使用 C 套接字在 HTTP 响应中发送二进制文件 [英] Send binary file in HTTP response using C sockets

问题描述

我正在尝试在 http 响应中发送二进制文件(png 图像).

I`m trying to send a binary file (png image) in http response.

FILE *file;
char *buffer;
int fileLen;

//Open file
file = fopen("1.png", "rb");
if (!file)
{
    return;
}

//Get file length
fseek(file, 0, SEEK_END);
fileLen=ftell(file);
fseek(file, 0, SEEK_SET);

//Allocate memory
buffer=(char *)malloc(fileLen+1);
if (!buffer)
{
    fprintf(stderr, "Memory error!");
    fclose(file);
    return;
}

//Read file contents into buffer
fread(buffer, fileLen, 1, file);
fclose(file);
//free(buffer);




char header[102400];

sprintf(header, 
"HTTP/1.1 200 OK
"
"Date: Thu, 19 Feb 2009 12:27:04 GMT
"
"Server: Apache/2.2.3
"
"Last-Modified: Wed, 18 Jun 2003 16:05:58 GMT
"
"ETag: "56d-9989200-1132c580"
"
"Content-Type: image/png
"
"Content-Length: %i
"
"Accept-Ranges: bytes
"
"Connection: close
"
        "
", fileLen);

char *reply = (char*)malloc(strlen(header)+fileLen);
strcpy(reply, header);
strcat(reply, buffer);

printf("msg %s
", reply);


//return 0;
int sd = socket(PF_INET, SOCK_STREAM, 0);

struct sockaddr_in addr;
bzero(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(8081);
addr.sin_addr.s_addr = INADDR_ANY;

if(bind(sd,&addr,sizeof(addr))!=0)
{
    printf("bind error
");
}

if (listen(sd, 16)!=0)
{
    printf("listen error
");
}

for(;;)
{
    int size = sizeof(addr);
    int client = accept(sd, &addr, &size);

    if (client > 0)
    {
        printf("client connected
");
        send(client, reply, strlen(reply), 0);
    }
}

但是我的浏览器不理解这个=(我到底做错了什么?

but my browser does not understand this =( What am I doing wrong exactly?

UPD:我尝试发送文本数据 - 没问题.但二进制数据失败

UPD: I tried to send text data - its OK. But binary data fails

推荐答案

问题是您的消息正文被视为以空字符结尾的文本字符串(您使用 strcat 和 strlen 上)，当它不是一个时:它是二进制数据(PNG 文件).因此，strcat 和 strlen 都在图像的第一个 0 字节处停止(通常很早).

The problem is that your message body is being treated as a null-terminated text string (you use strcat and strlen on it), when it isn't one: it is binary data (a PNG file). Therefore, strcat and strlen both stop on the first 0 byte in the image (typically quite early).

您的程序甚至打印出响应正文:请注意它给出了正确的标头，但是一旦 PNG 标头(二进制数据)开始，只有几个字节.

Your program is even printing out the response body: notice that it gives the correct header, but that once the PNG header (binary data) starts, there is only a few bytes.

1. strcat(reply, buffer) 行，其中 buffer 可能包含 0 个字节.改成 memcpy(reply+strlen(header), buffer, fileLen).
2. send(client, reply, strlen(reply), 0) 行，其中 reply 可能包含 0 个字节.预先计算回复的长度，或者将strlen替换为strlen(header)+fileLen.

1. The line strcat(reply, buffer), where buffer potentially contains 0 bytes. Change it to memcpy(reply+strlen(header), buffer, fileLen).
2. The line send(client, reply, strlen(reply), 0), where reply potentially contains 0 bytes. Pre-calculate the length of the reply, or replace the strlen with strlen(header)+fileLen.

另一个错误是您在完成后没有关闭连接，因此浏览器将永远等待.你需要这个，在 send 之后:

Another bug is that you aren't closing the connection when you're done, so the browser will just wait forever. You need this, after send:

close(client);

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