105 lines
2.8 KiB
Go
105 lines
2.8 KiB
Go
package context
|
|
|
|
import (
|
|
"context"
|
|
"runtime"
|
|
"time"
|
|
|
|
"github.com/docker/distribution/uuid"
|
|
)
|
|
|
|
// WithTrace allocates a traced timing span in a new context. This allows a
|
|
// caller to track the time between calling WithTrace and the returned done
|
|
// function. When the done function is called, a log message is emitted with a
|
|
// "trace.duration" field, corresponding to the elapsed time and a
|
|
// "trace.func" field, corresponding to the function that called WithTrace.
|
|
//
|
|
// The logging keys "trace.id" and "trace.parent.id" are provided to implement
|
|
// dapper-like tracing. This function should be complemented with a WithSpan
|
|
// method that could be used for tracing distributed RPC calls.
|
|
//
|
|
// The main benefit of this function is to post-process log messages or
|
|
// intercept them in a hook to provide timing data. Trace ids and parent ids
|
|
// can also be linked to provide call tracing, if so required.
|
|
//
|
|
// Here is an example of the usage:
|
|
//
|
|
// func timedOperation(ctx Context) {
|
|
// ctx, done := WithTrace(ctx)
|
|
// defer done("this will be the log message")
|
|
// // ... function body ...
|
|
// }
|
|
//
|
|
// If the function ran for roughly 1s, such a usage would emit a log message
|
|
// as follows:
|
|
//
|
|
// INFO[0001] this will be the log message trace.duration=1.004575763s trace.func=github.com/docker/distribution/context.traceOperation trace.id=<id> ...
|
|
//
|
|
// Notice that the function name is automatically resolved, along with the
|
|
// package and a trace id is emitted that can be linked with parent ids.
|
|
func WithTrace(ctx context.Context) (context.Context, func(format string, a ...interface{})) {
|
|
if ctx == nil {
|
|
ctx = Background()
|
|
}
|
|
|
|
pc, file, line, _ := runtime.Caller(1)
|
|
f := runtime.FuncForPC(pc)
|
|
ctx = &traced{
|
|
Context: ctx,
|
|
id: uuid.Generate().String(),
|
|
start: time.Now(),
|
|
parent: GetStringValue(ctx, "trace.id"),
|
|
fnname: f.Name(),
|
|
file: file,
|
|
line: line,
|
|
}
|
|
|
|
return ctx, func(format string, a ...interface{}) {
|
|
GetLogger(ctx,
|
|
"trace.duration",
|
|
"trace.id",
|
|
"trace.parent.id",
|
|
"trace.func",
|
|
"trace.file",
|
|
"trace.line").
|
|
Debugf(format, a...)
|
|
}
|
|
}
|
|
|
|
// traced represents a context that is traced for function call timing. It
|
|
// also provides fast lookup for the various attributes that are available on
|
|
// the trace.
|
|
type traced struct {
|
|
context.Context
|
|
id string
|
|
parent string
|
|
start time.Time
|
|
fnname string
|
|
file string
|
|
line int
|
|
}
|
|
|
|
func (ts *traced) Value(key interface{}) interface{} {
|
|
switch key {
|
|
case "trace.start":
|
|
return ts.start
|
|
case "trace.duration":
|
|
return time.Since(ts.start)
|
|
case "trace.id":
|
|
return ts.id
|
|
case "trace.parent.id":
|
|
if ts.parent == "" {
|
|
return nil // must return nil to signal no parent.
|
|
}
|
|
|
|
return ts.parent
|
|
case "trace.func":
|
|
return ts.fnname
|
|
case "trace.file":
|
|
return ts.file
|
|
case "trace.line":
|
|
return ts.line
|
|
}
|
|
|
|
return ts.Context.Value(key)
|
|
}
|