so that
+  // there is a good chance that any threads stopping as a result pick up this error.
+  error_ = Error::Canceled;
+  
+  // If there is anything ongoing right now, the ONLY thread-safe thing we can do
+  // is to shutdown_socket, so that threads using this socket suddenly discover
+  // they can't read/write any more and error out.
+  // Everything else (closing the socket, shutting ssl down) is unsafe because these
+  // actions are not thread-safe.
+  if (socket_requests_in_flight_ > 0) {
+    shutdown_socket(socket_);
+    // Aside from that, we set a flag for the socket to be closed when we're done.
+    socket_should_be_closed_when_request_is_done_ = true;
+    return;
   }
+
+  //Otherwise, sitll holding the mutex, we can shut everything down ourselves
+  shutdown_ssl(socket_, true);
+  shutdown_socket(socket_);
+  close_socket(socket_);
 }
 
 inline void ClientImpl::set_connection_timeout(time_t sec, time_t usec) {
@@ -5479,7 +5673,7 @@ inline void ClientImpl::set_default_headers(Headers headers) {
 inline void ClientImpl::set_tcp_nodelay(bool on) { tcp_nodelay_ = on; }
 
 inline void ClientImpl::set_socket_options(SocketOptions socket_options) {
-  socket_options_ = socket_options;
+  socket_options_ = std::move(socket_options);
 }
 
 inline void ClientImpl::set_compress(bool on) { compress_ = on; }
@@ -5554,9 +5748,12 @@ inline SSL *ssl_new(socket_t sock, SSL_CTX *ctx, std::mutex &ctx_mutex,
 }
 
 inline void ssl_delete(std::mutex &ctx_mutex, SSL *ssl,
-                       bool process_socket_ret) {
-  if (process_socket_ret) {
-    SSL_shutdown(ssl); // shutdown only if not already closed by remote
+                       bool shutdown_gracefully) {
+  // sometimes we may want to skip this to try to avoid SIGPIPE if we know
+  // the remote has closed the network connection
+  // Note that it is not always possible to avoid SIGPIPE, this is merely a best-efforts.
+  if (shutdown_gracefully) {
+    SSL_shutdown(ssl); 
   }
 
   std::lock_guard<std::mutex> guard(ctx_mutex);
@@ -5650,22 +5847,7 @@ inline SSLSocketStream::SSLSocketStream(socket_t sock, SSL *ssl,
       read_timeout_usec_(read_timeout_usec),
       write_timeout_sec_(write_timeout_sec),
       write_timeout_usec_(write_timeout_usec) {
-  {
-    timeval tv;
-    tv.tv_sec = static_cast<long>(read_timeout_sec);
-    tv.tv_usec = static_cast<decltype(tv.tv_usec)>(read_timeout_usec);
-
-    setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, reinterpret_cast<char *>(&tv),
-               sizeof(tv));
-  }
-  {
-    timeval tv;
-    tv.tv_sec = static_cast<long>(write_timeout_sec);
-    tv.tv_usec = static_cast<decltype(tv.tv_usec)>(write_timeout_usec);
-
-    setsockopt(sock, SOL_SOCKET, SO_SNDTIMEO, reinterpret_cast<char *>(&tv),
-               sizeof(tv));
-  }
+  SSL_clear_mode(ssl, SSL_MODE_AUTO_RETRY);
 }
 
 inline SSLSocketStream::~SSLSocketStream() {}
@@ -5680,8 +5862,27 @@ inline bool SSLSocketStream::is_writable() const {
 }
 
