package bolt import ( "errors" "fmt" "hash/fnv" "log" "os" "runtime" "runtime/debug" "strings" "sync" "time" "unsafe" ) // The largest step that can be taken when remapping the mmap. const maxMmapStep = 1 << 30 // 1GB // The data file format version. const version = 2 // Represents a marker value to indicate that a file is a Bolt DB. const magic uint32 = 0xED0CDAED // IgnoreNoSync specifies whether the NoSync field of a DB is ignored when // syncing changes to a file. This is required as some operating systems, // such as OpenBSD, do not have a unified buffer cache (UBC) and writes // must be synchronized using the msync(2) syscall. const IgnoreNoSync = runtime.GOOS == "openbsd" // Default values if not set in a DB instance. const ( DefaultMaxBatchSize int = 1000 DefaultMaxBatchDelay = 10 * time.Millisecond DefaultAllocSize = 16 * 1024 * 1024 ) // default page size for db is set to the OS page size. var defaultPageSize = os.Getpagesize() // DB represents a collection of buckets persisted to a file on disk. // All data access is performed through transactions which can be obtained through the DB. // All the functions on DB will return a ErrDatabaseNotOpen if accessed before Open() is called. type DB struct { // When enabled, the database will perform a Check() after every commit. // A panic is issued if the database is in an inconsistent state. This // flag has a large performance impact so it should only be used for // debugging purposes. StrictMode bool // Setting the NoSync flag will cause the database to skip fsync() // calls after each commit. This can be useful when bulk loading data // into a database and you can restart the bulk load in the event of // a system failure or database corruption. Do not set this flag for // normal use. // // If the package global IgnoreNoSync constant is true, this value is // ignored. See the comment on that constant for more details. // // THIS IS UNSAFE. PLEASE USE WITH CAUTION. NoSync bool // When true, skips the truncate call when growing the database. // Setting this to true is only safe on non-ext3/ext4 systems. // Skipping truncation avoids preallocation of hard drive space and // bypasses a truncate() and fsync() syscall on remapping. // // https://github.com/boltdb/bolt/issues/284 NoGrowSync bool // If you want to read the entire database fast, you can set MmapFlag to // syscall.MAP_POPULATE on Linux 2.6.23+ for sequential read-ahead. MmapFlags int // MaxBatchSize is the maximum size of a batch. Default value is // copied from DefaultMaxBatchSize in Open. // // If <=0, disables batching. // // Do not change concurrently with calls to Batch. MaxBatchSize int // MaxBatchDelay is the maximum delay before a batch starts. // Default value is copied from DefaultMaxBatchDelay in Open. // // If <=0, effectively disables batching. // // Do not change concurrently with calls to Batch. MaxBatchDelay time.Duration // AllocSize is the amount of space allocated when the database // needs to create new pages. This is done to amortize the cost // of truncate() and fsync() when growing the data file. AllocSize int path string file *os.File lockfile *os.File // windows only dataref []byte // mmap'ed readonly, write throws SEGV data *[maxMapSize]byte datasz int filesz int // current on disk file size meta0 *meta meta1 *meta pageSize int opened bool rwtx *Tx txs []*Tx freelist *freelist stats Stats pagePool sync.Pool batchMu sync.Mutex batch *batch rwlock sync.Mutex // Allows only one writer at a time. metalock sync.Mutex // Protects meta page access. mmaplock sync.RWMutex // Protects mmap access during remapping. statlock sync.RWMutex // Protects stats access. ops struct { writeAt func(b []byte, off int64) (n int, err error) } // Read only mode. // When true, Update() and Begin(true) return ErrDatabaseReadOnly immediately. readOnly bool } // Path returns the path to currently open database file. func (db *DB) Path() string { return db.path } // GoString returns the Go string representation of the database. func (db *DB) GoString() string { return fmt.Sprintf("bolt.DB{path:%q}", db.path) } // String returns the string representation of the database. func (db *DB) String() string { return fmt.Sprintf("DB<%q>", db.path) } // Open creates and opens a database at the given path. // If the file does not exist then it will be created automatically. // Passing in nil options will cause Bolt to open the database with the default options. func Open(path string, mode os.FileMode, options *Options) (*DB, error) { var db = &DB{opened: true} // Set default options if no options are provided. if options == nil { options = DefaultOptions } db.NoGrowSync = options.NoGrowSync db.MmapFlags = options.MmapFlags // Set default values for later DB operations. db.MaxBatchSize = DefaultMaxBatchSize db.MaxBatchDelay = DefaultMaxBatchDelay db.AllocSize = DefaultAllocSize flag := os.O_RDWR if options.ReadOnly { flag = os.O_RDONLY db.readOnly = true } // Open data file and separate sync handler for metadata writes. db.path = path var err error if db.file, err = os.OpenFile(db.path, flag|os.O_CREATE, mode); err != nil { _ = db.close() return nil, err } // Lock file so that other processes using Bolt in read-write mode cannot // use the database at the same time. This would cause corruption since // the two processes would write meta pages and free pages separately. // The database file is locked exclusively (only one process can grab the lock) // if !options.ReadOnly. // The database file is locked using the shared lock (more than one process may // hold a lock at the same time) otherwise (options.ReadOnly is set). if err := flock(db, mode, !db.readOnly, options.Timeout); err != nil { _ = db.close() return nil, err } // Default values for test hooks db.ops.writeAt = db.file.WriteAt // Initialize the database if it doesn't exist. if info, err := db.file.Stat(); err != nil { return nil, err } else if info.Size() == 0 { // Initialize new files with meta pages. if err := db.init(); err != nil { return nil, err } } else { // Read the first meta page to determine the page size. var buf [0x1000]byte if _, err := db.file.ReadAt(buf[:], 0); err == nil { m := db.pageInBuffer(buf[:], 0).meta() if err := m.validate(); err != nil { // If we can't read the page size, we can assume it's the same // as the OS -- since that's how the page size was chosen in the // first place. // // If the first page is invalid and this OS uses a different // page size than what the database was created with then we // are out of luck and cannot access the database. db.pageSize = os.Getpagesize() } else { db.pageSize = int(m.pageSize) } } } // Initialize page pool. db.pagePool = sync.Pool{ New: func() interface{} { return make([]byte, db.pageSize) }, } // Memory map the data file. if err := db.mmap(options.InitialMmapSize); err != nil { _ = db.close() return nil, err } // Read in the freelist. db.freelist = newFreelist() db.freelist.read(db.page(db.meta().freelist)) // Mark the database as opened and return. return db, nil } // mmap opens the underlying memory-mapped file and initializes the meta references. // minsz is the minimum size that the new mmap can be. func (db *DB) mmap(minsz int) error { db.mmaplock.Lock() defer db.mmaplock.Unlock() info, err := db.file.Stat() if err != nil { return fmt.Errorf("mmap stat error: %s", err) } else if int(info.Size()) < db.pageSize*2 { return fmt.Errorf("file size too small") } // Ensure the size is at least the minimum size. var size = int(info.Size()) if size < minsz { size = minsz } size, err = db.mmapSize(size) if err != nil { return err } // Dereference all mmap references before unmapping. if db.rwtx != nil { db.rwtx.root.dereference() } // Unmap existing data before continuing. if err := db.munmap(); err != nil { return err } // Memory-map the data file as a byte slice. if err := mmap(db, size); err != nil { return err } // Save references to the meta pages. db.meta0 = db.page(0).meta() db.meta1 = db.page(1).meta() // Validate the meta pages. We only return an error if both meta pages fail // validation, since meta0 failing validation means that it wasn't saved // properly -- but we can recover using meta1. And vice-versa. err0 := db.meta0.validate() err1 := db.meta1.validate() if err0 != nil && err1 != nil { return err0 } return nil } // munmap unmaps the data file from memory. func (db *DB) munmap() error { if err := munmap(db); err != nil { return fmt.Errorf("unmap error: " + err.Error()) } return nil } // mmapSize determines the appropriate size for the mmap given the current size // of the database. The minimum size is 32KB and doubles until it reaches 1GB. // Returns an error if the new mmap size is greater than the max allowed. func (db *DB) mmapSize(size int) (int, error) { // Double the size from 32KB until 1GB. for i := uint(15); i <= 30; i++ { if size <= 1< maxMapSize { return 0, fmt.Errorf("mmap too large") } // If larger than 1GB then grow by 1GB at a time. sz := int64(size) if