styleguide/README.md

# sneak/styleguide

The following is the first released version of my personal code styleguide.
There are many like it, but this one is mine.

Only the Go portion is "complete". The others are mostly just
placeholders.

Feedback and suggestions are not only welcome but explicitly encouraged.

[sneak@sneak.berlin](mailto:sneak@sneak.berlin)

# My 2024 Code Styleguide

## All

1. Every project/repo should have a `Makefile` in the root. At a minimum,
   `make clean`, `make run`, `make fmt`, and `make test` should work. Choose
   a sane default target (`test` for libraries, `run` or `publish` for
   binaries). `fmt` should invoke the appropriate formatters for the files
   in the repo, such as `go fmt`, `prettier`, `black`, etc. Other standard
   `Makefile` targets include `deploy`, `lint`. Consider the `Makefile` the
   official documentation about how to operate the repository.

1. If it's possible to write a `Dockerfile`, include at least a simple one.
   It should be possible to build and run the project with `docker build .`.

1. For F/OSS-licensed software, try to include the full source code of the
   current version (and any dependencies, such as vendored dependencies) in
   the docker image. They're small and should be included with the binary.

1. Under no circumstances should any credentials or secrets ever be
   committed to any repository, even private ones. Store secrets in
   environment variables, and if they are absolutely required, check on
   startup to make sure they are set/non-default and complain loudly if not.
   Exception, sometimes: public keys. (Public keys can still sometimes be
   secrets for operational security reasons.)

1. Avoid nesting `if` statements. If you have more than one level of
   nesting, consider inverting the condition and using `return` to exit
   early.

1. Almost all services/servers should accept their configuration via
   environment variables. Only go full config file if absolutely necessary.

1. For services/servers, log JSON to stdout. This makes it easier to parse
   and aggregate logs when run under `docker`. Use structured logging
   whenever possible. You may detect if the output is a terminal and
   pretty-print the logs in that case.

1. Debug mode is enabled by setting the environment variable `DEBUG` to a
   non-empty string. This should enable verbose logging and such. It will
   never be enabled in prod.

1. For services/servers, make a healthcheck available at
   `/.well-known/healthcheck`. This is out of spec but it is my personal
   standard. This should return a 200 OK if the service is healthy, along
   with a JSON object containing the service's name, uptime, and any other
   relevant information, and a key of "status" with a value of "ok" if the
   service is healthy. Make sure that in the event of a failure, the service
   returns a 5xx status code for that route.

1. If possible, for services/servers, include a /metrics endpoint that
   returns Prometheus-formatted metrics. This is not required for all
   services, but is a nice-to-have.

## Bash / Shell

1. Use `[[` instead of `[` for conditionals. It's a shell builtin and
   doesn't have to execute a separate process.

1. Use `$( )` instead of backticks. It's easier to read and nest.

1. Use `#!/usr/bin/env bash` as the shebang line. This allows the script to
   be run on systems where `bash` is not in `/bin`.

1. Use `set -euo pipefail` at the top of every script. This will cause the
   script to exit if any command fails, and will cause the script to exit if
   any variable is used before it is set.

1. Use `pv` for progress bars when piping data through a command. This makes
   it easier to see how much data has been processed.

1. Put all code in functions, even a main function. Define all functions
   then call main at the bottom of the file.

## JavaScript / ECMAScript / ES6

1. Use `const` for everything. If you need to reassign, use `let`. Never
   use `var`.

1. Use yarn for package management, avoid using npm.

1. Use LTS node versions.

1. Use `prettier` for code formatting, with four spaces for indentation.

1. At a minimum, `npm run test` and `npm run build` should work (complete
   the appropriate scripts in `package.json`). The `Makefile` should call
   these, do not duplicate the scripts in the `Makefile`.

## Docker Containers (for services)

1. Use `runit` with `runsvinit` as the entrypoint for all containers. This
   allows for easy service management and logging. In startup scripts
   (`/etc/service/*/run`) in the container, put a `sleep 1` at the top of
   the script to avoid spiking the cpu in the case of a fast-exiting process
   (such as in an error condition). This also limits the maximum number of
   error messages in logs to 86400/day.

