[feature] Add a request ID and include it in logs (#1476)

This adds a lightweight form of tracing to GTS. Each incoming request is
assigned a Request ID which we then pass on and log in all our log
lines. Any function that gets called downstream from an HTTP handler
should now emit a requestID=value pair whenever it logs something.

Co-authored-by: kim <grufwub@gmail.com>

internal/middleware/requestid.go

@@ -0,0 +1,111 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2023 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package middleware
+
+import (
+	"bufio"
+	"context"
+	"crypto/rand"
+	"encoding/base32"
+	"encoding/binary"
+	"io"
+	"sync"
+	"time"
+
+	"codeberg.org/gruf/go-kv"
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/log"
+)
+
+type ctxType string
+
+var (
+	// ridCtxKey is the key underwhich we store request IDs in a context.
+	ridCtxKey ctxType = "id"
+
+	// crand provides buffered reads of random input.
+	crand = bufio.NewReader(rand.Reader)
+	mrand sync.Mutex
+
+	// base32enc is a base 32 encoding based on a human-readable character set (no padding).
+	base32enc = base32.NewEncoding("0123456789abcdefghjkmnpqrstvwxyz").WithPadding(-1)
+)
+
+// generateID generates a new ID string.
+func generateID() string {
+	// 0:8  = timestamp
+	// 8:12 = entropy
+	//
+	// inspired by ULID.
+	b := make([]byte, 12)
+
+	// Get current time in milliseconds.
+	ms := uint64(time.Now().UnixMilli())
+
+	// Store binary time data in byte buffer.
+	binary.LittleEndian.PutUint64(b[0:8], ms)
+
+	mrand.Lock()
+	// Read random bits into buffer end.
+	_, _ = io.ReadFull(crand, b[8:12])
+	mrand.Unlock()
+
+	// Encode the binary time+entropy ID.
+	return base32enc.EncodeToString(b)
+}
+
+// RequestID fetches the stored request ID from context.
+func RequestID(ctx context.Context) string {
+	id, _ := ctx.Value(ridCtxKey).(string)
+	return id
+}
+
+// AddRequestID returns a gin middleware which adds a unique ID to each request (both response header and context).
+func AddRequestID(header string) gin.HandlerFunc {
+	log.Hook(func(ctx context.Context, kvs []kv.Field) []kv.Field {
+		if id, _ := ctx.Value(ridCtxKey).(string); id != "" {
+			// Add stored request ID to log entry fields.
+			return append(kvs, kv.Field{K: "requestID", V: id})
+		}
+		return kvs
+	})
+
+	return func(c *gin.Context) {
+		// Look for existing ID.
+		id := c.GetHeader(header)
+
+		if id == "" {
+			// Generate new ID.
+			//
+			// 0:8  = timestamp
+			// 8:12 = entropy
+			id = generateID()
+			// Set the request ID in the req header in case we pass the request along
+			// to another service
+			c.Request.Header.Set(header, id)
+		}
+
+		// Store request ID in new request ctx and set new gin request obj.
+		ctx := context.WithValue(c.Request.Context(), ridCtxKey, id)
+		c.Request = c.Request.WithContext(ctx)
+
+		// Set the request ID in the rsp header.
+		c.Writer.Header().Set(header, id)
+	}
+}