我将发布我自己的部分解决方案。它可以在 14.2kb png 上正常工作。高于此值可能会导致段错误，除非调整了如下所示的“幻数”。
我正在使用 Boost Asio HTTP Server 示例 C++11。
在 connection.hpp 中，更改...
//boost::array<char, 8192> buffer_;
boost::array<char, 512> buffer_;
另外，加...
boost::asio::streambuf strmbuffer_;
在connection.cpp中，这里是connection::handle_read()...
void connection::handle_read(const boost::system::error_code& e, std::size_t bytes_transferred)
{
if (!e)
{
//*** buffer_.data() for this file ***
//
//POST /post HTTP/1.1
//Host: localhost:3003
//User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:62.0) Gecko/20100101 Firefox/62.0
//Accept: */*
//Accept-Language: en-US,en;q=0.5
//Accept-Encoding: gzip, deflate
//Referer: http://localhost:3003/profile
//Content-type: multipart/form-data
//Content-Length: 14710
//Cookie: knowstoryadmin=7bdbed41954cd4133a172acb92988e58
//Connection: keep-alive
//
//-----------------------------14071968205478138611648202646
//Content-Disposition: form-data; name="admin_profile_image_load"; filename="tlc-logo.png"
//Content-Type: image/png
//
//�PNG
//▒
std::stringstream strm1;
std::string buffer_data = buffer_.data();
strm1 << buffer_data;
std::string method;
std::smatch match_method;
std::regex regex_method ("\\b([^ ]*)( )([^ ]*)( HTTP/1.1)([^ ]*)");
std::string content_type;
std::smatch match_content_type;
std::regex regex_content_type ("\\b(Content-type: )([^ ]*)");
std::string line;
while (std::getline(strm1, line)) {
if (std::regex_search(line, match_method, regex_method)) {
method = match_method[0];
method = method.substr(0, method.find(' '));
boost::trim(method);
//std::cout << method << std::endl;
}
if (std::regex_search(line, match_content_type, regex_content_type)) {
content_type = match_content_type[0];
boost::erase_all(content_type, "Content-type:");
boost::trim(content_type);
//std::cout << content_type << std::endl;
}
}
if (method == "POST") {
if (content_type == "multipart/form-data") {
std::string content_length;
std::smatch match_content_length;
std::regex regex_content_length ("\\b(Content-Length: )([^ ]*)");
std::string filename;
std::smatch match_filename;
std::regex regex_filename ("\\b(filename)([^ ]*)");
std::string action;
std::smatch match_action;
std::regex regex_action ("\\b(name)([^ ]*)");
std::string boundary;
std::smatch match_boundary;
std::regex regex_boundary ("([-]{10,}[0-9]{10,})");
std::string line;
strm1.clear();
strm1 << buffer_data;
while (std::getline(strm1, line)) {
if (std::regex_search(line, match_content_length, regex_content_length)) {
//Content-Length: 14710
content_length = match_content_length[0];
boost::erase_all(content_length, "Content-Length:");
boost::trim(content_length);
//std::cout << content_length << std::endl;
}
if (std::regex_search(line, match_filename, regex_filename)) {
filename = match_filename[0];
boost::erase_all(filename, "\"");
boost::erase_all(action, ";");
boost::erase_all(filename, "filename=");
std::size_t found = filename.find_last_of(".");
std::size_t len = filename.length();
std::string mime = filename.substr(found, len);
boost::trim(filename);
//std::cout << filename << std::endl;
//std::cout << mime << std::endl;
}
if (std::regex_search(line, match_action, regex_action)) {
action = match_action[0];
boost::erase_all(action, "\"");
boost::erase_all(action, ";");
boost::erase_all(action, "name=");
boost::trim(action);
//std::cout << action << std::endl;
}
if (std::regex_search(line, match_boundary, regex_boundary)) {
boundary = match_boundary[0];
boost::trim(boundary);
//std::cout << boundary << std::endl;
}
}
//pubseekpos works as expected, but useless here
//strmbuffer_.pubseekpos(bytes_transferred);
//content length minus bytes_transfered does NOT yield
//the right result. The number, 392, is the 'magic' number
//adjustment for this file size, approx 14.2kb, that i found
//by trial and error.
//Adjusting the magic number is necessary for every image size
//in order to avoid a segfault.
//bytes_transferred, for each read(), is the only 'reliable'
//number with which to work, as far as i know.
//If there is a brainier way of calculating this,
//i don't care, anymore.
int n_content_length = std::stoi(content_length);
int transfer = n_content_length - bytes_transferred + 392;
auto self(shared_from_this());
boost::asio::async_read(
socket_,
strmbuffer_,
boost::asio::transfer_exactly(transfer),
strand_.wrap(
[this, self, boundary](boost::system::error_code ec, std::size_t bytes_transferred)
{
std::stringstream strm2;
strm2 << &strmbuffer_;
std::string line;
unsigned bufsize = 512;
while (std::getline(strm2, line))
{
if(line.length() == 1){
std::string output_file = "../../upload/test.png";
std::ofstream outfile(output_file);
char c;
unsigned bl = boundary.length();
bool endfile = false;
if(outfile){
char buffer[bufsize];
while(!endfile){
unsigned j = 0;
unsigned k;
while(j < bufsize && strm2.get(c) && !endfile){
buffer[j] = c;
k = 0;
while(boundary[bl - 1 - k] == buffer[j - k]){
if(k >= bl - 1){
endfile = true;
break;
}
k++;
}
j++;
}
outfile.write(buffer, j);
j = 0;
};
outfile.close();
std::cout << "outfile close" << std::endl;
break;
}
}
}
}
)
);
}
else {
// POST AJAX
std::cout << "connection " << method << std::endl;
}
}
else {
boost::tribool result;
boost::tie(result, boost::tuples::ignore) = request_parser_.parse(
request_, buffer_.data(), buffer_.data() + bytes_transferred);
if (result)
{
request_handler_.handle_request(
request_,
reply_);
boost::asio::async_write(
socket_,
reply_.to_buffers(),
strand_.wrap(
boost::bind(
&connection::handle_write,
shared_from_this(),
boost::asio::placeholders::error)
));
}
else if (!result)
{
reply_ = reply::stock_reply(reply::bad_request);
boost::asio::async_write(
socket_,
reply_.to_buffers(),
strand_.wrap(
boost::bind(&connection::handle_write, shared_from_this(),
boost::asio::placeholders::error)));
}
else
{
socket_.async_read_some(
boost::asio::buffer(buffer_),
strand_.wrap(
boost::bind(
&connection::handle_read,
shared_from_this(),
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred)));
}
}
}
}
对于这个 Asio 示例，这种部分解决方案相当“不显眼”。request_handler 类没有改变并服务于 GET。
在连接::start() 中，我尝试了 async_read。但结果更难以预测。这意味着我必须附加两个字符串，一个来自 strmbuffer1_，另一个来自 strmbuffer2_，以便在文件输出循环中一起构造（破解）流。无论我的准备工作在 cout<< 中出现的多么精确，都缺少大约 500 或更多字节，写入了一个不完整的图像文件。
在内存中的某处存在并且必须存在我上传二进制文件所需的完整信息及其句柄。但是从 Asio 类中提取它似乎是不必要的棘手。
这就是我对 Boost Asio 的了解。这就是我所去的。对于我想要的，我的答案不在这里。