prepare switch to log/slog

This commit prepares the switch from log to log/slog, which was
introduced in Go 1.21.
slog provides some useful facilities to add metadata to log entries,
which should be helpful for debugging problems.

This commit also adds a small transaction ID generator. It provides a
common identifier between log messages, so that multiple errors can be
viewed together in their order.

1 files changed, 44 insertions, 1 deletions

diff --git a/cmd/monfront/server.go b/cmd/monfront/server.go
index 8e53c64..06afe11 100644
--- a/cmd/monfront/server.go
+++ b/cmd/monfront/server.go
@@ -2,12 +2,15 @@ package main
 
 import (
 	"compress/gzip"
+	"crypto/rand"
 	"database/sql"
 	"encoding/json"
 	"fmt"
 	"html/template"
 	"io"
 	"log"
+	"log/slog"
+	"math/big"
 	"net"
 	"net/http"
 	"strings"
@@ -19,6 +22,7 @@ type (
 		listen net.Listener
 		db     *sql.DB
 		h      *http.ServeMux
+		log    *slog.Logger
 		tmpl   *template.Template
 		auth   func(c *Context) error // authentication
 		autho  func(c *Context) error // authorization
@@ -32,6 +36,7 @@ type (
 		r    *http.Request
 		tmpl *template.Template
 		db   *sql.DB
+		log  *slog.Logger
 
 		User    string  `json:"-"`
 		Filter  *filter `json:"-"`
@@ -51,7 +56,7 @@ type (
 	}
 )
 
-func newServer(l net.Listener, db *sql.DB, tmpl *template.Template, auth func(c *Context) error, autho func(c *Context) error) *server {
+func newServer(l net.Listener, db *sql.DB, log *slog.Logger, tmpl *template.Template, auth func(c *Context) error, autho func(c *Context) error) *server {
 	s := &server{
 		listen: l,
 		db:     db,
@@ -59,6 +64,7 @@ func newServer(l net.Listener, db *sql.DB, tmpl *template.Template, auth func(c
 		h:      http.NewServeMux(),
 		auth:   auth,
 		autho:  autho,
+		log:    log,
 	}
 	return s
 }
@@ -70,11 +76,19 @@ func (s *server) ListenAndServe() error {
 
 func (s *server) Handle(path string, fun handleFunc) {
 	s.h.HandleFunc(path, func(w http.ResponseWriter, r *http.Request) {
+		txid, err := newTxId()
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte(`internal error occured`))
+			s.log.Error("could not create txid", "error", err)
+			return
+		}
 		c := &Context{
 			w:    w,
 			r:    r,
 			tmpl: s.tmpl,
 			db:   s.db,
+			log:  s.log.With("path", path, "txid", txid),
 		}
 		if err := s.auth(c); err != nil {
 			return
@@ -153,3 +167,32 @@ func (c *Context) SetCookie(name, val string, expire time.Time) {
 	http.SetCookie(c.w, &cook)
 	return
 }
+
+// Alphabet are the available characters used to generate the txids. The more
+// characters available the more bits can be represented with shorter IDs.
+const alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890-_"
+
+// alphalen is the number of available characters in the alphabet.
+var alphalen = big.NewInt(int64(len(alphabet)))
+
+// txlen is the length of the generated transaction IDs
+const txlen = 15
+
+// generate a new transaction ID
+//
+// This function generates a unique ID using the above parameters. If the IDs
+// generated are not unique enough to track a transaction, the txlen should
+// be raised.
+func newTxId() (string, error) {
+	s := make([]byte, txlen)
+	var err error
+	var num *big.Int
+	for i := 0; i < txlen; i++ {
+		num, err = rand.Int(rand.Reader, alphalen)
+		if err != nil {
+			return "", err
+		}
+		s[i] = alphabet[num.Int64()]
+	}
+	return string(s), nil
+}