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<div class="container">
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<h1>Package journal</h1>
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<div id="nav"></div>
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<!--
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Copyright 2009 The Go Authors. All rights reserved.
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Use of this source code is governed by a BSD-style
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license that can be found in the LICENSE file.
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-->
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<!--
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Note: Static (i.e., not template-generated) href and id
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attributes start with "pkg-" to make it impossible for
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correspond to Go identifiers).
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document.CALLGRAPH = null;
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</script>
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<div id="short-nav">
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<dl>
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<dd><code>import "github.com/syndtr/goleveldb/leveldb/journal"</code></dd>
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</dl>
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<dl>
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<dd><a href="index.html#pkg-overview" class="overviewLink">Overview</a></dd>
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<dd><a href="index.html#pkg-index" class="indexLink">Index</a></dd>
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</dl>
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</div>
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<!-- The package's Name is printed as title by the top-level template -->
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<div class="collapsed">
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<h2 class="toggleButton" title="Click to show Overview section">Overview ▹</h2>
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</div>
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<div class="expanded">
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<h2 class="toggleButton" title="Click to hide Overview section">Overview ▾</h2>
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<p>
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Package journal reads and writes sequences of journals. Each journal is a stream
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of bytes that completes before the next journal starts.
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</p>
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<p>
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When reading, call Next to obtain an io.Reader for the next journal. Next will
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return io.EOF when there are no more journals. It is valid to call Next
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without reading the current journal to exhaustion.
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</p>
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<p>
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When writing, call Next to obtain an io.Writer for the next journal. Calling
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Next finishes the current journal. Call Close to finish the final journal.
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</p>
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<p>
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Optionally, call Flush to finish the current journal and flush the underlying
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writer without starting a new journal. To start a new journal after flushing,
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call Next.
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</p>
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<p>
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Neither Readers or Writers are safe to use concurrently.
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</p>
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<p>
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Example code:
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</p>
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<pre>func read(r io.Reader) ([]string, error) {
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var ss []string
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journals := journal.NewReader(r, nil, true, true)
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for {
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j, err := journals.Next()
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if err == io.EOF {
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break
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}
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if err != nil {
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return nil, err
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}
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s, err := ioutil.ReadAll(j)
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if err != nil {
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return nil, err
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}
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ss = append(ss, string(s))
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}
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return ss, nil
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}
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func write(w io.Writer, ss []string) error {
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journals := journal.NewWriter(w)
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for _, s := range ss {
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j, err := journals.Next()
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if err != nil {
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return err
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}
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if _, err := j.Write([]byte(s)), err != nil {
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return err
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}
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}
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return journals.Close()
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}
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</pre>
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<p>
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The wire format is that the stream is divided into 32KiB blocks, and each
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block contains a number of tightly packed chunks. Chunks cannot cross block
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boundaries. The last block may be shorter than 32 KiB. Any unused bytes in a
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block must be zero.
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</p>
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<p>
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A journal maps to one or more chunks. Each chunk has a 7 byte header (a 4
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byte checksum, a 2 byte little-endian uint16 length, and a 1 byte chunk type)
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followed by a payload. The checksum is over the chunk type and the payload.
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</p>
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<p>
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There are four chunk types: whether the chunk is the full journal, or the
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first, middle or last chunk of a multi-chunk journal. A multi-chunk journal
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has one first chunk, zero or more middle chunks, and one last chunk.
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</p>
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<p>
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The wire format allows for limited recovery in the face of data corruption:
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on a format error (such as a checksum mismatch), the reader moves to the
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next block and looks for the next full or first chunk.
