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//------------------------------------------------------------------------------
// <copyright file="XmlAttributeCache.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
// <owner current="true" primary="true">Microsoft</owner>
//------------------------------------------------------------------------------
namespace System.Xml.Xsl.Runtime {
using System;
using System.Diagnostics;
using System.Xml;
using System.Xml.XPath;
using System.Xml.Schema;
/// <summary>
/// This writer supports only writer methods which write attributes. Attributes are stored in a
/// data structure until StartElementContent() is called, at which time the attributes are flushed
/// to the wrapped writer. In the case of duplicate attributes, the last attribute's value is used.
/// </summary>
internal sealed class XmlAttributeCache : XmlRawWriter, IRemovableWriter {
private XmlRawWriter wrapped;
private OnRemoveWriter onRemove; // Event handler that is called when cached attributes are flushed to wrapped writer
private AttrNameVal[] arrAttrs; // List of cached attribute names and value parts
private int numEntries; // Number of attributes in the cache
private int idxLastName; // The entry containing the name of the last attribute to be cached
private int hashCodeUnion; // Set of hash bits that can quickly guarantee a name is not a duplicate
/// <summary>
/// Initialize the cache. Use this method instead of a constructor in order to reuse the cache.
/// </summary>
public void Init(XmlRawWriter wrapped) {
SetWrappedWriter(wrapped);
// Clear attribute list
this.numEntries = 0;
this.idxLastName = 0;
this.hashCodeUnion = 0;
}
/// <summary>
/// Return the number of cached attributes.
/// </summary>
public int Count {
get { return this.numEntries; }
}
//-----------------------------------------------
// IRemovableWriter interface
//-----------------------------------------------
/// <summary>
/// This writer will raise this event once cached attributes have been flushed in order to signal that the cache
/// no longer needs to be part of the pipeline.
/// </summary>
public OnRemoveWriter OnRemoveWriterEvent {
get { return this.onRemove; }
set { this.onRemove = value; }
}
/// <summary>
/// The wrapped writer will callback on this method if it wishes to remove itself from the pipeline.
/// </summary>
private void SetWrappedWriter(XmlRawWriter writer) {
// If new writer might remove itself from pipeline, have it callback on this method when its ready to go
IRemovableWriter removable = writer as IRemovableWriter;
if (removable != null)
removable.OnRemoveWriterEvent = SetWrappedWriter;
this.wrapped = writer;
}
//-----------------------------------------------
// XmlWriter interface
//-----------------------------------------------
/// <summary>
/// Add an attribute to the cache. If an attribute if the same name already exists, replace it.
/// </summary>
public override void WriteStartAttribute(string prefix, string localName, string ns) {
int hashCode;
int idx = 0;
Debug.Assert(localName != null && localName.Length != 0 && prefix != null && ns != null);
// Compute hashcode based on first letter of the localName
hashCode = (1 << ((int) localName[0] & 31));
// If the hashcode is not in the union, then name will not be found by a scan
if ((this.hashCodeUnion & hashCode) != 0) {
// The name may or may not be present, so scan for it
Debug.Assert(this.numEntries != 0);
do {
if (this.arrAttrs[idx].IsDuplicate(localName, ns, hashCode))
break;
// Next attribute name
idx = this.arrAttrs[idx].NextNameIndex;
}
while (idx != 0);
}
else {
// Insert hashcode into union
this.hashCodeUnion |= hashCode;
}
// Insert new attribute; link attribute names together in a list
EnsureAttributeCache();
if (this.numEntries != 0)
this.arrAttrs[this.idxLastName].NextNameIndex = this.numEntries;
this.idxLastName = this.numEntries++;
this.arrAttrs[this.idxLastName].Init(prefix, localName, ns, hashCode);
}
/// <summary>
/// No-op.
/// </summary>
public override void WriteEndAttribute() {
}
/// <summary>
/// Pass through namespaces to underlying writer. If any attributes have been cached, flush them.
/// </summary>
internal override void WriteNamespaceDeclaration(string prefix, string ns) {
FlushAttributes();
this.wrapped.WriteNamespaceDeclaration(prefix, ns);
}
/// <summary>
/// Add a block of text to the cache. This text block makes up some or all of the untyped string
/// value of the current attribute.
/// </summary>
public override void WriteString(string text) {
Debug.Assert(text != null);
Debug.Assert(this.arrAttrs != null && this.numEntries != 0);
EnsureAttributeCache();
this.arrAttrs[this.numEntries++].Init(text);
}
/// <summary>
/// All other WriteValue methods are implemented by XmlWriter to delegate to WriteValue(object) or WriteValue(string), so
/// only these two methods need to be implemented.
/// </summary>
public override void WriteValue(object value) {
Debug.Assert(value is XmlAtomicValue, "value should always be an XmlAtomicValue, as XmlAttributeCache is only used by XmlQueryOutput");
Debug.Assert(this.arrAttrs != null && this.numEntries != 0);
EnsureAttributeCache();
this.arrAttrs[this.numEntries++].Init((XmlAtomicValue) value);
}
public override void WriteValue(string value) {
WriteValue(value);
}
/// <summary>
/// Send cached, non-overriden attributes to the specified writer. Calling this method has
/// the side effect of clearing the attribute cache.
