<%@ WebService Language="C#" Class="Snmp" %>

// ASP-based SNMP access via Web Services
//
// Copyright 2003 Ken Shirriff	Ken.Shirriff@sun.com
// http://www.righto.com/snmp
//
// This software comes with no warranty.  Chances are very good that it has memory leaks or
// other memory issues that may make it crash.
//
// To run: install Snmp.asmx in C:\Inetpub\Scripts
// Then access http://localhost/Scripts/Snmp.asmx.
// The exposed services are getSnmp and setSnmp, which will do the specified operation
// on the specified host and community.  Note that only a subset of SNMP is supported.
// This should be considered more of just a proof of concept.

using System;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Runtime.InteropServices;

[WebService(Namespace="http://www.righto.com")]
public class Snmp : WebService {
	// Reference: Microsoft SDK\Samples\netds\Snmp\SnmpUtil.C

	private IntPtr session;		// The SNMP session information
	private SnmpVarBindList variableBindings;	// The SNMP variable information

	// Helper to open SNMP connection
	private void SnmpOpen(String agent, String community) {
		int timeout = 2000; // Hardwire to 2 seconds, 3 retries.
		int retries = 3;
		if ((session = SnmpMgrOpen(agent, community, timeout, retries)) == IntPtr.Zero) {
			SnmpUtilVarBindListFree(ref variableBindings);
			throw new SoapException("SnmpMgrOpen fault occurred "+agent+" "+community,
				SoapException.ServerFaultCode);
		}
	}

	// Helper to close SNMP connection
	private void SnmpClose() {
		if (!SnmpMgrClose(session)) {
			SnmpUtilVarBindListFree(ref variableBindings);
			throw new SoapException("SnmpMgrClose fault occurred",
				SoapException.ServerFaultCode);
		}
	}

	// Helper method to create SnmpVarBindList from oidStr

	private void SnmpVarBindListCreate(String oidStr) {
		oidStr = "." + oidStr;	// Make SnmpMgrStrToOid use absolute OID, not internet subtree

		variableBindings = new SnmpVarBindList();

		SnmpVarBind varBind = new SnmpVarBind();

		// Create variable binding
		// SnmpMgrStrToOid will allocate memory for the oid, which must be freed later
		bool status = SnmpMgrStrToOid(oidStr, ref varBind.name);
		if (!status) {
			throw new SoapException("Oid fault occurred", SoapException.ClientFaultCode,
				Context.Request.Url.AbsoluteUri);
		}

		// Since sucessfull, add to the variable bindings list.

		// Code assumes one oid in the variableBindings list.
		IntPtr tmpVb;
                if ((tmpVb = SnmpUtilMemAlloc((uint)Marshal.SizeOf(typeof(SnmpVarBind)))) ==
			    IntPtr.Zero) {
                        SnmpUtilOidFree(ref varBind.name);
		        throw new SoapException("Oid allocation fault occurred",
				SoapException.ServerFaultCode, Context.Request.Url.AbsoluteUri);
  
		}
		// Note: tmpVb memory will be freed when variableBinding
		// is freed, since we're putting it in variableBindings.list.
		varBind.value.asnType = ASN_NULL;
		Marshal.StructureToPtr(varBind, tmpVb, false);
                variableBindings.list = tmpVb;
		variableBindings.len = 1;
	}

	// Helper method to do the request
	private void SnmpRequest(byte requestType) {
		int errorStatus = 0;
		int errorIndex = 0;
		if (SnmpMgrRequest(session, requestType, ref variableBindings,
				    ref errorStatus, ref errorIndex) == 0) {
			SnmpUtilVarBindListFree(ref variableBindings);
			throw new SoapException("SnmpMgrRequest fault occurred",
				SoapException.ServerFaultCode);
		}

		if (errorStatus == 2) {
			// Variable does not exist
			IntPtr sPtr = IntPtr.Zero;
			SnmpMgrOidToStr(variableBindings.list, ref sPtr);
			String s = Marshal.PtrToStringAnsi(sPtr);
			SnmpUtilMemFree(sPtr);
			throw new SoapException("SnmpMgrRequest: variable does not exist "+s,
				SoapException.ServerFaultCode);
		} else if (errorStatus > 0) {
			SnmpUtilVarBindListFree(ref variableBindings);
			throw new SoapException("SnmpMgrRequest fault occurred "+errorStatus+" "+
				errorIndex, SoapException.ServerFaultCode);
		}

