S7.NET读写西门子字符串处理
S7.NET读写西门子字符串处理
由于西门子字符串存储跟C#字符串的存储格式不一样，在与西门子通讯时，在解析/编码字符串时需要特殊处理。在没有看到S7.NET开源库前，一直都在琢磨怎么处理好，也一直没有想到很合理的解决办法，只能怪自己的水平不行。直到看到S7.NET采用特性的办法来处理，才眼前一亮。
S7.NET字符串的特性代码如下：
using System;
namespace S7.Net.Types
{
[AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
public sealed class S7StringAttribute : Attribute
{
private readonly S7StringType type;
private readonly int reservedLength;
/// <summary>
/// Initializes a new instance of the <see cref="S7StringAttribute"/> class.
/// </summary>
/// <param name="type">The string type.</param>
/// <param name="reservedLength">Reserved length of the string in characters.</param>
/// <exception cref="ArgumentException">Please use a valid value for the string type</exception>
public S7StringAttribute(S7StringType type, int reservedLength)
{
if (!Enum.IsDefined(typeof(S7StringType), type))
throw new ArgumentException("Please use a valid value for the string type");
this.type = type;
this.reservedLength = reservedLength;
}
/// <summary>
/// Gets the type of the string.
/// </summary>
/// <value>
/// The string type.
/// </value>
public S7StringType Type => type;
/// <summary>
/// Gets the reserved length of the string in characters.
/// </summary>
/// <value>
/// The reserved length of the string in characters.
/// </value>
public int ReservedLength => reservedLength;
/// <summary>
/// Gets the reserved length in bytes.
/// </summary>
/// <value>
/// The reserved length in bytes.
/// </value>
public int ReservedLengthInBytes => type == S7StringType.S7String ? reservedLength + 2 : (reservedLength * 2) + 4;
}
/// <summary>
/// String type.
/// </summary>
public enum S7StringType
{
/// <summary>
/// ASCII string.
/// </summary>
S7String = VarType.S7String,
/// <summary>
/// Unicode string.
/// </summary>
S7WString = VarType.S7WString
}
}
解码与编码字符串代码如下：
using System;
using System.Text;
namespace S7.Net.Types
{
/// <summary>
/// Contains the methods to convert from S7 strings to C# strings
/// An S7 String has a preceeding 2 byte header containing its capacity and length
/// </summary>
public static class S7String
{
private static Encoding stringEncoding = Encoding.ASCII;
/// <summary>
/// The Encoding used when serializing and deserializing S7String (Encoding.ASCII by default)
/// </summary>
/// <exception cref="ArgumentNullException">StringEncoding must not be null</exception>
public static Encoding StringEncoding
{
get => stringEncoding;
set => stringEncoding = value ?? throw new ArgumentNullException(nameof(StringEncoding));
}
/// <summary>
/// Converts S7 bytes to a string
/// </summary>
/// <param name="bytes"></param>
/// <returns></returns>
public static string FromByteArray(byte[] bytes)
{
if (bytes.Length < 2)
{
throw new PlcException(ErrorCode.ReadData, "Malformed S7 String / too short");
}
int size = bytes[0];
int length = bytes[1];
if (length > size)
{
throw new PlcException(ErrorCode.ReadData, "Malformed S7 String / length larger than capacity");
}
try
{
return StringEncoding.GetString(bytes, 2, length);
}
catch (Exception e)
{
throw new PlcException(ErrorCode.ReadData,
$"Failed to parse {VarType.S7String} from data. Following fields were read: size: '{size}', actual length: '{length}', total number of bytes (including header): '{bytes.Length}'.",
e);
}
}
/// <summary>
/// Converts a <see cref="T:string"/> to S7 string with 2-byte header.
/// </summary>
/// <param name="value">The string to convert to byte array.</param>
/// <param name="reservedLength">The length (in characters) allocated in PLC for the string.</param>
/// <returns>A <see cref="T:byte[]" /> containing the string header and string value with a maximum length of <paramref name="reservedLength"/> + 2.</returns>
public static byte[] ToByteArray(string value, int reservedLength)
{
if (value is null)
{
throw new ArgumentNullException(nameof(value));
}
if (reservedLength > 254) throw new ArgumentException($"The maximum string length supported is 254.");
var bytes = StringEncoding.GetBytes(value);
if (bytes.Length > reservedLength) throw new ArgumentException($"The provided string length ({bytes.Length} is larger than the specified reserved length ({reservedLength}).");
var buffer = new byte[2 + reservedLength];
Array.Copy(bytes, 0, buffer, 2, bytes.Length);
buffer[0] = (byte)reservedLength;
buffer[1] = (byte)bytes.Length;
return buffer;
}
}
}
在处理Class中使用方法如下：
using System;
using System.Text;
namespace S7.Net.Types
{
/// <summary>
/// Contains the methods to convert from S7 strings to C# strings
/// An S7 String has a preceeding 2 byte header containing its capacity and length
/// </summary>
public static class S7String
{
private static Encoding stringEncoding = Encoding.ASCII;
/// <summary>
/// The Encoding used when serializing and deserializing S7String (Encoding.ASCII by default)
/// </summary>
/// <exception cref="ArgumentNullException">StringEncoding must not be null</exception>
public static Encoding StringEncoding
{
get => stringEncoding;
set => stringEncoding = value ?? throw new ArgumentNullException(nameof(StringEncoding));
}
/// <summary>
/// Converts S7 bytes to a string
/// </summary>
/// <param name="bytes"></param>
/// <returns></returns>
public static string FromByteArray(byte[] bytes)
{
if (bytes.Length < 2)
{
throw new PlcException(ErrorCode.ReadData, "Malformed S7 String / too short");
}
int size = bytes[0];
int length = bytes[1];
if (length > size)
{
throw new PlcException(ErrorCode.ReadData, "Malformed S7 String / length larger than capacity");
}
try
{
return StringEncoding.GetString(bytes, 2, length);
}
catch (Exception e)
{
throw new PlcException(ErrorCode.ReadData,
$"Failed to parse {VarType.S7String} from data. Following fields were read: size: '{size}', actual length: '{length}', total number of bytes (including header): '{bytes.Length}'.",
e);
}
}
/// <summary>
/// Converts a <see cref="T:string"/> to S7 string with 2-byte header.
/// </summary>
/// <param name="value">The string to convert to byte array.</param>
/// <param name="reservedLength">The length (in characters) allocated in PLC for the string.</param>
/// <returns>A <see cref="T:byte[]" /> containing the string header and string value with a maximum length of <paramref name="reservedLength"/> + 2.</returns>
public static byte[] ToByteArray(string value, int reservedLength)
{
if (value is null)
{
throw new ArgumentNullException(nameof(value));
}
if (reservedLength > 254) throw new ArgumentException($"The maximum string length supported is 254.");
var bytes = StringEncoding.GetBytes(value);
if (bytes.Length > reservedLength) throw new ArgumentException($"The provided string length ({bytes.Length} is larger than the specified reserved length ({reservedLength}).");
var buffer = new byte[2 + reservedLength];
Array.Copy(bytes, 0, buffer, 2, bytes.Length);
buffer[0] = (byte)reservedLength;
buffer[1] = (byte)bytes.Length;
return buffer;
}
}
}
字符串使用方式,使用特性指定字符串长度：
[S7String(S7StringType.S7WString, 10)]
public string WStringVariable;
[S7String(S7StringType.S7String, 10)]
public string StringVariable;
大家如果有更好的办法，欢迎评论！
