Use a separate boolean to remember whether Content-Length was set.

Previous content_length == 0 was overloaded to mean that Content-Length
was set. But that was wrong when the Content-Length was actually 0.

The error message you got when running an HTTP proxy that received
0-length POSTs was
	POST request with no Content-Length.

ncat/http.c

@@ -843,6 +843,7 @@ void http_request_init(struct http_request *request)
     uri_init(&request->uri);
     request->version = HTTP_UNKNOWN;
     request->header = NULL;
+    request->content_length_set = 0;
     request->content_length = 0;
     request->bytes_transferred = 0;
 }
@@ -898,6 +899,7 @@ void http_response_init(struct http_response *response)
     response->code = 0;
     response->phrase = NULL;
     response->header = NULL;
+    response->content_length_set = 0;
     response->content_length = 0;
     response->bytes_transferred = 0;
 }
@@ -1053,7 +1055,7 @@ int http_parse_header(struct http_header **result, const char *header)
     return 0;
 }
 
-static int http_header_get_content_length(const struct http_header *header, unsigned long *content_length)
+static int http_header_get_content_length(const struct http_header *header, int *content_length_set, unsigned long *content_length)
 {
     char *content_length_s;
     char *tail;
@@ -1061,6 +1063,7 @@ static int http_header_get_content_length(const struct http_header *header, unsi
 
     content_length_s = http_header_get_first(header, "Content-Length");
     if (content_length_s == NULL) {
+        *content_length_set = 0;
         *content_length = 0;
         return 0;
     }
@@ -1068,6 +1071,7 @@ static int http_header_get_content_length(const struct http_header *header, unsi
     code = 0;
 
     errno = 0;
+    *content_length_set = 1;
     *content_length = parse_long(content_length_s, (char **) &tail);
     if (errno != 0 || *tail != '\0' || tail == content_length_s)
         code = 400;
@@ -1084,7 +1088,7 @@ int http_request_parse_header(struct http_request *request, const char *header)
     code = http_parse_header(&request->header, header);
     if (code != 0)
         return code;
-    code = http_header_get_content_length(request->header, &request->content_length);
+    code = http_header_get_content_length(request->header, &request->content_length_set, &request->content_length);
     if (code != 0)
         return code;
 
@@ -1099,7 +1103,7 @@ int http_response_parse_header(struct http_response *response, const char *heade
     code = http_parse_header(&response->header, header);
     if (code != 0)
         return code;
-    code = http_header_get_content_length(response->header, &response->content_length);
+    code = http_header_get_content_length(response->header, &response->content_length_set, &response->content_length);
     if (code != 0)
         return code;
 

ncat/http.h

@@ -184,6 +184,7 @@ struct http_request {
     struct uri uri;
     enum http_version version;
     struct http_header *header;
+    int content_length_set;
     unsigned long content_length;
     unsigned long bytes_transferred;
 };
@@ -193,6 +194,7 @@ struct http_response {
     int code;
     char *phrase;
     struct http_header *header;
+    int content_length_set;
     unsigned long content_length;
     unsigned long bytes_transferred;
 };

ncat/ncat_proxy.c

@@ -660,7 +660,7 @@ static int do_transaction(struct http_request *request,
        request) if it cannot determine the length of the message, or with 411
        (length required) if it wishes to insist on receiving a valid
        Content-Length." */
-    if (strcmp(request->method, "POST") == 0 && request->content_length == 0) {
+    if (strcmp(request->method, "POST") == 0 && !request->content_length_set) {
         if (o.debug)
             logdebug("POST request with no Content-Length.\n");
         return 400;
@@ -771,14 +771,16 @@ static int do_transaction(struct http_request *request,
     /* If the Content-Length is 0, read until the connection is closed.
        Otherwise read until the Content-Length. At this point it's too late to
        return our own error code so return 0 in case of any error. */
-    while (response.content_length == 0
+    while (!response.content_length_set
         || response.bytes_transferred < response.content_length) {
-        size_t remaining = response.content_length - response.bytes_transferred;
         size_t count;
 
         count = sizeof(buf);
-        if (response.content_length > 0 && remaining < count)
+        if (response.content_length_set) {
+            size_t remaining = response.content_length - response.bytes_transferred;
+            if (remaining < count)
                 count = remaining;
+        }
         n = socket_buffer_read(server_sock, buf, count);
         if (n <= 0)
             break;