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