Download Client Redirect Querry

Question

Hi, 
 
 I am using download_client to get a bigger file (100KB) to my memory via LTE-M. The Files are located in a bucket and I use a shortURL to get the signedDownload URL. If I use this short URL in Download Client I get the Error "http/1.1 301 moved permanently". This seems to be correct, the URL is initialy ofcourse a redirect. But how can I handle this in my code? I couldnt find a way to read the header files with download client nor do I see any option for redirect hops or something like this. Is there even a solution? Or is it the limits of the low level integration? 
 Thanks for helping and best regards

daniel

danielboe · Answer

I solved the Redirect now manually via socket. I read the complete http response and get my URL. If anybody else ever needs this here is my function:

#include <zephyr/net/socket.h>

char *redirectHttp(const char *endpoint, const char *path) {
    int fd = 0;
    int err = 0;
    int bytes;
    char send_packet[200];
    char recv_buf[1024] = {};
    struct addrinfo *res;
    struct addrinfo hints = {
        .ai_family = AF_INET,
        .ai_socktype = SOCK_STREAM,
    };

    err = getaddrinfo(endpoint, "80", &hints, &res);
    if (err) {
        LOG_ERR("[SOCKET] getaddrinfo err %d", errno);
        return 0;
    }
    ((struct sockaddr_in *)res->ai_addr)->sin_port = htons(80);

    fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);  // Set socket to tcp without tls
    if (fd == -1) {
        LOG_ERR("[SOCKET] failed to open");
        return 0;
    }
    char ipv4_addr[NET_IPV4_ADDR_LEN];
    inet_ntop(AF_INET, &((struct sockaddr_in *)res->ai_addr)->sin_port, ipv4_addr, sizeof(ipv4_addr));
    LOG_INF("[SOCKET] Connect to Addr IP: %s", ipv4_addr);
    err = connect(fd, res->ai_addr, sizeof(struct sockaddr_in));
    if (err) {
        LOG_ERR("[SOCKET] connect() err: %d", errno);
        return 0;
    }

    sprintf(send_packet,
            "GET %s HTTP/1.1\r\n"
            "Host: %s\r\n"
            "Accept: txt/plain\r\n\r\n",
            path, endpoint);
    bytes = send(fd, &send_packet, strlen(send_packet), 0);
    LOG_INF("[SOCKET] Sent %d bytes", bytes);
    bytes = blocking_recv(fd, recv_buf, sizeof(recv_buf), 0);
    LOG_INF("[SOCKET] Received %d bytes", bytes);

    const char *location_header = "Location: ";
    const char *start = strstr(recv_buf, location_header);
    if (start) {
        start += strlen(location_header);

        const char *end = strstr(start, "\r\n");
        if (!end) {
            end = start + strlen(start);  // End of string if no CRLF
        }

        size_t length = end - start;

        if (length < 1024) {
            char *url = (char *)malloc(length + 1);  // Allocate memory for the URL
            strncpy(url, start, length);
            url[length] = '\0';  // Null-terminate the string
            return url;
        } else {
            LOG_ERR("[SOCKET] URL is too long to fit in the buffer");
            return 0;
        }
    } else {
        LOG_ERR("[SOCKET] Location header not found in the response");
    }

    return 0;
}

Example Usage:

const char *endpoint = "ul1.epaperframe.de";
const char *path = "/tjoLta9.dl";
char *url = redirectHttp(endpoint, path);
printf("Redirected URL: %s\n", url);
free(url);  // Free the allocated memory

This ticket is solved for me now.