Context in COBOL

Here’s the translation of the Go code to COBOL, with explanations in Markdown format suitable for Hugo:

Our example demonstrates a simple HTTP server that uses context for controlling cancellation. In COBOL, we don’t have built-in HTTP server capabilities or context management, so we’ll simulate these concepts using file handling and basic program flow control.

       IDENTIFICATION DIVISION.
       PROGRAM-ID. CONTEXT-EXAMPLE.
       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT SIMULATED-REQUEST ASSIGN TO "REQUEST.TXT"
               ORGANIZATION IS LINE SEQUENTIAL.

       DATA DIVISION.
       FILE SECTION.
       FD SIMULATED-REQUEST.
       01 REQUEST-LINE PIC X(80).

       WORKING-STORAGE SECTION.
       01 WS-EOF         PIC A(1).
       01 WS-TIMER       PIC 9(8) VALUE 0.
       01 WS-CANCEL-FLAG PIC A(1) VALUE 'N'.

       PROCEDURE DIVISION.
       MAIN-PROCEDURE.
           DISPLAY "SERVER: STARTED"
           PERFORM HANDLE-REQUEST
           STOP RUN.

       HANDLE-REQUEST.
           OPEN INPUT SIMULATED-REQUEST
           READ SIMULATED-REQUEST
               AT END
                   MOVE 'Y' TO WS-EOF
               NOT AT END
                   DISPLAY "SERVER: REQUEST HANDLER STARTED"
                   PERFORM PROCESS-REQUEST
           END-READ
           CLOSE SIMULATED-REQUEST
           DISPLAY "SERVER: REQUEST HANDLER ENDED".

       PROCESS-REQUEST.
           PERFORM VARYING WS-TIMER FROM 1 BY 1 UNTIL WS-TIMER > 10
               IF WS-CANCEL-FLAG = 'Y'
                   DISPLAY "SERVER: REQUEST CANCELLED"
                   EXIT PERFORM
               END-IF
               CALL 'CBL_OC_NANOSLEEP' USING 1000000000
           END-PERFORM
           IF WS-CANCEL-FLAG = 'N'
               DISPLAY "SERVER: HELLO"
           ELSE
               DISPLAY "SERVER: INTERNAL SERVER ERROR"
           END-IF.

In this COBOL program:

We use a file (REQUEST.TXT) to simulate incoming HTTP requests.
The HANDLE-REQUEST paragraph simulates the HTTP server’s request handling.
PROCESS-REQUEST simulates the work done by the server, including the 10-second wait.
We use WS-CANCEL-FLAG to simulate context cancellation. In a real scenario, this flag could be set by another part of the program or by an external signal.
The CBL_OC_NANOSLEEP call is used to simulate the time.After functionality in Go. This is a non-standard extension and may not be available in all COBOL compilers.

To run this program:

Save the code in a file, for example, context-example.cob.
Create a REQUEST.TXT file with any content to simulate a request.
Compile and run the program using your COBOL compiler. The exact commands will depend on your COBOL environment.

$ cobc -x context-example.cob
$ ./context-example
SERVER: STARTED
SERVER: REQUEST HANDLER STARTED
SERVER: HELLO
SERVER: REQUEST HANDLER ENDED

To simulate cancellation, you would need to modify the program to set WS-CANCEL-FLAG to ‘Y’ during execution, which would result in:

SERVER: STARTED
SERVER: REQUEST HANDLER STARTED
SERVER: REQUEST CANCELLED
SERVER: INTERNAL SERVER ERROR
SERVER: REQUEST HANDLER ENDED

This example demonstrates how we can adapt concepts like context and cancellation to COBOL, even though the language doesn’t have built-in support for these features.

Command Line Flags in COBOL

Environment Variables in COBOL

Learn X By Example

Title here

Context in COBOL