Author Archives: bullgare

Maps internals in Go

Idea Map is passed as a value, but it consists of a pointer to hmap which has all the details on map implementation. So, if you change/add to map, it will be reflected everywhere. And that’s why you cannot assign to an uninitialized map (no memory allocated, no hash seed generated yet). runtime/map.go

type hmap struct {
	count     int // # live cells == size of map.  Must be first (used by len() builtin)
	B         uint8  // log_2 of # of buckets (can hold up to loadFactor * 2^B items)
	hash0     uint32 // hash seed

	buckets    unsafe.Pointer // array of 2^B Buckets. may be nil if count==0.
	oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing
	nevacuate  uintptr        // progress counter for evacuation (buckets less than this have been evacuated)
}

type hmap struct {

count int // # live cells == size of map. Must be first (used by len() builtin)

B uint8 // log_2 of # of buckets (can hold up to loadFactor * 2^B items)

hash0 uint32 // hash seed

buckets unsafe.Pointer // array of 2^B Buckets. may be nil if count==0.

oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing

nevacuate uintptr // progress counter for evacuation (buckets less than this have been evacuated)

}

Buckets …

mountebank for mocking and stubbing http services (rest+graphql+grpc)

http://www.mbtest.org/docs/api/stubs can be used to stub http(s)/tcp/smtp protocols. And has community plugins for grpc, graphql, websockets. You can configure it with imposters.ejs like below:

{
  "port": 80,
  "protocol": "http",
  "defaultResponse": {
    "statusCode": 404,
    "headers": {}
  },
  "stubs": [
    <% include stubs/service1.json %>,
    <% include stubs/service2.json %>,
    <% include stubs/service3.json %>
  ]
}

{

"port": 80,

"protocol": "http",

"defaultResponse": {

"statusCode": 404,

"headers": {}

"stubs": [

<% include stubs/service1.json %>,

<% include stubs/service2.json %>,

<% include stubs/service3.json %>

]

}

docker-compose.yml

version: "3.5"

services:
  mountebank:
    container_name: mountebank
    image: jkris/mountebank:latest
    volumes:
      - ./:/mountebank
    ports:
      - "15050:80"
    command: --configfile /mountebank/imposters.ejs --allowInjection

version: "3.5"

services:

mountebank:

container_name: mountebank

image: jkris/mountebank:latest

volumes:

- ./:/mountebank

ports:

- "15050:80"

command: --configfile /mountebank/imposters.ejs --allowInjection

HTTP Toolkit — another alternative to Charles Proxy for http calls interception

https://httptoolkit.com/ It has a free version which does something similar to Charles Proxy, so you can hack into the middle of any request/response according to the rules specified.

YouType to show flag icon for current locale on MacOS

It has reacher functionality, but I use it only to show a flag for my current locale in a tray. https://github.com/freefelt/YouType

Add new video sticker pack to telegram

If you have an animated gif-file, you can convert it to webm video respecting rules described in the docs (https://core.telegram.org/stickers#video-stickers-and-emoji): For stickers, one side must be exactly 512 pixels in size – the other side can be 512 pixels or less. For emoji, the video must be exactly 100×100 pixels in size Video duration must …

Docker and Kubernetes basics for developers

Docker Docker containers are much more lightweight compared to classic VMs as they leverage host OS instead of starting their own OS. Containers are using 2 features of Linux-based OS: Namespaces and Cgroups (Control Groups). Namespace Lets you allocate resources in an isolated environment (like a sandbox). On a container start, docker daemon generates a …

Go’s Concurrency and Channel Internals

Go is implementing CSP (Communicating Sequential Processing): processes are communicating through channels, they can block each other while waiting for read/writes to channels. Actor model makes inter-process communications more explicit and non-blocking. CSP vs Actor explained — https://dev.to/karanpratapsingh/csp-vs-actor-model-for-concurrency-1cpg. Channels requirements goroutine-safe store and pass data across goroutines FIFO can block/unblock goroutines

Protobuf: add header parameters

They finally added it to the grpc-gateway: https://github.com/grpc-ecosystem/grpc-gateway/pull/3010/files#diff-c255ac405628aada46c25a2c9765605e9f823bc523d3739fd3fa71d4bcbf5c99. So, to use it you can just update to the version 2.14.0 or above — https://github.com/grpc-ecosystem/grpc-gateway/releases/tag/v2.14.0, and add something like this to your protofile:

        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
            summary: "Create a new foo.";
            parameters: {
                headers: {
                    name: "My-Custom-Header";
                    description: "Some custom header description";
                    required: true;
                };
            };
        };

option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {

summary: "Create a new foo.";

parameters: {

headers: {

name: "My-Custom-Header";

description: "Some custom header description";

required: true;

};

Go scheduler details

Scheduler was implemented by Dmitry Vyukov in go 1.1 and lives in runtime/proc.go. Good resources https://www.youtube.com/watch?v=-K11rY57K7k — video by Dmitry Vyukov (slides as pdf) https://www.ardanlabs.com/blog/2018/08/scheduling-in-go-part2.html — nice article by Bill Kennedy in 3 parts. Most of the images below are taken from this article. Main ideas Goroutines are very light weight (~2KB+) and very cheap …

Golang. Adding a json body to POST request in protofile

It could be a bit tricky, and I failed to find a good example for it.