From c304e18810d3664d025174eec57f4e5fa0fc9372 Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Tue, 27 Aug 2019 14:34:04 -0700
Subject: [PATCH 01/10] feat: add srcset generation function

---
 src/Imgix/UrlBuilder.php | 60 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/src/Imgix/UrlBuilder.php b/src/Imgix/UrlBuilder.php
index 8489dc3..f4d30a2 100644
--- a/src/Imgix/UrlBuilder.php
+++ b/src/Imgix/UrlBuilder.php
@@ -57,4 +57,64 @@ public function createURL($path, $params=array()) {
 
         return $uh->getURL();
     }
+
+    public function createSrcSet($path, $params=array()) {
+        $width = array_key_exists('w', $params) ? $params['w'] : NULL;
+        $height = array_key_exists('h', $params) ? $params['h'] : NULL;
+        $aspectRatio = array_key_exists('ar', $params) ? $params['ar'] : NULL;
+
+        if (($width) || ($height && $aspectRatio)) {
+            return $this->createDPRSrcSet($path, $params);
+        }
+        else {
+            return $this->createSrcSetPairs($path, $params);
+        }
+    }
+
+    private function createDPRSrcSet($path, $params) {
+        $srcset = "";
+        $targetRatios = array(1, 2, 3, 4, 5);
+        $url = $this->createURL($path, $params);
+
+        $size = count($targetRatios);
+        for($i = 0; $i < $size; $i++) {
+            $currentRatio = $targetRatios[$i];
+            $srcset .= $url." ".$currentRatio."x,\n";
+        }
+
+        return substr($srcset, 0, strlen($srcset)-2);
+    }
+
+    private function createSrcSetPairs($path, $params) {
+        $srcset = "";
+        $currentWidth = NULL;
+        $currentParams = NULL;
+        $targetWidths = $this->targetWidths();
+
+        $size = count($targetWidths);
+        for($i = 0; $i < $size; $i++) {
+            $currentWidth = $targetWidths[$i];
+            $currentParams = $params;
+            $currentParams['w'] = $currentWidth;
+            $srcset .= $this->createURL($path, $currentParams) . " " . $currentWidth . "w,\n";
+        }
+
+        return substr($srcset, 0, strlen($srcset)-2);
+    }
+
+    private function targetWidths() {
+        $resolutions = array();
+        $prev = 100;
+        $INCREMENT_PERCENTAGE = 8;
+        $MAX_SIZE = 8192;
+
+
+        while ($prev <= $MAX_SIZE) {
+            array_push($resolutions, 2 * round($prev / 2));
+            $prev *= 1 + ($INCREMENT_PERCENTAGE / 100) * 2;
+        }
+
+        array_push($resolutions, $MAX_SIZE);
+        return $resolutions;
+    }
 }

From 3857ef43140eb0113c0d1bd1f360b3c67f89222e Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Tue, 27 Aug 2019 21:40:47 -0700
Subject: [PATCH 02/10] style: spacing; separate rounding to helper function

---
 src/Imgix/UrlBuilder.php | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/Imgix/UrlBuilder.php b/src/Imgix/UrlBuilder.php
index f4d30a2..600aef0 100644
--- a/src/Imgix/UrlBuilder.php
+++ b/src/Imgix/UrlBuilder.php
@@ -77,7 +77,7 @@ private function createDPRSrcSet($path, $params) {
         $url = $this->createURL($path, $params);
 
         $size = count($targetRatios);
-        for($i = 0; $i < $size; $i++) {
+        for ($i = 0; $i < $size; $i++) {
             $currentRatio = $targetRatios[$i];
             $srcset .= $url." ".$currentRatio."x,\n";
         }
@@ -92,7 +92,7 @@ private function createSrcSetPairs($path, $params) {
         $targetWidths = $this->targetWidths();
 
         $size = count($targetWidths);
-        for($i = 0; $i < $size; $i++) {
+        for ($i = 0; $i < $size; $i++) {
             $currentWidth = $targetWidths[$i];
             $currentParams = $params;
             $currentParams['w'] = $currentWidth;
@@ -108,9 +108,12 @@ private function targetWidths() {
         $INCREMENT_PERCENTAGE = 8;
         $MAX_SIZE = 8192;
 
