HTTP 的 multipart 类型-编程知识

上一篇文章讲到 http 的 MIME 类型 http MIME 类型里有一个 multipart 多部分对象集合类型，这个类型 http 指南里有讲到：MIME 中的 multipart（多部分）电子邮件报文中包含多个报文，它们合在一起作为单一的复杂报文发送。每一部分都是独立的，有各自的描述及内容的集；不同的部分之间用分界字符串连接在一起。HTTP 也支持多部分主体，不过，通常只用在下列两种情形之一：提交填写好的表格，或是作为承载若干文档片段的范围响应。

前端技术不懂，这里只用 postman 用为客户端来做示例。表格和文档形式，是不是像这样的呢？

当你选中其中一种情形时，http 的 Headers 里就会多出一个 Content-Type 表明这是一个多部分集合的类型报文：

表格情形还没试验过，这里主要讲文档情形的。所以呢，用客户端 postman 可以向服务端发送大的或是小的文档。下面给出服务端的例子：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <string>
#include <map>
#include <mutex>
#include <sstream>
#include <iostream>
#include "mongoose.h"
#include "../logFormatPrt/log.h"#define FILE_NAME_LEN 128
#define FILE_PATH_LEN 32void eventHandler(struct mg_connection *nc, int event, void *eventData);
void fileUpload(mg_connection* nc, const int ev, void* data);
bool validPath(const char *path);struct userData
{int index;
};struct FileInfo
{FILE *fp; //打开新文件的指针char fileName[FILE_NAME_LEN]; //文件名，包含路径char filePath[FILE_PATH_LEN]; //文件路径size_t size; //文件大小，暂时没有用到size_t byteWrite;//已经写的字节数
};//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[])
{   struct mg_mgr mgr;mg_mgr_init(&mgr, nullptr);int port = 8190;char buf[5] = {0};snprintf(buf, sizeof(buf), "%d", port);struct mg_connection *con = mg_bind(&mgr, buf, nullptr);if(con == NULL) {errorf("mg_bind fail\n");return -1;}mg_set_protocol_http_websocket(con);infof("listen ip[%s], port[%d]....\n", inet_ntoa(con->sa.sin.sin_addr), port); //uri是/fileUpload 时调用函数fileUploadmg_register_http_endpoint(con, "/fileUpload", fileUpload);while (1){mg_mgr_poll(&mgr, 100);}mg_mgr_free(&mgr);return 0;
}//触发的事件依次为：
//#define MG_EV_HTTP_MULTIPART_REQUEST 121 /* struct http_message */
//#define MG_EV_HTTP_PART_BEGIN 122        /* struct mg_http_multipart_part */
//#define MG_EV_HTTP_PART_DATA 123         /* struct mg_http_multipart_part */
//#define MG_EV_HTTP_PART_END 124          /* struct mg_http_multipart_part */
/* struct mg_http_multipart_part */
//#define MG_EV_HTTP_MULTIPART_REQUEST_END 125void fileUpload(mg_connection* nc, const int ev, void* data)
{//用户指针，用于保存文件大小，文件名struct FileInfo *userData = nullptr;//当事件ev是 MG_EV_HTTP_MULTIPART_REQUEST 时，data类型是http_messagestruct http_message *httpMsg = nullptr;if(MG_EV_HTTP_MULTIPART_REQUEST == ev){httpMsg = (struct http_message*)data;//初次请求时，申请内存if(userData == nullptr){userData = (struct FileInfo *)malloc(sizeof(struct FileInfo));memset(userData, 0, sizeof(struct FileInfo));}}else // 已经不是第一次请求了，nc->user_data 先前已经指向 userData，所以可以用了{userData = (struct FileInfo *)nc->user_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 *httpMulMsg = nullptr;if(ev >= MG_EV_HTTP_PART_BEGIN && ev <= MG_EV_HTTP_PART_END){httpMulMsg = (struct mg_http_multipart_part*)data;}switch(ev) {case MG_EV_HTTP_MULTIPART_REQUEST:{   ///query_string 为请求地址中的变量, key 名称约定好char filePath[32] = {0};std::string key("filePath");//从请求地址里获取 key 对应的值，所以这个需要和请求地址里的 key 一样//这里从地址中获取文件要上传到哪个路径if(mg_get_http_var(&httpMsg->query_string, key.c_str(), filePath, sizeof(filePath)) > 0) {tracef("upload file request, locate: %s = %s\n", key.c_str(), filePath); }if(!validPath(filePath)){tracef("no such directory of %s\n", filePath);std::string header;std::string body("no suce directory");header.append("HTTP/1.1 500 file fail").append("\r\n");header.append("Connection: close").append("\r\n");header.append("Content-Length: ").append(std::to_string(body.length())).append("\r\n").append("\r\n");header.append(body).append("\r\n");mg_send(nc, header.c_str(), header.length());nc->flags |= MG_F_SEND_AND_CLOSE;             }//保存路径，且 nc->user_data 指向该内存，下次请求就可以直接用了if(userData != nullptr){snprintf(userData->filePath, sizeof(userData->filePath), "%s", filePath);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(httpMulMsg->file_name != NULL && strlen(httpMulMsg->file_name) > 0){tracef("input fileName = %s\n", httpMulMsg->file_name);//保存文件名，且新建一个文件，支持目录带 "/" 及不带 "/"if(userData != nullptr){if(userData->filePath[strlen(userData->filePath)] == '/'){snprintf(userData->fileName, sizeof(userData->fileName), "%s%s", userData->filePath, httpMulMsg->file_name);}else{snprintf(userData->fileName, sizeof(userData->fileName), "%s/%s", userData->filePath, httpMulMsg->file_name);}userData->fp = fopen(userData->fileName, "wb+");//创建文件失败，回复，释放内存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);nc->user_data = nullptr;     return;}                    }}break;case MG_EV_HTTP_PART_DATA: //这一步写文件//tracef("upload file chunk size = %lu\n", httpMulMsg->data.len);if(userData != nullptr && userData->fp != NULL) {size_t ret = fwrite(httpMulMsg->data.p, 1, httpMulMsg->data.len, userData->fp);if(ret != httpMulMsg->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;}userData->byteWrite += ret;  }break;case MG_EV_HTTP_PART_END:tracef("file transfer end!\n");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 %lu bytes of POST data to a file\n\n",userData->byteWrite);//设置标志，发送完成数据（如果有）并且关闭连接nc->flags |= MG_F_SEND_AND_CLOSE;//关闭文件，释放内存fclose(userData->fp);tracef("upload file end, free userData(%p)\n", userData);free(userData);nc->user_data = NULL;       } else{mg_printf(nc,"HTTP/1.1 200 OK\r\n""Content-Type: text/plain\r\n""Connection: close\r\n\r\n""Written 0 of POST data to a file\n\n");                }       break;case MG_EV_HTTP_MULTIPART_REQUEST_END:tracef("http multipart request end!\n");break;default:break;}
}bool validPath(const char *path)
{struct stat st;if(lstat(path, &st) == 0){return true;}return false;
}