 inline ssize_t SSLSocketStream::read(char *ptr, size_t size) {
-  if (SSL_pending(ssl_) > 0 || is_readable()) {
+  if (SSL_pending(ssl_) > 0) {
     return SSL_read(ssl_, ptr, static_cast<int>(size));
+  } else if (is_readable()) {
+    auto ret = SSL_read(ssl_, ptr, static_cast<int>(size));
+    if (ret < 0) {
+      auto err = SSL_get_error(ssl_, ret);
+      while (err == SSL_ERROR_WANT_READ) {
+        if (SSL_pending(ssl_) > 0) {
+          return SSL_read(ssl_, ptr, static_cast<int>(size));
+        } else if (is_readable()) {
+          ret = SSL_read(ssl_, ptr, static_cast<int>(size));
+          if (ret >= 0) {
+            return ret;
+          }
+          err = SSL_get_error(ssl_, ret);
+        } else {
+          return -1;
+        }
+      }
+    }
+    return ret;
   }
   return -1;
 }
@@ -5788,9 +5989,12 @@ inline bool SSLServer::process_and_close_socket(socket_t sock) {
         });
 
     detail::ssl_delete(ctx_mutex_, ssl, ret);
+    detail::shutdown_socket(sock);
+    detail::close_socket(sock);
     return ret;
   }
 
+  detail::shutdown_socket(sock);
   detail::close_socket(sock);
   return false;
 }
@@ -5843,6 +6047,10 @@ inline SSLClient::SSLClient(const std::string &host, int port,
 
 inline SSLClient::~SSLClient() {
   if (ctx_) { SSL_CTX_free(ctx_); }
+  // Make sure to shut down SSL since shutdown_ssl will resolve to the
+  // base function rather than the derived function once we get to the
+  // base class destructor, and won't free the SSL (causing a leak).
+  SSLClient::shutdown_ssl(socket_, true);
 }
 
 inline bool SSLClient::is_valid() const { return ctx_; }
@@ -5876,11 +6084,11 @@ inline bool SSLClient::create_and_connect_socket(Socket &socket) {
   return is_valid() && ClientImpl::create_and_connect_socket(socket);
 }
 
+// Assumes that socket_mutex_ is locked and that there are no requests in flight
 inline bool SSLClient::connect_with_proxy(Socket &socket, Response &res,
                                           bool &success) {
   success = true;
   Response res2;
-
   if (!detail::process_client_socket(
           socket.sock, read_timeout_sec_, read_timeout_usec_,
           write_timeout_sec_, write_timeout_usec_, [&](Stream &strm) {
@@ -5889,7 +6097,10 @@ inline bool SSLClient::connect_with_proxy(Socket &socket, Response &res,
             req2.path = host_and_port_;
             return process_request(strm, req2, res2, false);
           })) {
-    close_socket(socket, true);
+    // Thread-safe to close everything because we are assuming there are no requests in flight
+    shutdown_ssl(socket, true);
+    shutdown_socket(socket);
+    close_socket(socket);
     success = false;
     return false;
   }
@@ -5912,7 +6123,10 @@ inline bool SSLClient::connect_with_proxy(Socket &socket, Response &res,
                       true));
                   return process_request(strm, req3, res3, false);
                 })) {
-          close_socket(socket, true);
+          // Thread-safe to close everything because we are assuming there are no requests in flight
+          shutdown_ssl(socket, true);
+          shutdown_socket(socket);
+          close_socket(socket);
           success = false;
           return false;
         }
@@ -6005,26 +6219,30 @@ inline bool SSLClient::initialize_ssl(Socket &socket) {
     return true;
   }
 
-  close_socket(socket, false);
+  shutdown_socket(socket);
+  close_socket(socket);
   return false;
 }
 
-inline void SSLClient::close_socket(Socket &socket, bool process_socket_ret) {
-  detail::close_socket(socket.sock);
-  socket_.sock = INVALID_SOCKET;
+inline void SSLClient::shutdown_ssl(Socket &socket, bool shutdown_gracefully) {
+  if (socket.sock == INVALID_SOCKET) {
+    assert(socket.ssl == nullptr);
+    return;
+  }
   if (socket.ssl) {
-    detail::ssl_delete(ctx_mutex_, socket.ssl, process_socket_ret);
-    socket_.ssl = nullptr;
+    detail::ssl_delete(ctx_mutex_, socket.ssl, shutdown_gracefully);
+    socket.ssl = nullptr;
   }
+  assert(socket.ssl == nullptr);
 }
 
