SAMMessage::header

The header properties of the message.

&reftitle.description; `object` `SAMMessage->header`

The `header` property is a container for any system or user properties that area associated with the message.

Properties may be assigned by the sender of a message to control the way the messaging systems handles it or may be assigned by the messaging system itself to tell the recipient extra information about the message or the way in which it has been handled.

Some properties are understood by SAM in which case constants have been defined for them. The majority of properties however are ignored by the SAM implementation and simply passed through to the underlying messaging systems allowing the application to use messaging specific property names or to define its own "user" properties.

The SAM defined properties are as follows:

Property name | Possible values
`SAM_MESSAGEID` | When a message is received this field contains the unique identifier of the message as allocated by the underlying messaging system. When sending a message this field is ignored.
`SAM_REPLY_TO` | A string providing the identity of the queue on to which responses to this message should be posted.
`SAM_TYPE` | An indication of the type of message to be sent. The value may be `SAM_TEXT` indicating the contents of the message body is a text string, or `SAM_BYTES` indicating the contents of the message body are some application defined format. The way in which this property is used may depend on the underlying messaging server. For instance a messaging server that supports the `JMS (Java Message Service)` specification may interpret this value and send messages of type "`jms_text`" and "`jms_bytes`". In addition, if the `SAM_TYPE` property is set to `SAM_TEXT` the data provided for the message body is expected to be a UTF8 encoded string.

When setting the values of properties it is often useful to give a hint as to the format in which the property should be delivered to the messaging system. By default property values are delivered as text and the following simple syntax may be used to set a value:

### Setting a text format property using the default syntax

    <?php
    $msg = new SAMMessage();

    $msg->header->myPropertyName = 'textData';
    ?>

If it is desired to pass type information an alternative syntax may be used where the value and the type hint are passed in an associative array:

### Setting a text format property using a type hint

    <?php
    $msg = new SAMMessage();

    $msg->header->myPropertyName = array('textData', SAM_STRING);
    ?>

When passing a type hint the type entry should be one of the SAM defined constant values as defined by the following table:

Constant | Type description
`SAM_BOOLEAN` | Any value passed will be interpreted as logical true or false. If the value cannot be interpreted as a PHP boolean value the value passed to the messaging system is undefined.
`SAM_BYTE` | An 8-bit signed integer value. SAM will attempt to convert the property value specified into a single byte value to pass to the messaging system. If a string value is passed an attempt will be made to interpret the string as a numeric value. If the numeric value cannot be expressed as an 8-bit signed binary value data may be lost in the conversion.
`SAM_DOUBLE` | A long floating point value. SAM will attempt to convert the property value specified into a floating point value with 15 digits of precision. If a string value is passed an attempt will be made to interpret the string as a numeric value. If the passed value cannot be expressed as a 15 digit floating point value data may be lost in the conversion.
`SAM_FLOAT` | A short floating point value. SAM will attempt to convert the property value specified into a floating point value with 7 digits of precision. If a string value is passed an attempt will be made to interpret the string as a numeric value. If the passed value cannot be expressed as a 7 digit floating point value data may be lost in the conversion.
`SAM_INT` | An 32-bit signed integer value. SAM will attempt to convert the property value specified into a 32-bit value to pass to the messaging system. If a string value is passed an attempt will be made to interpret the string as a numeric value. If the numeric value cannot be expressed as an 32-bit signed binary value data may be lost in the conversion.
`SAM_LONG` | An 64-bit signed integer value. SAM will attempt to convert the property value specified into a 64-bit value to pass to the messaging system. If a string value is passed an attempt will be made to interpret the string as a numeric value. If the numeric value cannot be expressed as an 64-bit signed binary value data may be lost in the conversion.
`SAM_STRING` | SAM will interpret the property value specified as a string and pass it to the messaging system accordingly.

&reftitle.examples;

### Setting properties as the sender of a message

    <?php
    $msg = new SAMMessage('This is a test message');

    // defining SAM specific properties...
    $msg->header->SAM_REPLY_TO = 'queue://test/replyQueue';

    // defining arbitrary properties...
    //
    // a default string property
    $msg->header->myStringProp1 = 'a string property';
    // a string property with a type hint
    $msg->header->myStringProp2 = array('another string property', SAM_STRING);

    // a boolean property
    $msg->header->myBoolProp = array(FALSE, SAM_BOOL);

    // numeric format properties
    $msg->header->myIntProp = array(32768, SAM_INT);
    $msg->header->myLongProp = array(9876543, SAM_LONG);
    $msg->header->myByteProp1 = array(123, SAM_BYTE);
    $msg->header->myByteProp2 = array('12', SAM_BYTE);
    $msg->header->myFloatProp = array(3.141592, SAM_FLOAT);
    $msg->header->myDoubleProp = array(3.14159265358979, SAM_DOUBLE);
    ?>

### Retreiving property values from a message

    <?php

    // accessing an application specific property
    $intProp = $msg->header->MyIntProp;

    // accessing a messaging system specific property
    $encoding = $msg->header->JMS_IBM_Msgtype;

    ?>

&reftitle.seealso;

- sammessage.body