Handle exceptions generating cache values (#70)

* feature: handle exceptions generating cache values
closes #13

* feature: handle exceptions generating cache values
closes #13

* ci: codacy

Author: g105b

.codacy.yml

@@ -0,0 +1,5 @@
+exclude_paths:
+  - ".github/**"
+  - "example/**"
+  - "test/**"
+

README.md

@@ -44,6 +44,10 @@ $location = $fileCache->get("lat-lon", $lookup);
 echo "Your location is: $location";
 ```
 
+If generating a fresh value fails, throw `Gt\FileCache\CacheValueGenerationException`
+from the callback. The cache will ignore that failure and skip writing a replacement
+value, which leaves `null` available as a legitimate cached value.
+
 # Proudly sponsored by
 
 [JetBrains Open Source sponsorship program](https://www.jetbrains.com/community/opensource/)

example/01-latlon.php

@@ -17,7 +17,26 @@
 function httpJson(string $uri):object {
 	$ch = curl_init($uri);
 	curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
-	return json_decode(curl_exec($ch));
+	curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 5);
+	curl_setopt($ch, CURLOPT_TIMEOUT, 10);
+
+	$response = curl_exec($ch);
+	if($response === false) {
+		throw new Gt\FileCache\CacheValueGenerationException(curl_error($ch));
+	}
+
+	try {
+		return json_decode($response, flags: JSON_THROW_ON_ERROR);
+	}
+	catch(JsonException $exception) {
+		throw new Gt\FileCache\CacheValueGenerationException(
+			"Invalid JSON returned from $uri",
+			previous: $exception,
+		);
+	}
+	finally {
+		curl_close($ch);
+	}
 }
 
 $ipAddress = $fileCache->get("ip", function():string {

src/Cache.php

@@ -29,9 +29,14 @@ public function get(
 			return $this->fileAccess->getData($name);
 		}
 		catch(FileNotFoundException|CacheInvalidException) {
-			$value = $callback();
-			$this->fileAccess->setData($name, $value);
-			return $value;
+			try {
+				$value = $callback();
+				$this->fileAccess->setData($name, $value);
+				return $value;
+			}
+			catch(CacheValueGenerationException) {
+				return null;
+			}
 		}
 	}
 

src/CacheValueGenerationException.php

@@ -0,0 +1,4 @@
+<?php
+namespace Gt\FileCache;
+
+class CacheValueGenerationException extends FileCacheException {}

test/phpunit/CacheTest.php

@@ -2,7 +2,10 @@
 namespace Gt\FileCache\Test;
 
 use Gt\FileCache\Cache;
+use Gt\FileCache\CacheInvalidException;
+use Gt\FileCache\CacheValueGenerationException;
 use Gt\FileCache\FileAccess;
+use Gt\FileCache\FileNotFoundException;
 use PHPUnit\Framework\TestCase;
 use SplFileInfo;
 use SplFixedArray;
@@ -49,6 +52,52 @@ public function testGet_multipleCallsDoesNotCallbackMultipleTimes():void {
 		self::assertSame(1, $count);
 	}
 
+	public function testGet_nullValueCanBeCached():void {
+		$sut = $this->getSut();
+		$count = 0;
+
+		$callback = function()use(&$count):null {
+			$count++;
+			return null;
+		};
+
+		self::assertNull($sut->get("test-null", $callback));
+		self::assertNull($sut->get("test-null", $callback));
+		self::assertSame(1, $count);
+	}
+
+	public function testGet_generationExceptionDoesNotWriteInvalidValue():void {
+		$fileAccess = self::createMock(FileAccess::class);
+		$fileAccess->expects(self::once())
+			->method("checkValidity")
+			->with("test", 3600)
+			->willThrowException(new FileNotFoundException("test"));
+		$fileAccess->expects(self::never())
+			->method("setData");
+
+		$sut = new Cache(fileAccess: $fileAccess);
+
+		self::assertNull($sut->get("test", function():never {
+			throw new CacheValueGenerationException("Lookup failed");
+		}));
+	}
+
+	public function testGet_invalidCache_generationExceptionDoesNotWriteReplacement():void {
+		$fileAccess = self::createMock(FileAccess::class);
+		$fileAccess->expects(self::once())
+			->method("checkValidity")
+			->with("test", 3600)
+			->willThrowException(new CacheInvalidException("test"));
+		$fileAccess->expects(self::never())
+			->method("setData");
+
+		$sut = new Cache(fileAccess: $fileAccess);
+
+		self::assertNull($sut->get("test", function():never {
+			throw new CacheValueGenerationException("Lookup failed");
+		}));
+	}
+
 	public function testGetString():void {
 		$value = uniqid();
 		$sut = $this->getSut([