http 协议之 Content-Type

Content-Type 字段是 http 服务端返回给客户端时，head 里面带上的，这个字段表明服务端返回给客户端的 body 是什么类型的，然后客户端就可以根据这个类型进行文件处理。如浏览器客户端，针对 text/html 类型时，是直接显示或解析成网页进行展示，针对 image/jpg 时，浏览器会展示成图片，针对 audio/mpeg 类型时，就当成音频播放，针对 video/mp4 类型时，就当成视频来播放。以下操作都是在 Chrome 浏览里进行。

1，Content-Type: text/html

此类型即为可读类型，text 文本时，直接显示，html 时，网页显示。

当点击 readme.txt 文件时，显示的内容：

但是当 text 不是ASCII 字符码时，需要指定字符集，否则可能会出现乱码，如：

此时需要在 Content-Type: text/plain 后加上对应的字符集，如： Content-Type: text/plain;charset=utf-8

当点击 upload.html 文件时，显示的就是一个网页：

2， Content-Type: image/jpeg

当点击 cpp.jpeg 图片时，浏览器里显示出一张图片：

3，Content-Type: audio/mpeg

当点击 wangjie.mp3 文件时，浏览器变成了一个音频播放器：

4，Content-Type: video/mp4

当点击 WeChat_20211225182819.mp4 文件时，浏览器变成了视频播放器：

5，Content-Type: application/octet-stream

若是不知道具体类型，或是不想判断是具体类型，可以一律按 application/octet-stream 进行处理，这样的话，点击文件就会进行下载操作。

这里只是演示一些最基本的一些类型操作，目前程序还是有问题的，比如目录和大文件，这两个后续研究再更新一下。

附上 main.cpp 源码，全部源码这里可以找到。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string>
#include <map>
#include <mutex>
#include "../webServer/mongoose.h"
#include "json/json.h"
#include "../webServer/webServer.h"
#include "networkAPI.h"
#include "comm/log.h"
#include "Base64.h"void eventHandler(struct mg_connection *nc, int event, void *eventData);
void handleRequest(struct mg_connection *connection, int32_t event, void *data);
void httpResponse(struct mg_connection *connection, Json::Value &body);
void httpFileResponse(struct mg_connection *con, const char *fileName);
bool hasHeader(const char *header);
void setHeader(const char *header, const char *value);
void* addConnection(struct mg_connection *nc);
void delConnection(void *usrData);
void webStart();
void fileUpload(mg_connection* nc, const int ev, void* data);
bool isFile(const char *file);enum FileType
{FILE_TYPE_UNKNOW = 0, //没有后缀按二进制文件对待FILE_TYPE_REGULAR,    //普通文本文件FILE_TYPE_MP3,FILE_TYPE_JPEG,FILE_TYPE_PNG,FILE_TYPE_MP4,FILE_TYPE_MAX
};const char *fileTypeStr[] = {"application/octet-stream","text/html","audio/mpeg","image/jpeg","image/png","video/mp4"
};struct userData
{int index;
};struct FileInfo
{FILE *fp;char fileName[32];char filePath[32];size_t size;
};std::map<std::string, std::string> g_headerMap;
std::map<int, void *> g_connectionMap; //连接映射表，当多线程时，用于找到对应连接进行应答
std::string g_protocol; //协议，如http /1.1
std::string g_stateStr; //状态描述，用于返回应答int g_status = 200;  //应答状态
int g_connectId = 0; //连接id的分配std::mutex g_mutex;//用postman 测试，linux需要关闭防火墙，否则收不到数据
int main(int argc, char *argv[])
{   if(argc < 2){errorf("Usage: %s port\n", argv[0]);return 1;}int port = atoi(argv[1]);// webStart();struct userData uData{100};struct mg_mgr mgr;//mgr里的user_data指针将会指向第二个参数，当有连接过来时//mg_connection中的mgr中的user_data指向的就是第二个参数mg_mgr_init(&mgr, &uData);char buf[32] = {0};snprintf(buf, sizeof(buf), "%d", port);struct mg_connection *con = mg_bind(&mgr, buf, eventHandler);if(con == NULL) {errorf("mg_bind fail\n");return -1;}mg_set_protocol_http_websocket(con);uData.index = 200;infof("listen ip[%s], port[%d]....\n", inet_ntoa(con->sa.sin.sin_addr), port);//uri是/fileUpload 时调用函数fileUpload// mg_register_http_endpoint(con, "/fileUpload", fileUpload);while (1){mg_mgr_poll(&mgr, 100);}mg_mgr_free(&mgr);return 0;
}void fileUpload(mg_connection* nc, const int ev, void* data)