		// General case is currently not handled
		if (requestType == SNMP_PDU_GET && variableBindings.len != 1) {
			uint len = variableBindings.len;
			SnmpUtilVarBindListFree(ref variableBindings);
			throw new SoapException("SNMP: unexpected return length "+len,
				SoapException.ServerFaultCode);
		}
	}

	// Helper method to convert SNMP variable to string
	String SnmpVarToString(SnmpVarBind varBind) {
		String result = "";
		switch (varBind.value.asnType) {
		case ASN_INTEGER:
			result = ""+varBind.value.asnValue.number;
			break;
		case ASN_OCTETSTRING:
			result = Marshal.PtrToStringAnsi(varBind.value.asnValue.str.stream,
				(int)varBind.value.asnValue.str.length);
			break;
		default:
			// Exercise for the reader
			throw new SoapException("Unimplemented ASN type: "+varBind.value.asnType,
				SoapException.ClientFaultCode,
				Context.Request.Url.AbsoluteUri);
			break;
		}
		return result;
	}

	// This performs a SNMP get of the specified agent, community, and oid, and returns
	// the results as a string.
	[WebMethod] public String SNMPget(String agent, String community, String oidStr) {

		// The try/catch makes it easier to see what's happening in a browser.
		// If you want to receive SOAP faults, remove the try/catch, but then
		// a browser will just give error 500, which isn't too informative.
		try {
		
		SnmpOpen(agent, community); // Open the connection
	
		SnmpVarBindListCreate(oidStr);	// Convert the oid into internal form

		SnmpRequest(SNMP_PDU_GET);		// Perform the request

		SnmpClose();		// Close the connection

		// Process the output, using the first entry in the variableBindings list.

		SnmpVarBind varBind = (SnmpVarBind)Marshal.PtrToStructure(variableBindings.list,
			typeof(SnmpVarBind));
		String result = SnmpVarToString(varBind);

		SnmpUtilVarBindListFree(ref variableBindings); // Clean up

		return result;

		} catch (Exception e) {
			return "Exception "+e;
		}
	}

	// This performs a SNMP set of an int to the specified agent, community, and oid.
	[WebMethod] public String SNMPset(String agent, String community, String oidStr, int value) {

		try{

		SnmpOpen(agent, community); // Open the connection
	
		SnmpVarBindListCreate(oidStr);	// Convert the oid into internal form

		// Set the value in variableBindings
		AsnAny asnValue = new AsnAny();
		asnValue.asnType = ASN_INTEGER;
		asnValue.asnValue.number = value;
		IntPtr valuePtr = (IntPtr) ((int)variableBindings.list +
			(int)Marshal.OffsetOf(typeof(SnmpVarBind), "value"));
		Marshal.StructureToPtr(asnValue, valuePtr, false);

		SnmpRequest(SNMP_PDU_SET);	// Perform the request

		SnmpClose();		// Close the connection

		SnmpUtilVarBindListFree(ref variableBindings); // Clean up

		return "Set was successful";

		} catch (Exception e) {
			return "Exception "+e;
		}
	}

	// The following prototypes map onto functions in the SNMP Management API.
	// The tricky part is that this API uses its own memory allocation
	// and free functions, so the automatic allocation/free of the .Net
	// marshaller cannot be used.  Instead, we need to use IntPtr, manually
	// marshal things, and use the API functions to allocate memory.  This
	// requires careful attention to which things are in managed (i.e. C#)
	// memory, and which things are in unmanaged memory (i.e. dll).  Hopefully
	// most of the details are correct.  Read the .NET SDK documentation on Interop
	// and Platform Invoke to see what I'm trying to do here.

	/*
	BOOL
	SNMP_FUNC_TYPE
	SnmpMgrStrToOid(
	    IN  LPSTR               string,         // OID string to be converted
	    OUT AsnObjectIdentifier *oid            // OID internal representation
	    );
	*/
	// oid will need to be freed with SnmpUtilOidFree, or will need
	// to be freed indirectly by SnmpUtilVarBindListFree
	[DllImport("mgmtapi.dll")]
	public static extern bool SnmpMgrStrToOid(
		string str,
		ref AsnObjectIdentifier oid
	);

	/*
	BOOL
	SNMP_FUNC_TYPE
	SnmpMgrOidToStr(
	    IN AsnObjectIdentifier *oid            // OID internal representation
	    OUT  LPSTR               *string,         // OID string to be converted
	    );
	*/
	[DllImport("mgmtapi.dll")]
	public static extern bool SnmpMgrOidToStr(
		ref AsnObjectIdentifier oid,
		IntPtr str
	);


