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package gcp
import (
"context"
"fmt"
"io"
"log/slog"
"net"
"net/http"
"os"
"runtime"
"strings"
"sync"
"time"
)
func insideTest() bool {
// Ask runtime.Callers for up to 10 PCs, including runtime.Callers itself.
pc := make([]uintptr, 10)
n := runtime.Callers(0, pc)
if n == 0 {
slog.Debug("WithCloudTraceContext: no PCs available")
return true
}
frames := runtime.CallersFrames(pc[:n])
for {
frame, more := frames.Next()
if !more {
break
}
if strings.HasPrefix(frame.Function, "testing.") &&
strings.HasSuffix(frame.File, "src/testing/testing.go") {
slog.Debug("WithCloudTraceContext: inside test", "function", frame.Function, "file", frame.File, "line", frame.Line)
return true
}
}
return false
}
var (
projectID string
lookupOnce sync.Once
)
// WithCloudTraceContext returns an http.handler that adds the GCP Cloud Trace
// ID to the context. This is used to correlate the structured logs with the
// request log.
func WithCloudTraceContext(h http.Handler) http.Handler {
// Get the project ID from the environment if specified
fromEnv := os.Getenv("GOOGLE_CLOUD_PROJECT")
if fromEnv != "" {
projectID = fromEnv
} else {
lookupOnce.Do(func() {
if insideTest() {
slog.Debug("WithCloudTraceContext: inside test, not looking up project ID")
return
}
// By default use the metadata IP; otherwise use the environment variable
// for consistency with https://pkg.go.dev/cloud.google.com/go/compute/metadata#Client.Get
host := "169.254.169.254"
if h := os.Getenv("GCE_METADATA_HOST"); h != "" {
host = h
}
req, err := http.NewRequest(http.MethodGet, fmt.Sprintf("http://%s/computeMetadata/v1/project/project-id", host), nil)
if err != nil {
slog.Debug("WithCloudTraceContext: could not get GCP project ID from metadata server", "err", err)
return
}
req.Header.Set("Metadata-Flavor", "Google")
resp, err := (&http.Client{ // Timeouts copied from https://pkg.go.dev/cloud.google.com/go/compute/metadata#Get
Transport: &http.Transport{
Dial: (&net.Dialer{Timeout: 2 * time.Second}).Dial,
},
Timeout: 5 * time.Second,
}).Do(req)
if err != nil {
slog.Debug("WithCloudTraceContext: could not get GCP project ID from metadata server", "err", err)
return
}
if resp.StatusCode != http.StatusOK {
slog.Debug("WithCloudTraceContext: could not get GCP project ID from metadata server", "code", resp.StatusCode, "status", resp.Status)
return
}
defer resp.Body.Close()
all, err := io.ReadAll(resp.Body)
if err != nil {
slog.Debug("WithCloudTraceContext: could not get GCP project ID from metadata server", "err", err)
return
}
projectID = string(all)
})
}
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
if projectID != "" {
var trace string
traceHeader := r.Header.Get("traceparent")
traceID := parseTraceFromW3CHeader(traceHeader)
if traceID != "" {
trace = fmt.Sprintf("projects/%s/traces/%s", projectID, traceID)
}
r = r.WithContext(context.WithValue(r.Context(), "trace", trace))
}
h.ServeHTTP(w, r)
})
}
func traceFromContext(ctx context.Context) string {
trace := ctx.Value("trace")
if trace == nil {
return ""
}
return trace.(string)
}
func parseTraceFromW3CHeader(traceparent string) string {
traceParts := strings.Split(traceparent, "-")
if len(traceParts) > 1 {
return traceParts[1]
}
return ""
}
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