evhttpd implementation

- *Replace usage of boost::asio with [libevent2](http://libevent.org/)*.
boost::asio is not part of C++11, so unlike other boost there is no
forwards-compatibility reason to stick with it. Together with #4738 (convert
json_spirit to UniValue), this rids Bitcoin Core of the worst offenders with
regard to compile-time slowness.

- *Replace spit-and-duct-tape http server with evhttp*. Front-end http handling
is handled by libevent, a work queue (with configurable depth and parallelism)
is used to handle application requests.

- *Wrap HTTP request in C++ class*; this makes the application code mostly
HTTP-server-neutral

- *Refactor RPC to move all http-specific code to a separate file*.
Theoreticaly this can allow building without HTTP server but with another RPC
backend, e.g. Qt's debug console (currently not implemented) or future RPC
mechanisms people may want to use.

- *HTTP dispatch mechanism*; services (e.g., RPC, REST) register which URL
paths they want to handle.

By using a proven, high-performance asynchronous networking library (also used
by Tor) and HTTP server, problems such as #5674, #5655, #344 should be avoided.

What works? bitcoind, bitcoin-cli, bitcoin-qt. Unit tests and RPC/REST tests
pass. The aim for now is everything but SSL support.

Configuration options:

- `-rpcthreads`: repurposed as "number of  work handler threads". Still
defaults to 4.

- `-rpcworkqueue`: maximum depth of work queue. When this is reached, new
requests will return a 500 Internal Error.

- `-rpctimeout`: inactivity time, in seconds, after which to disconnect a
client.

- `-debug=http`: low-level http activity logging

1 files changed, 93 insertions, 40 deletions

diff --git a/src/bitcoin-cli.cpp b/src/bitcoin-cli.cpp
index 1c5a312874..2e094fde22 100644
--- a/src/bitcoin-cli.cpp
+++ b/src/bitcoin-cli.cpp
@@ -11,6 +11,12 @@
 #include "utilstrencodings.h"
 
 #include <boost/filesystem/operations.hpp>
+#include <stdio.h>
+
+#include <event2/event.h>
+#include <event2/http.h>
+#include <event2/buffer.h>
+#include <event2/keyvalq_struct.h>
 
 #include "univalue/univalue.h"
 
@@ -32,9 +38,6 @@ std::string HelpMessageCli()
     strUsage += HelpMessageOpt("-rpcuser=<user>", _("Username for JSON-RPC connections"));
     strUsage += HelpMessageOpt("-rpcpassword=<pw>", _("Password for JSON-RPC connections"));
 
-    strUsage += HelpMessageGroup(_("SSL options: (see the Bitcoin Wiki for SSL setup instructions)"));
-    strUsage += HelpMessageOpt("-rpcssl", _("Use OpenSSL (https) for JSON-RPC connections"));
-
     return strUsage;
 }
 
@@ -92,32 +95,75 @@ static bool AppInitRPC(int argc, char* argv[])
         fprintf(stderr, "Error: Invalid combination of -regtest and -testnet.\n");
         return false;
     }
+    if (GetBoolArg("-rpcssl", false))
+    {
+        fprintf(stderr, "Error: SSL mode for RPC (-rpcssl) is no longer supported.\n");
+        return false;
+    }
     return true;
 }
 
-UniValue CallRPC(const string& strMethod, const UniValue& params)
+
+/** Reply structure for request_done to fill in */
+struct HTTPReply
 {
-    // Connect to localhost
-    bool fUseSSL = GetBoolArg("-rpcssl", false);
-    boost::asio::io_service io_service;
-    boost::asio::ssl::context context(io_service, boost::asio::ssl::context::sslv23);
-    context.set_options(boost::asio::ssl::context::no_sslv2 | boost::asio::ssl::context::no_sslv3);
-    boost::asio::ssl::stream<boost::asio::ip::tcp::socket> sslStream(io_service, context);
-    SSLIOStreamDevice<boost::asio::ip::tcp> d(sslStream, fUseSSL);
-    boost::iostreams::stream< SSLIOStreamDevice<boost::asio::ip::tcp> > stream(d);
-
-    const bool fConnected = d.connect(GetArg("-rpcconnect", "127.0.0.1"), GetArg("-rpcport", itostr(BaseParams().RPCPort())));
-    if (!fConnected)
-        throw CConnectionFailed("couldn't connect to server");
+    int status;
+    std::string body;
+};
+
+static void http_request_done(struct evhttp_request *req, void *ctx)
+{
+    HTTPReply *reply = static_cast<HTTPReply*>(ctx);
+
+    if (req == NULL) {
+        /* If req is NULL, it means an error occurred while connecting, but
+         * I'm not sure how to find out which one. We also don't really care.
+         */
+        reply->status = 0;
+        return;
+    }
 
