curl: fix POST request with empty body

CURLOPT_POST option without explicitly set CURLOPT_POSTFIELDS caused
libcurl to use some internal implementation of CURLOPT_READFUNCTION,
which reads body from stdin by default.

Provided test case only covers argument handling because there is no
repetable way to check reads from stdin from our test suite.

Closes #2530

src/httpc.c

@@ -327,13 +327,19 @@ httpc_request_new(struct httpc_env *env, const char *method,
 		curl_easy_setopt(req->easy, CURLOPT_HTTPGET, 1L);
 	} else if (strcmp(method, "HEAD") == 0) {
 		curl_easy_setopt(req->easy, CURLOPT_NOBODY, 1L);
-	} else if (strcmp(method, "POST") == 0) {
+	} else if (strcmp(method, "POST") == 0 ||
+		   strcmp(method, "PUT") == 0 ||
+		   strcmp(method, "PATCH")) {
+		/*
+		 * Set CURLOPT_POSTFIELDS to "" and CURLOPT_POSTFIELDSSIZE 0
+		 * to avoid the read callback in any cases even if user
+		 * forgot to call httpc_set_body() for POST request.
+		 * @see https://curl.haxx.se/libcurl/c/CURLOPT_POSTFIELDS.html
+		 */
 		curl_easy_setopt(req->easy, CURLOPT_POST, 1L);
-		if (httpc_set_header(req, "Accept: */*") < 0)
-			goto error;
-	} else if (strcmp(method, "PUT") == 0 || strcmp(method, "PATCH") == 0) {
+		curl_easy_setopt(req->easy, CURLOPT_POSTFIELDS, "");
+		curl_easy_setopt(req->easy, CURLOPT_POSTFIELDSIZE, 0);
 		curl_easy_setopt(req->easy, CURLOPT_CUSTOMREQUEST, method);
-		curl_easy_setopt(req->easy, CURLOPT_POST, 1L);
 		if (httpc_set_header(req, "Accept: */*") < 0)
 			goto error;
 	} else {

test/app-tap/http_client.test.lua

@@ -78,7 +78,7 @@ test:test("cancel and timeout", function(test)
 end)
 
 test:test("basic http post/get", function(test)
-    test:plan(16)
+    test:plan(19)
 
     local http = client.new()
     test:ok(http ~= nil, "client is created")
@@ -89,7 +89,7 @@ test:test("basic http post/get", function(test)
     local responses = {}
     local data = {a = 'b'}
     headers['Content-Type'] = 'application/json'
-    local fibers = 6
+    local fibers = 7
     local ch = fiber.channel(fibers)
     local _
     fiber.create(function()
@@ -104,6 +104,10 @@ test:test("basic http post/get", function(test)
         responses.good_post = http:post(URL, json_body, {headers = headers})
         ch:put(1)
     end)
+    fiber.create(function()
+        responses.empty_post = http:post(URL, nil, {headers = headers})
+        ch:put(1)
+    end)
     fiber.create(function()
         responses.good_put = http:put(URL, json_body, {headers = headers})
         ch:put(1)
@@ -133,6 +137,12 @@ test:test("basic http post/get", function(test)
     test:is(r.status, 500, "GET: absent method http code page exists")
     test:is(r.body, "No such method", "GET: absent method right body")
 
+    r = responses.empty_post
+    test:is(r.status, 200, "POST: good status")
+    test:ok(r.headers['header1'] == headers.header1 and
+        r.headers['header2'] == headers.header2, "POST: good headers")
+    test:isnil(r.body, "POST: empty body")
+
     r = responses.good_post
     test:is(r.status, 200, "POST: good status")
     test:ok(r.headers['header1'] == headers.header1 and