http: support cookie redaction when tracing

When using GIT_TRACE_CURL, Git already redacts the "Authorization:" and
"Proxy-Authorization:" HTTP headers. Extend this redaction to a
user-specified list of cookies, specified through the
"GIT_REDACT_COOKIES" environment variable.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git.txt

@@ -646,6 +646,12 @@ of clones and fetches.
 	variable.
 	See `GIT_TRACE` for available trace output options.
 
+`GIT_REDACT_COOKIES`::
+	This can be set to a comma-separated list of strings. When a curl trace
+	is enabled (see `GIT_TRACE_CURL` above), whenever a "Cookies:" header
+	sent by the client is dumped, values of cookies whose key is in that
+	list (case-sensitive) are redacted.
+
 `GIT_LITERAL_PATHSPECS`::
 	Setting this variable to `1` will cause Git to treat all
 	pathspecs literally, rather than as glob patterns. For example,

http.c

@@ -13,8 +13,10 @@
 #include "transport.h"
 #include "packfile.h"
 #include "protocol.h"
+#include "string-list.h"
 
 static struct trace_key trace_curl = TRACE_KEY_INIT(CURL);
+static struct string_list cookies_to_redact = STRING_LIST_INIT_DUP;
 #if LIBCURL_VERSION_NUM >= 0x070a08
 long int git_curl_ipresolve = CURL_IPRESOLVE_WHATEVER;
 #else
@@ -575,6 +577,54 @@ static void redact_sensitive_header(struct strbuf *header)
 		/* Everything else is opaque and possibly sensitive */
 		strbuf_setlen(header,  sensitive_header - header->buf);
 		strbuf_addstr(header, " <redacted>");
+	} else if (cookies_to_redact.nr &&
+		   skip_prefix(header->buf, "Cookie:", &sensitive_header)) {
+		struct strbuf redacted_header = STRBUF_INIT;
+		char *cookie;
+
+		while (isspace(*sensitive_header))
+			sensitive_header++;
+
+		/*
+		 * The contents of header starting from sensitive_header will
+		 * subsequently be overridden, so it is fine to mutate this
+		 * string (hence the assignment to "char *").
+		 */
+		cookie = (char *) sensitive_header;
+
+		while (cookie) {
+			char *equals;
+			char *semicolon = strstr(cookie, "; ");
+			if (semicolon)
+				*semicolon = 0;
+			equals = strchrnul(cookie, '=');
+			if (!equals) {
+				/* invalid cookie, just append and continue */
+				strbuf_addstr(&redacted_header, cookie);
+				continue;
+			}
+			*equals = 0; /* temporarily set to NUL for lookup */
+			if (string_list_lookup(&cookies_to_redact, cookie)) {
+				strbuf_addstr(&redacted_header, cookie);
+				strbuf_addstr(&redacted_header, "=<redacted>");
+			} else {
+				*equals = '=';
+				strbuf_addstr(&redacted_header, cookie);
+			}
+			if (semicolon) {
+				/*
+				 * There are more cookies. (Or, for some
+				 * reason, the input string ends in "; ".)
+				 */
+				strbuf_addstr(&redacted_header, "; ");
+				cookie = semicolon + strlen("; ");
+			} else {
+				cookie = NULL;
+			}
+		}
+
+		strbuf_setlen(header, sensitive_header - header->buf);
+		strbuf_addbuf(header, &redacted_header);
 	}
 }
 
@@ -807,6 +857,11 @@ static CURL *get_curl_handle(void)
 	if (getenv("GIT_CURL_VERBOSE"))
 		curl_easy_setopt(result, CURLOPT_VERBOSE, 1L);
 	setup_curl_trace(result);
+	if (getenv("GIT_REDACT_COOKIES")) {
+		string_list_split(&cookies_to_redact,
+				  getenv("GIT_REDACT_COOKIES"), ',', -1);
+		string_list_sort(&cookies_to_redact);
+	}
 
 	curl_easy_setopt(result, CURLOPT_USERAGENT,
 		user_agent ? user_agent : git_user_agent());

t/t5551-http-fetch-smart.sh

@@ -364,5 +364,26 @@ test_expect_success 'custom http headers' '
 		submodule update sub
 '
 
+test_expect_success 'GIT_REDACT_COOKIES redacts cookies' '
+	rm -rf clone &&
+	echo "Set-Cookie: Foo=1" >cookies &&
+	echo "Set-Cookie: Bar=2" >>cookies &&
+	GIT_TRACE_CURL=true GIT_REDACT_COOKIES=Bar,Baz \
+		git -c "http.cookieFile=$(pwd)/cookies" clone \
+		$HTTPD_URL/smart/repo.git clone 2>err &&
+	grep "Cookie:.*Foo=1" err &&
+	grep "Cookie:.*Bar=<redacted>" err &&
+	! grep "Cookie:.*Bar=2" err
+'
+
+test_expect_success 'GIT_REDACT_COOKIES handles empty values' '
+	rm -rf clone &&
+	echo "Set-Cookie: Foo=" >cookies &&
+	GIT_TRACE_CURL=true GIT_REDACT_COOKIES=Foo \
+		git -c "http.cookieFile=$(pwd)/cookies" clone \
+		$HTTPD_URL/smart/repo.git clone 2>err &&
+	grep "Cookie:.*Foo=<redacted>" err
+'
+
 stop_httpd
 test_done