Checks and delay before reading header infos

- Added some checks that stream variable is not NULL before using it
(just to make sure)
- To avoid header-read errors that happened sometimes implement a check
for available data with a maximum timeout of 1000ms (configurable via
defines in header file). With my default settings we wait 20 ms and
then check again if at least 17 characters are available to read (which
should be a normal HTTP-header first line). This is done at max 50
times before the read is tried

HTTPClient.cpp

@@ -203,6 +203,10 @@ char
 HTTPClient::sendUriAndHeaders(FILE* stream, char* hostName, const char* requestType, char* uri,
     http_client_parameter parameters[], http_client_parameter headers[])
 {
+  if (stream == NULL)
+  {
+    return 0;
+  }
   fprintf_P(stream, requestType, uri);
   fprintf_P(stream, PSTR(" "), uri);
   //encode but use reserved characters
@@ -256,6 +260,10 @@ HTTPClient::sendUriAndHeaders(FILE* stream, char* hostName, const char* requestT
 char
 HTTPClient::sendContentPayload(FILE* stream, char* data)
 {
+  if (stream == NULL)
+  {
+    return 0;
+  }
   //calculate the content length
   int content_length = 0;
   if (data != NULL)
@@ -402,9 +410,20 @@ HTTPClient::skipHeader(FILE* stream)
   //skip over the header
   int httpReturnCode;
   lastReturnCode = NULL;
+
+  if (stream == NULL) return NULL;
+  http_stream_udata* udata = (http_stream_udata*) fdev_get_udata(stream);
+  HTTPClient* client = udata->client;
+
+  int delayReadHeaderCount=0;
+  // check if at least the first HTTP-response available, up to 1000ms=1s
+  while ((client->available()<17) && (delayReadHeaderCount++<HTTPCLIENT_HEADER_READ_DELAY_MAXCOUNT)) 
+     delay(HTTPCLIENT_HEADER_READ_DELAY_ONCE);
+
   int res=fscanf_P(stream, PSTR("HTTP/1.1 %i"), &httpReturnCode);
   if (res!=1) return NULL;
-  lastReturnCode = httpReturnCode; // only set class variable when successfully matched
+  lastReturnCode = httpReturnCode; // only set class variable when successfully matched, else it is NULL
+
   char inByte = '\0';
   char lastByte = '\0';
   while (!(inByte == '\n' && lastByte == '\n'))

HTTPClient.h

@@ -26,7 +26,14 @@
 #define HTTPCLIENT_H_
 
 #include <inttypes.h>
-#include "EthernetClient.h"
+#include <EthernetClient.h>
+
+/* With this we try a delay of 20 ms before checking again if content is available
+ * and we try this up to 50 times.
+ * So max: 20x50ms=1000ms=1s
+ */
+#define HTTPCLIENT_HEADER_READ_DELAY_ONCE 20
+#define HTTPCLIENT_HEADER_READ_DELAY_MAXCOUNT 50
 
 /* This struct is used to pass parameters as URI paramters and additional HTTP headers.
  * normally you pass this as a array. The last entry must have the NULL-Pointer as name.