remainder := sz % int64(maxMmapStep); remainder > 0 { sz += int64(maxMmapStep) - remainder } // Ensure that the mmap size is a multiple of the page size. // This should always be true since we're incrementing in MBs. pageSize := int64(db.pageSize) if (sz % pageSize) != 0 { sz = ((sz / pageSize) + 1) * pageSize } // If we've exceeded the max size then only grow up to the max size. if sz > maxMapSize { sz = maxMapSize } return int(sz), nil } // init creates a new database file and initializes its meta pages. func (db *DB) init() error { // Set the page size to the OS page size. db.pageSize = os.Getpagesize() // Create two meta pages on a buffer. buf := make([]byte, db.pageSize*4) for i := 0; i < 2; i++ { p := db.pageInBuffer(buf[:], pgid(i)) p.id = pgid(i) p.flags = metaPageFlag // Initialize the meta page. m := p.meta() m.magic = magic m.version = version m.pageSize = uint32(db.pageSize) m.freelist = 2 m.root = bucket{root: 3} m.pgid = 4 m.txid = txid(i) m.checksum = m.sum64() } // Write an empty freelist at page 3. p := db.pageInBuffer(buf[:], pgid(2)) p.id = pgid(2) p.flags = freelistPageFlag p.count = 0 // Write an empty leaf page at page 4. p = db.pageInBuffer(buf[:], pgid(3)) p.id = pgid(3) p.flags = leafPageFlag p.count = 0 // Write the buffer to our data file. if _, err := db.ops.writeAt(buf, 0); err != nil { return err } if err := fdatasync(db); err != nil { return err } return nil } // Close releases all database resources. // All transactions must be closed before closing the database. func (db *DB) Close() error { db.rwlock.Lock() defer db.rwlock.Unlock() db.metalock.Lock() defer db.metalock.Unlock() db.mmaplock.RLock() defer db.mmaplock.RUnlock() return db.close() } func (db *DB) close() error { if !db.opened { return nil } db.opened = false db.freelist = nil // Clear ops. db.ops.writeAt = nil // Close the mmap. if err := db.munmap(); err != nil { return err } // Close file handles. if db.file != nil { // No need to unlock read-only file. if !db.readOnly { // Unlock the file. if err := funlock(db); err != nil { log.Printf("bolt.Close(): funlock error: %s", err) } } // Close the file descriptor. if err := db.file.Close(); err != nil { return fmt.Errorf("db file close: %s", err) } db.file = nil } db.path = "" return nil } // Begin starts a new transaction. // Multiple read-only transactions can be used concurrently but only one // write transaction can be used at a time. Starting multiple write transactions // will cause the calls to block and be serialized until the current write // transaction finishes. // // Transactions should not be dependent on one another. Opening a read // transaction and a write transaction in the same goroutine can cause the // writer to deadlock because the database periodically needs to re-mmap itself // as it grows and it cannot do that while a read transaction is open. // // If a long running read transaction (for example, a snapshot transaction) is // needed, you might want to set DB.InitialMmapSize to a large enough value // to avoid potential blocking of write transaction. // // IMPORTANT: You must close read-only transactions after you are finished or // else the database will not reclaim old pages. func (db *DB) Begin(writable bool) (*Tx, error) { if writable { return db.beginRWTx() } return db.beginTx() } func (db *DB) beginTx() (*Tx, error) { // Lock the meta pages while we initialize the transaction. We obtain // the meta lock before the mmap lock because that's the order that the // write transaction will obtain them. db.metalock.Lock() // Obtain a read-only lock on the mmap. When the mmap is remapped it will // obtain a write lock so all transactions must finish before it can be // remapped. db.mmaplock.RLock() // Exit if the database is not open yet. if !db.opened { db.mmaplock.RUnlock() db.metalock.Unlock() return nil, ErrDatabaseNotOpen } // Create a transaction associated with the database. t := &Tx{} t.init(db) // Keep track of transaction until it closes. db.txs = append(db.txs, t) n := len(db.txs) // Unlock the meta pages. db.metalock.Unlock() // Update the transaction stats. db.statlock.Lock() db.stats.TxN++ db.stats.OpenTxN = n db.statlock.Unlock() return t, nil } func (db *DB) beginRWTx() (*Tx, error) { // If the database was opened with Options.ReadOnly, return an error. if db.readOnly { return nil, ErrDatabaseReadOnly } // Obtain writer lock. This is released by the transaction when it closes. // This enforces only one writer transaction at a