Author: dustin

Jenkins: Accessing REST API for a Specific Plugin

Some plugins may extent the Jenkins API with additional functionality. To [blindly] determine if this is the case for a particular plugin of interest, first enumerate the list of installed plugins:

https://<jenkins server>/pluginManager/api/json?depth=2

Then, find the plugin in the list and get the value from its “shortName” field:

Selection_20193009-23:57:31_01.png

That value is the name used in the API URL. In this case, that URL would be https://<jenkins server>/gerrit-trigger​. This might be enough to get you what you need, though, depending on the plugin, you might have to reverse-engineer the plugins’ sourcecode in order to find which further nouns/entity subpaths are available from here. You might do a Google search and then grep for the paths that you find from that in order to discover siblings.

This is not meant to be a complicated post, though the information is made complicated by the effort required to find the information.

go-exfat

I’m a Linux guy, but the lure of a new filesystem spec can not be denied.

This is a read-only exFAT impementation in pure Go. This provides a direct API, but several command-line tools were also made available with which to inspect the filesystem’s structure. There’s 90% test-coverage and an A+ on the score-card.

https://github.com/dsoprea/go-exfat

Go: An In-Memory ReadWriteSeeker

The SeekableBuffer type is similar to a bytes.Buffer in that you can perform both reads and writes against it, but has the following two main differences:

  1. You can seek on it.
  2. After writing to it, the current position will be on the byte following whatever you wrote. This is the typical behavior for a file resource on almost any platform but not for a bytes.Buffer.

Eccentric usage of seek, read, and write behavior, such as the following, will work as expected:

  • seeking but not writing
  • seeking past the end of the file and writing
  • seeking past the end of the file and reading
  • writing N+M bytes when positioned only N bytes from the end of the file

Usage (from the unit-tests):

sb := NewSeekableBuffer()

// Write first string.

data := []byte("word1-word2")

_, err := sb.Write(data)
log.PanicIf(err)

// Seek and replace partway through, and replace more data than we
// currently have.

_, err = sb.Seek(6, os.SEEK_SET)
log.PanicIf(err)

data2 := []byte("word3-word4")

_, err = sb.Write(data2)
log.PanicIf(err)

// Read contents.

_, err = sb.Seek(0, os.SEEK_SET)
log.PanicIf(err)

buffer := make([]byte, 20)

_, err = sb.Read(buffer)
log.PanicIf(err)

// `buffer` currently has "word1-word3-word4".

Image Processing: Identifying Groups of Bracketed Images

A new project to recursively scan through a tree of images and determine which were captured as part of an auto-bracketing image capture operation.

bracketed_image_finder

Example:

$ bif_find tests/assets/images --json
[
    {
        "entries": [
            {
                "exposure_value": 0.0,
                "rel_filepath": "DSC08196.JPG",
                "timestamp": "2019-02-13T00:31:50"
            },
            {
                "exposure_value": -0.7,
                "rel_filepath": "DSC08197.JPG",
                "timestamp": "2019-02-13T00:31:50"
            },
            {
                "exposure_value": 0.7,
                "rel_filepath": "DSC08198.JPG",
                "timestamp": "2019-02-13T00:31:50"
            },
            {
                "exposure_value": -1.3,
                "rel_filepath": "DSC08199.JPG",
                "timestamp": "2019-02-13T00:31:50"
            },
            {
                "exposure_value": 1.3,
                "rel_filepath": "DSC08200.JPG",
                "timestamp": "2019-02-13T00:31:51"
            }
        ],
        "type": "periodic"
    },
    {
        "entries": [
            {
                "exposure_value": 0.0,
                "rel_filepath": "DSC08201.JPG",
                "timestamp": "2019-02-13T00:32:09"
            },
            {
                "exposure_value": -0.7,
                "rel_filepath": "DSC08202.JPG",
                "timestamp": "2019-02-13T00:32:09"
            },
            {
                "exposure_value": 0.7,
                "rel_filepath": "DSC08203.JPG",
                "timestamp": "2019-02-13T00:32:10"
            },
            {
                "exposure_value": -1.3,
                "rel_filepath": "DSC08204.JPG",
                "timestamp": "2019-02-13T00:32:10"
            },
            {
                "exposure_value": 1.3,
                "rel_filepath": "DSC08205.JPG",
                "timestamp": "2019-02-13T00:32:10"
            }
        ],
        "type": "periodic"
    }
]

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.

Receive Daily Digest Emails with Active Github Issues

go-github-reminders is a project that you can schedule in order to receive periodic emails of recently updated Github issues that you are involved in (technically, subscribed to) that you have not recently responded to.

For those of us with a lot to do, this keeps us on top of things.

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]