通过TLS将HTTP2帧发送到服务器

Question

I am trying to learn how the HTTP2 protocol works. I see that Apple uses it for their push notification server. I am using the specification for the frame from Discover HTTP .

As a test, I wrote code that is supposed to communicate with that server. However, I keep getting the error that I'm missing the "Settings" frame.

My code is as follows:

#include <iostream>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <dlfcn.h>
#include <unistd.h>
#include <openssl/ssl.h>

#define SOCKET_ERROR -1

struct Frame  //Represents and HTTP2 Frame.
{
    char len[24];
    char type[8];
    char flags[8];
    char identifier[31];
    char payload[];
} __attribute__((packed));

void writeFrame(SSL* ssl)
{
    //First thing after connecting is to send the PREFACE.
    std::string preface = "PRI * HTTP/2.0\r\n\r\n";
    preface += "SM\r\n\r\n";

    SSL_write(ssl, preface.c_str(), preface.length());

    //Now to send the first frame. Aka the SETTINGS frame.
    Frame* frame = (Frame *)malloc(sizeof(Frame));
    memset(frame, 0, sizeof(Frame));

    int frameSize = 100;
    memcpy(frame->len, &frameSize, sizeof(frameSize));
    memcpy(frame->type, "SETTINGS", strlen("SETTINGS"));
    memcpy(frame->identifier, "SETTINGS", strlen("SETTINGS"));

    SSL_write(ssl, frame, sizeof(Frame));

    //Read server response.
    char buffer[10000];
    memset(buffer, 0, sizeof(buffer));
    int dataLen;
    while ((dataLen = SSL_read(ssl, buffer, sizeof(buffer)) > 0))
    {
        int i = 0;
        while (buffer[i] >= 32 || buffer[i] == '\n' || buffer[i] == '\r') {
            std::cout << buffer[i];
            i += 1;
        }
    }

    //The above gives me the error: 
    //First received frame was not SETTINGS. 
    //Hex dump for first 5 bytes: 6400000000

    //Try to POST to the server now.
    std::string payload = "POST /3/device HTTP/2.0\r\n";
    payload += ":method:POST\r\n";
    payload += ":scheme: https\r\n";
    payload += "cache-control: no-cache\r\n";
    payload += "user-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.95 Safari/537.36\r\n";
    payload += "content-type: text/plain;charset=UTF-8\r\n\r\n";

    int sentBytes = SSL_write(ssl, payload.c_str(), payload.length());

    if (sentBytes < payload.length() || sentBytes == SOCKET_ERROR)
    {
        return;
    }        

    memset(buffer, 0, sizeof(buffer));
    while ((dataLen = SSL_read(ssl, buffer, sizeof(buffer)) > 0))
    {
        int i = 0;
        while (buffer[i] >= 32 || buffer[i] == '\n' || buffer[i] == '\r') {
            std::cout << buffer[i];
            i += 1;
        }
    }
}

int main(int argc, const char * argv[]) {

    SSL_library_init();
    SSL_load_error_strings();
    OpenSSL_add_all_algorithms();

    std::string address = "api.development.push.apple.com";
    struct addrinfo hints = {0};
    struct addrinfo* result = nullptr;

    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    hints.ai_flags = AI_PASSIVE;

    getaddrinfo(address.c_str(), nullptr, &hints, &result);

    int sock = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
    if (sock == -1)
    {
        return -1;
    }

    struct sockaddr_in sockAddr;
    sockAddr.sin_addr = reinterpret_cast<struct sockaddr_in*>(result->ai_addr)->sin_addr;
    sockAddr.sin_family = result->ai_family;
    sockAddr.sin_port = htons(443);
    freeaddrinfo(result);

    if (connect(sock, reinterpret_cast<sockaddr *>(&sockAddr), sizeof(sockAddr)) == SOCKET_ERROR)
    {
        close(sock);
        return -1;
    }

    SSL_CTX* ctx = SSL_CTX_new(TLSv1_2_method());
    SSL* ssl = SSL_new(ctx);
    SSL_set_fd(ssl, sock);
    SSL_connect(ssl);

    writeFrame(ssl);

    SSL_CTX_free(ctx);
    SSL_shutdown(ssl);
    SSL_free(ssl);
    close(sock);
    return 0;
}

How can I send the SETTINGS frame and other frames to the server? What have I missed?

Answer 1

You have several errors.

First of all, the Frame data structure, where the lengths of the array fields are wrong. You seem to have copied their length in bits, but reported them in the Frame data structure in bytes. You want this instead:

struct Frame {
    char len[3];
    char type;
    char flags;
    char identifier[4];
    char payload[];
}

Furthermore, the type of the frame is not a string, nor is the identifier.

Finally, the format of the request is completely wrong, resembling HTTP/1.1, while the HTTP/2 format is completely different and based on HPACK.

I suggest you have a careful read of the HTTP/2 specification before writing further code.