{struct FileInfo *userData = (struct FileInfo*)(nc->user_data);//当事件ev是MG_EV_HTTP_MULTIPART_REQUEST时，data类型是http_messagestruct http_message *hp = (struct http_message*)data;//当事件ev是MG_EV_HTTP_PART_BEGIN/MG_EV_HTTP_PART_DATA/MG_EV_HTTP_PART_END时，data类型是mg_http_multipart_partstruct mg_http_multipart_part *mp = (struct mg_http_multipart_part*)data;std::string value;switch(ev) {case MG_EV_HTTP_MULTIPART_REQUEST:{   ///query_string为请求地址中的变量std::string queryStr(hp->query_string.p, hp->query_string.len);infof("upload file request, queryStr = %s\n", queryStr.c_str());char fileName[32];std::string key("file_name");if(mg_get_http_var(&hp->query_string, key.c_str(), fileName, sizeof(fileName)) > 0) {infof("upload file request, %s = %s\n", key.c_str(), fileName); }mg_str *var;userData = (struct FileInfo *)malloc(sizeof(struct FileInfo));var = mg_get_http_header(hp, "Content-Length");std::string fileLen(var->p, var->len);tracef("userData = %p\n", userData);userData->size = std::atoi(fileLen.c_str());nc->user_data = (void *)userData;}break;case MG_EV_HTTP_PART_BEGIN:  ///这一步获取文件名tracef("upload file begin!\n");if(mp->file_name != NULL && strlen(mp->file_name) > 0) {infof("input fileName = %s, userData->filePath = %s\n", mp->file_name, userData->filePath);snprintf(userData->fileName, sizeof(userData->fileName), "%s", mp->file_name);userData->fp = fopen(userData->fileName, "wb+");if(userData->fp == NULL) {mg_printf(nc, "%s", "HTTP/1.1 500 file fail\r\n""Content-Length: 25\r\n""Connection: close\r\n\r\n""Failed to open a file\r\n");nc->flags |= MG_F_SEND_AND_CLOSE;free(userData);       return;}}break;case MG_EV_HTTP_PART_DATA:tracef("upload file push data!\n");if(mp->file_name != NULL && strlen(mp->file_name) > 0) {if(userData != NULL && userData->fp != NULL) {if(fwrite(mp->data.p, 1, mp->data.len, userData->fp) != mp->data.len) {mg_printf(nc, "%s","HTTP/1.1 500 write fail\r\n""Content-Length: 29\r\n\r\n""Failed to write to a file\r\n");nc->flags |= MG_F_SEND_AND_CLOSE;return;}                } else {mg_printf(nc, "%s","HTTP/1.1 500 write fail\r\n""Content-Length: 29\r\n\r\n""Failed to write to a file\r\n");errorf("send response to client in push data\n");          }///var_name 为form-data类型时的key, data里就为key对应的value} else if(mp->var_name != NULL && strlen(mp->var_name) > 0 && strcmp(mp->var_name, "path") == 0) {std::string filePath(mp->data.p, mp->data.len);infof("var_name = %s, value = %s\n", mp->var_name, filePath.c_str());snprintf(userData->filePath, sizeof(userData->filePath), "%s", filePath.c_str());}nc->flags |= MG_F_SEND_AND_CLOSE;break;case MG_EV_HTTP_PART_END:infof("file transfer end!\n");break;case MG_EV_HTTP_MULTIPART_REQUEST_END:if(userData != NULL && userData->fp != NULL) {mg_printf(nc,"HTTP/1.1 200 OK\r\n""Content-Type: text/plain\r\n""Connection: close\r\n\r\n""Written %ld of POST data to a file\n\n",(long)ftell(userData->fp));nc->flags |= MG_F_SEND_AND_CLOSE;fclose(userData->fp);tracef("upload file end, free userData(%p)\n", userData);free(userData);nc->user_data = NULL;           }        default:break;}
}bool isFile(const char *file) 
{if(file == nullptr) {errorf("file is null\n");return false;}const char *pFile = file + 1;FILE *fp = nullptr;fp = fopen(pFile, "rb");if(fp == nullptr) {errorf("no such file of %s\n", pFile);return false;}fclose(fp);return true;
}//把处理类加到webServer里
void webStart()
{std::shared_ptr<CNetworkAPI> network(new CNetworkAPI);CWebServer::instance()->addController(network);
}void eventHandler(struct mg_connection *nc, int event, void *eventData)
{switch (event){case MG_EV_ACCEPT:// tracef("a new accept!!\n");// nc->user_data = addConnection(nc); //delConnection时用uc进行connctionID的传递break;case MG_EV_HTTP_REQUEST:// tracef("a new http request!!\n");      handleRequest(nc, event, eventData);break;case MG_EV_CLOSE:// tracef("request close!!\n");delConnection(nc->user_data);nc->user_data = nullptr;break;default:break;}