 inline bool
-SSLClient::process_socket(Socket &socket,
+SSLClient::process_socket(const Socket &socket,
                           std::function<bool(Stream &strm)> callback) {
   assert(socket.ssl);
   return detail::process_client_socket_ssl(
       socket.ssl, socket.sock, read_timeout_sec_, read_timeout_usec_,
-      write_timeout_sec_, write_timeout_usec_, callback);
+      write_timeout_sec_, write_timeout_usec_, std::move(callback));
 }
 
 inline bool SSLClient::is_ssl() const { return true; }
@@ -6175,6 +6393,8 @@ inline Client::Client(const char *scheme_host_port,
 #else
     if (!scheme.empty() && scheme != "http") {
 #endif
+      std::string msg = "'" + scheme + "' scheme is not supported.";
+      throw std::invalid_argument(msg);
       return;
     }
 
@@ -6187,28 +6407,28 @@ inline Client::Client(const char *scheme_host_port,
 
     if (is_ssl) {
 #ifdef CPPHTTPLIB_OPENSSL_SUPPORT
-      cli_ = std::make_shared<SSLClient>(host.c_str(), port, client_cert_path,
-                                         client_key_path);
+      cli_ = detail::make_unique<SSLClient>(host.c_str(), port,
+                                            client_cert_path, client_key_path);
       is_ssl_ = is_ssl;
 #endif
     } else {
-      cli_ = std::make_shared<ClientImpl>(host.c_str(), port, client_cert_path,
-                                          client_key_path);
+      cli_ = detail::make_unique<ClientImpl>(host.c_str(), port,
+                                             client_cert_path, client_key_path);
     }
   } else {
-    cli_ = std::make_shared<ClientImpl>(scheme_host_port, 80, client_cert_path,
-                                        client_key_path);
+    cli_ = detail::make_unique<ClientImpl>(scheme_host_port, 80,
+                                           client_cert_path, client_key_path);
   }
 }
 
 inline Client::Client(const std::string &host, int port)
-    : cli_(std::make_shared<ClientImpl>(host, port)) {}
+    : cli_(detail::make_unique<ClientImpl>(host, port)) {}
 
 inline Client::Client(const std::string &host, int port,
                       const std::string &client_cert_path,
                       const std::string &client_key_path)
-    : cli_(std::make_shared<ClientImpl>(host, port, client_cert_path,
-                                        client_key_path)) {}
+    : cli_(detail::make_unique<ClientImpl>(host, port, client_cert_path,
+                                           client_key_path)) {}
 
 inline Client::~Client() {}
 
@@ -6221,11 +6441,11 @@ inline Result Client::Get(const char *path, const Headers &headers) {
   return cli_->Get(path, headers);
 }
 inline Result Client::Get(const char *path, Progress progress) {
-  return cli_->Get(path, progress);
+  return cli_->Get(path, std::move(progress));
 }
 inline Result Client::Get(const char *path, const Headers &headers,
                           Progress progress) {
-  return cli_->Get(path, headers, progress);
+  return cli_->Get(path, headers, std::move(progress));
 }
 inline Result Client::Get(const char *path, ContentReceiver content_receiver) {
   return cli_->Get(path, std::move(content_receiver));
@@ -6262,7 +6482,8 @@ inline Result Client::Get(const char *path, ResponseHandler response_handler,
 inline Result Client::Get(const char *path, const Headers &headers,
                           ResponseHandler response_handler,
                           ContentReceiver content_receiver, Progress progress) {
-  return cli_->Get(path, headers, response_handler, content_receiver, progress);
+  return cli_->Get(path, headers, std::move(response_handler),
+                   std::move(content_receiver), std::move(progress));
 }
 
