Add manual instrumentation steps for PHP 7.3 (#37)

* Add PHP 7.3 manual instrumentation

* Update README

php/.gitignore

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+/vendor/
+vendor/
+.env
+.env.backup
+.phpunit.result.cache 

php/core/7.3/Dockerfile

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+FROM php:7.3-apache
+
+RUN apt-get update && apt-get install -y \
+    git \
+    unzip \
+    libzip-dev \
+    && docker-php-ext-install zip
+
+RUN curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
+
+WORKDIR /var/www/html
+
+COPY . .
+
+# Install Composer dependencies
+RUN composer require guzzlehttp/guzzle
+
+RUN chown -R www-data:www-data /var/www/html
+
+RUN a2enmod rewrite

php/core/7.3/README.md

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+# PHP 7.3 Manual-Instrumentation with OpenTelemetry and Last9
+
+This guide explains how to use Last9's OpenTelemetry traces endpoint to ingest PHP 7.3 application traces using OpenTelemetry.
+
+## Note
+
+Note that this is a manual instrumentation, which means that you need to instrument each endpoint manually. OpenTelemetry Auto-Instrumentation is not supported for PHP 7.3 which is why we need to do this manually.
+
+## Prerequisites
+
+- PHP 7.3
+- Composer
+
+## Setting up instrumentation
+
+Add the following to your `composer.json` file:
+
+```
+"require": {
+    "guzzlehttp/guzzle": "^7.0"
+}
+```
+
+Create `instrumentation.php` file with the following content:
+```
+<?php
+use GuzzleHttp\Client;
+
+// Replace with your Last9 OpenTelemetry endpoint
+define('OTLP_COLLECTOR_URL', '$last9_otlp_endpoint/v1/traces');
+
+// Function to create and send traces to Last9
+function instrumentHTTPRequest($operationName, $attributes = []) {
+    $traceId = bin2hex(random_bytes(16));
+    $spanId = bin2hex(random_bytes(8));
+    $timestamp = (int)(microtime(true) * 1e6);
+
+    $tracePayload = [
+        "resourceSpans" => [
+            [
+                "resource" => [
+                    "attributes" => [
+                        ["key" => "service.name", "value" => ["stringValue" => "<service_name>"]],
+                        ["key" => "deployment.environment", "value" => ["stringValue" => "<environment>"]],
+                        ["key" => "host.name", "value" => ["stringValue" => gethostname()]],
+                        ["key" => "os.type", "value" => ["stringValue" => PHP_OS]],
+                        ["key" => "process.runtime.name", "value" => ["stringValue" => "php"]],
+                        ["key" => "process.runtime.version", "value" => ["stringValue" => PHP_VERSION]]
+                    ]
+                ],
+                "scopeSpans" => [
+                    [
+                        "spans" => [
+                            [
+                                "traceId" => $traceId,
+                                "spanId" => $spanId,
+                                "name" => $operationName,
+                                "kind" => 2, // Server = 2 as per OTEL spec
+                                "startTimeUnixNano" => $timestamp * 1000,
+                                "endTimeUnixNano" => ($timestamp + 1000) * 1000,
+                                "attributes" => array_merge(
+                                    array_map(function ($key, $value) {
+                                        return ["key" => $key, "value" => ["stringValue" => (string)$value]];
+                                    }, array_keys($attributes), $attributes),
+                                    [
+                                        ["key" => "http.method", "value" => ["stringValue" => $_SERVER['REQUEST_METHOD'] ?? 'UNKNOWN']],
+                                        ["key" => "http.target", "value" => ["stringValue" => $_SERVER['REQUEST_URI'] ?? '']],
+                                        ["key" => "http.host", "value" => ["stringValue" => $_SERVER['HTTP_HOST'] ?? '']],
+                                        ["key" => "http.scheme", "value" => ["stringValue" => isset($_SERVER['HTTPS']) ? 'https' : 'http']],
+                                        ["key" => "http.status_code", "value" => ["intValue" => http_response_code()]],
+                                        ["key" => "http.response_content_length", "value" => ["intValue" => isset($response) ? strlen($response) : 0]],
+                                        ["key" => "http.user_agent", "value" => ["stringValue" => $_SERVER['HTTP_USER_AGENT'] ?? '']],
+                                        ["key" => "net.peer.ip", "value" => ["stringValue" => $_SERVER['REMOTE_ADDR'] ?? '']]
+                                    ]
+                                ),
+                                "status" => [
+                                    "code" => http_response_code() < 400 ? 1 : 2, // OK = 1, ERROR = 2
+                                    "message" => http_response_code() >= 400 ? "HTTP " . http_response_code() : ""
+                                ]
+                            ]
+                        ]
+                    ]
+                ]
+            ]
+        ]
+    ];
+
+    try {
+        // Send the main response to the client first
+        if (function_exists('fastcgi_finish_request')) {
+            fastcgi_finish_request();
+        }
+        
+        // Prevent the script from being terminated even if the client disconnects
+        ignore_user_abort(true);
+        
+        // Set unlimited time for the background process
+        set_time_limit(0);
+        
+        $client = new Client([
+            'timeout' => 5, // Add a timeout to prevent hanging
+            'connect_timeout' => 2
+        ]);
+        
+        $response = $client->post(OTLP_COLLECTOR_URL, [
+            'json' => $tracePayload,
+            'headers' => [
+                'Content-Type' => 'application/json',
+                'Authorization' => 'Basic <$last9_otlp_header>')
+            ]
+        ]);
+        
+        error_log("[OpenTelemetry] Trace sent successfully: " . $operationName);
+        return true;
+    } catch (\Exception $e) {
+        error_log("[OpenTelemetry] Failed to send trace: " . $e->getMessage());
+        return false;
+    }
+}
+```
+
+Replace `<service_name>` and `<environment>` with your service name and environment.
+
+## Instrumenting HTTP endpoints
+
+For any endpoint that you want to instrument, you can call the `instrumentHTTPRequest` function with the operation name and attributes. All attributes are optional, but they will help you to filter traces in Last9. 
+
+For example, if you want to instrument the `/rolldice` endpoint, you can call the `instrumentHTTPRequest` function with the operation name and attributes.
+
+```
+instrumentHTTPRequest('GET /rolldice', ['result' => strval($result)]);
+```
+
+Operation name is the HTTP method and path. You can standardize it as follows:
+
+```
+$method = $_SERVER['REQUEST_METHOD'];
+$operationName = $method . ' ' . $uri;
+```
+
+## Visualizing traces in Last9
+
+You can visualize traces in Last9 by going to the [Trace Explorer](https://app.last9.io/traces) and filtering by the operation name.

php/core/7.3/composer.json

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+{
+    "require": {
+        "guzzlehttp/guzzle": "^7.0"
+    },
+    "autoload": {
+        "psr-4": {
+            "App\\": "src/"
+        }
+    }
+}