diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -813,6 +813,8 @@
     'DiffusionGitResponse' => 'applications/diffusion/response/DiffusionGitResponse.php',
     'DiffusionGitSSHWorkflow' => 'applications/diffusion/ssh/DiffusionGitSSHWorkflow.php',
     'DiffusionGitUploadPackSSHWorkflow' => 'applications/diffusion/ssh/DiffusionGitUploadPackSSHWorkflow.php',
+    'DiffusionGitUploadPackWireProtocol' => 'applications/diffusion/protocol/DiffusionGitUploadPackWireProtocol.php',
+    'DiffusionGitWireProtocol' => 'applications/diffusion/protocol/DiffusionGitWireProtocol.php',
     'DiffusionGraphController' => 'applications/diffusion/controller/DiffusionGraphController.php',
     'DiffusionHistoryController' => 'applications/diffusion/controller/DiffusionHistoryController.php',
     'DiffusionHistoryListView' => 'applications/diffusion/view/DiffusionHistoryListView.php',
@@ -6460,6 +6462,8 @@
       'DiffusionRepositoryClusterEngineLogInterface',
     ),
     'DiffusionGitUploadPackSSHWorkflow' => 'DiffusionGitSSHWorkflow',
+    'DiffusionGitUploadPackWireProtocol' => 'DiffusionGitWireProtocol',
+    'DiffusionGitWireProtocol' => 'Phobject',
     'DiffusionGraphController' => 'DiffusionController',
     'DiffusionHistoryController' => 'DiffusionController',
     'DiffusionHistoryListView' => 'DiffusionHistoryView',
diff --git a/src/applications/diffusion/protocol/DiffusionGitUploadPackWireProtocol.php b/src/applications/diffusion/protocol/DiffusionGitUploadPackWireProtocol.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/protocol/DiffusionGitUploadPackWireProtocol.php
@@ -0,0 +1,335 @@
+<?php
+
+final class DiffusionGitUploadPackWireProtocol
+  extends DiffusionGitWireProtocol {
+
+  private $readMode = 'length';
+  private $readBuffer;
+  private $readFrameLength;
+  private $readFrames = array();
+
+  private $readFrameMode = 'refs';
+  private $refFrames = array();
+
+  private $readMessages = array();
+
+  public function willReadBytes($bytes) {
+    if ($this->readBuffer === null) {
+      $this->readBuffer = new PhutilRope();
+    }
+    $buffer = $this->readBuffer;
+
+    $buffer->append($bytes);
+
+    while (true) {
+      $len = $buffer->getByteLength();
+      switch ($this->readMode) {
+        case 'length':
+          // We're expecting 4 bytes containing the length of the protocol
+          // frame as hexadecimal in ASCII text, like "01ab". Wait until we
+          // see at least 4 bytes on the wire.
+          if ($len < 4) {
+            if ($len > 0) {
+              $bytes = $this->peekBytes($len);
+              if (!preg_match('/^[0-9a-f]+\z/', $bytes)) {
+                throw new Exception(
+                  pht(
+                    'Bad frame length character in Git protocol ("%s"), '.
+                    'expected a 4-digit hexadecimal value encoded as ASCII '.
+                    'text.',
+                    $bytes));
+              }
+            }
+
+            // We can't make any more progress until we get enough bytes, so
+            // we're done with state processing.
+            break 2;
+          }
+
+          $frame_length = $this->readBytes(4);
+          $frame_length = hexdec($frame_length);
+
+          // Note that the frame length includes the 4 header bytes, so we
+          // usually expect a length of 5 or larger. Frames with length 0
+          // are boundaries.
+          if ($frame_length === 0) {
+            $this->readFrames[] = $this->newProtocolFrame('null', '');
+          } else if ($frame_length >= 1 && $frame_length <= 3) {
+            throw new Exception(
+              pht(
+                'Encountered Git protocol frame with unexpected frame '.
+                'length (%s)!',
+                $frame_length));
+          } else {
+            $this->readFrameLength = $frame_length - 4;
+            $this->readMode = 'frame';
+          }
+
+          break;
+        case 'frame':
+          // We're expecting a protocol frame of a specified length. Note that
+          // it is possible for a frame to have length 0.
+
+          // We don't have enough bytes yet, so wait for more.
+          if ($len < $this->readFrameLength) {
+            break 2;
+          }
+
+          if ($this->readFrameLength > 0) {
+            $bytes = $this->readBytes($this->readFrameLength);
+          } else {
+            $bytes = '';
+          }
+
+          // Emit a protocol frame.
+          $this->readFrames[] = $this->newProtocolFrame('data', $bytes);
+          $this->readMode = 'length';
+          break;
+      }
+    }
+
+    while (true) {
+      switch ($this->readFrameMode) {
+        case 'refs':
+          if (!$this->readFrames) {
+            break 2;
+          }
+
+          foreach ($this->readFrames as $key => $frame) {
+            unset($this->readFrames[$key]);
+
+            if ($frame['type'] === 'null') {
+              $ref_frames = $this->refFrames;
+              $this->refFrames = array();
+
+              $ref_frames[] = $frame;
+
+              $this->readMessages[] = $this->newProtocolRefMessage($ref_frames);
+              $this->readFrameMode = 'passthru';
+              break;
+            } else {
+              $this->refFrames[] = $frame;
+            }
+          }
+
+          break;
+        case 'passthru':
+          if (!$this->readFrames) {
+            break 2;
+          }
+
+          $this->readMessages[] = $this->newProtocolDataMessage(
+            $this->readFrames);
+          $this->readFrames = array();
+
+          break;
+      }
+    }
+
+    $wire = array();
+    foreach ($this->readMessages as $key => $message) {