 inline Result Client::Head(const char *path) { return cli_->Head(path); }
@@ -6282,13 +6503,14 @@ inline Result Client::Post(const char *path, const Headers &headers,
 inline Result Client::Post(const char *path, size_t content_length,
                            ContentProvider content_provider,
                            const char *content_type) {
-  return cli_->Post(path, content_length, content_provider, content_type);
+  return cli_->Post(path, content_length, std::move(content_provider),
+                    content_type);
 }
 inline Result Client::Post(const char *path, const Headers &headers,
                            size_t content_length,
                            ContentProvider content_provider,
                            const char *content_type) {
-  return cli_->Post(path, headers, content_length, content_provider,
+  return cli_->Post(path, headers, content_length, std::move(content_provider),
                     content_type);
 }
 inline Result Client::Post(const char *path, const Params &params) {
@@ -6306,6 +6528,11 @@ inline Result Client::Post(const char *path, const Headers &headers,
                            const MultipartFormDataItems &items) {
   return cli_->Post(path, headers, items);
 }
+inline Result Client::Post(const char *path, const Headers &headers,
+                           const MultipartFormDataItems &items,
+                           const std::string &boundary) {
+  return cli_->Post(path, headers, items, boundary);
+}
 inline Result Client::Put(const char *path) { return cli_->Put(path); }
 inline Result Client::Put(const char *path, const std::string &body,
                           const char *content_type) {
@@ -6318,13 +6545,14 @@ inline Result Client::Put(const char *path, const Headers &headers,
 inline Result Client::Put(const char *path, size_t content_length,
                           ContentProvider content_provider,
                           const char *content_type) {
-  return cli_->Put(path, content_length, content_provider, content_type);
+  return cli_->Put(path, content_length, std::move(content_provider),
+                   content_type);
 }
 inline Result Client::Put(const char *path, const Headers &headers,
                           size_t content_length,
                           ContentProvider content_provider,
                           const char *content_type) {
-  return cli_->Put(path, headers, content_length, content_provider,
+  return cli_->Put(path, headers, content_length, std::move(content_provider),
                    content_type);
 }
 inline Result Client::Put(const char *path, const Params &params) {
@@ -6345,13 +6573,14 @@ inline Result Client::Patch(const char *path, const Headers &headers,
 inline Result Client::Patch(const char *path, size_t content_length,
                             ContentProvider content_provider,
                             const char *content_type) {
-  return cli_->Patch(path, content_length, content_provider, content_type);
+  return cli_->Patch(path, content_length, std::move(content_provider),
+                     content_type);
 }
 inline Result Client::Patch(const char *path, const Headers &headers,
                             size_t content_length,
                             ContentProvider content_provider,
                             const char *content_type) {
-  return cli_->Patch(path, headers, content_length, content_provider,
+  return cli_->Patch(path, headers, content_length, std::move(content_provider),
                      content_type);
 }
 inline Result Client::Delete(const char *path) { return cli_->Delete(path); }
@@ -6386,7 +6615,7 @@ inline void Client::set_default_headers(Headers headers) {
 
 inline void Client::set_tcp_nodelay(bool on) { cli_->set_tcp_nodelay(on); }
 inline void Client::set_socket_options(SocketOptions socket_options) {
-  cli_->set_socket_options(socket_options);
+  cli_->set_socket_options(std::move(socket_options));
 }
 
 inline void Client::set_connection_timeout(time_t sec, time_t usec) {
diff --git a/src/web_service/web_backend.cpp b/src/web_service/web_backend.cpp
index f264b98a0..67183e64c 100644
--- a/src/web_service/web_backend.cpp
+++ b/src/web_service/web_backend.cpp
@@ -71,11 +71,6 @@ struct Client::Impl {
             return {};
         }
 
-        if (!cli->is_socket_open()) {
-            LOG_ERROR(WebService, "Failed to open socket, skipping request!");
-            return {};
-        }
-
         cli->set_connection_timeout(TIMEOUT_SECONDS);
         cli->set_read_timeout(TIMEOUT_SECONDS);
         cli->set_write_timeout(TIMEOUT_SECONDS);