+        $ensureEven = function($n) {
+            return 2 * round($n / 2);
+        };
 
         while ($prev <= $MAX_SIZE) {
-            array_push($resolutions, 2 * round($prev / 2));
+            array_push($resolutions, $ensureEven($prev));
             $prev *= 1 + ($INCREMENT_PERCENTAGE / 100) * 2;
         }
 

From fc84c0a06a182b30a6f664087c6bd448689e9e22 Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Tue, 27 Aug 2019 21:41:13 -0700
Subject: [PATCH 03/10] test: add srcset tests

---
 tests/Imgix/Tests/UrlBuilderTest.php | 255 +++++++++++++++++++++++++++
 1 file changed, 255 insertions(+)

diff --git a/tests/Imgix/Tests/UrlBuilderTest.php b/tests/Imgix/Tests/UrlBuilderTest.php
index 9901279..9422061 100644
--- a/tests/Imgix/Tests/UrlBuilderTest.php
+++ b/tests/Imgix/Tests/UrlBuilderTest.php
@@ -139,5 +139,260 @@ public function test_invalid_domain_append_dash() {
         
         $builder = new UrlBuilder("demos.imgix.net-", true, "",  false);
     }
+
+    private function srcsetBuilder($params=array()) {
+        $builder = new UrlBuilder("demos.imgix.net", true, "my-key", false);
+        return $builder->createSrcSet("bridge.png", $params); 
+    }
+
+    // parse the width as an int, eg "100w" => 100
+    private function parseWidth($width) {
+        return (int)substr($width, 0, strlen($width)-1);
+    }
+    
+    public function testNoParametersGeneratesSrcsetPairs() {
+        $srcset = $this->srcsetBuilder();
+        $expectedNumberOfPairs = 31;
+        $this->assertEquals($expectedNumberOfPairs, count(explode(",", $srcset)));
+    }
+
+    public function testSrcsetPairValues() {
+        $srcset = $this->srcsetBuilder();
+        $index = 0;
+        // array of expected resolutions generated by srcset
+        $resolutions = array(100, 116, 134, 156, 182, 210, 244, 282,
+                             328, 380, 442, 512, 594, 688, 798, 926,
+                             1074, 1246, 1446, 1678, 1946, 2258, 2618,
+                             3038, 3524, 4088, 4742, 5500, 6380, 7400, 8192);
+        $srclist = explode(",", $srcset);
+        $matches = array();
+        
+        foreach ($srclist as $src) {
+            $width = explode(" ", $src)[1];
+            
+            // extract width int values
+            preg_match("/\d+/", $width, $matches);
+            $this->assertEquals($resolutions[$index], $matches[0]);
+            $index ++;
+        }
+    }
+
+    public function testGivenWidthSrcsetIsDPR() {
+        $srcset = $this->srcsetBuilder(array("w"=>300));
+        $devicePixelRatio = 1;
+        $srclist = explode(",", $srcset);
+
+        foreach ($srclist as $src) {
+            $generatedRatio = explode(" ", $src)[1];
+            $dprStr = $devicePixelRatio . "x";
+            $this->assertEquals($dprStr, $generatedRatio);
+            $devicePixelRatio += 1;
+        }
+    }
+
+    public function testGivenWidthSignsURLs() {
+        $srcset = $this->srcsetBuilder(array("w"=>300));
+        $expectedSignature = "65bff01b598e97ddeb1f39a56930ec30";
+        $srclist = explode(",", $srcset);
+
+        foreach ($srclist as $src) {
+            $url = explode(" ", $src)[0];
+            $this->assertStringContainsString("s=", $url);
+
+            // extract the sign parameter
+            $generatedSignature = substr($url, strrpos($url, "s=")+2);
+            $this->assertEquals($expectedSignature, $generatedSignature);
+        }
+    }
+
+    public function testGivenHeightSrcsetGeneratesPairs() {
+        $srcset = $this->srcsetBuilder(array("h"=>300));
+        $expectedNumberOfPairs = 31;
+        $this->assertEquals($expectedNumberOfPairs, count(explode(",", $srcset)));
+    }
+
+    public function testGivenHeightRespectsParameter() {
+        $srcset = $this->srcsetBuilder(array("h"=>300));
+        $srclist = explode(",", $srcset);
+
+        foreach ($srclist as $src) {
+            $this->assertStringContainsString("h=300", $src);
+        }
+    }
+
+    public function testGivenHeightSrcsetPairsWithinBounds() {
+        $srcset = $this->srcsetBuilder(array("h"=>300));
+        $srclist = explode(",", $srcset);
+
+        $minParsed = explode(" ", $srclist[0])[1];
+        $maxParsed = explode(" ", $srclist[count($srclist)-1])[1];
+        $min = $this->parseWidth($minParsed);
+        $max = $this->parseWidth($maxParsed);
+
+        $this->assertGreaterThanOrEqual(100, $min);
+        $this->assertLessThanOrEqual(8192, $max);
+    }
+
+    public function testGivenHeightSrcsetIteratesEighteenPercent() {
+        $incrementAllowed = .18;
+        $srcset = $this->srcsetBuilder(array("h"=>300));
+        $srclist = explode(",", $srcset);
+
+        $widths = array_map(function ($src) {
+            return $this->parseWidth(explode(" ", $src)[1]);
+        }, $srclist);
+
+        $prev = $widths[0];
+        $size = count($widths);
+        for ($i = 1; $i < $size; $i++) {
+            $width = $widths[$i];
+            $this->assertLessThan((1 + $incrementAllowed), ($width / $prev));
+            $prev = $width;
+        }
+    }
+
+    public function testGivenHeightSrcsetSignsUrls() {
