From 854459cb11d29093bf8dc6e98c3cfb6ba208ec6c Mon Sep 17 00:00:00 2001
From: Lars-Dominik Braun <lars@6xq.net>
Date: Tue, 31 Oct 2017 13:23:59 +0100
Subject: Initial commit

---
 .gitignore   |  2 ++
 Makefile     |  3 +++
 README.rst   | 15 +++++++++++++++
 curlfilter.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 66 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 README.rst
 create mode 100644 curlfilter.c

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a7d3377
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*.sw?
+curlfilter.so
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..4e1fac1
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,3 @@
+curlfilter.so: curlfilter.c
+	gcc -Wl,-init=init -o $@ -std=c11 -shared -fPIC -ldl -lpcre $<
+
diff --git a/README.rst b/README.rst
new file mode 100644
index 0000000..9ef00ce
--- /dev/null
+++ b/README.rst
@@ -0,0 +1,15 @@
+curlfilter
+==========
+
+Filter URLs passed to libcurl’s easy interface by regular expression. Can be
+used to implement per-application ad-blocking.
+
+Compile with::
+
+    make
+
+For Spotify run::
+
+    export CURLFILTER_PATTERN="spclient.wg.spotify.com/ad[-s]"
+    LD_PRELOAD=/path/to/curlfilter.so spotify
+
diff --git a/curlfilter.c b/curlfilter.c
new file mode 100644
index 0000000..5984edc
--- /dev/null
+++ b/curlfilter.c
@@ -0,0 +1,46 @@
+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <stdarg.h>
+#include <assert.h>
+#include <string.h>
+#include <curl/curl.h>
+#include <pcre.h>
+/* the function is actually a macro, which prevents us from redefining it
+ * properly */
+#undef curl_easy_setopt
+ 
+typedef CURLcode (*orig_curl_easy_setopt) (CURL *handle, CURLoption option, ...); 
+
+static pcre *re = NULL;
+
+CURL_EXTERN CURLcode curl_easy_setopt (CURL *handle, CURLoption option, ...) {
+	va_list args;
+	va_start (args, option);
+	void *parameter = va_arg (args, void *);
+
+	if (re != NULL && option == CURLOPT_URL) {
+		int matches[3];
+		if (pcre_exec (re, NULL, parameter, strlen (parameter), 0, 0, matches, 3) >= 0) {
+			/* not allowed */
+			return CURLE_URL_MALFORMAT;
+		}
+	}
+
+    orig_curl_easy_setopt orig_setopt;
+	orig_setopt = (orig_curl_easy_setopt) dlsym (RTLD_NEXT, "curl_easy_setopt");
+    return orig_setopt (handle, option, parameter);
+}
+
+void init () {
+	const char * const pattern = getenv ("CURLFILTER_PATTERN");
+	const char *errmsg = NULL;
+	int errpos;
+	if (pattern == NULL) {
+		fprintf (stderr, "Environment variable CURLFILTER_PATTERN is not set\n");
+		return;
+	}
+	if ((re = pcre_compile (pattern, 0, &errmsg, &errpos, NULL)) == NULL) {
+		fprintf (stderr, "Cannot compile regex %s: %s\n", pattern, errmsg);
+		return;
+	}
+}
-- 
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