Utilities for Go

A small, focused collection of helper functions and type shortcuts frequently used across services. Utilities are grouped around a few common themes:

• Pointers and generics helpers
• Struct reflection helpers (read/write fields, mapping, tabular output)
• CLI/table printing helpers
• JWT helpers (create, validate, extract, gin integration)
• Process/daemon helpers (PID discovery)
• Host/filesystem helpers
• File utilities (MIME type)
• Network helpers (ARP lookup)
• Validation helpers (email, IP, URL, FQDN/hostname, phone, credit card Luhn, UUID, base64, hex colors, alphanumeric)
• Database DSN helper and driver.Valuer utilities
• Common type aliases

This repository contains:

• Root package: github.com/dan-sherwin/go-utilities
• Subpackage: github.com/dan-sherwin/go-utilities/ginutils (gin-only JWT conveniences)

Installation

• Root package: go get github.com/dan-sherwin/go-utilities

• Gin helpers: go get github.com/dan-sherwin/go-utilities/ginutils

Go version: see go.mod (currently Go 1.24).

Quick Start

• Create a JWT:

  token, err := utilities.GenerateJWT(struct{UserID string}{"123"}, time.Hour, []byte("secret"))

• Validate & read claims:

  claims, err := utilities.ExtractJwtClaims(token, []byte("secret"))

• Pointers:

  sPtr := utilities.Ptr("hello") // *string v := utilities.PtrVal(sPtr) // "hello" nonNil := utilities.PtrZeroNil(5) // *int isEq := utilities.PtrCompare(&v, &v) // true

• Struct table printing:

  type User struct { ID int; Name string } _ = utilities.PrintStructTable([]User{{1, "Ada"}, {2, "Linus"}})

• Process helpers:

  if utilities.DaemonAlreadyRunning("my-app") { /* ... */ } pid, err := utilities.FindDaemonProcessPID("my-app")

• MIME type by filename:

  mime := utilities.MimeTypeFromExtension("photo.JPG") // image/jpeg

• Network (ARP):

  mac, err := utilities.GetMacAddressFromIp("192.168.1.20")

• Validation helpers:

  utilities.IsEmail("[email protected]") // true utilities.IsURL("https://example.com") // true utilities.IsCreditCard("4242 4242 4242 4242") // true (Luhn) utilities.IsIPv4("192.168.1.1") // true utilities.IsUUID("550e8400-e29b-41d4-a716-446655440000") // true

• Gin integration:

  func handler(c *gin.Context) { claims, err := ginutils.ExtractJwtClaimsFromContext(c, []byte("secret")) // ... }

Package Layout

• utilities: general-purpose helpers used across services.
• utilities/ginutils: helpers for extracting JWTs from gin.Context Authorization headers.

Detailed API (Root package: utilities)

Below is a complete list of exported functions and types with concise descriptions. Examples above show typical usage.

Pointers and Value Utilities

• func Ptr[T any](v T) *T Returns a pointer to v.
• func PtrZeroNil[T any](v T) *T Returns &v if v is non-zero; otherwise nil.
• func PtrVal[T any](p *T) T Dereferences p or returns zero value if p is nil.
• func PtrCompare[T comparable](p1, p2 *T) bool True if both nil or both non-nil and equal.
• func CopyIfNotNil[T any](src, dest *T) Copies *src into *dest if both are non-nil.
• func CopyIfNotZero[T any](src T, dest *T) Copies src into *dest if src is non-zero and dest != nil.
• func NilIfEmpty[T any](in []T) *[]T Returns nil if the slice is empty; otherwise pointer to the slice.
• func NilIfZeroPtr[T comparable](in *T) *T Returns nil if in != nil and *in is zero; else returns in.

Struct Reflection Helpers

• func ZeroStructFieldByName(ptr interface{}, fieldName string) error Sets named field to its zero value. ptr must be pointer to struct.
• func SetStructFieldByName(ptr interface{}, fieldName string, value interface{}) error Sets named field to value with basic type checking.
• func StructFieldNames(s interface{}) []string Returns field names of a struct or pointer to struct.
• func StructToStringMap(s interface{}) map[string]string Maps field names to string values; dereferences pointers and marks nil pointers as "".

CLI/Table Helpers

• func PrintMapArray(input any) error Prints a []map[string]any, []map[string]string, or []utilities.StrMap as a table to stdout.
• func PrintStructMap(obj any) error Treats any map's values as structs and prints a table.
• func PrintSortedStructMap(obj any) error Like PrintStructMap but sorts columns and rows for stable output.
• func PrintStructTable(obj any) error Prints a struct or slice/array of structs (or pointers) as a table to stdout.
• func PrintStringSlice(input any) error Prints a slice of strings with index.
• func PrintAnySlice(input any) error Prints a slice of any type using fmt.Sprint.
• func PrintMap(input any, headers ...string) error Prints a single map with optional headers.
• func PrintStringsTable(headers []string, rows [][]string) error Renders arbitrary headers and rows.
• func PrintSlice(input any) error Prints a slice/array determined via reflection.

JWT Helpers

• func GenerateJWT(claims interface{}, duration time.Duration, secretKey []byte) (string, error) Creates a JWT (HS256) with iat and exp added.
• func ValidateJWT(tokenString string, secretKey []byte) (*jwt.Token, error) Parses and validates an HS256 token.
• func ExtractJwtClaims(tokenString string, secretKey []byte) (map[string]interface{}, error) Returns validated claims as a map.
• func ExtractJwtClaimsInto(tokenString string, secretKey []byte, out interface{}) error Decodes validated claims into your struct.