+        $srcset = $this->srcsetBuilder(array("h"=>300));
+        $srclist = explode(",", $srcset);
+
+        $srcs = array_map(function ($src) {
+            return explode(" ", $src)[0];
+        }, $srclist);
+
+        foreach ($srcs as $src) {
+            $this->assertStringContainsString("s=", $src);
+
+            // parse out query params
+            $params = substr($src, strrpos($src, "?"));
+            $params = substr($params, 0, strrpos($params, "s=")-1);
+
+            // parse out sign parameter
+            $generatedSignature = substr($src, strrpos($src, "s=")+2);
+
+            $signatureBase = "my-key" . "/bridge.png" . $params;
+            $expectSignature = md5($signatureBase);
+
+            $this->assertEquals($expectSignature, $generatedSignature);
+        }
+    }
+    
+    public function testGivenWidthAndHeightSrcsetIsDPR() {
+        $srcset = $this->srcsetBuilder(array("w"=>300, "h"=>"400"));
+        $devicePixelRatio = 1;
+        $srclist = explode(",", $srcset);
+
+        foreach ($srclist as $src) {
+            $generatedRatio = explode(" ", $src)[1];
+            $dprStr = $devicePixelRatio . "x";
+            $this->assertEquals($dprStr, $generatedRatio);
+            $devicePixelRatio += 1;
+        }
+    }
+
+    public function testGivenWidthAndHeightSignsURLs() {
+        $srcset = $this->srcsetBuilder(array("w"=>300, "h"=>"400"));
+        $expectedSignature = "27e4d1ec19ed834a3d8b7ec89dda0e20";
+        $srclist = explode(",", $srcset);
+
+        foreach ($srclist as $src) {
+            $url = explode(" ", $src)[0];
+            $this->assertStringContainsString("s=", $url);
+
+            // extract the sign parameter
+            $generatedSignature = substr($url, strrpos($url, "s=")+2);
+            $this->assertEquals($expectedSignature, $generatedSignature);
+        }
+    }
+
+    public function testGivenAspectRatioSrcsetGeneratesPairs() {
+        $srcset = $this->srcsetBuilder(array("ar"=>"3:2"));
+        $expectedNumberOfPairs = 31;
+        $this->assertEquals($expectedNumberOfPairs, count(explode(",", $srcset)));
+    }
+
+    public function testGivenAspectRatioSrcsetPairsWithinBounds() {
+        $srcset = $this->srcsetBuilder(array("ar"=>"3:2"));
+        $srclist = explode(",", $srcset);
+
+        $minParsed = explode(" ", $srclist[0])[1];
+        $maxParsed = explode(" ", $srclist[count($srclist)-1])[1];
+        $min = $this->parseWidth($minParsed);
+        $max = $this->parseWidth($maxParsed);
+
+        $this->assertGreaterThanOrEqual(100, $min);
+        $this->assertLessThanOrEqual(8192, $max);
+    }
+
+    public function testGivenAspectRatioSrcsetIteratesEighteenPercent() {
+        $incrementAllowed = .18;
+        $srcset = $this->srcsetBuilder(array("ar"=>"3:2"));
+        $srclist = explode(",", $srcset);
+
+        $widths = array_map(function ($src) {
+            return $this->parseWidth(explode(" ", $src)[1]);
+        }, $srclist);
+
+        $prev = $widths[0];
+        $size = count($widths);
+        for ($i = 1; $i < $size; $i++) {
+            $width = $widths[$i];
+            $this->assertLessThan((1 + $incrementAllowed), ($width / $prev));
+            $prev = $width;
+        }
+    }
+
+    public function testGivenAspectRatioSrcsetSignsUrls() {
+        $srcset = $this->srcsetBuilder(array("ar"=>"3:2"));
+        $srclist = explode(",", $srcset);
+
+        $srcs = array_map(function ($src) {
+            return explode(" ", $src)[0];
+        }, $srclist);
+
+        foreach ($srcs as $src) {
+            $this->assertStringContainsString("s=", $src);
+
+            // parse out query params
+            $params = substr($src, strrpos($src, "?"));
+            $params = substr($params, 0, strrpos($params, "s=")-1);
+
+            // parse out sign parameter
+            $generatedSignature = substr($src, strrpos($src, "s=")+2);
+
+            $signatureBase = "my-key" . "/bridge.png" . $params;
+            $expectSignature = md5($signatureBase);
+
+            $this->assertEquals($expectSignature, $generatedSignature);
+        }
+    }
+
+    public function testGivenAspectRatioAndHeightSrcsetIsDPR() {
+        $srcset = $this->srcsetBuilder(array("h"=>400,"ar"=>"3:2"));
+        $devicePixelRatio = 1;
+        $srclist = explode(",", $srcset);
+
+        foreach ($srclist as $src) {
+            $generatedRatio = explode(" ", $src)[1];
+            $dprStr = $devicePixelRatio . "x";
+            $this->assertEquals($dprStr, $generatedRatio);
+            $devicePixelRatio += 1;
+        }
+    }
+
+    public function testGivenAspectRatioAndHeightSignsURLs() {
+        $srcset = $this->srcsetBuilder(array("h"=>400,"ar"=>"3:2"));
+        $expectedSignature = "96e491fd2b81c3306545a6d88ccbe7eb";
+        $srclist = explode(",", $srcset);
+
+        foreach ($srclist as $src) {
+            $url = explode(" ", $src)[0];
+            $this->assertStringContainsString("s=", $url);
+
+            // extract the sign parameter
+            $generatedSignature = substr($url, strrpos($url, "s=")+2);
+            $this->assertEquals($expectedSignature, $generatedSignature);
+        }
+    }
+
   }
 ?>

