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requestid.go
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requestid.go
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package middleware
import (
"crypto/rand"
"encoding/base64"
"fmt"
"net/http"
"strings"
"sync/atomic"
"github.com/jatolentino/tutorialspoint/api/web"
"context"
)
const (
// RequestIDHeader is the name of the header used to transmit the request ID.
RequestIDHeader = "X-Request-Id"
// DefaultRequestIDLengthLimit is the default maximum length for the request ID header value.
DefaultRequestIDLengthLimit = 128
)
// reqIDKeyCtx is the private type used to store the request id in the context.
// It is private to avoid possible collisions with keys used by other packages.
type reqIDKeyCtx int
// reqIDKey is the context key used to store the request ID value.
const reqIDKey reqIDKeyCtx = 1
// Counter used to create new request ids.
var reqID int64
// Common prefix to all newly created request ids for this process.
var reqPrefix string
// Initialize common prefix on process startup.
// Algorithm taken from https://github.com/zenazn/goji/blob/master/web/middleware/request_id.go#L44-L50 .
func init() {
var buf [12]byte
var b64 string
for len(b64) < 10 {
_, _ = rand.Read(buf[:])
b64 = base64.StdEncoding.EncodeToString(buf[:])
b64 = strings.NewReplacer("+", "", "/", "").Replace(b64)
}
reqPrefix = string(b64[0:10])
}
// RequestID is a middleware that injects a request ID into the context of each request.
// Retrieve it using ctx.Value(ReqIDKey). If the incoming request has a RequestIDHeader header then
// that value is used else a random value is generated.
func RequestID() web.Middleware {
lengthLimit := DefaultRequestIDLengthLimit
m := func(handler web.Handler) web.Handler {
h := func(ctx context.Context, w http.ResponseWriter, r *http.Request) error {
id := r.Header.Get(RequestIDHeader)
if id == "" {
id = fmt.Sprintf("%s-%d", reqPrefix, atomic.AddInt64(&reqID, 1))
} else if lengthLimit >= 0 && len(id) > lengthLimit {
id = id[:lengthLimit]
}
ctx = context.WithValue(ctx, reqIDKey, id)
return handler(ctx, w, r)
}
return h
}
return m
}
// ContextRequestID extracts the Request ID from the context.
func ContextRequestID(ctx context.Context) (reqID string) {
id := ctx.Value(reqIDKey)
if id != nil {
reqID = id.(string)
}
return
}