}// 添加一个连接
void* addConnection(struct mg_connection *nc)
{userData *data = new userData; //此内存在delConnection时进行释放std::lock_guard<std::mutex> lockGuard(g_mutex);g_connectId += 1;data->index = g_connectId;g_connectionMap.insert(std::pair<int, void*>(g_connectId, nc));return data;
}// 删除一个连接
void delConnection(void *usrData)
{userData *data = (userData*)usrData;if(data == NULL){return;}if(g_connectionMap.find(data->index) != g_connectionMap.end()){tracef("delete connection id: %d\n", data->index);g_connectionMap.erase(data->index);}delete data; //释放addConnection时申请的内存
}void handleRequest(struct mg_connection *connection, int32_t event, void *data)
{struct http_message* msg = (struct http_message*)data;//请求正文std::string body(msg->body.p, msg->body.len);if(body.length() > 0){tracef("body size: %u, %s\n", body.length(), body.c_str());}//请求的地址，不包括ip地址和端口号std::string uri(msg->uri.p, msg->uri.len);// tracef("connect from ip: %s, uri = %s\n", inet_ntoa(connection->sa.sin.sin_addr), uri.c_str());//设置资源根目录if(uri == "/"){// tracef("url size: %lu, %s\n", uri.length(), url.c_str());struct mg_serve_http_opts opts;memset(&opts, 0, sizeof(opts));opts.enable_directory_listing = "yes";opts.document_root = "./";mg_serve_http(connection, msg, opts);}//请求的方法，GET、POST、PUT等std::string method(msg->method.p, msg->method.len);tracef("request method: %s\n", method.c_str());if(connection->mgr->user_data != NULL){struct userData *data = (userData*)connection->mgr->user_data;// tracef("mgr->user_data is not null, content = %d\n", data->index);}//保存头部信息，用于应答for (int32_t index = 0; index < MG_MAX_HTTP_HEADERS; ++index) {if (msg->header_names[index].p == nullptr || msg->header_names[index].len == 0) {continue;}std::string header(msg->header_names[index].p, msg->header_names[index].len);std::string value(msg->header_values[index].p, msg->header_values[index].len);// infof("head[%s] - value[%s]\n", header.c_str(), value.c_str());g_headerMap.insert(std::pair<std::string, std::string>(header, value));}//添加版本信息，应答使用g_headerMap.insert(std::pair<std::string, std::string>("web", "1.0"));//保存协议信息g_protocol = std::string(msg->proto.p, msg->proto.len);if(uri.length() > 1 && method == "GET" && isFile(uri.c_str())) {std::string file;// file.assign(uri, );httpFileResponse(connection, uri.c_str());} else {//尝试用webServer处理，获取处理结果进行返回Json::Value bodyData;controllerPtr handler = CWebServer::instance()->getController(uri);if(handler != nullptr){handler->process(method.c_str(), uri.c_str(), bodyData);}else{tracef("no find route[%s]\n", uri.c_str());bodyData["data"] = "404";}//应答httpResponse(connection, bodyData);        }}void setContent(Json::Value &content)
{Json::Value msg;msg["code"] = "0000111";msg["message"] = "success";msg["data"]["httpPort"] = 8080;msg["data"]["httpsPort"] = 8090;msg["data"]["rtspPort"] = 554;content = msg;
}/*严格按照http应答头格式进行填写：如果有正文，需要在头部字段里写明** 协议版本|空格|状态码|空格|状态码描述|回车|换行
** 头部字段名|冒号|字段值|回车|换行
** 头部字段名|冒号|字段值|回车|换行
** 头部字段名|冒号|字段值|回车|换行
** .....
** 回车|换行
** 响应正文*/
void httpResponse(struct mg_connection *connection, Json::Value &body) 
{std::string head(g_protocol);head.append(" ").append(std::to_string(g_status)).append(" ");if(g_stateStr.empty()){g_stateStr = mg_status_message(g_status); //获取对应的状态描述符}head.append(g_stateStr).append("\r\n");// Json::Value data;// setContent(data); std::string content = body.toStyledString();//添加响应报文长度，以让客户端快速读取消息setHeader("Content-Length", std::to_string(content.length()).c_str());//添加头部for(auto ite = g_headerMap.begin(); ite != g_headerMap.end(); ite++){head.append(ite->first).append(":").append(ite->second).append("\r\n");}//添加正文head.append("\r\n").append(content).append("\r\n");// tracef("send response: \n%s\n", head.c_str());mg_send(connection, head.c_str(), head.length());