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</p>
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</div>
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</div>
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<div id="pkg-index" class="toggleVisible">
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<div class="collapsed">
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<h2 class="toggleButton" title="Click to show Index section">Index ▹</h2>
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</div>
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<div class="expanded">
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<h2 class="toggleButton" title="Click to hide Index section">Index ▾</h2>
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<!-- Table of contents for API; must be named manual-nav to turn off auto nav. -->
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<div id="manual-nav">
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<dl>
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<dd><a href="index.html#Dropper">type Dropper</a></dd>
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<dd><a href="index.html#ErrCorrupted">type ErrCorrupted</a></dd>
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<dd> <a href="index.html#ErrCorrupted.Error">func (e *ErrCorrupted) Error() string</a></dd>
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<dd><a href="index.html#Reader">type Reader</a></dd>
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<dd> <a href="index.html#NewReader">func NewReader(r io.Reader, dropper Dropper, strict, checksum bool) *Reader</a></dd>
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<dd> <a href="index.html#Reader.Next">func (r *Reader) Next() (io.Reader, error)</a></dd>
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<dd> <a href="index.html#Reader.Reset">func (r *Reader) Reset(reader io.Reader, dropper Dropper, strict, checksum bool) error</a></dd>
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<dd><a href="index.html#Writer">type Writer</a></dd>
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<dd> <a href="index.html#NewWriter">func NewWriter(w io.Writer) *Writer</a></dd>
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<dd> <a href="index.html#Writer.Close">func (w *Writer) Close() error</a></dd>
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<dd> <a href="index.html#Writer.Flush">func (w *Writer) Flush() error</a></dd>
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<dd> <a href="index.html#Writer.Next">func (w *Writer) Next() (io.Writer, error)</a></dd>
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<dd> <a href="index.html#Writer.Reset">func (w *Writer) Reset(writer io.Writer) (err error)</a></dd>
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</dl>
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</div><!-- #manual-nav -->
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<h4>Package files</h4>
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<p>
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<span style="font-size:90%">
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<a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go">journal.go</a>
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</span>
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</p>
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</div><!-- .expanded -->
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</div><!-- #pkg-index -->
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<div id="pkg-callgraph" class="toggle" style="display: none">
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<div class="collapsed">
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<h2 class="toggleButton" title="Click to show Internal Call Graph section">Internal call graph ▹</h2>
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</div> <!-- .expanded -->
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<div class="expanded">
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<h2 class="toggleButton" title="Click to hide Internal Call Graph section">Internal call graph ▾</h2>
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<p>
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In the call graph viewer below, each node
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is a function belonging to this package
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and its children are the functions it
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calls—perhaps dynamically.
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</p>
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<p>
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The root nodes are the entry points of the
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package: functions that may be called from
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outside the package.
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There may be non-exported or anonymous
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functions among them if they are called
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dynamically from another package.
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</p>
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<p>
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Click a node to visit that function's source code.
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From there you can visit its callers by
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clicking its declaring <code>func</code>
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token.
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</p>
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<p>
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Functions may be omitted if they were
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determined to be unreachable in the
|
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particular programs or tests that were
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analyzed.
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</p>
|
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<!-- Zero means show all package entry points. -->
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<ul style="margin-left: 0.5in" id="callgraph-0" class="treeview"></ul>
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</div>
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</div> <!-- #pkg-callgraph -->
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<h2 id="Dropper">type <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=3899:3942#L109">Dropper</a></h2>
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<pre>type Dropper interface {
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Drop(err <a href="../../../../../builtin/index.html#error">error</a>)
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}</pre>
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<p>
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Dropper is the interface that wrap simple Drop method. The Drop
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method will be called when the journal reader dropping a block or chunk.
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</p>
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<h2 id="ErrCorrupted">type <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=3561:3616#L98">ErrCorrupted</a></h2>
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<pre>type ErrCorrupted struct {
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Size <a href="../../../../../builtin/index.html#int">int</a>
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Reason <a href="../../../../../builtin/index.html#string">string</a>
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}</pre>
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<p>
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ErrCorrupted is the error type that generated by corrupted block or chunk.
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</p>
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<h3 id="ErrCorrupted.Error">func (*ErrCorrupted) <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=3618:3655#L103">Error</a></h3>
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<pre>func (e *<a href="index.html#ErrCorrupted">ErrCorrupted</a>) Error() <a href="../../../../../builtin/index.html#string">string</a></pre>
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<h2 id="Reader">type <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=3999:4660#L114">Reader</a></h2>
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<pre>type Reader struct {
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<span class="comment">// contains filtered or unexported fields</span>
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}</pre>
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<p>
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Reader reads journals from an underlying io.Reader.
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</p>
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<h3 id="NewReader">func <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=4820:4895#L142">NewReader</a></h3>
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<pre>func NewReader(r <a href="../../../../../io/index.html">io</a>.<a href="../../../../../io/index.html#Reader">Reader</a>, dropper <a href="index.html#Dropper">Dropper</a>, strict, checksum <a href="../../../../../builtin/index.html#bool">bool</a>) *<a href="index.html#Reader">Reader</a></pre>
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<p>
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NewReader returns a new reader. The dropper may be nil, and if
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strict is true then corrupted or invalid chunk will halt the journal
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reader entirely.
