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// Licensed under the MIT License.
using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Management.Automation;
using System.Management.Automation.Internal;
using System.Management.Automation.Provider;
using Dbg = System.Management.Automation;
namespace Microsoft.PowerShell.Commands
{
/// <summary>
/// A command to get the content of an item at a specified path.
/// </summary>
[Cmdlet(VerbsCommon.Get, "Content", DefaultParameterSetName = "Path", SupportsTransactions = true, HelpUri = "https://go.microsoft.com/fwlink/?LinkID=2096490")]
public class GetContentCommand : ContentCommandBase
{
#region Parameters
/// <summary>
/// The number of content items to retrieve per block.
/// By default this value is 1 which means read one block
/// at a time. To read all blocks at once, set this value
/// to a negative number.
/// </summary>
[Parameter(ValueFromPipelineByPropertyName = true)]
public long ReadCount { get; set; } = 1;
/// <summary>
/// The number of content items to retrieve.
/// </summary>
[Parameter(ValueFromPipelineByPropertyName = true)]
[ValidateRange(0, long.MaxValue)]
[Alias("First", "Head")]
public long TotalCount { get; set; } = -1;
/// <summary>
/// The number of content items to retrieve from the back of the file.
/// </summary>
[Parameter(ValueFromPipelineByPropertyName = true)]
[ValidateRange(0, int.MaxValue)]
[Alias("Last")]
public int Tail { get; set; } = -1;
/// <summary>
/// A virtual method for retrieving the dynamic parameters for a cmdlet. Derived cmdlets
/// that require dynamic parameters should override this method and return the
/// dynamic parameter object.
/// </summary>
/// <param name="context">
/// The context under which the command is running.
/// </param>
/// <returns>
/// An object representing the dynamic parameters for the cmdlet or null if there
/// are none.
/// </returns>
internal override object GetDynamicParameters(CmdletProviderContext context)
{
if (Path != null && Path.Length > 0)
{
return InvokeProvider.Content.GetContentReaderDynamicParameters(Path[0], context);
}
return InvokeProvider.Content.GetContentReaderDynamicParameters(".", context);
}
#endregion Parameters
#region Command code
/// <summary>
/// Gets the content of an item at the specified path.
/// </summary>
protected override void ProcessRecord()
{
// TotalCount and Tail should not be specified at the same time.
// Throw out terminating error if this is the case.
if (TotalCount != -1 && Tail != -1)
{
string errMsg = StringUtil.Format(SessionStateStrings.GetContent_TailAndHeadCannotCoexist, "TotalCount", "Tail");
ErrorRecord error = new(new InvalidOperationException(errMsg), "TailAndHeadCannotCoexist", ErrorCategory.InvalidOperation, null);
WriteError(error);
return;
}
if (TotalCount == 0)
{
// Don't read anything
return;
}
// Get the content readers
CmdletProviderContext currentContext = CmdletProviderContext;
contentStreams = this.GetContentReaders(Path, currentContext);
try
{
// Iterate through the content holders reading the content
foreach (ContentHolder holder in contentStreams)
{
long countRead = 0;
Dbg.Diagnostics.Assert(holder.Reader != null, "All holders should have a reader assigned");
if (Tail != -1 && holder.Reader is not FileSystemContentReaderWriter)
{
string errMsg = SessionStateStrings.GetContent_TailNotSupported;
ErrorRecord error = new(new InvalidOperationException(errMsg), "TailNotSupported", ErrorCategory.InvalidOperation, Tail);
WriteError(error);
continue;
}
// If Tail is -1, we are supposed to read all content out. This is same
// as reading forwards. So we read forwards in this case.
// If Tail is positive, we seek the right position. Or, if the seek failed
// because of an unsupported encoding, we scan forward to get the tail content.
if (Tail >= 0)
{
bool seekSuccess = false;
try
{
seekSuccess = SeekPositionForTail(holder.Reader);
}
catch (Exception e)
{
ProviderInvocationException providerException =
new(
"ProviderContentReadError",
SessionStateStrings.ProviderContentReadError,
holder.PathInfo.Provider,
holder.PathInfo.Path,
e);
// Log a provider health event
MshLog.LogProviderHealthEvent(
this.Context,
holder.PathInfo.Provider.Name,
providerException,
Severity.Warning);
WriteError(new ErrorRecord(
providerException.ErrorRecord,
providerException));
continue;
}
// If the seek was successful, we start to read forwards from that
// point. Otherwise, we need to scan forwards to get the tail content.
