Send binary file in HTTP response using C sockets

Question

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

mgiuca · Accepted Answer · 2011-03-31 07:39:53Z

10

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.

The line strcat(reply, buffer), where buffer potentially contains 0 bytes. Change it to memcpy(reply+strlen(header), buffer, fileLen).
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);

answered Mar 31, 2011 at 7:39

mgiuca

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1 Comment

mgiuca Over a year ago

Note that this won't actually fix up the debugging print you put in, since that uses printf and will stop when it hits the null byte. But the socket behaviour will be correct; I tested this in a web browser and it worked.

Morten Kristensen · Accepted Answer · 2011-03-31 06:55:02Z

1

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

answered Mar 31, 2011 at 6:55

Morten Kristensen

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2 Comments

spe Over a year ago

No, that didnt help. I tried to send text data - its OK with "\n". But binary data fails

dns Over a year ago

Windows automatically convert \n to \r\n on output

CyberDem0n · Accepted Answer · 2011-03-31 07:38:23Z

0

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

answered Mar 31, 2011 at 7:38

CyberDem0n

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1 Comment

mgiuca Over a year ago

Not only that; notice that the strcat from buffer to reply also fails when it hits a null byte -- see my answer.

Yuan Fu · Accepted Answer · 2017-12-22 01:22:15Z

0

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);

answered Dec 22, 2017 at 1:22

Yuan Fu

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