time. db.rwlock.Lock() // Once we have the writer lock then we can lock the meta pages so that // we can set up the transaction. db.metalock.Lock() defer db.metalock.Unlock() // Exit if the database is not open yet. if !db.opened { db.rwlock.Unlock() return nil, ErrDatabaseNotOpen } // Create a transaction associated with the database. t := &Tx{writable: true} t.init(db) db.rwtx = t // Free any pages associated with closed read-only transactions. var minid txid = 0xFFFFFFFFFFFFFFFF for _, t := range db.txs { if t.meta.txid < minid { minid = t.meta.txid } } if minid > 0 { db.freelist.release(minid - 1) } return t, nil } // removeTx removes a transaction from the database. func (db *DB) removeTx(tx *Tx) { // Release the read lock on the mmap. db.mmaplock.RUnlock() // Use the meta lock to restrict access to the DB object. db.metalock.Lock() // Remove the transaction. for i, t := range db.txs { if t == tx { db.txs = append(db.txs[:i], db.txs[i+1:]...) break } } n := len(db.txs) // Unlock the meta pages. db.metalock.Unlock() // Merge statistics. db.statlock.Lock() db.stats.OpenTxN = n db.stats.TxStats.add(&tx.stats) db.statlock.Unlock() } // Update executes a function within the context of a read-write managed transaction. // If no error is returned from the function then the transaction is committed. // If an error is returned then the entire transaction is rolled back. // Any error that is returned from the function or returned from the commit is // returned from the Update() method. // // Attempting to manually commit or rollback within the function will cause a panic. func (db *DB) Update(fn func(*Tx) error) error { t, err := db.Begin(true) if err != nil { return err } // Make sure the transaction rolls back in the event of a panic. defer func() { if t.db != nil { t.rollback() } }() // Mark as a managed tx so that the inner function cannot manually commit. t.managed = true // If an error is returned from the function then rollback and return error. err = fn(t) t.managed = false if err != nil { _ = t.Rollback() return err } return t.Commit() } // View executes a function within the context of a managed read-only transaction. // Any error that is returned from the function is returned from the View() method. // // Attempting to manually rollback within the function will cause a panic. func (db *DB) View(fn func(*Tx) error) error { t, err := db.Begin(false) if err != nil { return err } // Make sure the transaction rolls back in the event of a panic. defer func() { if t.db != nil { t.rollback() } }() // Mark as a managed tx so that the inner function cannot manually rollback. t.managed = true // If an error is returned from the function then pass it through. err = fn(t) t.managed = false if err != nil { _ = t.Rollback() return err } if err := t.Rollback(); err != nil { return err } return nil } // Batch calls fn as part of a batch. It behaves similar to Update, // except: // // 1. concurrent Batch calls can be combined into a single Bolt // transaction. // // 2. the function passed to Batch may be called multiple times, // regardless of whether it returns error or not. // // This means that Batch function side effects must be idempotent and // take permanent effect only after a successful return is seen in // caller. // // The maximum batch size and delay can be adjusted with DB.MaxBatchSize // and DB.MaxBatchDelay, respectively. // // Batch is only useful when there are multiple goroutines calling it. func (db *DB) Batch(fn func(*Tx) error) error { errCh := make(chan error, 1) db.batchMu.Lock() if (db.batch == nil) || (db.batch != nil && len(db.batch.calls) >= db.MaxBatchSize) { // There is no existing batch, or the existing batch is full; start a new one. db.batch = &batch{ db: db, } db.batch.timer = time.AfterFunc(db.MaxBatchDelay, db.batch.trigger) } db.batch.calls = append(db.batch.calls, call{fn: fn, err: errCh}) if len(db.batch.calls) >= db.MaxBatchSize { // wake up batch, it's ready to run go db.batch.trigger() } db.batchMu.Unlock() err := <-errCh if err == trySolo { err = db.Update(fn) } return err } type call struct { fn func(*Tx) error err chan<- error } type batch struct { db *DB timer *time.Timer start sync.Once calls []call } // trigger runs the batch if it hasn't already been run. func (b *batch) trigger() { b.start.Do(b.run) } // run performs the transactions in the batch and communicates results // back to DB.Batch. func (b *batch) run() { b.db.batchMu.Lock() b.timer.Stop() // Make sure no new