- Fixed forward stream seeking emulation in streams that don't support seeking

in situations where the read operation gives back less data than requested
  and when there was data in the buffer before the emulation started. Also made
  more consistent its behavior -- should return failure every time less data
  than was requested was skipped.
- Small performance improvement by correcting off-by-one error that generate an
  invalid call to the seek handler or read handler. in _php_stream_seek.

NEWS

@@ -28,6 +28,11 @@
 - Fixed inconsistent backlog default value (-1) in FPM on many systems. (fat)
 - Fixed bug in the Windows implementation of dns_get_record, where the two
   last parameters wouldn't be filled unless the type were DNS_ANY (Gustavo).
+- Fixed forward stream seeking emulation in streams that don't support seeking
+  in situations where the read operation gives back less data than requested
+  and when there was data in the buffer before the emulation started. Also made
+  more consistent its behavior -- should return failure every time less data
+  than was requested was skipped. (Gustavo)
 
 - Fixed bug #53021 (In html_entity_decode, failure to convert numeric entities
   with ENT_NOQUOTES and ISO-8859-1). Fixed and extended the fix of ENT_NOQUOTES 

main/streams/streams.c

@@ -1097,8 +1097,8 @@ PHPAPI int _php_stream_seek(php_stream *stream, off_t offset, int whence TSRMLS_
 	if ((stream->flags & PHP_STREAM_FLAG_NO_BUFFER) == 0) {
 		switch(whence) {
 			case SEEK_CUR:
-				if (offset > 0 && offset < stream->writepos - stream->readpos) {
-					stream->readpos += offset;
+				if (offset > 0 && offset <= stream->writepos - stream->readpos) {
+					stream->readpos += offset; /* if offset = ..., then readpos = writepos */
 					stream->position += offset;
 					stream->eof = 0;
 					return 0;
@@ -1106,7 +1106,7 @@ PHPAPI int _php_stream_seek(php_stream *stream, off_t offset, int whence TSRMLS_
 				break;
 			case SEEK_SET:
 				if (offset > stream->position &&
-						offset < stream->position + stream->writepos - stream->readpos) {
+						offset <= stream->position + stream->writepos - stream->readpos) {
 					stream->readpos += offset - stream->position;
 					stream->position = offset;
 					stream->eof = 0;
@@ -1149,14 +1149,12 @@ PHPAPI int _php_stream_seek(php_stream *stream, off_t offset, int whence TSRMLS_
 	/* emulate forward moving seeks with reads */
 	if (whence == SEEK_CUR && offset > 0) {
 		char tmp[1024];
-		while(offset >= sizeof(tmp)) {
-			if (php_stream_read(stream, tmp, sizeof(tmp)) == 0) {
+		size_t didread;
+		while(offset > 0) {
+			if ((didread = php_stream_read(stream, tmp, MIN(offset, sizeof(tmp)))) == 0) {
 				return -1;
 			}
-			offset -= sizeof(tmp);
-		}
-		if (offset && (php_stream_read(stream, tmp, offset) == 0)) {
-			return -1;
+			offset -= didread;
 		}
 		stream->eof = 0;
 		return 0;