Process/Daemon Helpers

• func DaemonAlreadyRunning(appName string) bool True if a matching process already exists.
• func MustFindDaemonProcessPID(appName string) int Returns PID if found; returns 0 if not found.
• func FindDaemonProcessPID(appName string) (int, error) Cross-platform PID lookup (Linux /proc and macOS variant).
• func FindDaemonProcessPIDWithArg(appName string, argName string) (int, error) As above; requires presence of argName in process args.
• func FindProcessPIDMAC(appName string) (int, error) macOS-specific lookup using ps.

Host/Filesystem Helpers

• func AmAdmin() bool True if running as root (euid == 0).
• func DirCreateIfNotExists(dir string) error mkdir -p behavior with 0755 on missing dirs.

Debug Helpers

• func LitterCheckErr[T any](out T, err error) T Dumps value with litter and logs an error if present, then returns out.

File Helpers

• func MimeTypeFromExtension(filename string) string Returns MIME by extension; defaults to application/octet-stream.

Network Helpers

• func GetMacAddressFromIp(ipAddress string) (string, error) Looks up MAC by IP using local ARP table.

Validation Helpers

• func IsEmail(s string) bool Valid email using net/mail; ensures domain is FQDN/hostname or IP.
• func IsIP(s string) bool IPv4 or IPv6 literal.
• func IsIPv4(s string) bool IPv4 literal only.
• func IsIPv6(s string) bool IPv6 literal only.
• func IsMAC(s string) bool Hardware address (MAC-48/EUI-64).
• func IsURL(s string) bool http/https URL with valid host (IPv4/IPv6/FQDN/hostname).
• func IsFQDN(s string) bool Fully-qualified domain name per common DNS label rules.
• func IsHostname(s string) bool Single-label hostnames, same label rules as FQDN labels.
• func IsCreditCard(s string) bool Digits with optional spaces/dashes, validated via Luhn checksum.
• func IsPhone(s string) bool Basic E.164 (+8..15 digits) or national digits (7..15).
• func IsUUID(s string) bool UUID v1–v5 canonical format.
• func IsBase64(s string) bool Base64 (padded or raw), ignoring whitespace.
• func IsHexColor(s string) bool #RGB, #RRGGBB, #RGBA, #RRGGBBAA (with or without #).
• func IsAlphaNumeric(s string) bool ASCII letters and digits only.

Database Helpers

• type DbDSNConfig struct { Server string; Port int; Name string; User string; Password string; SSLMode bool; TimeZone string } Source values for DSN generation.
• func DbDSN(cfg DbDSNConfig) string Assembles a postgres-style DSN from config.
• func ToValuers[T driver.Valuer](in []T) []driver.Valuer Useful when building driver.Valuer slices (e.g., for WHERE IN bindings).

Map Helpers

• func Merge[K comparable, V any](a, b map[K]V) map[K]V Returns a new map with values from b overwriting a.
• func MergeInto[K comparable, V any](a, b map[K]V) Merges b into a in-place.

Common Type Aliases

• General maps
  • type StrMap map[string]string
  • type StrAny map[string]any
  • type IntMap map[string]int
  • type AnyMap map[string]any
• JSON
  • type JSON map[string]any
• Slices
  • type Strs []string
  • type Ints []int
  • type Floats []float64
  • type Anys []any
• Functions
  • type Handler func() error
  • type Callback func(any) error
  • type Predicate[T any] func(T) bool
  • type Mapper[T any, R any] func(T) R
• Channels
  • type ErrChan chan error
  • type StrChan chan string
  • type AnyChan chan any

Subpackage: ginutils

Helpers for extracting JWTs from gin-gonic request contexts.

Import path: github.com/dan-sherwin/go-utilities/ginutils

• func ExtractJwtClaimsFromContext(c *gin.Context, secretKey []byte) (map[string]interface{}, error) Reads Authorization: Bearer and returns validated claims.
• func ExtractJwtClaimsFromContextInto(c *gin.Context, secretKey []byte, out interface{}) error As above, but decodes into your struct.
• func ExtractCookieJwtClaimsFromContext(c *gin.Context, secretKey []byte) (map[string]interface{}, error) Reads Cookie token and returns validated claims.
• func ExtractCookieJwtClaimsFromContextInto(c *gin.Context, secretKey []byte, out interface{}) error As above, but decodes into your struct.

Example:

r := gin.Default() r.GET("/me", func(c *gin.Context) { var claims struct{ UserID string json:"uid" } if err := ginutils.ExtractJwtClaimsFromContextInto(c, []byte("secret"), &claims); err != nil { c.AbortWithStatusJSON(401, gin.H{"error": "invalid token"}) return } c.JSON(200, gin.H{"user": claims.UserID}) })

Notes and Caveats

• Security: JWT helpers use HS256. Ensure secret key management follows your org’s standards. Consider key rotation and short expirations.
• Time: GenerateJWT injects iat and exp based on time.Now().
• Process helpers: Linux uses /proc parsing; macOS uses ps output. Caller’s own PID is ignored. Provide the correct app name (and arg name when applicable).
• Table printing: Helpers write to os.Stdout using tablewriter. In non-TTY contexts, ensure stdout capture is acceptable.
• Network/ARP: GetMacAddressFromIp relies on local ARP cache; may fail if the IP has not been resolved on the local network.
• DSN: DbDSN builds a PostgreSQL-like connection string; adjust as needed for your driver.

Versioning

This project follows Semantic Versioning. See CHANGELOG.md for a human‑friendly list of notable changes. The next release is expected to be v1.2.3 (documentation and CI only).

License

Released under the MIT License. See LICENSE for the full text.

Contributing

• Keep functions small and well-documented (Go doc comments above declarations).
• Prefer generic helpers where it improves ergonomics without obscuring types.
• Add examples to this README when adding new exported functions.