+      $wire[] = $message;
+      unset($this->readMessages[$key]);
+    }
+    $wire = implode('', $wire);
+
+    return $wire;
+  }
+
+  public function willWriteBytes($bytes) {
+    return $bytes;
+  }
+
+  private function readBytes($count) {
+    $buffer = $this->readBuffer;
+
+    $bytes = $buffer->getPrefixBytes($count);
+    $buffer->removeBytesFromHead($count);
+
+    return $bytes;
+  }
+
+  private function peekBytes($count) {
+    $buffer = $this->readBuffer;
+    return $buffer->getPrefixBytes($count);
+  }
+
+  private function newProtocolFrame($type, $bytes) {
+    return array(
+      'type' => $type,
+      'length' => strlen($bytes),
+      'bytes' => $bytes,
+    );
+  }
+
+  private function newProtocolRefMessage(array $frames) {
+    $head_key = head_key($frames);
+    $last_key = last_key($frames);
+
+    $output = array();
+    foreach ($frames as $key => $frame) {
+      $is_last = ($key === $last_key);
+      if ($is_last) {
+        $output[] = $frame;
+        // This is a "0000" frame at the end of the list of refs, so we pass
+        // it through unmodified.
+        continue;
+      }
+
+      $is_first = ($key === $head_key);
+
+      // Otherwise, we expect a list of:
+      //
+      //   <hash> <ref-name>\0<capabilities>
+      //   <hash> <ref-name>
+      //   ...
+
+      $bytes = $frame['bytes'];
+      $matches = array();
+      if ($is_first) {
+        $ok = preg_match(
+          '('.
+            '^'.
+            '(?P<hash>[0-9a-f]{40})'.
+            ' '.
+            '(?P<name>[^\0\n]+)'.
+            '\0'.
+            '(?P<capabilities>[^\n]+)'.
+            '\n'.
+            '\z'.
+          ')',
+          $bytes,
+          $matches);
+        if (!$ok) {
+          throw new Exception(
+            pht(
+              'Unexpected "git upload-pack" initial protocol frame: expected '.
+              '"<hash> <name>\0<capabilities>\n", got "%s".',
+              $bytes));
+        }
+      } else {
+        $ok = preg_match(
+          '('.
+            '^'.
+            '(?P<hash>[0-9a-f]{40})'.
+            ' '.
+            '(?P<name>[^\0\n]+)'.
+            '\n'.
+            '\z'.
+          ')',
+          $bytes,
+          $matches);
+        if (!$ok) {
+          throw new Exception(
+            pht(
+              'Unexpected "git upload-pack" protocol frame: expected '.
+              '"<hash> <name>\n", got "%s".',
+              $bytes));
+        }
+      }
+
+      $hash = $matches['hash'];
+      $name = $matches['name'];
+      $capabilities = idx($matches, 'capabilities');
+
+      $ref = array(
+        'hash' => $hash,
+        'name' => $name,
+        'capabilities' => $capabilities,
+      );
+
+      $old_ref = $ref;
+
+      $ref = $this->willReadRef($ref);
+
+      $new_ref = $ref;
+
+      $this->didRewriteRef($old_ref, $new_ref);
+
+      if ($ref === null) {
+        continue;
+      }
+
+      if (isset($ref['capabilities'])) {
+        $result = sprintf(
+          "%s %s\0%s\n",
+          $ref['hash'],
+          $ref['name'],
+          $ref['capabilities']);
+      } else {
+        $result = sprintf(
+          "%s %s\n",
+          $ref['hash'],
+          $ref['name']);
+      }
+
+      $output[] = $this->newProtocolFrame('data', $result);
+    }
+
+    return $this->newProtocolDataMessage($output);
+  }
+
+  private function newProtocolDataMessage(array $frames) {
+    $message = array();
+
+    foreach ($frames as $frame) {
+      switch ($frame['type']) {
+        case 'null':
+          $message[] = '0000';
+          break;
+        case 'data':
+          $message[] = sprintf(
+            '%04x%s',
+            $frame['length'] + 4,
+            $frame['bytes']);
+          break;
+      }
+    }
+
+    $message = implode('', $message);
+
+    return $message;
+  }
+
+  private function willReadRef(array $ref) {
+    return $ref;
+  }
+
+  private function didRewriteRef($old_ref, $new_ref) {
+    $log = $this->getProtocolLog();
+    if (!$log) {
+      return;
+    }
+
+    if (!$old_ref) {
+      $old_name = null;
+    } else {
+      $old_name = $old_ref['name'];
+    }
+
+    if (!$new_ref) {
+      $new_name = null;
+    } else {
+      $new_name = $new_ref['name'];
+    }
+
+    if ($old_name === $new_name) {
+      return;
+    }
+
+    if ($old_name === null) {
+      $old_name = '<null>';
+    }
+
+    if ($new_name === null) {
+      $new_name = '<null>';
+    }
+
+    $log->didWriteFrame(
+      pht(
+        'Rewrite Ref: %s -> %s',
+        $old_name,
+        $new_name));
+  }
+
+}
diff --git a/src/applications/diffusion/protocol/DiffusionGitWireProtocol.php b/src/applications/diffusion/protocol/DiffusionGitWireProtocol.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/protocol/DiffusionGitWireProtocol.php
@@ -0,0 +1,19 @@
+<?php
+
+abstract class DiffusionGitWireProtocol extends Phobject {
+
+  private $protocolLog;
+
+  final public function setProtocolLog(PhabricatorProtocolLog $protocol_log) {
+    $this->protocolLog = $protocol_log;
+    return $this;
+  }
+
+  final public function getProtocolLog() {
+    return $this->protocolLog;
+  }
+
+  abstract public function willReadBytes($bytes);
+  abstract public function willWriteBytes($bytes);
+
+}
diff --git a/src/applications/diffusion/ssh/DiffusionGitSSHWorkflow.php b/src/applications/diffusion/ssh/DiffusionGitSSHWorkflow.php
--- a/src/applications/diffusion/ssh/DiffusionGitSSHWorkflow.php
+++ b/src/applications/diffusion/ssh/DiffusionGitSSHWorkflow.php
@@ -7,6 +7,8 @@
   private $engineLogProperties = array();
   private $protocolLog;
 