From 2d514dc5824ba92d9cb03ebda5993715f9bc0170 Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Wed, 28 Aug 2019 11:17:18 -0700
Subject: [PATCH 04/10] test: replace assertStringContainsString with phpunit
 backwards compatible function

---
 tests/Imgix/Tests/UrlBuilderTest.php | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/tests/Imgix/Tests/UrlBuilderTest.php b/tests/Imgix/Tests/UrlBuilderTest.php
index 9422061..2313869 100644
--- a/tests/Imgix/Tests/UrlBuilderTest.php
+++ b/tests/Imgix/Tests/UrlBuilderTest.php
@@ -197,7 +197,7 @@ public function testGivenWidthSignsURLs() {
 
         foreach ($srclist as $src) {
             $url = explode(" ", $src)[0];
-            $this->assertStringContainsString("s=", $url);
+            $this->assertRegExp("/s=/", $url);
 
             // extract the sign parameter
             $generatedSignature = substr($url, strrpos($url, "s=")+2);
@@ -216,7 +216,7 @@ public function testGivenHeightRespectsParameter() {
         $srclist = explode(",", $srcset);
 
         foreach ($srclist as $src) {
-            $this->assertStringContainsString("h=300", $src);
+            $this->assertRegExp("/h=300/", $src);
         }
     }
 
@@ -260,7 +260,7 @@ public function testGivenHeightSrcsetSignsUrls() {
         }, $srclist);
 
         foreach ($srcs as $src) {
-            $this->assertStringContainsString("s=", $src);
+            $this->assertRegExp("/s=/", $src);
 
