HTTP fixes for cellular: timeout cannot be zero. (#1086)

Cellular modules return an error if an attempt is made to set the HTTP timeout to zero:

AT+UHTTP=0,7,0
+CME ERROR: Operation not supported

This is pointed out in the description of uCellHttpOpen() and does not occur if the intended pattern of assigning uHttpClientConnection_t to U_HTTP_CLIENT_CONNECTION_DEFAULT when calling pUHttpClientOpen() is followed. However that pattern is not documented in the description of pUHttpClientOpen() and uCellHttpOpen() allows the timeout to be set to zero, which it should not.

Our thanks to jamal-mouline for highlighting this.

cell/src/u_cell_http.c

@@ -476,7 +476,7 @@ int32_t uCellHttpOpen(uDeviceHandle_t cellHandle, const char *pServerName,
         errorCodeOrHandle = (int32_t) U_ERROR_COMMON_INVALID_PARAMETER;
         if ((pServerName != NULL) && (strlen(pServerName) <= U_CELL_HTTP_SERVER_NAME_MAX_LEN_BYTES) &&
             ((pUserName != NULL) || (pPassword == NULL)) &&
-            (timeoutSeconds >= 0) && (pCallback != NULL)) {
+            (timeoutSeconds > 0) && (pCallback != NULL)) {
             errorCodeOrHandle = (int32_t) U_ERROR_COMMON_NO_MEMORY;
             pHttpContext = pCellInstance->pHttpContext;
             if (pHttpContext == NULL) {

common/http_client/api/u_http_client.h

@@ -233,6 +233,11 @@ typedef struct {
  *                                 potentially a callback function which
  *                                 would make the HTTP request functions
  *                                 non-blocking; cannot be NULL.
+ *                                 IT IS GOOD PRACTICE to assign this,
+ *                                 initially, to
+ *                                 #U_HTTP_CLIENT_CONNECTION_DEFAULT and
+ *                                 then modify the members you want
+ *                                 to be different to the default value.
  * @param[in] pSecurityTlsSettings a pointer to the security settings to
  *                                 be applied if you wish to make an HTTPS
  *                                 connection, NULL for no security.