http-backend: respect CONTENT_LENGTH as specified by rfc3875

http-backend reads whole input until EOF. However, the RFC 3875 specifies
that a script must read only as many bytes as specified by CONTENT_LENGTH
environment variable. Web server may exercise the specification by not closing
the script's standard input after writing content. In that case http-backend
would hang waiting for the input. The issue is known to happen with
IIS/Windows, for example.

Make http-backend read only CONTENT_LENGTH bytes, if it's defined, rather than
the whole input until EOF. If the variable is not defined, keep older behavior
of reading until EOF because it is used to support chunked transfer-encoding.

Signed-off-by: Florian Manschwetus <manschwetus@cs-software-gmbh.de>
[mk: fixed trivial build failures and polished style issues]
Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 51 insertions, 2 deletions

diff --git a/config.c b/config.c
index adb7d7a3e5..be71cb15d1 100644
--- a/config.c
+++ b/config.c
@@ -853,7 +853,7 @@ int git_parse_ulong(const char *value, unsigned long *ret)
 	return 1;
 }
 
-static int git_parse_ssize_t(const char *value, ssize_t *ret)
+int git_parse_ssize_t(const char *value, ssize_t *ret)
 {
 	intmax_t tmp;
 	if (!git_parse_signed(value, &tmp, maximum_signed_value_of_type(ssize_t)))
diff --git a/config.h b/config.h
index a49d264416..84ec617c01 100644
--- a/config.h
+++ b/config.h
@@ -48,6 +48,7 @@ extern void git_config(config_fn_t fn, void *);
 extern int config_with_options(config_fn_t fn, void *,
 			       struct git_config_source *config_source,
 			       const struct config_options *opts);
+extern int git_parse_ssize_t(const char *, ssize_t *);
 extern int git_parse_ulong(const char *, unsigned long *);
 extern int git_parse_maybe_bool(const char *);
 extern int git_config_int(const char *, const char *);
diff --git a/http-backend.c b/http-backend.c
index f3dc218b2a..69570d16e7 100644
--- a/http-backend.c
+++ b/http-backend.c
@@ -281,7 +281,7 @@ static struct rpc_service *select_service(struct strbuf *hdr, const char *name)
  * hit max_request_buffer we die (we'd rather reject a
  * maliciously large request than chew up infinite memory).
  */
-static ssize_t read_request(int fd, unsigned char **out)
+static ssize_t read_request_eof(int fd, unsigned char **out)
 {
 	size_t len = 0, alloc = 8192;
 	unsigned char *buf = xmalloc(alloc);
@@ -318,6 +318,54 @@ static ssize_t read_request(int fd, unsigned char **out)
 	}
 }
 
+static ssize_t read_request_fixed_len(int fd, ssize_t req_len, unsigned char **out)
+{
+	unsigned char *buf = NULL;
+	ssize_t cnt = 0;
+
+	if (max_request_buffer < req_len) {
+		die("request was larger than our maximum size (%lu): %lu;"
+			    " try setting GIT_HTTP_MAX_REQUEST_BUFFER",
+			    max_request_buffer,
+			    req_len);
+	}
+
+	if (req_len <= 0) {
+		*out = NULL;
+		return 0;
+	}
+
+	buf = xmalloc(req_len);
+	cnt = read_in_full(fd, buf, req_len);
+	if (cnt < 0) {
+		free(buf);
+		return -1;
+	} else {
+		*out = buf;
+		return cnt;
+	}
+}
+
+static ssize_t env_content_length(void)
+{
+	ssize_t val = -1;
+	const char *str = getenv("CONTENT_LENGTH");
+
+	if (str && !git_parse_ssize_t(str, &val))
+		die("failed to parse CONTENT_LENGTH: %s", str);
+	return val;
+}
+
+static ssize_t read_request(int fd, unsigned char **out)
+{
+	ssize_t req_len = env_content_length();
+
+	if (req_len < 0)
+		return read_request_eof(fd, out);
+	else
+		return read_request_fixed_len(fd, req_len, out);
+}
+
 static void inflate_request(const char *prog_name, int out, int buffer_input)
 {
 	git_zstream stream;