work is added to this batch, but don't break // other batches. if b.db.batch == b { b.db.batch = nil } b.db.batchMu.Unlock() retry: for len(b.calls) > 0 { var failIdx = -1 err := b.db.Update(func(tx *Tx) error { for i, c := range b.calls { if err := safelyCall(c.fn, tx); err != nil { failIdx = i return err } } return nil }) if failIdx >= 0 { // take the failing transaction out of the batch. it's // safe to shorten b.calls here because db.batch no longer // points to us, and we hold the mutex anyway. c := b.calls[failIdx] b.calls[failIdx], b.calls = b.calls[len(b.calls)-1], b.calls[:len(b.calls)-1] // tell the submitter re-run it solo, continue with the rest of the batch c.err <- trySolo continue retry } // pass success, or bolt internal errors, to all callers for _, c := range b.calls { if c.err != nil { c.err <- err } } break retry } } // trySolo is a special sentinel error value used for signaling that a // transaction function should be re-run. It should never be seen by // callers. var trySolo = errors.New("batch function returned an error and should be re-run solo") type panicked struct { reason interface{} } func (p panicked) Error() string { if err, ok := p.reason.(error); ok { return err.Error() } return fmt.Sprintf("panic: %v", p.reason) } func safelyCall(fn func(*Tx) error, tx *Tx) (err error) { defer func() { if p := recover(); p != nil { err = panicked{p} } }() return fn(tx) } // Sync executes fdatasync() against the database file handle. // // This is not necessary under normal operation, however, if you use NoSync // then it allows you to force the database file to sync against the disk. func (db *DB) Sync() error { return fdatasync(db) } // Stats retrieves ongoing performance stats for the database. // This is only updated when a transaction closes. func (db *DB) Stats() Stats { db.statlock.RLock() defer db.statlock.RUnlock() return db.stats } // This is for internal access to the raw data bytes from the C cursor, use // carefully, or not at all. func (db *DB) Info() *Info { return &Info{uintptr(unsafe.Pointer(&db.data[0])), db.pageSize} } // page retrieves a page reference from the mmap based on the current page size. func (db *DB) page(id pgid) *page { pos := id * pgid(db.pageSize) return (*page)(unsafe.Pointer(&db.data[pos])) } // pageInBuffer retrieves a page reference from a given byte array based on the current page size. func (db *DB) pageInBuffer(b []byte, id pgid) *page { return (*page)(unsafe.Pointer(&b[id*pgid(db.pageSize)])) } // meta retrieves the current meta page reference. func (db *DB) meta() *meta { // We have to return the meta with the highest txid which doesn't fail // validation. Otherwise, we can cause errors when in fact the database is // in a consistent state. metaA is the one with the higher txid. metaA := db.meta0 metaB := db.meta1 if db.meta1.txid > db.meta0.txid { metaA = db.meta1 metaB = db.meta0 } // Use higher meta page if valid. Otherwise fallback to previous, if valid. if err := metaA.validate(); err == nil { return metaA } else if err := metaB.validate(); err == nil { return metaB } // This should never be reached, because both meta1 and meta0 were validated // on mmap() and we do fsync() on every write. panic("bolt.DB.meta(): invalid meta pages") } // allocate returns a contiguous block of memory starting at a given page. func (db *DB) allocate(count int) (*page, error) { // Allocate a temporary buffer for the page. var buf []byte if count == 1 { buf = db.pagePool.Get().([]byte) } else { buf = make([]byte, count*db.pageSize) } p := (*page)(unsafe.Pointer(&buf[0])) p.overflow = uint32(count - 1) // Use pages from the freelist if they are available. if p.id = db.freelist.allocate(count); p.id != 0 { return p, nil } // Resize mmap() if we're at the end. p.id = db.rwtx.meta.pgid var minsz = int((p.id+pgid(count))+1) * db.pageSize if minsz >= db.datasz { if err := db.mmap(minsz); err != nil { return nil, fmt.Errorf("mmap allocate error: %s", err) } } // Move the page id high water mark. db.rwtx.meta.pgid += pgid(count) return p, nil } // grow grows the size of the database to the given sz. func (db *DB) grow(sz int) error { // Ignore if the new size is less than available file size. if sz <= db.filesz { return nil } // If the data is smaller than the alloc size then only allocate what's needed. // Once it goes over the allocation size then allocate in chunks. if db.datasz < db.AllocSize { sz = db.datasz } else { sz += db.AllocSize } // Truncate and fsync to