+  private $wireProtocol;
+
   protected function writeError($message) {
     // Git assumes we'll add our own newlines.
     return parent::writeError($message."\n");
@@ -74,14 +76,24 @@
     return null;
   }
 
-  protected function getProtocolLog() {
+  final protected function getProtocolLog() {
     return $this->protocolLog;
   }
 
-  protected function setProtocolLog(PhabricatorProtocolLog $log) {
+  final protected function setProtocolLog(PhabricatorProtocolLog $log) {
     $this->protocolLog = $log;
   }
 
+  final protected function getWireProtocol() {
+    return $this->wireProtocol;
+  }
+
+  final protected function setWireProtocol(
+    DiffusionGitWireProtocol $protocol) {
+    $this->wireProtocol = $protocol;
+    return $this;
+  }
+
   public function willWriteMessageCallback(
     PhabricatorSSHPassthruCommand $command,
     $message) {
@@ -91,6 +103,11 @@
       $log->didWriteBytes($message);
     }
 
+    $protocol = $this->getWireProtocol();
+    if ($protocol) {
+      $message = $protocol->willWriteBytes($message);
+    }
+
     return $message;
   }
 
@@ -103,6 +120,11 @@
       $log->didReadBytes($message);
     }
 
+    $protocol = $this->getWireProtocol();
+    if ($protocol) {
+      $message = $protocol->willReadBytes($message);
+    }
+
     return $message;
   }
 
diff --git a/src/applications/diffusion/ssh/DiffusionGitUploadPackSSHWorkflow.php b/src/applications/diffusion/ssh/DiffusionGitUploadPackSSHWorkflow.php
--- a/src/applications/diffusion/ssh/DiffusionGitUploadPackSSHWorkflow.php
+++ b/src/applications/diffusion/ssh/DiffusionGitUploadPackSSHWorkflow.php
@@ -60,6 +60,16 @@
       $log->didStartSession($command);
     }
 
+    if (!$is_proxy) {
+      if (PhabricatorEnv::getEnvConfig('phabricator.show-prototypes')) {
+        $protocol = new DiffusionGitUploadPackWireProtocol();
+        if ($log) {
+          $protocol->setProtocolLog($log);
+        }
+        $this->setWireProtocol($protocol);
+      }
+    }
+
     $err = $this->newPassthruCommand()
       ->setIOChannel($this->getIOChannel())
       ->setCommandChannelFromExecFuture($future)
diff --git a/src/infrastructure/log/PhabricatorProtocolLog.php b/src/infrastructure/log/PhabricatorProtocolLog.php
--- a/src/infrastructure/log/PhabricatorProtocolLog.php
+++ b/src/infrastructure/log/PhabricatorProtocolLog.php
@@ -41,6 +41,26 @@
     $this->buffer[] = $bytes;
   }
 
+  public function didReadFrame($frame) {
+    $this->writeFrame('<*', $frame);
+  }
+
+  public function didWriteFrame($frame) {
+    $this->writeFrame('>*', $frame);
+  }
+
+  private function writeFrame($header, $frame) {
+    $this->flush();
+
+    $frame = explode("\n", $frame);
+    foreach ($frame as $key => $line) {
+      $frame[$key] = $header.'  '.$this->escapeBytes($line);
+    }
+    $frame = implode("\n", $frame)."\n\n";
+
+    $this->writeMessage($frame);
+  }
+
   private function setMode($mode) {
     if ($this->mode === $mode) {
       return $this;