I kept hearing about the term wire protocol especially Postgres wire protocol in the recent days (Looking at you cockroachdb, yugabytedb - in a good way) but never really quite understood it. Decided to implement something simple in Go to understand it better. As always, if you find anything wrong or I misunderstood please correct me. In simple terms, “wire” - something over network generally (but PG also supports over domain sockets)

I saw this pattern of a function taking optional parameters (variadic arguments) and I never understood why they do that until today. There is a bit of a background on why I need to use functional pattern. Let’s say I don’t use functional option. Then, all the arguments need to be passed. Also, difficult to set default values and implement logic for default values. package main import ( "fmt" "log" ) type Config struct { Host string Port uint Visibility bool } type clientOption func(c *Config) error func newConfig(host string, opts .

double pointers A pointer (whose value is another variable’s address) which points to another pointer copying a pointer to another pointer copies the address copying a de-referenced pointer to another de-referenced pointer updates the value of the one to another https://gist.github.com/viggy28/604cda186ff1b872d562b31ca3976732 package main import "fmt" type DB struct { Name string } // double pointer // a pointer which points to another pointer func wrapperFunc(config **DB) func() error { return func() error { cfg := &DB{} (*cfg).

context is a standard package. Context is an interface in context package. type Context interface { Deadline() (deadline time.Time, ok bool) Done() <-chan struct{} Err() error Value(key interface{}) interface{} } There are 4 methods in Context interface. Most of the times, we don’t define our own types which satisfy the interface (which off course we can do), but we mostly use the factory functions provided by the context package itself.

go run command go run command is a quick way to run go program. However, what it does behind the screen is it compiles the program and runs an executable and removes it once the program is stopped. byte is a built-in alias of uint8. rune is a built-in alias of int32. The semicolon insertion rule In Go, I thought there is no need for semicolon at the end of the statement.

closure is a function inside another function where you can reference variable defined in the outer function. I have seen them useful in dealing with packages where a function expects an type func() as an argument where the func() doesn’t take any argument. example from package github.com/cenkalti/backoff signature of backoff.Retry is as below backoff.Retry(o backoff.Operation, b backoff.Backoff) where backoff.Operation is of type func() error type Operation func() error func main() { func retryWrapper(imp string) func() error{ return func() { funcThatCouldFail(imp) retun nil } } err := backoff.

defer is one of the unique keywords in Go. What does defer do? As the name suggests, it defers something. It defers function calls. A deferred function gets invoked right after the surrounding function returns. func outer() { defer inner() log.Println("outer got called") } func inner() { log.Println("inner got called") } outer got called prints first then inner got called. What the main use of defer statement? It helps mainly with actions that need to happen but not immediately.

I came across this piece of code from The Go Programming Language book. loop: for { select { case size, ok := <-fileSizes: if !ok { break loop // fileSizes was closed } nfiles++ nbytes += size case <-tick: printDiskUsage(nfiles, nbytes) } } The complete program is available in Github Named break statement allows to break perhaps multiple control statements. In this example, break loop breaks the select and for statement.

I was going through The Go Programming Language and in chapter 5 there was a section Caveat: Capturing Iteration Variables. The example is like this: var rmdirs []func() for _, dir := range tempDirs() { // 1 os.MkdirAll(dir, 0755) // 2 rmdirs = append(rmdirs, func() { os.RemoveAll(dir) // NOTE: incorrect! // 3 }) } dir is the same variable. i.e. the address of the variable is same dir’s value evaluated at this point is different at each iteration IMPORTANT dir is not evaluated here.

Concurrency channels are like typed pipes, Where you can send something from one side and receive from other side. using channel direction operator <-. Depends on the direction of the variables around the operator, its either sending or receiving. x := <-c // receive from c c <- sum // send sum to c fmt.Println(“channel receive happening”, <-c) channels are reference type. similar to maps. So when we pass channel as an argument to a function or copy we are passing the reference.

In Go, copying generally does a copy by value. So modifying the destination, doesn’t modify the source. However, that holds good only if you are copying value types not reference types (i.e. pointer, slice, map etc.) package main import ( "fmt" ) func main() { type Cat struct { age int name string Friends []string //reference type } wilson := Cat{7, "Wilson", []string{"Tom", "Tabata", "Willie"}} // shallow copy nikita := wilson // modifies both nikita and wilson nikita.

Disclaimer: Whatever I write here is my learnings. So, don’t take these words as granted or reference. Also, please lmk if there are any errors. I have often come across this term JWT. I knew the definition - Json Web Token, but honestly that’s all I knew for a veryyyy longgg time. Recently, I came across a problem where I have been told that JWT might be a good solution for it.

Libpq-Postgres-Go After I started working on Postgres, I have heard this term libpq enough times, but never had a good grasp of it. After digging around this topic for a couple of days, here is my understanding. From the Postgres doc https://www.postgresql.org/docs/9.5/libpq.html, libpq is the C application programmer’s interface to PostgreSQL. libpq is a set of library functions that allow client programs to pass queries to the PostgreSQL backend server and to receive the results of these queries

Understanding context in Golang through Postgres I was trying to learn Go package context especially with respect to Postgres. On a very high level context provides context to the operation. Yeah, I agree, the previous statement doesn’t really add much value, but hold on I don’t really know how to explain it, rather let’s go over some code. Sometimes its easier to understand by seeing it in action :)

Initializing embedded field: The field name of an anonymous field during a struct instantiation is the name of the struct (Time) type Event struct { ID int time.Time } event := Event{ ID: 1234, Time: time.Now(), } If an embedded field type implements an interface, the struct containing the embedded field will also implement this interface

program1 package main import ( "log" ) func main() { done := make(chan struct{}) go func() { log.Println("done") }() <-done //wait for background goroutine to finish } program2 run nc -l 8000 on another terminal package main import ( "log" "net" ) func main() { conn, err := net.Dial("tcp", "localhost:8000") if err != nil { log.Fatal(err) } conn.Close() done := make(chan struct{}) go func() { log.Println("done") }() <-done //wait for background goroutine to finish } Both of those examples have a receive statement from a channel that no one ever sends to.