             // parse out query params
             $params = substr($src, strrpos($src, "?"));
@@ -296,7 +296,7 @@ public function testGivenWidthAndHeightSignsURLs() {
 
         foreach ($srclist as $src) {
             $url = explode(" ", $src)[0];
-            $this->assertStringContainsString("s=", $url);
+            $this->assertRegExp("/s=/", $url);
 
             // extract the sign parameter
             $generatedSignature = substr($url, strrpos($url, "s=")+2);
@@ -350,7 +350,7 @@ public function testGivenAspectRatioSrcsetSignsUrls() {
         }, $srclist);
 
         foreach ($srcs as $src) {
-            $this->assertStringContainsString("s=", $src);
+            $this->assertRegExp("/s=/", $src);
 
             // parse out query params
             $params = substr($src, strrpos($src, "?"));
@@ -386,7 +386,7 @@ public function testGivenAspectRatioAndHeightSignsURLs() {
 
         foreach ($srclist as $src) {
             $url = explode(" ", $src)[0];
-            $this->assertStringContainsString("s=", $url);
+            $this->assertRegExp("/s=/", $url);
 
             // extract the sign parameter
             $generatedSignature = substr($url, strrpos($url, "s=")+2);

From 11c9e63c9922553f90349a1b2c426c68131aa78a Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Wed, 28 Aug 2019 12:59:07 -0700
Subject: [PATCH 05/10] docs: add documentation for srcset generation

