Send binary file in HTTP response using C sockets

问题:

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

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

printf("msg %s\n", 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\n");
}

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

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

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

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

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

回答1:

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).

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. 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.

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);

回答2:

The HTTP protocol specifies that it expects "\r\n" instead of "\n". Try that. :)

回答3:

strcat(reply, buffer); // this is incorrect, because png(buffer) may contain zero byte
send(client, reply, strlen(reply), 0);
strlen(reply) // this is incorrect, because png may contain zero byte

回答4:

I tried to follow what you did but could not get it to work. Instead, I found it easier to just send header and file separately.

e.g.

send(client, header, strlen(header), 0);
send(client, buffer, fileLen + 1, 0);