## Python

1. Format all code with `black`, with four space indents.

2. Put all code in functions. If you are writing a script, put the script
   in a function called `main` and call `main()` at the end of the script
   using the standard invocation:

    ```python
    if __name__ == "__main__":
        main()
    ```

## Golang

1.  Try to hard wrap long lines at 77 characters or less.

1.  Don't commit anything that hasn't been `go fmt`'d. The only exception is
    when committing things that aren't yet syntactically valid, which should
    only happen pre-v0.0.1 or on a non-`main` branch.

1.  Even if you are planning to deal with only positive integers, use
    `int`/`int64` types instead of `uint`/`uint64` types. This is for
    consistency and compatibility with the standard library; it's better
    than casting all the time.

1.  Any project that has more than 2 or 3 modules should use the
    `go.uber.org/fx` dependency injection framework to keep things tidy.

1.  If you have to choose between readable and clever, opt for readable.
    It's ok to make the code less concise or slightly less idiomatic if you
    can keep it dead simple.

1.  Embed the git commit hash into the binary and include it in startup logs
    and in health check output. This is to make it easier to correlate
    running instances with their code. Do not include build time or build
    user, as these will make the build nondeterministic.

    Example relevant Makefile sections:

    Given a `main.go` like:

    ```go
    package main

    import (
        "fmt"
    )

    var (
        Version   string
        Buildarch string
    )

    func main() {
        fmt.Printf("Version: %s\n", Version)
        fmt.Printf("Buildarch: %s\n", Buildarch)
    }
    ```

    ```make
    VERSION := $(shell git describe --always --dirty)
    BUILDARCH := $(shell uname -m)

    GOLDFLAGS += -X main.Version=$(VERSION)
    GOLDFLAGS += -X main.Buildarch=$(BUILDARCH)

    # osx can't statically link apparently?!
    ifeq ($(UNAME_S),Darwin)
            GOFLAGS := -ldflags "$(GOLDFLAGS)"
    endif

    ifneq ($(UNAME_S),Darwin)
            GOFLAGS = -ldflags "-linkmode external -extldflags -static $(GOLDFLAGS)"
    endif

    ./httpd: ./pkg/*/*.go ./internal/*/*.go cmd/httpd/*.go
        go build -o $@ $(GOFLAGS) ./cmd/httpd/*.go
    ```

1.  Avoid obvious footguns. For example, use range instead of for loops for
    iterating.

1.  Try to use zerolog for logging. It's fast and has a nice API. For
    smaller/quick projects, the standard library's `log` package (and
    specifically `log/slog`) is fine. In that case, log structured logs
    whenever possible, and import `sneak.berlin/go/simplelog` to configure
    it appropriately. Example:

    ```go
    package main

    import (
        "log/slog"
        _ "sneak.berlin/go/simplelog"
    )

    func main() {
        slog.Info("Starting up")
    }
    ```

1.  Commit at least a single test file to check compilation. The test file
    can be empty, but it should exist. This is to ensure that `go test
./...` will always function as a syntax check at a minimum.

1.  Full TDD and coverage isn't that important, but when fixing a specific
    bug, try to write a test that reproduces the bug before fixing it. This
    will help ensure that the bug doesn't come back later, and crystallizes
    the experience of discovering the bug and the resulting fix into the
    repository's history.

1.  For anything beyond a simple script or tool, or anything that is going to
    run in any sort of "production" anywhere, make sure it passes
    `golangci-lint`.

1.  Write a `Dockerfile` for every repo, even if it only runs the tests and
    linting. `docker build .` should always make sure that the code is in an
    able-to-be-compiled state, linted, and any tests run. The Docker build
    should fail if linting doesn't pass.

1.  Include a `Makefile` with targets for at least `clean` and `test`. If
    there are multiple binaries, include a target for each binary. If there
    are multiple binaries, include a target for `all` that builds all
    binaries.

