Switch to reading content streams on the fly during interpretation.

Previously, before interpreting a pages content stream we would
load it entirely into a buffer. Then we would interpret that
buffer. This has a cost in memory use.

Here, we update the code to read from a stream on the fly.

This has required changes in various different parts of the code.

Firstly, we have removed all use of the FILE lock - as stream
reads can now safely be interrupted by resource (or object) reads
from elsewhere in the file, the file lock becomes a very hard
thing to maintain, and doesn't actually benefit us at all. The
choices were to either use a recursive lock, or to remove it
entirely; I opted for the latter.

The file lock enum value remains as a placeholder for future use in
extendable data streams.

Secondly, we add a new 'concat' filter that concatenates a series of
streams together into one, optionally putting whitespace between each
stream (as the pdf parser requires this).

Finally, we change page/xobject/pattern content streams to work
on the fly, but we leave type3 glyphs using buffers (as presumably
these will be run repeatedly).

1 files changed, 10 insertions, 20 deletions

diff --git a/xps/xps_zip.c b/xps/xps_zip.c
index ff43abf2..bb6857ee 100644
--- a/xps/xps_zip.c
+++ b/xps/xps_zip.c
@@ -108,13 +108,11 @@ xps_read_zip_entry(xps_document *doc, xps_entry *ent, unsigned char *outbuf)
 	int code;
 	fz_context *ctx = doc->ctx;
 
-	fz_lock(ctx, FZ_LOCK_FILE);
 	fz_seek(doc->file, ent->offset, 0);
 
 	sig = getlong(doc->file);
 	if (sig != ZIP_LOCAL_FILE_SIG)
 	{
-		fz_unlock(ctx, FZ_LOCK_FILE);
 		fz_throw(doc->ctx, "wrong zip local file signature (0x%x)", sig);
 	}
 
@@ -137,7 +135,7 @@ xps_read_zip_entry(xps_document *doc, xps_entry *ent, unsigned char *outbuf)
 	}
 	else if (method == 8)
 	{
-		inbuf = fz_malloc(doc->ctx, ent->csize);
+		inbuf = fz_malloc(ctx, ent->csize);
 
 		fz_read(doc->file, inbuf, ent->csize);
 
@@ -153,34 +151,29 @@ xps_read_zip_entry(xps_document *doc, xps_entry *ent, unsigned char *outbuf)
 		code = inflateInit2(&stream, -15);
 		if (code != Z_OK)
 		{
-			fz_unlock(ctx, FZ_LOCK_FILE);
-			fz_free(doc->ctx, inbuf);
-			fz_throw(doc->ctx, "zlib inflateInit2 error: %s", stream.msg);
+			fz_free(ctx, inbuf);
+			fz_throw(ctx, "zlib inflateInit2 error: %s", stream.msg);
 		}
 		code = inflate(&stream, Z_FINISH);
 		if (code != Z_STREAM_END)
 		{
 			inflateEnd(&stream);
-			fz_unlock(ctx, FZ_LOCK_FILE);
-			fz_free(doc->ctx, inbuf);
-			fz_throw(doc->ctx, "zlib inflate error: %s", stream.msg);
+			fz_free(ctx, inbuf);
+			fz_throw(ctx, "zlib inflate error: %s", stream.msg);
 		}
 		code = inflateEnd(&stream);
 		if (code != Z_OK)
 		{
-			fz_unlock(ctx, FZ_LOCK_FILE);
-			fz_free(doc->ctx, inbuf);
-			fz_throw(doc->ctx, "zlib inflateEnd error: %s", stream.msg);
+			fz_free(ctx, inbuf);
+			fz_throw(ctx, "zlib inflateEnd error: %s", stream.msg);
 		}
 
-		fz_free(doc->ctx, inbuf);
+		fz_free(ctx, inbuf);
 	}
 	else
 	{
-		fz_unlock(ctx, FZ_LOCK_FILE);
-		fz_throw(doc->ctx, "unknown compression method (%d)", method);
+		fz_throw(ctx, "unknown compression method (%d)", method);
 	}
-	fz_unlock(ctx, FZ_LOCK_FILE);
 }
 
 /*
@@ -306,7 +299,6 @@ xps_find_and_read_zip_dir(xps_document *doc)
 	int i, n;
 	fz_context *ctx = doc->ctx;
 
-	fz_lock(ctx, FZ_LOCK_FILE);
 	fz_seek(doc->file, 0, SEEK_END);
 	file_size = fz_tell(doc->file);
 
@@ -322,7 +314,6 @@ xps_find_and_read_zip_dir(xps_document *doc)
 			if (!memcmp(buf + i, "PK\5\6", 4))
 			{
 				xps_read_zip_dir(doc, file_size - back + i);
-				fz_unlock(ctx, FZ_LOCK_FILE);
 				return;
 			}
 		}
@@ -330,8 +321,7 @@ xps_find_and_read_zip_dir(xps_document *doc)
 		back += sizeof buf - 4;
 	}
 
-	fz_unlock(ctx, FZ_LOCK_FILE);
-	fz_throw(doc->ctx, "cannot find end of central directory");
+	fz_throw(ctx, "cannot find end of central directory");
 }
 
 /*