/// </summary>
internal override void StartElementContent() {
FlushAttributes();
// Call StartElementContent on wrapped writer
this.wrapped.StartElementContent();
}
public override void WriteStartElement(string prefix, string localName, string ns) {
Debug.Assert(false, "Should never be called on XmlAttributeCache.");
}
internal override void WriteEndElement(string prefix, string localName, string ns) {
Debug.Assert(false, "Should never be called on XmlAttributeCache.");
}
public override void WriteComment(string text) {
Debug.Assert(false, "Should never be called on XmlAttributeCache.");
}
public override void WriteProcessingInstruction(string name, string text) {
Debug.Assert(false, "Should never be called on XmlAttributeCache.");
}
public override void WriteEntityRef(string name) {
Debug.Assert(false, "Should never be called on XmlAttributeCache.");
}
/// <summary>
/// Forward call to wrapped writer.
/// </summary>
public override void Close() {
this.wrapped.Close();
}
/// <summary>
/// Forward call to wrapped writer.
/// </summary>
public override void Flush() {
this.wrapped.Flush();
}
//-----------------------------------------------
// Helper methods
//-----------------------------------------------
private void FlushAttributes() {
int idx = 0, idxNext;
string localName;
while (idx != this.numEntries) {
// Get index of next attribute's name (0 if this is the last attribute)
idxNext = this.arrAttrs[idx].NextNameIndex;
if (idxNext == 0)
idxNext = this.numEntries;
// If localName is null, then this is a duplicate attribute that has been marked as "deleted"
localName = this.arrAttrs[idx].LocalName;
if (localName != null) {
string prefix = this.arrAttrs[idx].Prefix;
string ns = this.arrAttrs[idx].Namespace;
this.wrapped.WriteStartAttribute(prefix, localName, ns);
// Output all of this attribute's text or typed values
while (++idx != idxNext) {
string text = this.arrAttrs[idx].Text;
if (text != null)
this.wrapped.WriteString(text);
else
this.wrapped.WriteValue(this.arrAttrs[idx].Value);
}
this.wrapped.WriteEndAttribute();
}
else {
// Skip over duplicate attributes
idx = idxNext;
}
}
// Notify event listener that attributes have been flushed
if (this.onRemove != null)
this.onRemove(this.wrapped);
}
private struct AttrNameVal {
private string localName;
private string prefix;
private string namespaceName;
private string text;
private XmlAtomicValue value;
private int hashCode;
private int nextNameIndex;
public string LocalName { get { return this.localName; } }
public string Prefix { get { return this.prefix; } }
public string Namespace { get { return this.namespaceName; } }
public string Text { get { return this.text; } }
public XmlAtomicValue Value { get { return this.value; } }
public int NextNameIndex { get { return this.nextNameIndex; } set { this.nextNameIndex = value; } }
/// <summary>
/// Cache an attribute's name and type.
/// </summary>
public void Init(string prefix, string localName, string ns, int hashCode) {
this.localName = localName;
this.prefix = prefix;
this.namespaceName = ns;
this.hashCode = hashCode;
this.nextNameIndex = 0;
}
/// <summary>
/// Cache all or part of the attribute's string value.
/// </summary>
public void Init(string text) {
this.text = text;
this.value = null;
}
/// <summary>
/// Cache all or part of the attribute's typed value.
/// </summary>
public void Init(XmlAtomicValue value) {
this.text = null;
this.value = value;
}
/// <summary>
/// Returns true if this attribute has the specified name (and thus is a duplicate).
/// </summary>
public bool IsDuplicate(string localName, string ns, int hashCode) {
// If attribute is not marked as deleted
if (this.localName != null) {
// And if hash codes match,
if (this.hashCode == hashCode) {
// And if local names match,
if (this.localName.Equals(localName)) {
// And if namespaces match,
if (this.namespaceName.Equals(ns)) {
// Then found duplicate attribute, so mark the attribute as deleted
this.localName = null;
return true;
}
}
}
}
return false;
}
}
#if DEBUG
private const int DefaultCacheSize = 2;
#else
private const int DefaultCacheSize = 32;
#endif
/// <summary>
/// Ensure that attribute array has been created and is large enough for at least one
/// additional entry.
/// </summary>
private void EnsureAttributeCache() {
if (this.arrAttrs == null) {
// Create caching array
this.arrAttrs = new AttrNameVal[DefaultCacheSize];
}
else if (this.numEntries >= this.arrAttrs.Length) {
// Resize caching array
Debug.Assert(this.numEntries == this.arrAttrs.Length);
AttrNameVal[] arrNew = new AttrNameVal[this.numEntries * 2];
Array.Copy(this.arrAttrs, arrNew, this.numEntries);
this.arrAttrs = arrNew;
}
}
}
}
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