1.  If you are writing a single-module library, `.go` files are okay in the
    repo root.

1.  If you are writing a multi-module project, put all `.go` files in a
    `pkg/` or `internal/` subdirectory. `internal/` is for modules used
    only by the current repo, and `pkg/` is for modules that can be consumed
    externally. This is to keep the repo root as clean as possible.

1.  Binaries go in `cmd/` directories. Each binary should have its own
    directory. This is to keep the root clean and to make it easier to see
    what is a library and what is a binary. Only package `main` files
    should be in `cmd/*` directories.

1.  Keep the `main()` function as small as possible.

1.  Keep the `main` package as small as possible. Move as much code as is
    feasible to a library package, even if it's an internal one. `main` is
    just an entrypoint to your code, not a place for implementations.
    Exception: single-file scripts.

1.  HTTP HandleFuncs should be returned from methods or functions that need
    to handle HTTP requests. Don't use methods or our top level functions
    as handlers.

1.  Provide a .gitignore file that ignores at least `*.log`, `*.out`, and
    `*.test` files, as well as any binaries.

1.  Constructors should be called `New()` whenever possible.
    `modulename.New()` works great if you name the packages properly.

1.  Don't make packages too big. Break them up.

1.  Don't make functions or methods too big. Break them up.

1.  Use descriptive names for functions and methods. Don't be afraid to
    make them a bit long.

1.  Use descriptive names for modules and filenames. Avoid generic names
    like `server`. `util` is banned.

1.  Constructors should take a Params struct if they need more than 1-2
    arguments. Positional arguments are an endless source of bugs and
    should be avoided whenever possible.

1.  Use `context.Context` for all functions that need it. If you don't need
    it, you can pass `context.Background()`. Anything long-running should
    get and abide by a Context. A context does not count against your
    number of function or method arguments for purposes of calculating
    whether or not you need a Params struct, because the `ctx` is always
    first.

1.  Contexts are always named `ctx`.

1.  Use `context.WithTimeout` or `context.WithDeadline` for any function
    that could potentially run for a long time. This is especially true for
    any function that makes a network call. Sane timeouts are essential.

1.  If a structure/type is only used in one function or method, define it
    there. If it's used in more than one, define it in the package. Keep it
    close to its usages. For example:

    ```go
    func (m *Mothership) tvPost() http.HandlerFunc {

        type MSTVRequest struct {
                URL string `json:"URL"`
        }

        type MSTVResponse struct {
        }

        return func(w http.ResponseWriter, r *http.Request) {
            // parse json from request
            var reqParsed MSTVRequest
            err = json.NewDecoder(r.Body).Decode(&reqParsed)
            ...

            if err != nil {
                    SendErrorResponse(w, MSGenericError)
                    return
            }

            log.Info().Msgf("Casting to %s: %s", tvName, streamURL)
            SendSuccessResponse(w, &MSTVResponse{})
        }
    }
    ```

1.  Avoid global state, especially global variables. If you need to store
    state that is global to your launch or application instance, use a
    package `globals` or `appstate` with a struct and a constructor and
    require it as a dependency in your constructors. This will allow
    consumers to be more easily testable and will make it easier to reason
    about the state of your application. Alternately, if your dependency
    graph allows for it, put it in the main struct/object of your
    application, but remember that this harms testability.

1.  Package-global "variables" are ok if they are constants, such as static
    strings or integers or errors.

1.  Whenever possible, avoid hardcoding numbers or values in your code. Use
    descriptively-named constants instead. Recall the famous SICP quote:
    "Programs must be written for people to read, and only incidentally for
    machines to execute." Rather than comments, a descriptive constant name
    is much cleaner.

    Example:

    ```go

    const jsonContentType = "application/json; charset=utf-8"

    func (s *Handlers) respondJSON(w http.ResponseWriter, r *http.Request, data interface{}, status int) {
         w.WriteHeader(status)
         w.Header().Set("Content-Type", jsonContentType)
         ...
     }
    ```

1.  Define your struct types near their constructors.

1.  Define your interface types near the functions that use them, or if you
    have multiple conformant types, put the interface(s) in their own file.