ensure file size metadata is flushed. // https://github.com/boltdb/bolt/issues/284 if !db.NoGrowSync && !db.readOnly { if runtime.GOOS != "windows" { if err := db.file.Truncate(int64(sz)); err != nil { return fmt.Errorf("file resize error: %s", err) } } if err := db.file.Sync(); err != nil { return fmt.Errorf("file sync error: %s", err) } } db.filesz = sz return nil } func (db *DB) IsReadOnly() bool { return db.readOnly } // Options represents the options that can be set when opening a database. type Options struct { // Timeout is the amount of time to wait to obtain a file lock. // When set to zero it will wait indefinitely. This option is only // available on Darwin and Linux. Timeout time.Duration // Sets the DB.NoGrowSync flag before memory mapping the file. NoGrowSync bool // Open database in read-only mode. Uses flock(..., LOCK_SH |LOCK_NB) to // grab a shared lock (UNIX). ReadOnly bool // Sets the DB.MmapFlags flag before memory mapping the file. MmapFlags int // InitialMmapSize is the initial mmap size of the database // in bytes. Read transactions won't block write transaction // if the InitialMmapSize is large enough to hold database mmap // size. (See DB.Begin for more information) // // If <=0, the initial map size is 0. // If initialMmapSize is smaller than the previous database size, // it takes no effect. InitialMmapSize int } // DefaultOptions represent the options used if nil options are passed into Open(). // No timeout is used which will cause Bolt to wait indefinitely for a lock. var DefaultOptions = &Options{ Timeout: 0, NoGrowSync: false, } // Stats represents statistics about the database. type Stats struct { // Freelist stats FreePageN int // total number of free pages on the freelist PendingPageN int // total number of pending pages on the freelist FreeAlloc int // total bytes allocated in free pages FreelistInuse int // total bytes used by the freelist // Transaction stats TxN int // total number of started read transactions OpenTxN int // number of currently open read transactions TxStats TxStats // global, ongoing stats. } // Sub calculates and returns the difference between two sets of database stats. // This is useful when obtaining stats at two different points and time and // you need the performance counters that occurred within that time span. func (s *Stats) Sub(other *Stats) Stats { if other == nil { return *s } var diff Stats diff.FreePageN = s.FreePageN diff.PendingPageN = s.PendingPageN diff.FreeAlloc = s.FreeAlloc diff.FreelistInuse = s.FreelistInuse diff.TxN = other.TxN - s.TxN diff.TxStats = s.TxStats.Sub(&other.TxStats) return diff } func (s *Stats) add(other *Stats) { s.TxStats.add(&other.TxStats) } type Info struct { Data uintptr PageSize int } type meta struct { magic uint32 version uint32 pageSize uint32 flags uint32 root bucket freelist pgid pgid pgid txid txid checksum uint64 } // validate checks the marker bytes and version of the meta page to ensure it matches this binary. func (m *meta) validate() error { if m.magic != magic { return ErrInvalid } else if m.version != version { return ErrVersionMismatch } else if m.checksum != 0 && m.checksum != m.sum64() { return ErrChecksum } return nil } // copy copies one meta object to another. func (m *meta) copy(dest *meta) { *dest = *m } // write writes the meta onto a page. func (m *meta) write(p *page) { if m.root.root >= m.pgid { panic(fmt.Sprintf("root bucket pgid (%d) above high water mark (%d)", m.root.root, m.pgid)) } else if m.freelist >= m.pgid { panic(fmt.Sprintf("freelist pgid (%d) above high water mark (%d)", m.freelist, m.pgid)) } // Page id is either going to be 0 or 1 which we can determine by the transaction ID. p.id = pgid(m.txid % 2) p.flags |= metaPageFlag // Calculate the checksum. m.checksum = m.sum64() m.copy(p.meta()) } // generates the checksum for the meta. func (m *meta) sum64() uint64 { var h = fnv.New64a() _, _ = h.Write((*[unsafe.Offsetof(meta{}.checksum)]byte)(unsafe.Pointer(m))[:]) return h.Sum64() } // _assert will panic with a given formatted message if the given condition is false. func _assert(condition bool, msg string, v ...interface{}) { if !condition { panic(fmt.Sprintf("assertion failed: "+msg, v...)) } } func warn(v ...interface{}) { fmt.Fprintln(os.Stderr, v...) } func warnf(msg string, v ...interface{}) { fmt.Fprintf(os.Stderr, msg+"\n", v...) } func printstack() { stack := strings.Join(strings.Split(string(debug.Stack()), "\n")[2:], "\n") fmt.Fprintln(os.Stderr, stack) }