logtree: implement LeveledLogger interface
This implementes the equivalent of StructuredLogger from go/logtree as
a pure interface for further implementation by LogTree (or other logging
mechanism, eg. in tests).
StructuredLogger was a slightly poor name (because of the unfortunate
industry understanding of what structured logging is), so we go ahead
and rename that. Once this change goes through, the design document will
be reflected to rename 'Structured Logging' to 'Leveled Logging'.
We base the API off of github.com/golang/glog, but without a single
global instance. Other API differences include:
- No {Info,Warning,Error,Fatal}ln calls, as these are pretty much
equivalent to {Info,Warning,Error,Fatal} calls.
- V(n) now returns an interface with .Enabled(), instead of a boolean
value. This is necessary as the returned value will have to carry
its corresponding LeveledLogger instead of calling global functions.
Test Plan: plain interface, untested
X-Origin-Diff: phab/D620
GitOrigin-RevId: 06c7e3a88751ff7503e8106fac2360cf8de621c4
diff --git a/core/pkg/logtree/BUILD.bazel b/core/pkg/logtree/BUILD.bazel
new file mode 100644
index 0000000..c3d1bd8
--- /dev/null
+++ b/core/pkg/logtree/BUILD.bazel
@@ -0,0 +1,8 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+ name = "go_default_library",
+ srcs = ["leveled.go"],
+ importpath = "git.monogon.dev/source/nexantic.git/core/pkg/logtree",
+ visibility = ["//visibility:public"],
+)
diff --git a/core/pkg/logtree/leveled.go b/core/pkg/logtree/leveled.go
new file mode 100644
index 0000000..7e93d24
--- /dev/null
+++ b/core/pkg/logtree/leveled.go
@@ -0,0 +1,78 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package logtree
+
+// LeveledLogger is a generic interface for glog-style logging. There are four hardcoded log severities, in increasing
+// order: INFO, WARNING, ERROR, FATAL. Logging at a certain severity level logs not only to consumers expecting data
+// at that severity level, but also all lower severity levels. For example, an ERROR log will also be passed to
+// consumers looking at INFO or WARNING logs.
+type LeveledLogger interface {
+ // Info logs at the INFO severity. Arguments are handled in the manner of fmt.Print, a terminating newline is added
+ // if missing.
+ Info(args ...interface{})
+ // Infof logs at the INFO severity. Arguments are handled in the manner of fmt.Printf, a terminating newline is
+ // added if missing.
+ Infof(format string, args ...interface{})
+
+ // Warning logs at the WARNING severity. Arguments are handled in the manner of fmt.Print, a terminating newline is
+ // added if missing.
+ Warning(args ...interface{})
+ // Warningf logs at the WARNING severity. Arguments are handled in the manner of fmt.Printf, a terminating newline
+ // is added if missing.
+ Warningf(format string, args ...interface{})
+
+ // Error logs at the ERROR severity. Arguments are handled in the manner of fmt.Print, a terminating newline is
+ // added if missing.
+ Error(args ...interface{})
+ // Errorf logs at the ERROR severity. Arguments are handled in the manner of fmt.Printf, a terminating newline is
+ // added if missing.
+ Errorf(format string, args ...interface{})
+
+ // Fatal logs at the FATAL severity and aborts the current program. Arguments are handled in the manner of
+ // fmt.Print, a terminating newline is added if missing.
+ Fatal(args ...interface{})
+ // Fatalf logs at the FATAL severity and aborts the current program. Arguments are handled in the manner of
+ // fmt.Printf, a terminating newline is added if missing.
+ Fatalf(format string, args ...interface{})
+
+ // V returns a VerboseLeveledLogger at a given verbosity level. These verbosity levels can be dynamically set and
+ // unset on a package-granular level by consumers of the LeveledLogger logs. The returned value represents whether
+ // logging at the given verbosity level was active at that time, and as such should not be a long-lived object
+ // in programs.
+ // This construct is further refered to as 'V-logs'.
+ V(level VerbosityLevel) VerboseLeveledLogger
+}
+
+// VerbosityLevel is a verbosity level defined for V-logs. This can be changed programmatically per Go package. When
+// logging at a given VerbosityLevel V, the current level must be equal or higher to V for the logs to be recorded.
+// Conversely, enabling a V-logging at a VerbosityLevel V also enables all logging at lower levels [Int32Min .. (V-1)].
+type VerbosityLevel int32
+
+type VerboseLeveledLogger interface {
+ // Enabled returns if this level was enabled. If not enabled, all logging into this logger will be discarded
+ // immediately.
+ // Thus, Enabled() can be used to check the verbosity level before performing any logging:
+ // if l.V(3).Enabled() { l.Info("V3 is enabled") }
+ // or, in simple cases, the convenience function .Info can be used:
+ // l.V(3).Info("V3 is enabled")
+ // The second form is shorter and more convenient, but more expensive, as its arguments are always evaluated.
+ Enabled() bool
+ // Info is the equivalent of a LeveledLogger's Info call, guarded by whether this VerboseLeveledLogger is enabled.
+ Info(args ...interface{})
+ // Infof is the equivalent of a LeveledLogger's Infof call, guarded by whether this VerboseLeveledLogger is enabled.
+ Infof(format string, args ...interface{})
+}