如果想要直接编译则需要把头文件 #include "../logFormatPrt/log.h" 去掉，编译选项还得加上 -lssl -lcrypto，Makefile 如下：

#中间文件存放目录，如.o 和 .d 文件
COMPILE_DIR = compile
BIN_DIR = bin# 可编译arm版本
#CROSS = arm-himix200-linux-
CC = gcc -m32
CPP = $(CROSS)g++ -std=c++11 -m32
CFLAGS = -Werror -gLIB = -lpthread -lssl -lcrypto
#CPP_SRCS = $(wildcard *.cpp)
CPP_SRCS = $(shell ls -t | grep "\.cpp$$" | head -1)
CPP_OBJS = $(patsubst %.cpp, $(COMPILE_DIR)/%.o, $(CPP_SRCS))
CPP_DEP = $(patsubst %.cpp, $(COMPILE_DIR)/%.cpp.d, $(CPP_SRCS))C_SRCS = mongoose.c
C_OBJS = $(patsubst %.c, $(COMPILE_DIR)/%.o, $(C_SRCS))
C_DEP = $(patsubst %.c, $(COMPILE_DIR)/%.c.d, $(C_SRCS))OBJS = $(CPP_OBJS) $(C_OBJS)
DEP_ALL = $(CPP_DEP) $(C_DEP)$(shell if [ ! -d $(COMPILE_DIR) ]; then mkdir $(COMPILE_DIR); fi)
$(shell if [ ! -d $(BIN_DIR) ]; then mkdir $(BIN_DIR); fi)BIN =
ifeq ($(target), ) #如果是空的
BIN = a.out
else
BIN := $(target)
endifTARGET=$(BIN_DIR)/$(BIN)all: $(TARGET)-include $(DEP_ALL)$(TARGET): $(OBJS)$(CPP) $(CFLAGS) $^ -o $@ $(LIB)$(COMPILE_DIR)/%.o: %.cpp $(COMPILE_DIR)/%.cpp.d$(CPP) $(CFLAGS) -c $< -o $@$(COMPILE_DIR)/%.cpp.d: %.cpp$(CPP) $(CFLAGS) -MM -E -c $< -o $@@sed 's/.*\.o/$(subst /,\/,$(dir $@))&/g' $@ > $@.tmp@mv $@.tmp $@$(COMPILE_DIR)/%.o: %.c $(COMPILE_DIR)/%.c.d$(CC) $(CFLAGS) -c $< -o $@$(COMPILE_DIR)/%.c.d: %.c$(CC) $(CFLAGS) -MM -E -c $< -o $@@sed 's/.*\.o/$(subst /,\/,$(dir $@))&/g' $@ > $@.tmp@mv $@.tmp $@.PHONY: clean
clean:rm -rf $(COMPILE_DIR) $(BIN_DIR)