1.  Define errors as package-level variables. Use a descriptive name for the
    error. Use `errors.New` to create the error. If you need to include
    additional information in the error, use a struct that implements the
    `error` interface.

1.  Use lowerCamelCase for local function/variable names. Use UpperCamelCase
    for type names, and exported function/variable names. Use snake_case for
    JSON keys. Use lowercase for filenames.

1.  Explicitly specify UTC for datetimes unless you have a very good reason
    not to. Use `time.Now().UTC()` to get the current time in UTC.

1.  String dates should always be ISO8601 formatted. Use `time.Time.Format`
    with `time.RFC3339` to get the correct format.

1.  Use `time.Time` for all date and time values. Do not use `int64` or
    `string` for dates or times internally.

1.  When using `time.Time` in a struct, use a pointer to `time.Time` so that
    you can differentiate between a zero value and a null value.

1.  Use `time.Duration` for all time durations. Do not use `int64` or
    `string` for durations internally.

1.  When using `time.Duration` in a struct, use a pointer to `time.Duration`
    so that you can differentiate between a zero value and a null value.

1.  Whenever possible, in argument types and return types, try to use
    standard library interfaces instead of concrete types. For example, use
    `io.Reader` instead of `*os.File`. Tailor these to the needs of the
    specific function or method. Examples:

    - **`io.Reader`** instead of `*os.File`:

      -   `io.Reader` is a common interface for reading data, which can be
          implemented by many types, including `*os.File`, `bytes.Buffer`,
          `strings.Reader`, and network connections like `net.Conn`.

    - **`io.Writer`** instead of `*os.File` or `*bytes.Buffer`:

      -   `io.Writer` is used for writing data. It can be implemented by
          `*os.File`, `bytes.Buffer`, `net.Conn`, and more.

    - **`io.ReadWriter`** instead of `*os.File`:

      -   `io.ReadWriter` combines `io.Reader` and `io.Writer`. It is often
          used for types that can both read and write, such as `*os.File`
          and `net.Conn`.

    - **`io.Closer`** instead of `*os.File` or `*net.Conn`:

      -   `io.Closer` is used for types that need to be closed, including
          `*os.File`, `net.Conn`, and other resources that require cleanup.

    - **`io.ReadCloser`** instead of `*os.File` or `http.Response.Body`:

      -   `io.ReadCloser` combines `io.Reader` and `io.Closer`, and is
          commonly used for types like `*os.File` and `http.Response.Body`.

    - **`io.WriteCloser`** instead of `*os.File` or `*gzip.Writer`:

      -   `io.WriteCloser` combines `io.Writer` and `io.Closer`. It is used
          for types like `*os.File` and `gzip.Writer`.

    - **`io.ReadWriteCloser`** instead of `*os.File` or `*net.TCPConn`:

      -   `io.ReadWriteCloser` combines `io.Reader`, `io.Writer`, and
          `io.Closer`. Examples include `*os.File` and `net.TCPConn`.

    - **`fmt.Stringer`** instead of implementing a custom `String` method:

      -   `fmt.Stringer` is an interface for types that can convert
          themselves to a string. Any type that implements the `String()
          string` method satisfies this interface.

    - **`error`** instead of custom error types:

      -   The `error` interface is used for representing errors. Instead of
          defining custom error types, you can use the `errors.New`
          function or the `fmt.Errorf` function to create errors.

    - **`net.Conn`** instead of `*net.TCPConn` or `*net.UDPConn`:

      -   `net.Conn` is a generic network connection interface that can be
          implemented by TCP, UDP, and other types of network connections.

    - **`http.Handler`** instead of custom HTTP handlers:

      -   `http.Handler` is an interface for handling HTTP requests.
          Instead of creating custom handler types, you can use types that
          implement the `ServeHTTP(http.ResponseWriter, *http.Request)`
          method.

    - **`http.HandlerFunc`** instead of creating a new type:

      -   `http.HandlerFunc` is a type that allows you to use functions as
          HTTP handlers by implementing the `http.Handler` interface.

