From 939068c5334482e7a6b905aa963cd68ebe6c6dd9 Mon Sep 17 00:00:00 2001
From: Philip Hughes <phil@hughesbox.co.uk>
Date: Tue, 10 Mar 2015 10:21:20 +0000
Subject: [PATCH] Swap to gzip compression (fixes #262 and #266)

Instead of making the browser sniffing more complicated, it's probably
better to use code that works for all current browsers. As such, this
swaps to use gzip compression encoding instead of deflate and drops the
IE browser sniffing code. This means shellinabox works in IE11 and
should work in every version of IE since IE7. From this commit, IE6 is
no longer supported. Thanks @lfourquaux.
---
 libhttp/httpconnection.c | 28 ++++++----------------------
 1 file changed, 6 insertions(+), 22 deletions(-)

diff --git a/libhttp/httpconnection.c b/libhttp/httpconnection.c
index 521d610..cd9601a 100644
--- a/libhttp/httpconnection.c
+++ b/libhttp/httpconnection.c
@@ -564,15 +564,6 @@ void httpTransfer(struct HttpConnection *http, char *msg, int len) {
   check(msg);
   check(len >= 0);
 
-  // Internet Explorer seems to have difficulties with compressed data. It
-  // also has difficulties with SSL connections that are being proxied.
-  int ieBug                 = 0;
-  const char *userAgent     = getFromHashMap(&http->header, "user-agent");
-  const char *msie          = userAgent ? strstr(userAgent, "Trident") : NULL;
-  if (msie) {
-    ieBug++;
-  }
-
   char *header              = NULL;
   int headerLength          = 0;
   int bodyOffset            = 0;
@@ -612,10 +603,10 @@ void httpTransfer(struct HttpConnection *http, char *msg, int len) {
 
         #ifdef HAVE_ZLIB
         // Compress replies that might exceed the size of a single IP packet
-        compress            = !ieBug && !isHead &&
+        compress            = !isHead &&
                               !http->isPartialReply &&
                               len > 1400 &&
-                              httpAcceptsEncoding(http, "deflate");
+                              httpAcceptsEncoding(http, "gzip");
         #endif
         break;
       } else {
@@ -630,7 +621,7 @@ void httpTransfer(struct HttpConnection *http, char *msg, int len) {
       line                  = eol + 1;
     }
 
-    if (ieBug || compress) {
+    if (compress) {
       if (l >= 2 && !memcmp(line, "\r\n", 2)) {
         line               += 2;
         l                  -= 2;
@@ -640,10 +631,6 @@ void httpTransfer(struct HttpConnection *http, char *msg, int len) {
       check(header          = malloc(headerLength));
       memcpy(header, msg, headerLength);
     }
-    if (ieBug) {
-      removeHeader(header, &headerLength, "connection:");
-      addHeader(&header, &headerLength, "Connection: close\r\n");
-    }
 
     if (compress) {
       #ifdef HAVE_ZLIB
@@ -659,7 +646,8 @@ void httpTransfer(struct HttpConnection *http, char *msg, int len) {
                                 .avail_out = len,
                                 .next_out  = (unsigned char *)compressed
                               };
-      if (deflateInit(&strm, Z_DEFAULT_COMPRESSION) == Z_OK) {
+      if (deflateInit2(&strm, Z_DEFAULT_COMPRESSION, Z_DEFLATED,
+                       31, 8, Z_DEFAULT_STRATEGY) == Z_OK) {
         if (deflate(&strm, Z_FINISH) == Z_STREAM_END) {
           // Compression was successful and resulted in reduction in size
           debug("Compressed response from %d to %d", len, len-strm.avail_out);
@@ -670,7 +658,7 @@ void httpTransfer(struct HttpConnection *http, char *msg, int len) {
           removeHeader(header, &headerLength, "content-length:");
           removeHeader(header, &headerLength, "content-encoding:");
           addHeader(&header, &headerLength, "Content-Length: %d\r\n", len);
-          addHeader(&header, &headerLength, "Content-Encoding: deflate\r\n");
+          addHeader(&header, &headerLength, "Content-Encoding: gzip\r\n");
         } else {
           free(compressed);
         }
@@ -773,10 +761,6 @@ void httpTransfer(struct HttpConnection *http, char *msg, int len) {
       }
     }
   }
-
-  if (ieBug) {
-    httpCloseRead(http);
-  }
 }
 
 void httpTransferPartialReply(struct HttpConnection *http, char *msg, int len){