---
 README.md | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/README.md b/README.md
index 2a597b5..76efe88 100644
--- a/README.md
+++ b/README.md
@@ -81,3 +81,42 @@ echo $builder->createURL("bridge.png", $params);
 // Prints out:
 // http://demos.imgix.net/bridge.png?h=100&w=100&s=bb8f3a2ab832e35997456823272103a4
 ```
+
+## Srcset Generation
+
+The imgix library allows for generation of custom `srcset` attributes, which can be invoked through `createSrcSet()`. By default, the `srcset` generated will allow for responsive size switching by building a list of image-width mappings.
+
+```php
+$builder = new UrlBuilder("demos.imgix.net", true, "my-key", false);
+$builder->createSrcSet("bridge.png");
+```
+
+Will produce the following attribute value, which can then be served to the client:
+
+```html
+https://demos.imgix.net/bridge.png?w=100&s=ac331d314510e3039a33aa1a7ebc23ee 100w,
+https://demos.imgix.net/bridge.png?w=116&s=aac0667a00791c8c8801a2fef134e78a 116w,
+https://demos.imgix.net/bridge.png?w=134&s=2fcd42d984155efe26cc1e36e16b2897 134w,
+                                    ...
+https://demos.imgix.net/bridge.png?w=7400&s=6a6cbe01416dc4e0c65d1a2f87b868ac 7400w,
+https://demos.imgix.net/bridge.png?w=8192&s=9e6b0a94e81e929ad71829fcccf4d2d8 8192w
+```
+
+In cases where enough information is provided about an image's dimensions, `createSrcSet()` will instead build a `srcset` that will allow for an image to be served at different resolutions. The parameters taken into consideration when determining if an image is fixed-width are `w`, `h`, and `ar`. By invoking `createSrcSet()` with either a width **or** the height and aspect ratio (along with `fit=crop`, typically) provided, a different `srcset` will be generated for a fixed-size image instead.
+
+```php
+$builder = new UrlBuilder("demos.imgix.net", true, "my-key", false);
+$builder->createSrcSet("bridge.png", array("h"=>800, "ar"=>"3:2", "fit"=>"crop"));
+```
+
+Will produce the following attribute value:
+
+```html
+https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=1&fit=crop&h=800&s=39eb37ad41acf7170343aa463424ae49 1x,
+https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=2&fit=crop&h=800&s=a8ab13a2c7a17b91db42cb86e45f7c9d 2x,
+https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=3&fit=crop&h=800&s=8fefe5daf312f04fb6912a101afbf704 3x,
+https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=4&fit=crop&h=800&s=74a6167d6ef8ba410109feda814b9ac0 4x,
+https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=5&fit=crop&h=800&s=4449b7f44ba7d6d0527a16d9a10b6e39 5x
+```
+
+For more information to better understand `srcset`, we highly recommend [Eric Portis' "Srcset and sizes" article](https://ericportis.com/posts/2014/srcset-sizes/) which goes into depth about the subject.

From 6e7751a58af4430e6961dbacf7b45fff8b883238 Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Wed, 28 Aug 2019 13:12:58 -0700
Subject: [PATCH 06/10] fix: add dpr as a parameter when generated a
 fixed-width srcset

---
 src/Imgix/UrlBuilder.php             |  6 ++-
 tests/Imgix/Tests/UrlBuilderTest.php | 57 ++++++++++++++++++++++------
 2 files changed, 49 insertions(+), 14 deletions(-)

diff --git a/src/Imgix/UrlBuilder.php b/src/Imgix/UrlBuilder.php
index 600aef0..1ce6d0b 100644
--- a/src/Imgix/UrlBuilder.php
+++ b/src/Imgix/UrlBuilder.php
@@ -74,12 +74,14 @@ public function createSrcSet($path, $params=array()) {
     private function createDPRSrcSet($path, $params) {
         $srcset = "";
         $targetRatios = array(1, 2, 3, 4, 5);
-        $url = $this->createURL($path, $params);
 
         $size = count($targetRatios);
         for ($i = 0; $i < $size; $i++) {
             $currentRatio = $targetRatios[$i];
-            $srcset .= $url." ".$currentRatio."x,\n";
+            $currentParams = $params;
+            $dpr_value = array("dpr"=>($i+1));
+            $currentParams += $dpr_value;
+            $srcset .= $this->createURL($path, $currentParams) . " " . $currentRatio . "x,\n";
         }
 
         return substr($srcset, 0, strlen($srcset)-2);
diff --git a/tests/Imgix/Tests/UrlBuilderTest.php b/tests/Imgix/Tests/UrlBuilderTest.php
index 2313869..b288bc3 100644
--- a/tests/Imgix/Tests/UrlBuilderTest.php
+++ b/tests/Imgix/Tests/UrlBuilderTest.php
@@ -183,25 +183,36 @@ public function testGivenWidthSrcsetIsDPR() {
         $srclist = explode(",", $srcset);
 
         foreach ($srclist as $src) {
-            $generatedRatio = explode(" ", $src)[1];
+            list($generatedURL, $generatedRatio) = explode(" ", $src);
+            
             $dprStr = $devicePixelRatio . "x";
             $this->assertEquals($dprStr, $generatedRatio);
+            
+            $this->assertRegExp("/dpr=".$devicePixelRatio."/", $generatedURL);
+            
             $devicePixelRatio += 1;