    - **`encoding.BinaryMarshaler` and `encoding.BinaryUnmarshaler`**
      instead of custom marshal/unmarshal methods:

      -   These interfaces are used for binary serialization and
          deserialization. Implementing these interfaces allows types to
          be encoded and decoded in a standard way.

    - **`encoding.TextMarshaler` and `encoding.TextUnmarshaler`** instead
      of custom text marshal/unmarshal methods:

      -   These interfaces are used for text-based serialization and
          deserialization. They are useful for types that need to be
          represented as text.

    - **`sort.Interface`** instead of custom sorting logic:

      -   `sort.Interface` is an interface for sorting collections. By
          implementing the `Len`, `Less`, and `Swap` methods, you can sort
          any collection using the `sort.Sort` function.

    - **`flag.Value`** instead of custom flag parsing:
        -   `flag.Value` is an interface for defining custom command-line
            flags. Implementing the `String` and `Set` methods allows you to
            use custom types with the `flag` package.

1.  Avoid using `panic` in library code. Instead, return errors to allow
    the caller to handle them. Reserve `panic` for truly exceptional
    conditions.

1.  Use `defer` to ensure resources are properly cleaned up, such as
    closing files or network connections. Place `defer` statements
    immediately after resource acquisition.

1.  When calling a function with `go`, wrap the function call in an
    anonymous function to ensure it runs in the new goroutine context:

    Right:

    ```go
    go func() {
        someFunction(arg1, arg2)
    }()
    ```

    Wrong:

    ```go
    go someFunction(arg1, arg2)
    ```

1.  Use `iota` to define enumerations in a type-safe way. This ensures that
    the constants are properly grouped and reduces the risk of errors.

    Example:

    ```go

    type HandScore int

    const (
        ScoreHighCard = HandScore(iota * 100_000_000_000)
        ScorePair
        ScoreTwoPair
        ScoreThreeOfAKind
        ScoreStraight
        ScoreFlush
        ScoreFullHouse
        ScoreFourOfAKind
        ScoreStraightFlush
        ScoreRoyalFlush
    )
    ```

    Example 2:

    ```go
    type ByteSize float64

    const (
        _           = iota // ignore first value by assigning to blank identifier
        KB ByteSize = 1 << (10 * iota)
        MB
        GB
        TB
        PB
        EB
        ZB
        YB
    )
    ```

1.  Don't hardcode big lists of things in your normal code. Either isolate
    lists in their own module/package and write some getters, or use a third
    party library. For example, if you need a list of country codes, you can
    use
    [https://github.com/emvi/iso-639-1](https://github.com/emvi/iso-639-1).
    It's okay to embed a data file (use `go embed`) in your binary if you
    need to, but make sure you parse it once as a singleton and don't read
    it from disk every time you need it. Don't use too much memory for
    this, embedding anything more than perhaps 25MiB (uncompressed) is
    probably too much. Compress the file before embedding and uncompress
    during the reading/parsing step for efficiency.

1.  When storing numeric values that represent a number of units, either
    include the unit in the variable name (e.g. `uptimeSeconds`,
    `delayMsec`, `coreTemperatureCelsius`), or use a type alias (that
    includes the unit name), or use a 3p library such as
    [github.com/alecthomas/units](https://github.com/alecthomas/units) for
    SI/IEC byte units, or
    [github.com/bcicen/go-units](https://github.com/bcicen/go-units) for
    temperatures (and others). The type system is your friend, use it.

1.  Once you have a working program, run `go mod tidy` to clean up your
    `go.mod` and `go.sum` files. Tag a v0.0.1 or v1.0.0. Push your `main`
    branch and tag(s). Subsequent work should happen on branches so that
    `main` is "always releasable". "Releasable" in this context means that
    it builds and functions as expected, and that all tests and linting
    passes.

## Other Golang Tips and Best Practices (Optional)

1. For any internet-facing http server, set appropriate timeouts and limits
   to protect against slowloris attacks or huge uploads that can consume
   server resources even without authentication.

