Hi, I am trying to present a blocking, pull interface to a client using curl internally (this interface is already implemented using WinHTTP on Windows and I would like to port it to Linux and OSX using curl as the internal HTTP engine). The a simplified portion of the interface looks something like:
int Get(url); size_t Read(char* buffer, size_t length); The user calls Get() which will return the response code and can then optionally call Read() until it returns 0. This allows the client to read as much/little and at what rate suits them. Under the covers I use a multihandle and curl_multi_perform. When I originally designed this I assumed that a curl_multi_perform would invoke either 0 or 1 of my write callbacks. Testing seems to indicate this is not necessarily the case. Question 1: Can a single call to curl_multi_perform result in multiple write callbacks? Internally my library wrapper keeps a fixed-buffer of size CURL_MAX_WRITE_SIZE of the data provided by curl calling the write callback. Assuming a 1-1 perform/callback the flow would go: 1) Caller invokes Read() 2) If my lib has data buffered, copy data to caller buffer and return bytes copied otherwise call curl_multi_perform() 3) If no data from curl, select and loop until data (client is blocked on Read()) 4) If callback was invoked, copy data from library buffer to caller buffer and return bytes copied The problem I have with this, is if the write callback is invoked multiple times before an intervening caller Read() drains the libraries internal buffer, data is lost (overwritten in my libraries internal buffer). Question 2: Are all my observations correct up to this point? Question 3: What is the best way to craft an interface like this using curl? Can I use curl_easy_pause() after each write callback and then unpause after the client drains my internal buffer and my library needs more data from curl? I figured I would ask for some pointers or guidance before pursuing any additional lines of research. Thank you. Rich ------------------------------------------------------------------- List admin: http://cool.haxx.se/list/listinfo/curl-library Etiquette: http://curl.haxx.se/mail/etiquette.html
