Enables bignums for span IDs (#192)

* enables bignums for span IDs

* only uses baseConvert if the span ID is sufficiently large

* fix cs

* correct variable name

* minor optimization

Author: bshaffer

src/Trace/Propagator/CloudTraceFormatter.php

@@ -42,7 +42,7 @@ public function deserialize($header)
             return new SpanContext(
                 strtolower($matches[1]),
                 array_key_exists(2, $matches) && !empty($matches[2])
-                    ? dechex((int)($matches[2]))
+                    ? $this->decToHex($matches[2])
                     : null,
                 array_key_exists(3, $matches) ? $matches[3] == '1' : null,
                 true
@@ -61,11 +61,65 @@ public function serialize(SpanContext $context)
     {
         $ret = '' . $context->traceId();
         if ($context->spanId()) {
-            $ret .= '/' . hexdec($context->spanId());
+            $ret .= '/' . $this->hexToDec($context->spanId());
         }
         if ($context->enabled() !== null) {
             $ret .= ';o=' . ($context->enabled() ? '1' : '0');
         }
         return $ret;
     }
+
+    private function decToHex($numstring)
+    {
+        $int = (int) $numstring;
+        if ($this->isBigNum($int)) {
+            return $this->baseConvert($numstring, 10, 16);
+        }
+        return dechex($int);
+    }
+
+    private function hexToDec($numstring)
+    {
+        $dec = hexdec($numstring);
+        if ($this->isBigNum($dec)) {
+            return $this->baseConvert($numstring, 16, 10);
+        }
+        return $dec;
+    }
+
+    private function isBigNum($number)
+    {
+        return $number >= PHP_INT_MAX;
+    }
+
+    private function baseConvert($numstring, $fromBase, $toBase)
+    {
+        $chars = "0123456789abcdefghijklmnopqrstuvwxyz";
+        $newstring = substr($chars, 0, $toBase);
+
+        $length = strlen($numstring);
+        $result = '';
+
+        for ($i = 0; $i < $length; $i++) {
+            $number[$i] = strpos($chars, $numstring{$i});
+        }
+
+        do {
+            $divide = 0;
+            $newlen = 0;
+            for ($i = 0; $i < $length; $i++) {
+                $divide = $divide * $fromBase + $number[$i];
+                if ($divide >= $toBase) {
+                    $number[$newlen++] = (int)($divide / $toBase);
+                    $divide = $divide % $toBase;
+                } elseif ($newlen > 0) {
+                    $number[$newlen++] = 0;
+                }
+            }
+            $length = $newlen;
+            $result = $newstring{$divide} . $result;
+        } while ($newlen != 0);
+
+        return $result;
+    }
 }

tests/unit/Trace/Propagator/CloudTraceFormatterTest.php

@@ -71,6 +71,7 @@ public function traceHeaders()
             ['123456789012345678901234567890ab', null, false,  '123456789012345678901234567890ab;o=0'],
             ['123456789012345678901234567890ab', null, true,   '123456789012345678901234567890ab;o=1'],
             ['123456789012345678901234567890ab', null, null,   '123456789012345678901234567890ab'],
+            ['123456789012345678901234567890ab', 'adced0062fba0812', null,   '123456789012345678901234567890ab/12524176338753030162'],
         ];
     }
 
@@ -83,6 +84,7 @@ public function upperTraceHeaders()
             ['123456789012345678901234567890ab', null, false,  '123456789012345678901234567890AB;o=0'],
             ['123456789012345678901234567890ab', null, true,   '123456789012345678901234567890AB;o=1'],
             ['123456789012345678901234567890ab', null, null,   '123456789012345678901234567890AB'],
+            ['123456789012345678901234567890ab', 'adced0062fba0812', null,   '123456789012345678901234567890ab/12524176338753030162'],
         ];
     }
 }