Month: January 2019

Python: Parsing XML and Retaining the Comments

By default, Python’s built-in ElementTree module strips comments as it reads them. The solution is just obscure enough to be hard to find.

import xml.etree.ElementTree as ET

class _CommentedTreeBuilder(ET.TreeBuilder):
    def comment(self, data):
        self.start('!comment', {})
        self.data(data)
        self.end('!comment')

def parse(filepath):
    ctb = _CommentedTreeBuilder()
    xp = ET.XMLParser(target=ctb)
    tree = ET.parse(filepath, parser=xp)

    root = tree.getroot()
    # ...

When enumerating the parsed nodes, the comments will have a tag-name of “!comment”.

ssl: Promoting Existing Client Socket to SSL in C/C++

You may be in a situation where something else produces the sockets for you (such as an event-loop) or you otherwise need to manage the socket rather then allowing something else to.

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <openssl/ssl.h>

int main(int argc, char *argv[])
{
    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (!sockfd) {
        printf("Error creating socket.\n");
        return -1;
    }

    struct sockaddr_in sa;
    memset (&sa, 0, sizeof(sa));

    sa.sin_family = AF_INET;
    sa.sin_addr.s_addr = inet_addr("172.217.2.196");
    sa.sin_port = htons (443); 

    socklen_t socklen = sizeof(sa);
    if (connect(sockfd, (struct sockaddr *)&sa, socklen)) {
        printf("Error connecting to server.\n");
        return -1;
    }

    SSL_library_init();
    SSLeay_add_ssl_algorithms();
    SSL_load_error_strings();

    const SSL_METHOD *meth = TLSv1_2_client_method();
    SSL_CTX *ctx = SSL_CTX_new (meth);

    SSL *ssl = SSL_new (ctx);
    if (ssl == NULL) {
        printf("Could not create SSL context.\n");
        return -1;
    }

    SSL_set_fd(ssl, sockfd);

    int err = SSL_connect(ssl);
    if (err <= 0) {
        printf("Could not connect.\n");
        return -1;
    }

    printf ("SSL connection using %s\n", SSL_get_cipher (ssl));

    // Do send/receive here.

    return 0;
}

Adapted from openssl-in-c-socket-connection-https-client, and works with both OpenSSL and BoringSSL.

Go: Parsing Time Expressions

go-time-parse will parse time expressions into time.Duration quantities. From the example:

actualDuration, phraseType, err := ParseDuration("24 days from now")
log.PanicIf(err)

fmt.Printf("%d [%s]\n", actualDuration/time.Hour/24, phraseType)

actualDuration, phraseType, err = ParseDuration("now")
log.PanicIf(err)

fmt.Printf("%d [%s]\n", actualDuration, phraseType)

actualDuration, phraseType, err = ParseDuration("12m")
log.PanicIf(err)

fmt.Printf("%d [%s]\n", actualDuration/time.Minute, phraseType)

actualDuration, phraseType, err = ParseDuration("every 6 hours")
log.PanicIf(err)

fmt.Printf("%d [%s]\n", actualDuration/time.Hour, phraseType)

Output:

24 [time]
0 [time]
12 [interval]
6 [interval]