Make "metamta.differential.inline-patches" imply a reasonable byte limit, not just a line limit

Summary:
Fixes T11748. This option currently implies a line limit (e.g., inline patches that are less than 100 lines long). This breaks down if a diff has a 10MB line, like a huge blob of JSON all on one line.

For now, imply a reasonable byte limit (256 bytes per line).

See T11767 for future work to make this and related options more cohesive.

Test Plan:
  - With option at `1000`: sent Differential email, saw patches inlined.
  - With option at `10`: sent Differential email, saw patches dropped because of the byte limit.
  - `var_dump()`'d the actual limits and used `bin/worker execute --id ...` to sanity check that things were working properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11748

Differential Revision: https://secure.phabricator.com/D16714

src/applications/differential/config/PhabricatorDifferentialConfigOptions.php

@@ -70,6 +70,19 @@ final class PhabricatorDifferentialConfigOptions
       );
     }
 
+    $inline_description = $this->deformat(
+      pht(<<<EOHELP
+To include patches inline in email bodies, set this option to a positive
+integer. Patches will be inlined if they are at most that many lines and at
+most 256 times that many bytes.
+
+For example, a value of 100 means "inline patches if they are at not more than
+100 lines long and not more than 25,600 bytes large".
+
+By default, patches are not inlined.
+EOHELP
+      ));
+
     return array(
       $this->newOption(
         'differential.fields',
@@ -254,13 +267,7 @@ final class PhabricatorDifferentialConfigOptions
         'int',
         0)
         ->setSummary(pht('Inline patches in email, as body text.'))
-        ->setDescription(
+        ->setDescription($inline_description),
-          pht(
-            "To include patches inline in email bodies, set this to a ".
-            "positive integer. Patches will be inlined if they are at most ".
-            "that many lines. For instance, a value of 100 means 'inline ".
-            "patches if they are no longer than 100 lines'. By default, ".
-            "patches are not inlined.")),
       $this->newOption(
         'metamta.differential.patch-format',
         'enum',

src/applications/differential/editor/DifferentialTransactionEditor.php

@@ -1264,11 +1264,30 @@ final class DifferentialTransactionEditor
       $config_attach = PhabricatorEnv::getEnvConfig($config_key_attach);
 
       if ($config_inline || $config_attach) {
-        $patch = $this->buildPatchForMail($diff);
+        $body_limit = PhabricatorEnv::getEnvConfig('metamta.email-body-limit');
-        $lines = substr_count($patch, "\n");
 
-        if ($config_inline && ($lines <= $config_inline)) {
+        $patch = $this->buildPatchForMail($diff);
+        if ($config_inline) {
+          $lines = substr_count($patch, "\n");
+          $bytes = strlen($patch);
+
+          // Limit the patch size to the smaller of 256 bytes per line or
+          // the mail body limit. This prevents degenerate behavior for patches
+          // with one line that is 10MB long. See T11748.
+          $byte_limits = array();
+          $byte_limits[] = (256 * $config_inline);
+          $byte_limits[] = $body_limit;
+          $byte_limit = min($byte_limits);
+
+          $lines_ok = ($lines <= $config_inline);
+          $bytes_ok = ($bytes <= $byte_limit);
+
+          if ($lines_ok && $bytes_ok) {
             $this->appendChangeDetailsForMail($object, $diff, $patch, $body);
+          } else {
+            // TODO: Provide a helpful message about the patch being too
+            // large or lengthy here.
+          }
         }
 
         if ($config_attach) {