-    // Find credentials to use
+    reply->status = evhttp_request_get_response_code(req);
+
+    struct evbuffer *buf = evhttp_request_get_input_buffer(req);
+    if (buf)
+    {
+        size_t size = evbuffer_get_length(buf);
+        const char *data = (const char*)evbuffer_pullup(buf, size);
+        if (data)
+            reply->body = std::string(data, size);
+        evbuffer_drain(buf, size);
+    }
+}
+
+UniValue CallRPC(const string& strMethod, const UniValue& params)
+{
+    std::string host = GetArg("-rpcconnect", "127.0.0.1");
+    int port = GetArg("-rpcport", BaseParams().RPCPort());
+
+    // Create event base
+    struct event_base *base = event_base_new(); // TODO RAII
+    if (!base)
+        throw runtime_error("cannot create event_base");
+
+    // Synchronously look up hostname
+    struct evhttp_connection *evcon = evhttp_connection_base_new(base, NULL, host.c_str(), port); // TODO RAII
+    if (evcon == NULL)
+        throw runtime_error("create connection failed");
+    evhttp_connection_set_timeout(evcon, GetArg("-rpctimeout", 30));
+
+    HTTPReply response;
+    struct evhttp_request *req = evhttp_request_new(http_request_done, (void*)&response); // TODO RAII
+    if (req == NULL)
+        throw runtime_error("create http request failed");
+
+    // Get credentials
     std::string strRPCUserColonPass;
     if (mapArgs["-rpcpassword"] == "") {
         // Try fall back to cookie-based authentication if no password is provided
         if (!GetAuthCookie(&strRPCUserColonPass)) {
             throw runtime_error(strprintf(
-                _("You must set rpcpassword=<password> in the configuration file:\n%s\n"
-                  "If the file does not exist, create it with owner-readable-only file permissions."),
+                _("Could not locate RPC credentials. No authentication cookie could be found, and no rpcpassword is set in the configuration file (%s)"),
                     GetConfigFile().string().c_str()));
 
         }
@@ -125,34 +171,41 @@ UniValue CallRPC(const string& strMethod, const UniValue& params)
         strRPCUserColonPass = mapArgs["-rpcuser"] + ":" + mapArgs["-rpcpassword"];
     }
 
-    // HTTP basic authentication
-    map<string, string> mapRequestHeaders;
-    mapRequestHeaders["Authorization"] = string("Basic ") + EncodeBase64(strRPCUserColonPass);
-
-    // Send request
-    string strRequest = JSONRPCRequest(strMethod, params, 1);
-    string strPost = HTTPPost(strRequest, mapRequestHeaders);
-    stream << strPost << std::flush;
-
-    // Receive HTTP reply status
-    int nProto = 0;
-    int nStatus = ReadHTTPStatus(stream, nProto);
+    struct evkeyvalq *output_headers = evhttp_request_get_output_headers(req);
+    assert(output_headers);
+    evhttp_add_header(output_headers, "Host", host.c_str());
+    evhttp_add_header(output_headers, "Connection", "close");
+    evhttp_add_header(output_headers, "Authorization", (std::string("Basic ") + EncodeBase64(strRPCUserColonPass)).c_str());
+
+    // Attach request data
+    std::string strRequest = JSONRPCRequest(strMethod, params, 1);
+    struct evbuffer * output_buffer = evhttp_request_get_output_buffer(req);
+    assert(output_buffer);
+    evbuffer_add(output_buffer, strRequest.data(), strRequest.size());
+
+    int r = evhttp_make_request(evcon, req, EVHTTP_REQ_POST, "/");
+    if (r != 0) {
+        evhttp_connection_free(evcon);
+        event_base_free(base);
+        throw CConnectionFailed("send http request failed");
+    }
 
-    // Receive HTTP reply message headers and body
-    map<string, string> mapHeaders;
-    string strReply;
-    ReadHTTPMessage(stream, mapHeaders, strReply, nProto, std::numeric_limits<size_t>::max());
+    event_base_dispatch(base);
+    evhttp_connection_free(evcon);
+    event_base_free(base);
 
-    if (nStatus == HTTP_UNAUTHORIZED)
+    if (response.status == 0)
+        throw CConnectionFailed("couldn't connect to server");
+    else if (response.status == HTTP_UNAUTHORIZED)
         throw runtime_error("incorrect rpcuser or rpcpassword (authorization failed)");
-    else if (nStatus >= 400 && nStatus != HTTP_BAD_REQUEST && nStatus != HTTP_NOT_FOUND && nStatus != HTTP_INTERNAL_SERVER_ERROR)
-        throw runtime_error(strprintf("server returned HTTP error %d", nStatus));
-    else if (strReply.empty())
+    else if (response.status >= 400 && response.status != HTTP_BAD_REQUEST && response.status != HTTP_NOT_FOUND && response.status != HTTP_INTERNAL_SERVER_ERROR)
+        throw runtime_error(strprintf("server returned HTTP error %d", response.status));
+    else if (response.body.empty())
         throw runtime_error("no response from server");
 
     // Parse reply
     UniValue valReply(UniValue::VSTR);
-    if (!valReply.read(strReply))
+    if (!valReply.read(response.body))
         throw runtime_error("couldn't parse reply from server");
     const UniValue& reply = valReply.get_obj();
     if (reply.empty())