	/*
	LPSNMP_MGR_SESSION
	SNMP_FUNC_TYPE
	SnmpMgrOpen(
	    IN LPSTR lpAgentAddress,                // Name/address of target agent
	    IN LPSTR lpAgentCommunity,              // Community for target agent
	    IN INT   nTimeOut,                      // Comm time-out in milliseconds
	    IN INT   nRetries                       // Comm time-out/retry count
	);
	*/
	[DllImport("mgmtapi.dll")]
	public static extern IntPtr SnmpMgrOpen(
		string	lpAgentAddress,
		string	lpAgentCommunity,
		int	nTimeOut,
		int	nRetries
	);

	/*
	BOOL
	SNMP_FUNC_TYPE
	SnmpMgrClose(
	    IN LPSNMP_MGR_SESSION session           // SNMP session pointer
	    );
	*/
	[DllImport("mgmtapi.dll")]
	public static extern bool SnmpMgrClose(
		IntPtr	session
	);

	/*
	SNMPAPI
	SNMP_FUNC_TYPE
	SnmpMgrRequest(
	    IN     LPSNMP_MGR_SESSION session,           // SNMP session pointer
	    IN     BYTE               requestType,       // Get, GetNext, or Set
	    IN OUT RFC1157VarBindList *variableBindings, // Varible bindings
	       OUT AsnInteger         *errorStatus,      // Result error status
	       OUT AsnInteger         *errorIndex        // Result error index
	    );
	*/
	[DllImport("mgmtapi.dll")]
	public static extern int SnmpMgrRequest(
		IntPtr	session,
		byte	requestType,
		ref SnmpVarBindList variableBindings,
		ref int	errorStatus,
		ref int errorIndex
	);

	/*
	VOID
	SNMP_FUNC_TYPE
	SnmpUtilVarBindFree(
	    SnmpVarBind * pVb
	    );
    	*/
	[DllImport("snmpapi.dll")]
	public static extern void SnmpUtilVarBindFree(
		IntPtr pVb
	);

	/*
	VOID
	SNMP_FUNC_TYPE
	SnmpUtilMemFree(
	    LPVOID pMem
	    );
	*/
	[DllImport("snmpapi.dll")]
	public static extern void SnmpUtilMemFree(
		IntPtr	pMem
	);

	/*
	LPVOID
	SNMP_FUNC_TYPE
	SnmpUtilMemAlloc(
	    UINT nBytes
	    );
	*/
	[DllImport("snmpapi.dll")]
	public static extern IntPtr SnmpUtilMemAlloc(
		uint	nBytes
	);

	/*
	VOID
	SNMP_FUNC_TYPE
	SnmpUtilVarBindListFree(
	    SnmpVarBindList * pVbl
	    );
	*/
	[DllImport("snmpapi.dll")]
	public static extern void SnmpUtilVarBindListFree(
		ref SnmpVarBindList pVbl
	);

	/*
	VOID
	SNMP_FUNC_TYPE
	SnmpUtilOidFree(
	    AsnObjectIdentifier * pOid
	    );
	*/
	// This frees the oids in the AsnObjectIdentifier
	[DllImport("snmpapi.dll")]
	public static extern void SnmpUtilOidFree(
		ref AsnObjectIdentifier pOid
	);

	const byte ASN_INTEGER = (0x0 | 0x0 | 0x2);
	const byte ASN_OCTETSTRING = (0x0 | 0x0 | 0x4);
	const byte ASN_NULL = (0x0 | 0x0 | 0x5);

	const byte SNMP_PDU_GET = (0x80 | 0x20 | 0x0);
	const byte SNMP_PDU_SET = (0x80 | 0x20 | 0x3);
}

[ StructLayout( LayoutKind.Sequential)]
public struct SnmpVarBindList {
	public IntPtr	list;	// SnmpVarBind *
	public uint	len;
}

[ StructLayout( LayoutKind.Sequential)]
public struct AsnObjectIdentifier {
	public uint	idLength;
	public IntPtr	ids;	// UINT *
}

[ StructLayout( LayoutKind.Explicit)]
public struct AsnUnion {
	[FieldOffset(0)]
	public int number;
	[FieldOffset(0)]
	public AsnOctetString str;
}

[ StructLayout( LayoutKind.Sequential)]
public struct AsnOctetString {
	public IntPtr	stream;
	public uint	length;
	public bool	dynamic;
}

[ StructLayout( LayoutKind.Sequential)]
public struct AsnAny {
	public byte	asnType;
	public AsnUnion	asnValue;
}

[ StructLayout( LayoutKind.Sequential)]
public struct SnmpVarBind {
	public AsnObjectIdentifier name;
	public AsnAny	value;
}