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// Copyright (c) 2023 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
// Package stacktrace provides support for gathering stack traces
// efficiently.
package stacktrace
import (
"runtime"
"go.uber.org/zap/buffer"
"go.uber.org/zap/internal/bufferpool"
"go.uber.org/zap/internal/pool"
)
var _stackPool = pool.New(func() *Stack {
return &Stack{
storage: make([]uintptr, 64),
}
})
// Stack is a captured stack trace.
type Stack struct {
pcs []uintptr // program counters; always a subslice of storage
frames *runtime.Frames
// The size of pcs varies depending on requirements:
// it will be one if the only the first frame was requested,
// and otherwise it will reflect the depth of the call stack.
//
// storage decouples the slice we need (pcs) from the slice we pool.
// We will always allocate a reasonably large storage, but we'll use
// only as much of it as we need.
storage []uintptr
}
// Depth specifies how deep of a stack trace should be captured.
type Depth int
const (
// First captures only the first frame.
First Depth = iota
// Full captures the entire call stack, allocating more
// storage for it if needed.
Full
)
// Capture captures a stack trace of the specified depth, skipping
// the provided number of frames. skip=0 identifies the caller of
// Capture.
//
// The caller must call Free on the returned stacktrace after using it.
func Capture(skip int, depth Depth) *Stack {
stack := _stackPool.Get()
switch depth {
case First:
stack.pcs = stack.storage[:1]
case Full:
stack.pcs = stack.storage
}
// Unlike other "skip"-based APIs, skip=0 identifies runtime.Callers
// itself. +2 to skip captureStacktrace and runtime.Callers.
numFrames := runtime.Callers(
skip+2,
stack.pcs,
)
// runtime.Callers truncates the recorded stacktrace if there is no
// room in the provided slice. For the full stack trace, keep expanding
// storage until there are fewer frames than there is room.
if depth == Full {
pcs := stack.pcs
for numFrames == len(pcs) {
pcs = make([]uintptr, len(pcs)*2)
numFrames = runtime.Callers(skip+2, pcs)
}
// Discard old storage instead of returning it to the pool.
// This will adjust the pool size over time if stack traces are
// consistently very deep.
stack.storage = pcs
stack.pcs = pcs[:numFrames]
} else {
stack.pcs = stack.pcs[:numFrames]
}
stack.frames = runtime.CallersFrames(stack.pcs)
return stack
}
// Free releases resources associated with this stacktrace
// and returns it back to the pool.
func (st *Stack) Free() {
st.frames = nil
st.pcs = nil
_stackPool.Put(st)
}
// Count reports the total number of frames in this stacktrace.
// Count DOES NOT change as Next is called.
func (st *Stack) Count() int {
return len(st.pcs)
}
// Next returns the next frame in the stack trace,
// and a boolean indicating whether there are more after it.
func (st *Stack) Next() (_ runtime.Frame, more bool) {
return st.frames.Next()
}
// Take returns a string representation of the current stacktrace.
//
// skip is the number of frames to skip before recording the stack trace.
// skip=0 identifies the caller of Take.
func Take(skip int) string {
stack := Capture(skip+1, Full)
defer stack.Free()
buffer := bufferpool.Get()
defer buffer.Free()
stackfmt := NewFormatter(buffer)
stackfmt.FormatStack(stack)
return buffer.String()
}
// Formatter formats a stack trace into a readable string representation.
type Formatter struct {
b *buffer.Buffer
nonEmpty bool // whehther we've written at least one frame already
}
// NewFormatter builds a new Formatter.
func NewFormatter(b *buffer.Buffer) Formatter {
return Formatter{b: b}
}
// FormatStack formats all remaining frames in the provided stacktrace -- minus
// the final runtime.main/runtime.goexit frame.
func (sf *Formatter) FormatStack(stack *Stack) {
// Note: On the last iteration, frames.Next() returns false, with a valid
// frame, but we ignore this frame. The last frame is a runtime frame which
// adds noise, since it's only either runtime.main or runtime.goexit.
for frame, more := stack.Next(); more; frame, more = stack.Next() {
sf.FormatFrame(frame)
}
}
// FormatFrame formats the given frame.
func (sf *Formatter) FormatFrame(frame runtime.Frame) {
if sf.nonEmpty {
sf.b.AppendByte('\n')
}
sf.nonEmpty = true
sf.b.AppendString(frame.Function)
sf.b.AppendByte('\n')
sf.b.AppendByte('\t')
sf.b.AppendString(frame.File)
sf.b.AppendByte(':')
sf.b.AppendInt(int64(frame.Line))
}
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