    Example to limit request body size:

    ```go
    package main

     import (
         "fmt"
         "net/http"
     )

     func main() {
         http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
             // Limit the request body to 10MB
             r.Body = http.MaxBytesReader(w, r.Body, 10<<20)
             if err := r.ParseForm(); err != nil {
                 http.Error(w, "Request body too large", http.StatusRequestEntityTooLarge)
                 return
             }
             fmt.Fprintf(w, "Hello, World!")
         })

         http.ListenAndServe(":8080", nil)
     }
    ```

    Example to set appropriate timeouts:

    ```go
    package main

    import (
        "net/http"
        "time"
    )

    func main() {
        server := &http.Server{
            Addr:         ":8080",
            ReadTimeout:  5 * time.Second,
            WriteTimeout: 10 * time.Second,
            Handler:      http.DefaultServeMux,
        }

        http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
            fmt.Fprintf(w, "Hello, World!")
        })

        server.ListenAndServe()
    }
    ```

1. When passing channels to goroutines, use read-only (`<-chan`) or
   write-only (`chan<-`) channels to communicate the direction of data flow
   clearly.

1. Use `io.MultiReader` to concatenate multiple readers and
   `io.MultiWriter` to duplicate writes to multiple writers. This can
   simplify the handling of multiple data sources or destinations.

1. For simple counters and flags, use the `sync/atomic` package to avoid
   the overhead of mutexes.

1. When using mutexes, minimize the scope of locking to reduce contention
   and potential deadlocks. Prefer to lock only the critical sections of
   code. Try to encapsulate the critical section in its own function or
   method. Acquire the lock as the first line of the function, defer
   release of the lock as the second line of the function, and lines 3-5
   should perform the task. Try to keep it as short as possible. Avoid
   using mutexes in the middle of a function. In short, build atomic
   functions.

1. Design types to be immutable where possible. This can help avoid issues
   with concurrent access and make the code easier to reason about.

1. Global state can lead to unpredictable behavior and makes the code
   harder to test. Use dependency injection to manage state.

1. Avoid using `init` functions unless absolutely necessary as they can
   lead to unpredictable initialization order and make the code harder to
   understand.

1. Provide comments for all public interfaces explaining what they do and
   how they should be used. This helps other developers understand the
   intended use.

1. Be mindful of resource leaks when using `time.Timer` and `time.Ticker`.
   Always stop them when they are no longer needed.

1. Use `sync.Pool` to manage a pool of reusable objects, which can help
   reduce GC overhead and improve performance in high-throughput scenarios.

1. Avoid using large buffer sizes for channels. Unbounded channels can
   lead to memory leaks. Use appropriate buffer sizes based on the
   application's needs.

1. Always handle the case where a channel might be closed. This prevents
   panic and ensures graceful shutdowns.

1. For small structs, use value receivers to avoid unnecessary heap
   allocations. Use pointer receivers for large structs or when mutating
   the receiver.

1. Only use goroutines when necessary. Excessive goroutines can lead to
   high memory consumption and increased complexity.

1. Use `sync.Cond` for more complex synchronization needs that cannot be
   met with simple mutexes and channels.

1. Reflection is powerful but should be used sparingly as it can lead to
   code that is hard to understand and maintain. Prefer type-safe
   solutions.

1. Avoid storing large or complex data in context. Context should be used
   for request-scoped values like deadlines, cancellation signals, and
   authentication tokens.

1. Use `runtime.Callers` and `runtime.CallersFrames` to capture stack
   traces for debugging and logging purposes.

1. Use the `testing.TB` interface to write helper functions that can be
   used with both `*testing.T` and `*testing.B`.

1. Use struct embedding to reuse code across multiple structs. This is a
   form of composition that can simplify code reuse.

1. Prefer defining explicit interfaces in your packages rather than
   relying on implicit interfaces. This makes the intended use of
   interfaces clearer and the code more maintainable.

# Author

[@sneak](https://sneak.berlin) &lt;[sneak@sneak.berlin](mailto:sneak@sneak.berlin)&gt;

# License

[WTFPL](./LICENSE)

Do with it what you will. There is no warranty, express or implied,
including but not limited to merchantability or fitness for a particular
purpose. Use at your own risk.

# Credit