}bool parseFileType(const char *fileName, std::string &fileType)
{char command[32] = {0};snprintf(command, sizeof(command), "%s %s", "file", fileName);FILE *fp = popen(command, "r");if(fp != NULL){char buf[1024] = {0};fread(buf, sizeof(buf) - 1 , 1, fp);// infof("buf string: %s\n", buf);int len = strlen(buf);if(len == 0){return false;}std::string parseStr(buf, len);if(parseStr.find("text") != std::string::npos){fileType = "text/html";}else if(parseStr.find("ELF") != std::string::npos ||parseStr.find("PE32") != std::string::npos){fileType = "application/octet-stream";}else if(parseStr.find("image") != std::string::npos){fileType = "image";if(parseStr.find("PNG") != std::string::npos){fileType.append("/png");}else if(parseStr.find("JPEG") != std::string::npos){fileType.append("/jpeg");}}else if(parseStr.find("bitmap") != std::string::npos){fileType = "image/bmp";}else if(parseStr.find("MPEG") != std::string::npos){fileType = "audio/mpeg";}else if(parseStr.find("MPEG v4") != std::string::npos){fileType = "video/mp4";}else  //默认为不确定的格式进行处理{fileType = "application/octet-stream";}pclose(fp);return true;}return false;
}int getFileType(const char *fileName)
{if(fileName == nullptr){return -1;}std::string parseStr(fileName);if(parseStr.find(".") == std::string::npos){return FILE_TYPE_UNKNOW;}else if(parseStr.find(".mp3") != std::string::npos){return FILE_TYPE_MP3;}else if(parseStr.find(".mp4") != std::string::npos){return FILE_TYPE_MP4;}else if(parseStr.find(".jpg") != std::string::npos || parseStr.find(".jpeg") != std::string::npos){return FILE_TYPE_JPEG;}else if(parseStr.find(".png") != std::string::npos){return FILE_TYPE_PNG;}else if(parseStr.find(".txt") != std::string::npos || parseStr.find(".html") != std::string::npos){return FILE_TYPE_REGULAR;}return FILE_TYPE_UNKNOW;
}void httpFileResponse(struct mg_connection *con, const char *fileName) {std::string head(g_protocol);head.append(" ").append(std::to_string(g_status)).append(" ");if(g_stateStr.empty()){g_stateStr = mg_status_message(g_status); //获取对应的状态描述符}head.append(g_stateStr).append("\r\n");//正文std::string content;const char *pFile = fileName + 1;FILE *fp = nullptr;fp = fopen(pFile, "r");if(fp == nullptr) {errorf("no such file of %s\n", pFile);setHeader("Content-Length", std::to_string(0).c_str());} else {fseek(fp, 0, SEEK_END);size_t len = ftell(fp);fseek(fp, 0, SEEK_SET);char *buffer = new char[len];fread(buffer, len, 1, fp);content.assign(buffer, len);//添加响应报文长度，以让客户端快速读取消息setHeader("Content-Length", std::to_string(len).c_str());delete []buffer;}//添加头部for(auto ite = g_headerMap.begin(); ite != g_headerMap.end(); ite++){head.append(ite->first).append(":").append(ite->second).append("\r\n");}int type = 0;std::string contentType;//可能没有 file 命令if(parseFileType(pFile, contentType)){head.append("Content-Type: ").append(contentType).append("\r\n");}else if((type = getFileType(pFile)) != -1){head.append("Content-Type: ").append(fileTypeStr[type]).append("\r\n");}else{errorf("no such file or directory!\n");return; }//添加正文head.append("\r\n").append(content).append("\r\n");mg_send(con, head.c_str(), head.length());
}bool hasHeader(const char *header)
{return g_headerMap.find(header) != g_headerMap.end();
}void setHeader(const char *header, const char *value)
{g_headerMap[header] = value;
}