if (!seekSuccess && !ScanForwardsForTail(holder, currentContext))
{
continue;
}
}
IList results = null;
do
{
long countToRead = ReadCount;
// Make sure we only ask for the amount the user wanted
// I am using TotalCount - countToRead so that I don't
// have to worry about overflow
if (TotalCount > 0 && (countToRead == 0 || TotalCount - countToRead < countRead))
{
countToRead = TotalCount - countRead;
}
try
{
results = holder.Reader.Read(countToRead);
}
catch (Exception e) // Catch-all OK. 3rd party callout
{
ProviderInvocationException providerException =
new(
"ProviderContentReadError",
SessionStateStrings.ProviderContentReadError,
holder.PathInfo.Provider,
holder.PathInfo.Path,
e);
// Log a provider health event
MshLog.LogProviderHealthEvent(this.Context, holder.PathInfo.Provider.Name, providerException, Severity.Warning);
WriteError(new ErrorRecord(providerException.ErrorRecord, providerException));
break;
}
if (results != null && results.Count > 0)
{
countRead += results.Count;
if (ReadCount == 1)
{
// Write out the content as a single object
WriteContentObject(results[0], countRead, holder.PathInfo, currentContext);
}
else
{
// Write out the content as an array of objects
WriteContentObject(results, countRead, holder.PathInfo, currentContext);
}
}
} while (results != null && results.Count > 0 && (TotalCount == -1 || countRead < TotalCount));
}
}
finally
{
// Close all the content readers
CloseContent(contentStreams, false);
// Empty the content holder array
contentStreams = new List<ContentHolder>();
}
}
/// <summary>
/// Scan forwards to get the tail content.
/// </summary>
/// <param name="holder"></param>
/// <param name="currentContext"></param>
/// <returns>
/// true if no error occurred
/// false if there was an error
/// </returns>
private bool ScanForwardsForTail(in ContentHolder holder, CmdletProviderContext currentContext)
{
var fsReader = holder.Reader as FileSystemContentReaderWriter;
Dbg.Diagnostics.Assert(fsReader != null, "Tail is only supported for FileSystemContentReaderWriter");
Queue<object> tailResultQueue = new();
IList results = null;
ErrorRecord error = null;
do
{
try
{
results = fsReader.ReadWithoutWaitingChanges(ReadCount);
}
catch (Exception e)
{
ProviderInvocationException providerException =
new(
"ProviderContentReadError",
SessionStateStrings.ProviderContentReadError,
holder.PathInfo.Provider,
holder.PathInfo.Path,
e);
// Log a provider health event
MshLog.LogProviderHealthEvent(
this.Context,
holder.PathInfo.Provider.Name,
providerException,
Severity.Warning);
// Create and save the error record. The error record
// will be written outside the while loop.
// This is to make sure the accumulated results get written
// out before the error record when the 'scanForwardForTail' is true.
error = new ErrorRecord(
providerException.ErrorRecord,
providerException);
break;
}
if (results != null && results.Count > 0)
{
foreach (object entry in results)
{
if (tailResultQueue.Count == Tail)
{
tailResultQueue.Dequeue();
}
tailResultQueue.Enqueue(entry);
}
}
} while (results != null && results.Count > 0);
if (tailResultQueue.Count > 0)
{
// Respect the ReadCount parameter.
// Output single object when ReadCount == 1; Output array otherwise
int count = 0;
if (ReadCount <= 0 || (ReadCount >= tailResultQueue.Count && ReadCount != 1))
{
count = tailResultQueue.Count;
// Write out the content as an array of objects
WriteContentObject(tailResultQueue.ToArray(), count, holder.PathInfo, currentContext);
}
else if (ReadCount == 1)
{
// Write out the content as single object
while (tailResultQueue.Count > 0)
{
WriteContentObject(tailResultQueue.Dequeue(), count++, holder.PathInfo, currentContext);
}
}
else // ReadCount < Queue.Count
{
while (tailResultQueue.Count >= ReadCount)
{
List<object> outputList = new((int)ReadCount);
for (int idx = 0; idx < ReadCount; idx++, count++)
{
outputList.Add(tailResultQueue.Dequeue());
}
// Write out the content as an array of objects
WriteContentObject(outputList.ToArray(), count, holder.PathInfo, currentContext);
}
if (tailResultQueue.Count > 0)
{
// Write out the content as an array of objects
WriteContentObject(tailResultQueue.ToArray(), count, holder.PathInfo, currentContext);
}
}
}
if (error != null)
{
WriteError(error);
return false;
}
return true;
}
/// <summary>
/// Seek position to the right place.
/// </summary>
/// <param name="reader">
/// reader should be able to be casted to FileSystemContentReader
/// </param>
/// <returns>
/// true if the stream pointer is moved to the right place
/// false if we cannot seek
/// </returns>
private bool SeekPositionForTail(IContentReader reader)
{
var fsReader = reader as FileSystemContentReaderWriter;
Dbg.Diagnostics.Assert(fsReader != null, "Tail is only supported for FileSystemContentReaderWriter");
try
{
fsReader.SeekItemsBackward(Tail);
return true;
}
catch (BackReaderEncodingNotSupportedException)
{
// Move to the head
fsReader.Seek(0, SeekOrigin.Begin);
return false;
}
}
/// <summary>
/// Be sure to clean up.
/// </summary>
protected override void EndProcessing()
{
Dispose(true);
}
#endregion Command code
}
}
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