add dlerror() information (#32)

When the uplink library cannot be loaded, there is currently a generic
message originating from PHP. This is in all PHP versions.

This change adds extra information which will help the user diagnose the
issue.

Example of old output:

Fatal error: Uncaught FFI\Exception: Failed loading '/app/build/libuplink-x86_64-linux.so' in /app/src/Uplink.php:42

Example of new output:

Fatal error: Uncaught FFI\Exception: Failed loading '/app/build/libuplink-x86_64-linux.so'. /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by /app/build/libuplink-x86_64-linux.so) in /app/src/Uplink.php:60

Fixes #21

Jenkinsfile

@@ -147,7 +147,7 @@ pipeline {
         stage('PHPStan') {
             agent {
                 docker {
-                    image 'ghcr.io/phpstan/phpstan:1.0.2'
+                    image 'ghcr.io/phpstan/phpstan:1.8.1'
                     args '--mount type=volume,source=phpstan-cache,destination=/tmp/phpstan ' +
                         '--user root:root ' +
                         "--entrypoint='' "

phpstan.neon

@@ -6,14 +6,6 @@ parameters:
 	ignoreErrors:
 		- '/Call to an undefined method FFI::.*/'
 		- '/Access to an undefined property FFI\\CData::.*/'
-		-
-			message: '/Binary operation "-" between numeric-string and string results in an error./'
-			paths:
-			- test/ListObjectsTest.php
-		-
-			message: "#^Binary operation \"\\-\" between int and string results in an error\\.$#"
-			count: 1
-			path: test/StatObjectTest.php
 		-
 			message: "#^Property Storj\\\\Uplink\\\\Access\\:\\:\\$scope is never read, only written\\.$#"
 			count: 1

src/Uplink.php

@@ -36,10 +36,45 @@ public static function create(): self
         $os = str_replace(' ', '_', strtolower(php_uname('s')));
         $extension = strpos($os, 'windows') !== false ? 'dll' : 'so';
 
-        $ffi = FFI::cdef(
-            file_get_contents($root . '/build/uplink-php.h'),
-            "{$root}/build/libuplink-{$arch}-{$os}.{$extension}"
-        );
+        $libuplinkSo = "{$root}/build/libuplink-{$arch}-{$os}.{$extension}";
+        try {
+            $ffi = FFI::cdef(
+                file_get_contents($root . '/build/uplink-php.h'),
+                $libuplinkSo
+            );
+        } catch (\FFI\Exception $ffiException) {
+            // dlerror() may have a more detailed error.
+            // Example: no permission, wrong glibc version, unknown binary format etc.
+            // This check should really be in PHP core.
+            try {
+                $ffi2 = FFI::cdef("
+                    void *dlopen(const char *filename, int flags);
+                    char *dlerror();
+                    int dlclose(void *handle); 
+                ");
+                $handle = $ffi2->dlopen($libuplinkSo, 1);
+                $scope = Scope::exit(function() use ($handle, $ffi2) {
+                    if ($handle !== null) {
+                        $ffi2->dlclose($handle);
+                    }
+                });
+                $cError = $ffi2->dlerror();
+            } catch (\Throwable $innerException) {
+                // error when calling dlopen/dlerror, rethrow original error
+                throw $ffiException;
+            }
+
+            if ($cError == null) {
+                // dlerror had no info, rethrow original error
+                throw $ffiException;
+            }
+
+            $dlErrorMessage = FFI::string($cError);
+
+            throw new \FFI\Exception(
+                $ffiException->getMessage() . ": " . $dlErrorMessage
+            );
+        }
 
         return new self($ffi);
     }