         }
     }
 
     public function testGivenWidthSignsURLs() {
         $srcset = $this->srcsetBuilder(array("w"=>300));
-        $expectedSignature = "65bff01b598e97ddeb1f39a56930ec30";
         $srclist = explode(",", $srcset);
 
         foreach ($srclist as $src) {
             $url = explode(" ", $src)[0];
             $this->assertRegExp("/s=/", $url);
 
-            // extract the sign parameter
+            // parse out query params
+            $params = substr($url, strrpos($url, "?"));
+            $params = substr($params, 0, strrpos($params, "s=")-1);
+
+            // parse out sign parameter
             $generatedSignature = substr($url, strrpos($url, "s=")+2);
-            $this->assertEquals($expectedSignature, $generatedSignature);
+
+            $signatureBase = "my-key" . "/bridge.png" . $params;
+            $expectSignature = md5($signatureBase);
+
+            $this->assertEquals($expectSignature, $generatedSignature);
         }
     }
 
@@ -282,25 +293,36 @@ public function testGivenWidthAndHeightSrcsetIsDPR() {
         $srclist = explode(",", $srcset);
 
         foreach ($srclist as $src) {
-            $generatedRatio = explode(" ", $src)[1];
+            list($generatedURL, $generatedRatio) = explode(" ", $src);
+            
             $dprStr = $devicePixelRatio . "x";
             $this->assertEquals($dprStr, $generatedRatio);
+            
+            $this->assertRegExp("/dpr=".$devicePixelRatio."/", $generatedURL);
+            
             $devicePixelRatio += 1;
         }
     }
 
     public function testGivenWidthAndHeightSignsURLs() {
         $srcset = $this->srcsetBuilder(array("w"=>300, "h"=>"400"));
-        $expectedSignature = "27e4d1ec19ed834a3d8b7ec89dda0e20";
         $srclist = explode(",", $srcset);
 
         foreach ($srclist as $src) {
             $url = explode(" ", $src)[0];
             $this->assertRegExp("/s=/", $url);
+            
+            // parse out query params
+            $params = substr($url, strrpos($url, "?"));
+            $params = substr($params, 0, strrpos($params, "s=")-1);
 
-            // extract the sign parameter
+            // parse out sign parameter
             $generatedSignature = substr($url, strrpos($url, "s=")+2);
-            $this->assertEquals($expectedSignature, $generatedSignature);
+
+            $signatureBase = "my-key" . "/bridge.png" . $params;
+            $expectSignature = md5($signatureBase);
+
+            $this->assertEquals($expectSignature, $generatedSignature);
         }
     }
 
@@ -372,25 +394,36 @@ public function testGivenAspectRatioAndHeightSrcsetIsDPR() {
         $srclist = explode(",", $srcset);
 
         foreach ($srclist as $src) {
-            $generatedRatio = explode(" ", $src)[1];
+            list($generatedURL, $generatedRatio) = explode(" ", $src);
+            
             $dprStr = $devicePixelRatio . "x";
             $this->assertEquals($dprStr, $generatedRatio);
+            
+            $this->assertRegExp("/dpr=".$devicePixelRatio."/", $generatedURL);
+            
             $devicePixelRatio += 1;
         }
     }
 
     public function testGivenAspectRatioAndHeightSignsURLs() {
         $srcset = $this->srcsetBuilder(array("h"=>400,"ar"=>"3:2"));
-        $expectedSignature = "96e491fd2b81c3306545a6d88ccbe7eb";
         $srclist = explode(",", $srcset);
 
         foreach ($srclist as $src) {
             $url = explode(" ", $src)[0];
             $this->assertRegExp("/s=/", $url);
+ 
+            // parse out query params
+            $params = substr($url, strrpos($url, "?"));
+            $params = substr($params, 0, strrpos($params, "s=")-1);
 
-            // extract the sign parameter
+            // parse out sign parameter
             $generatedSignature = substr($url, strrpos($url, "s=")+2);
-            $this->assertEquals($expectedSignature, $generatedSignature);
+
+            $signatureBase = "my-key" . "/bridge.png" . $params;
+            $expectSignature = md5($signatureBase);
+
+            $this->assertEquals($expectSignature, $generatedSignature);
         }
     }
 

From 715b48b0ce1c115f5ccd4f5c770776d23766a840 Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Wed, 28 Aug 2019 13:19:55 -0700
Subject: [PATCH 07/10] add dpr parameter in a different way, overwrites
 user-passed dpr

---
 src/Imgix/UrlBuilder.php | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/Imgix/UrlBuilder.php b/src/Imgix/UrlBuilder.php
index 1ce6d0b..0619c33 100644
--- a/src/Imgix/UrlBuilder.php
+++ b/src/Imgix/UrlBuilder.php
@@ -79,8 +79,7 @@ private function createDPRSrcSet($path, $params) {
         for ($i = 0; $i < $size; $i++) {
             $currentRatio = $targetRatios[$i];
             $currentParams = $params;
-            $dpr_value = array("dpr"=>($i+1));