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</p>
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<h3 id="Reader.Next">func (*Reader) <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=7607:7649#L238">Next</a></h3>
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<pre>func (r *<a href="index.html#Reader">Reader</a>) Next() (<a href="../../../../../io/index.html">io</a>.<a href="../../../../../io/index.html#Reader">Reader</a>, <a href="../../../../../builtin/index.html#error">error</a>)</pre>
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<p>
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Next returns a reader for the next journal. It returns io.EOF if there are no
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more journals. The reader returned becomes stale after the next Next call,
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and should no longer be used. If strict is false, the reader will returns
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io.ErrUnexpectedEOF error when found corrupted journal.
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</p>
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<h3 id="Reader.Reset">func (*Reader) <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=7987:8073#L256">Reset</a></h3>
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<pre>func (r *<a href="index.html#Reader">Reader</a>) Reset(reader <a href="../../../../../io/index.html">io</a>.<a href="../../../../../io/index.html#Reader">Reader</a>, dropper <a href="index.html#Dropper">Dropper</a>, strict, checksum <a href="../../../../../builtin/index.html#bool">bool</a>) <a href="../../../../../builtin/index.html#error">error</a></pre>
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<p>
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Reset resets the journal reader, allows reuse of the journal reader. Reset returns
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last accumulated error.
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</p>
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<h2 id="Writer">type <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=9292:9945#L334">Writer</a></h2>
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<pre>type Writer struct {
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<span class="comment">// contains filtered or unexported fields</span>
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}</pre>
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<p>
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Writer writes journals to an underlying io.Writer.
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</p>
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<h3 id="NewWriter">func <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=9982:10017#L358">NewWriter</a></h3>
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<pre>func NewWriter(w <a href="../../../../../io/index.html">io</a>.<a href="../../../../../io/index.html#Writer">Writer</a>) *<a href="index.html#Writer">Writer</a></pre>
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<p>
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NewWriter returns a new Writer.
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</p>
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<h3 id="Writer.Close">func (*Writer) <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=11240:11270#L412">Close</a></h3>
|
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<pre>func (w *<a href="index.html#Writer">Writer</a>) Close() <a href="../../../../../builtin/index.html#error">error</a></pre>
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<p>
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Close finishes the current journal and closes the writer.
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</p>
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<h3 id="Writer.Flush">func (*Writer) <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=11550:11580#L424">Flush</a></h3>
|
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<pre>func (w *<a href="index.html#Writer">Writer</a>) Flush() <a href="../../../../../builtin/index.html#error">error</a></pre>
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<p>
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Flush finishes the current journal, writes to the underlying writer, and
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flushes it if that writer implements interface{ Flush() error }.
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</p>
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<h3 id="Writer.Next">func (*Writer) <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=12261:12303#L458">Next</a></h3>
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<pre>func (w *<a href="index.html#Writer">Writer</a>) Next() (<a href="../../../../../io/index.html">io</a>.<a href="../../../../../io/index.html#Writer">Writer</a>, <a href="../../../../../builtin/index.html#error">error</a>)</pre>
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<p>
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Next returns a writer for the next journal. The writer returned becomes stale
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after the next Close, Flush or Next call, and should no longer be used.
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</p>
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<h3 id="Writer.Reset">func (*Writer) <a href="http://localhost:6060/src/github.com/syndtr/goleveldb/leveldb/journal/journal.go?s=11852:11904#L439">Reset</a></h3>
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<pre>func (w *<a href="index.html#Writer">Writer</a>) Reset(writer <a href="../../../../../io/index.html">io</a>.<a href="../../../../../io/index.html#Writer">Writer</a>) (err <a href="../../../../../builtin/index.html#error">error</a>)</pre>
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<p>
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Reset resets the journal writer, allows reuse of the journal writer. Reset
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will also closes the journal writer if not already.
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</p>
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<div id="footer">
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Except as <a href="https://developers.google.com/site-policies#restrictions">noted</a>,
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the content of this page is licensed under the
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Creative Commons Attribution 3.0 License,
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<script type="text/javascript" src="../../../../../../lib/godoc/jquery.js"></script>
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<script type="text/javascript" src="../../../../../../lib/godoc/jquery.treeview.js"></script>
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<script type="text/javascript" src="../../../../../../lib/godoc/jquery.treeview.edit.js"></script>
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<script type="text/javascript" src="../../../../../../lib/godoc/godocs.js"></script>
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</body>
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</html>
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