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AMC - ABAP Messaging Channels

ABAP messaging channels (AMC) are a method of communication between ABAP programs using messages. Using a publish-and-subscribe mechanism, messages can be exchanged between any AS ABAP programs, including communication between different user sessions and application services. Data objects with specific data types are allowed as messages. Messages that can be sent and received are:

• Text strings

• Byte strings

• Content that can be serialized in accordance with fixed protocols. Helper classes are available for serializations and deserializations.

ABAP messaging channels are implemented as repository objects that can be accessed in sender and receiver programs using an interface-based an class-based programming interface (API). The classes and interfaces of the API use the naming convention CL_AMC_... and IF_AMC_... respectively. . Communication between different application servers takes places across the message server.

• Messaging Channels as Repository Objects

• Sending AMC Messages

• Receiving AMC Messages

• Point-to-Point Communication

• AMC Security

• AMC - Exceptions

• AMC - Test and Analysis

• More Information

Notes

• Any data object can be sent by being serialized in a suitable way by the sender and deserialized by the receiver. Possible formats include XML or JSON in strings or SAP's own Push Channel Protocol.

• The sendable messages

The length of messages that can be sent is currently restricted to approximately 1 MB. Character strings are converted to the UTF-8 format. The limit can be increased by changing the profile parameter rdisp/long_messages/max_length.

Messaging Channels as Repository Objects

An ABAP messaging channel defined as a repository object must exist for each AMC communication. An ABAP messaging channel like this can be created in Repository Browser in ABAP Workbench by opening the context menu of a package and choosing Connectivity. Connectivity Browser in Object Navigator provides another means of access. To open Object Navigator for AMCs, use transaction SAMC.

An ABAP messaging channel is identified by its assignment to an application and by its name. The name must start with a forward slash character (/) and is not case-sensitive. The following properties can be defined for an ABAP messaging channel:

• Message type

The message type determines the data type of the data objects that can be sent as messaging channels messages. Current scopes are

• TEXT for text strings

• BINARY for byte strings

• PCP for SAP's own Push Channel Protocol (PCP)

• Scope

The scope defines who can receive a message sent using this messaging channel. Current scopes are

• System

All programs of all users sessions in the current AS ABAP can receive messages.

• Client

All programs of user sessions in the current AS ABAP logged on with the same client ID as the sender program can receive messages.

• User

Only programs of user sessions in the current AS ABAP logged on with the same user name and the same client ID as the sender program can receive messages.

No other restrictions apply apart from these settings. More specifically, it is possible to send and receive messages between different application servers.

• Authorized programs

Each program that is authorized to send or receive messages using the messaging channel (or a predecessor program in the current call sequence) must be specified with the appropriate activity in a whitelist. Possible activities are:

• Send, which authorizes the program to send AMC messages

• Receive, which authorizes the program to receive AMC messages

• Bind APC WebSocket as consumer, which authorizes the program (usually the class pool of an APC handler class) to bind its WebSocket connection to an ABAP Messaging Channel. This makes the APC connection partners (such as Web browsers) into AMC consumers.

Example

See the messaging channels /demo_text and /demo_binary of the application DEMO_AMC in the package SABAPDEMOS.

Sending AMC Messages

Before an AMC message can be sent in an authorized program (known as the publish part), the factory method CREATE_MESSAGE_PRODUCER of the system class CL_AMC_CHANNEL_MANAGER must be used to create a sender object for a messaging channel from the repository. The application and name of the channel are passed here. The returned reference variable of type IF_AMC_MESSAGE_PRODUCER must be cast to a type-specific interface that contains a method SEND used to send type-friendly messages. The following interfaces are possible, depending on the type of messaging channel used:

• IF_AMC_MESSAGE_PRODUCER_TEXT

• IF_AMC_MESSAGE_PRODUCER_BINARY

• IF_AMC_MESSAGE_PRODUCER_PCP

Objects of the class CL_AC_MESSAGE_TYPE_PCP, which implement the interface IF_AC_MESSAGE_TYPE_PCP, can be used to create messages for the Push Channel Protocol.

Notes

• The sender of an AMC message implements the publish part of the publish-and-subscribe mechanism in AMC. The sender does not usually know whether receivers are registered for the AMC message.

• The parameter I_SUPPRESS_ECHO of the method CREATE_MESSAGE_PRODUCER can be used to specify whether messages are sent to the current ABAP session or not. It may be helpful to suppress messages like these when joining AMC with APC to stop superfluous messages from being sent.

Executable Examples

• Sending AMC Messages

• Suppressing standalone messages

Receiving AMC Messages

Before an AMC message can be received in an authorized program (known as the subscribe part), the factory method CREATE_MESSAGE_PRODUCER of the system class CL_AMC_CHANNEL_MANAGER must be used to create a consumer for a messaging channel from the repository. The application and name of the channel are passed here. The returned reference variable has the type IF_AMC_MESSAGE_CONSUMER. The consumer methods START_MESSAGE_DELIVERY and STOP_MESSAGE_DELIVERY have two tasks:

• Definition of the AMC receiver phase

The method START_MESSAGE_DELIVERY makes the receiver program for the messaging channel of the consumer ready to receive messages. The method STOP_MESSAGE_DELIVERY undoes this step. Messages sent using the messaging channel are received only if the program is made ready to receive.

• Registration of the receiver objects for messaging channel messages

Receiver objects are instances of local or global classes that implement at least one of the type-specific interfaces

• IF_AMC_MESSAGE_RECEIVER_TEXT

• IF_AMC_MESSAGE_RECEIVER_BINARY

• IF_AMC_MESSAGE_RECEIVER_PCP

. These interfaces each have a RECEIVE method used as a callback routine for the messaging channel for which a receiver object is registered. The input parameters of the callback routines receive the messages sent during registration in a type-friendly way and can be processed or forwarded in the methods. An object of the class CL_AC_MESSAGE_TYPE_PCP, pointed to by the attribute PCP_MESSAGE of the receiver object, can be used to read messages in SAP's own Push Channel Protocol.

When the receiver objects are registered, object references to them are created in the AMC framework to keep them alive. It is also possible to deregister the objects using the method STOP_MESSAGE_DELIVERY. This deletes the references. The objects are deregistered implicitly at the end of the program.

Once one or more receiver objects have been registered, the statement WAIT FOR MESSAGING CHANNELS can be used to put the program in a wait state where it is ready to receive the messages. If, while the program is waiting, a message is received through a messaging channel for which a receiver object is registered, the associated RECEIVE method is executed and a check is made to see whether a logical condition is true or false. The wait state is persisted as long as the condition is false (but a maximum duration can be configured). In this way, multiple messages can be consumed until a message is received that ends the wait state.

Notes

• The methods START_MESSAGE_DELIVERY and STOP_MESSAGE_DELIVERY both cause a database commit.

• It is not possible to receive AMC messages during the update process.

Executable Example

Receiving AMC Messages

Point-to-Point Communication

Alongside the publish-and-subscribe mechanism, where the sender of message does not know the receivers, AMC also provides point-to-point communication, where a sender can create an AMC message for a specific receiver. The ID of the receiver session is required here.

• A receiver can use the static method GET_CONSUMER_SESSION_ID of the class CL_AMC_CHANNEL_MANAGER to get the ID of its session and pass it to the sender in an appropriate way.

• A sender that knows the ID of a receiver session can use the factory method CREATE_MESSAGE_PRODUCER_BY_ID of the class CL_AMC_CHANNEL_MANAGER to create a special sender object for point-to-point communication for this receiver session. An AMC message sent using an object like this is only processed by the receiver of the receiver session passed to the parameter I_CONSUMER_SESSION_ID.

The parameter I_COMMUNICATION_TYPE of the method CREATE_MESSAGE_PRODUCER_BY_ID can be used to configure whether a message is sent synchronously or asynchronously, with the latter the default. When a message is sent synchronously, the sender waits for confirmation that the message was passed to the receiver session. It raises an exception if this is not the case.

Executable Example

The executable example Receiving AMC Messages displays the ID of the receiver session. If this ID is entered in the example Sending AMC Messages, the message is sent synchronously and to this receiver session only.

AMC Security

Access to an ABAP messaging channel is controlled by specifying the authorized programs and their activities. When binding an APC WebSocket and when receiving using an APC WebSocket as a consumer, it is also possible to specify a virus scan profile to be used for the check performed by the virus scan interface (VSI).

AMC - Exceptions

Error situations in sender and receiver programs (such as violations of rules set by the properties of a messaging channel) raise exceptions of the class CX_AMC_ERROR.

AMC - Test and Analysis

AMC messages are both sent and received in AS ABAP, which means that existing test and analysis tools, such as ABAP Debugger, runtime analysis, or performance trace can be used as previously. There is also a special AMC logger:

• The transaction AMC_LOG_ADMIN can be used to switch AMC logging on and off for specific ABAP messaging channels.

• The transaction AMC_LOG_PROCESSING can be used to manage the AMC log entries.

The transaction SMAMC provides an overview of all ABAP messaging channels for which AMC consumers are registered.

More Information

Detailed information about AMC can be found in the ABAP Channels documentation in SAP Help Portal.

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WAIT FOR MESSAGING CHANNELS
Examples of AMC