-            $currentParams += $dpr_value;
+            $currentParams['dpr'] = $i+1;
             $srcset .= $this->createURL($path, $currentParams) . " " . $currentRatio . "x,\n";
         }
 

From 777af4da516f5008cbc08fc29445e3ca9261e030 Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Thu, 29 Aug 2019 15:21:10 -0700
Subject: [PATCH 08/10] address PR feedback

---
 src/Imgix/UrlBuilder.php | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/src/Imgix/UrlBuilder.php b/src/Imgix/UrlBuilder.php
index 0619c33..10547f4 100644
--- a/src/Imgix/UrlBuilder.php
+++ b/src/Imgix/UrlBuilder.php
@@ -9,6 +9,9 @@ class UrlBuilder {
     private $useHttps;
     private $signKey;
 
+    private const TARGETRATIOS = array(1, 2, 3, 4, 5);
+    private $targetWidths;
+
     public function __construct($domain, $useHttps = false, $signKey = "", $includeLibraryParam = true) {
 
         if (!is_string($domain)) {
@@ -21,6 +24,7 @@ public function __construct($domain, $useHttps = false, $signKey = "", $includeL
         $this->useHttps = $useHttps;
         $this->signKey = $signKey;
         $this->includeLibraryParam = $includeLibraryParam;
+        $this->targetWidths = $this->targetWidths();
     }
 
     private function validateDomain($domain) {
@@ -73,34 +77,32 @@ public function createSrcSet($path, $params=array()) {
 
     private function createDPRSrcSet($path, $params) {
         $srcset = "";
-        $targetRatios = array(1, 2, 3, 4, 5);
 
-        $size = count($targetRatios);
+        $size = count(self::TARGETRATIOS);
         for ($i = 0; $i < $size; $i++) {
-            $currentRatio = $targetRatios[$i];
+            $currentRatio = self::TARGETRATIOS[$i];
             $currentParams = $params;
             $currentParams['dpr'] = $i+1;
             $srcset .= $this->createURL($path, $currentParams) . " " . $currentRatio . "x,\n";
         }
 
-        return substr($srcset, 0, strlen($srcset)-2);
+        return substr($srcset, 0, strlen($srcset) - 2);
     }
 
     private function createSrcSetPairs($path, $params) {
         $srcset = "";
         $currentWidth = NULL;
         $currentParams = NULL;
-        $targetWidths = $this->targetWidths();
 
-        $size = count($targetWidths);
+        $size = count($this->targetWidths);
         for ($i = 0; $i < $size; $i++) {
-            $currentWidth = $targetWidths[$i];
+            $currentWidth = $this->targetWidths[$i];
             $currentParams = $params;
             $currentParams['w'] = $currentWidth;
             $srcset .= $this->createURL($path, $currentParams) . " " . $currentWidth . "w,\n";
         }
 
-        return substr($srcset, 0, strlen($srcset)-2);
+        return substr($srcset, 0, strlen($srcset) - 2);
     }
 
     private function targetWidths() {

From bf5ae680d93facd90b8b4bfbe5f04532d595804b Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Thu, 29 Aug 2019 15:29:55 -0700
Subject: [PATCH 09/10] remove const visibility modifier as it is not supported
 in all php versions

---
 src/Imgix/UrlBuilder.php | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/Imgix/UrlBuilder.php b/src/Imgix/UrlBuilder.php
index 10547f4..99b9396 100644
--- a/src/Imgix/UrlBuilder.php
+++ b/src/Imgix/UrlBuilder.php
@@ -9,7 +9,10 @@ class UrlBuilder {
     private $useHttps;
     private $signKey;
 
-    private const TARGETRATIOS = array(1, 2, 3, 4, 5);
+    // define class constants
+    // should be private; but visibility modifiers are not supported php version <7.1
+    const TARGETRATIOS = array(1, 2, 3, 4, 5);
+    // constants cannot be dynamically assigned; keeping as a class variable instead
     private $targetWidths;
 
     public function __construct($domain, $useHttps = false, $signKey = "", $includeLibraryParam = true) {

From 4d5b349e9da7cee67789a8fe850bb73b457b791d Mon Sep 17 00:00:00 2001
From: Sherwin H <sherwin@imgix.com>
Date: Thu, 29 Aug 2019 16:10:38 -0700
Subject: [PATCH 10/10] docs: add to example

---
 README.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 76efe88..9a952bb 100644
--- a/README.md
+++ b/README.md
@@ -88,7 +88,7 @@ The imgix library allows for generation of custom `srcset` attributes, which can
 
 ```php
 $builder = new UrlBuilder("demos.imgix.net", true, "my-key", false);
-$builder->createSrcSet("bridge.png");
+echo $builder->createSrcSet("bridge.png");
 ```
 
 Will produce the following attribute value, which can then be served to the client:
@@ -106,7 +106,7 @@ In cases where enough information is provided about an image's dimensions, `crea
 
 ```php
 $builder = new UrlBuilder("demos.imgix.net", true, "my-key", false);
-$builder->createSrcSet("bridge.png", array("h"=>800, "ar"=>"3:2", "fit"=>"crop"));
+echo $builder->createSrcSet("bridge.png", array("h"=>800, "ar"=>"3:2", "fit"=>"crop"));
 ```
 
 Will produce the following attribute value: