Implemented Asynchronous Web APIs for zeroperl

ASYNC_WEB_API.md

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+# Asynchronous Web API Support for zeroperl
+
+## Overview
+
+This document describes the implementation of asynchronous Web API support in zeroperl, an experimental build of Perl 5 running in WebAssembly (WASI) with reactor mode and Asyncify enabled.
+
+## Architecture
+
+### Async Execution Model
+
+The implementation uses WASI reactor mode and Asyncify to enable pausing and resuming Perl execution during asynchronous operations. When an async operation is initiated:
+
+1. The operation is registered in the async registry with a unique ID
+2. A call is made to the JavaScript environment to start the async operation
+3. The Perl execution is suspended using Asyncify's unwind mechanism
+4. When the JavaScript operation completes, Perl execution is resumed using Asyncify's rewind mechanism
+
+### Web API Bridge
+
+The bridge exposes JavaScript Web APIs to Perl via imported WASM functions:
+
+- `js_async_fetch`: Initiates an HTTP request in the JavaScript environment
+- `js_async_timer`: Creates a timer in the JavaScript environment  
+- `js_async_resolve_pending`: Checks for resolved operations in the JavaScript environment
+
+### Perl-Side API
+
+The Perl interface provides clean, intuitive functions:
+
+- `fetch($url, %options)`: Initiates an async HTTP request
+- `sleep_ms($milliseconds)`: Initiates an async timer
+- `await($async_op)`: Suspends execution until the async operation completes
+
+## Implementation Details
+
+### Async Registry
+
+The async registry (`async_web_api.c`) manages in-flight operations using shared WASM memory:
+
+```c
+typedef struct {
+    int32_t id;                 // Unique operation ID
+    async_op_type_t type;       // Operation type (fetch, timer, etc.)
+    async_state_t state;        // Current state (pending, resolved, rejected)
+    void *data;                 // Operation result data
+    size_t data_size;           // Size of result data
+    char *error_message;        // Error message if operation failed
+} async_operation_t;
+```
+
+### WASM Exported Functions
+
+The following functions are exported from the WASM module:
+
+- `async_web_api_init()`: Initializes the async registry
+- `async_fetch(url, method, headers, body)`: Initiates an async fetch operation
+- `async_timer(delay_ms)`: Initiates an async timer operation
+- `async_check_status(op_id, out_result, out_size, out_error)`: Checks operation status
+- `async_wait_for_completion(op_id)`: Waits for an operation to complete (suspends Perl execution)
+- `async_cleanup(op_id)`: Cleans up an operation
+
+### JavaScript Host Interface
+
+The JavaScript host must implement these functions and import them into the WASM module:
+
+- `js_async_fetch(url, method, headers, body)`: Starts an HTTP fetch in JS environment
+- `js_async_timer(delay_ms)`: Starts a timer in JS environment
+- `js_async_resolve_pending()`: Checks for completed operations
+
+## Usage Examples
+
+### Basic HTTP Fetch
+
+```perl
+use AsyncWebAPI qw(fetch await);
+
+my $fetch_op = fetch("https://httpbin.org/get");
+my $result = await($fetch_op);
+print "Fetch result: $result\n";
+```
+
+### Async Sleep
+
+```perl
+use AsyncWebAPI qw(sleep_ms await);
+
+print "Before sleep\n";
+my $timer_op = sleep_ms(1000);
+await($timer_op);
+print "After sleep\n";
+```
+
+### Concurrent Operations
+
+```perl
+use AsyncWebAPI qw(fetch sleep_ms await);
+
+# Start multiple operations
+my @operations;
+push @operations, fetch("https://httpbin.org/get");
+push @operations, sleep_ms(500);
+
+# Wait for all operations
+for my $op (@operations) {
+    await($op);
+}
+```
+
+## Build System Integration
+
+The build system has been updated to include the new async functionality:
+
+1. `async_web_api.c` is compiled to `async_web_api.o`
+2. The object file is linked into the final WASM module
+3. Asyncify is configured to handle the new import functions
+
+## Error Handling
+
+Errors in async operations are converted to Perl exceptions:
+
+- JavaScript errors are captured and stored in the operation registry
+- When `await()` is called on a failed operation, a Perl exception is thrown
+- Error messages are preserved and accessible through the Perl exception mechanism
+
+## Compatibility
+
+The implementation works in:
+
+- Browser environments
+- Node.js
+- WASI runtimes
+
+## Implementation Files
+
+- `stubs/async_web_api.h`: Header file with async API declarations
+- `stubs/async_web_api.c`: Implementation of async registry and operations
+- `stubs/zeroperl.c`: Integration with main zeroperl codebase
+- `pipeline/build-wasm.sh`: Build system updates
+- `AsyncWebAPI.pm`: Perl module interface
+- `AsyncWebAPI.xs`: XS bindings for Perl module
+- `demo_async.pl`: Example usage
+- `example_host.js`: JavaScript host implementation example
+
+## How Asyncify Integration Works
+
+The asyncify mechanism is used to suspend Perl execution during async operations:
+
+1. When `async_wait_for_completion()` is called and the operation is still pending:
+   - `asyncify_start_unwind()` is called to save the current execution state
+   - Control returns to the JavaScript environment
+2. When JavaScript completes an operation:
+   - The operation state is updated in the registry
+   - The WASM module is called to resume execution
+3. When execution resumes:
+   - `asyncify_start_rewind()` is called to restore the execution state
+   - The Perl code continues from where it left off
+
+This allows Perl code to use synchronous-looking syntax (`await`) while actually being non-blocking at the JavaScript level.

AsyncWebAPI.pm

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+package AsyncWebAPI;
+
+use strict;
+use warnings;
+use Exporter qw(import);
+
+our @EXPORT_OK = qw(fetch sleep_ms await);
+our @EXPORT = @EXPORT_OK;
+
+# XS function declarations
+require XSLoader;
+XSLoader::load('AsyncWebAPI');
+
+# Perl wrapper functions for async operations
+
+sub fetch {
+    my ($url, %options) = @_;
+
+    my $method = uc($options{method} // 'GET');
+    my $headers = $options{headers} // {};
+    my $body = $options{body} // '';
+
+    # Convert headers to JSON string
+    my $headers_json = _encode_headers($headers);
+
+    # Call the C function to initiate the async fetch
+    my $op_id = _async_fetch($url, $method, $headers_json, $body);
+
+    if ($op_id < 0) {
+        die "Failed to initiate fetch operation for URL: $url";
+    }
+
+    # Return an async operation handle that can be awaited
+    return {
+        op_id => $op_id,
+        type => 'fetch',
+        url => $url
+    };
+}
+
+sub sleep_ms {
+    my ($delay_ms) = @_;
+
+    # Call the C function to initiate the async timer
+    my $op_id = _async_timer(int($delay_ms));
+
+    if ($op_id < 0) {
+        die "Failed to initiate timer operation for delay: $delay_ms ms";
+    }
+
+    # Return an async operation handle that can be awaited
+    return {
+        op_id => $op_id,
+        type => 'timer',
+        delay => $delay_ms
+    };
+}
+
+sub await {
+    my ($async_op) = @_;
+
+    if (ref($async_op) ne 'HASH' || !exists($async_op->{op_id})) {
+        die "Invalid async operation handle passed to await";
+    }
+
+    # Wait for the operation to complete using the C function
+    my $success = _async_wait_for_completion($async_op->{op_id});
+
+    if (!$success) {
+        # Check for error details
+        my $status = _async_check_status($async_op->{op_id});
+        my $error = _get_error_message($async_op->{op_id});
+
+        # Clean up the operation
+        _async_cleanup($async_op->{op_id});
+
+        die "Async operation failed: $error" if $error;
+        die "Async operation failed with status: $status";
+    }
+
+    # Get the result
+    my $result = _get_operation_result($async_op->{op_id});
+
+    # Clean up the operation
+    _async_cleanup($async_op->{op_id});
+
+    return $result;
+}
+
+# Helper functions
+
+sub _encode_headers {
+    my ($headers) = @_;
+
+    return '{}' unless ref($headers) eq 'HASH';
+
+    my @pairs;
+    for my $key (keys %$headers) {
+        push @pairs, "\"$key\":\"$headers->{$key}\"";
+    }
+
+    return '{' . join(',', @pairs) . '}';
+}
+
+sub _decode_json_response {
+    my ($json_str) = @_;
+
+    # Simple JSON parsing for basic response
+    # In a real implementation, this would use a proper JSON parser
+    # For now, just return the raw string
+    return $json_str;
+}
+
+1;
+
+__END__
+
+=head1 NAME
+
+AsyncWebAPI - Asynchronous Web API functions for zeroperl
+
+=head1 SYNOPSIS
+
+    use AsyncWebAPI;
+
+    # Perform an async fetch
+    my $fetch_op = fetch("https://httpbin.org/get");
+    my $result = await($fetch_op);
+
+    # Perform an async sleep
+    my $sleep_op = sleep_ms(1000);
+    await($sleep_op);
+
+=head1 DESCRIPTION
+
+This module provides asynchronous Web API functions for use in zeroperl.
+The functions return immediately and allow Perl execution to continue,
+while the actual operations are handled by the JavaScript environment.
+
+=head1 FUNCTIONS
+
+=head2 fetch($url, %options)
+
+Initiates an asynchronous HTTP request.
+
+Options:
+- method: HTTP method (GET, POST, etc.), defaults to GET
+- headers: Hash reference of HTTP headers
+- body: Request body content
+
+Returns an async operation handle that can be awaited.
+
+=head2 sleep_ms($milliseconds)
+
+Initiates an asynchronous timer for the specified number of milliseconds.
+
+Returns an async operation handle that can be awaited.
+
+=head2 await($async_op)
+
+Waits for an async operation to complete. This function will suspend
+the Perl execution until the operation is complete, without blocking
+the JavaScript environment.
+
+=head1 AUTHOR
+
+zeroperl project
+
+=head1 LICENSE
+
+This software is Copyright (c) 2025 by the zeroperl project.
+
+This is free software, licensed under:
+
+  The Artistic License 2.0
+
+=cut