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Diffstat (limited to 'vendor/github.com/docker/distribution/context/doc.go')
| -rw-r--r-- | vendor/github.com/docker/distribution/context/doc.go | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/vendor/github.com/docker/distribution/context/doc.go b/vendor/github.com/docker/distribution/context/doc.go new file mode 100644 index 000000000..9b623074e --- /dev/null +++ b/vendor/github.com/docker/distribution/context/doc.go @@ -0,0 +1,89 @@ +// Package context provides several utilities for working with +// golang.org/x/net/context in http requests. Primarily, the focus is on +// logging relevant request information but this package is not limited to +// that purpose. +// +// The easiest way to get started is to get the background context: +// +// ctx := context.Background() +// +// The returned context should be passed around your application and be the +// root of all other context instances. If the application has a version, this +// line should be called before anything else: +// +// ctx := context.WithVersion(context.Background(), version) +// +// The above will store the version in the context and will be available to +// the logger. +// +// Logging +// +// The most useful aspect of this package is GetLogger. This function takes +// any context.Context interface and returns the current logger from the +// context. Canonical usage looks like this: +// +// GetLogger(ctx).Infof("something interesting happened") +// +// GetLogger also takes optional key arguments. The keys will be looked up in +// the context and reported with the logger. The following example would +// return a logger that prints the version with each log message: +// +// ctx := context.Context(context.Background(), "version", version) +// GetLogger(ctx, "version").Infof("this log message has a version field") +// +// The above would print out a log message like this: +// +// INFO[0000] this log message has a version field version=v2.0.0-alpha.2.m +// +// When used with WithLogger, we gain the ability to decorate the context with +// loggers that have information from disparate parts of the call stack. +// Following from the version example, we can build a new context with the +// configured logger such that we always print the version field: +// +// ctx = WithLogger(ctx, GetLogger(ctx, "version")) +// +// Since the logger has been pushed to the context, we can now get the version +// field for free with our log messages. Future calls to GetLogger on the new +// context will have the version field: +// +// GetLogger(ctx).Infof("this log message has a version field") +// +// This becomes more powerful when we start stacking loggers. Let's say we +// have the version logger from above but also want a request id. Using the +// context above, in our request scoped function, we place another logger in +// the context: +// +// ctx = context.WithValue(ctx, "http.request.id", "unique id") // called when building request context +// ctx = WithLogger(ctx, GetLogger(ctx, "http.request.id")) +// +// When GetLogger is called on the new context, "http.request.id" will be +// included as a logger field, along with the original "version" field: +// +// INFO[0000] this log message has a version field http.request.id=unique id version=v2.0.0-alpha.2.m +// +// Note that this only affects the new context, the previous context, with the +// version field, can be used independently. Put another way, the new logger, +// added to the request context, is unique to that context and can have +// request scoped variables. +// +// HTTP Requests +// +// This package also contains several methods for working with http requests. +// The concepts are very similar to those described above. We simply place the +// request in the context using WithRequest. This makes the request variables +// available. GetRequestLogger can then be called to get request specific +// variables in a log line: +// +// ctx = WithRequest(ctx, req) +// GetRequestLogger(ctx).Infof("request variables") +// +// Like above, if we want to include the request data in all log messages in +// the context, we push the logger to a new context and use that one: +// +// ctx = WithLogger(ctx, GetRequestLogger(ctx)) +// +// The concept is fairly powerful and ensures that calls throughout the stack +// can be traced in log messages. Using the fields like "http.request.id", one +// can analyze call flow for a particular request with a simple grep of the +// logs. +package context |