From 302be04d826a3f09c8cd3d313592f7976fa8c0cb Mon Sep 17 00:00:00 2001
From: Sean Allred <code@seanallred.com>
Date: Mon, 10 Nov 2014 22:53:10 -0500
Subject: Proper GZIP testing

Test for a GZIP'd using magic bytes.  See the appropriate answer on
Emacs.SE (1) for details.

(1): http://emacs.stackexchange.com/a/2978
---
 sx-encoding.el | 29 +++++++++++++++++++++++++++++
 sx-request.el  | 28 +++++++++++-----------------
 2 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/sx-encoding.el b/sx-encoding.el
index 8ac12ca..98f3a7c 100644
--- a/sx-encoding.el
+++ b/sx-encoding.el
@@ -74,6 +74,35 @@
                                                        (substring ss 1))))))))
     (replace-regexp-in-string "&[^; ]*;" get-function string)))
 
+(defun sx-encoding-gzipped-p (data)
+  "Checks for magic bytes in DATA.
+
+Check if the first two bytes of a string in DATA match magic
+numbers identifying the gzip file format. See [1] for the file
+format description.
+
+http://www.gzip.org/zlib/rfc-gzip.html
+
+http://emacs.stackexchange.com/a/2978"
+  (equal (substring (string-as-unibyte data) 0 2)
+         (unibyte-string 31 139)))
+
+(defun sx-encoding-gzipped-buffer-p (filename)
+  "Check if the BUFFER is gzip-compressed.
+
+See `gzip-check-magic' for details."
+  (sx-encoding-gzip-check-magic (buffer-string)))
+
+(defun sx-encoding-gzipped-file-p (file)
+  "Check if the FILE is gzip-compressed.
+
+See `gzip-check-magic' for details."
+  (let ((first-two-bytes (with-temp-buffer
+                           (set-buffer-multibyte nil)
+                           (insert-file-contents-literally file nil 0 2)
+                           (buffer-string))))
+    (gzip-check-magic first-two-bytes)))
+
 (provide 'sx-encoding)
 ;;; sx-encoding.el ends here
 
diff --git a/sx-request.el b/sx-request.el
index 9d9dca4..12d2b14 100644
--- a/sx-request.el
+++ b/sx-request.el
@@ -92,24 +92,18 @@ number of requests left every time it finishes a call.")
                              (error "Response headers missing; response corrupt")
                            (delete-region (point-min) (point))
                            (buffer-string))))
-                 (response (ignore-errors
+                 (response-zipped-p (sx-encoding-gzipped-p data))
+                 (data (if (not response-zipped-p) data
+                         (shell-command-on-region
+                          (point-min) (point-max)
+                          sx-request-unzip-program
+                          nil t)
+                         (buffer-string)))
+                 (response (with-demoted-errors "`json' error: %S"
                              (json-read-from-string data))))
-            ;; If the response isn't nil, the response was in plain text
-            (unless response
-              ;; try to decompress the response
-              (setq response
-                    (with-demoted-errors "`json-read' error: %S"
-                      (shell-command-on-region
-                       (point-min) (point-max)
-                       sx-request-unzip-program
-                       nil t)
-                      (json-read-from-string
-                       (buffer-substring
-                        (point-min) (point-max)))))
-              ;; if it still fails, error outline
-              (unless response
-                (sx-message "Unable to parse response: %S" response)
-                (error "Response could not be read by `json-read-from-string'")))
+            (unless (not (and (not response) (string-equal data "{}")))
+              (sx-message "Unable to parse response: %S" response)
+              (error "Response could not be read by `json-read-from-string'"))
             ;; If we get here, the response is a valid data structure
             (sx-assoc-let response
               (when error_id
-- 
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