From 5096de91a10b58bcf35a3564a5ced3ae39fb01fc Mon Sep 17 00:00:00 2001
From: Mark Harmstone <mark@harmstone.com>
Date: Thu, 28 Oct 2021 12:36:46 +0100
Subject: [PATCH] Allow mdb_open_buffer to work when fmemopen not available

---
 include/mdbtools.h.in |  2 ++
 src/libmdb/file.c     | 67 ++++++++++++++++++++++++-------------------
 src/libmdb/write.c    | 28 ++++++++++++------
 3 files changed, 60 insertions(+), 37 deletions(-)

diff --git a/include/mdbtools.h.in b/include/mdbtools.h.in
index acc9309..266c527 100644
--- a/include/mdbtools.h.in
+++ b/include/mdbtools.h.in
@@ -256,6 +256,8 @@ typedef struct {
 
 typedef struct {
 	FILE        *stream;
+	void		*data;
+	size_t		data_len;
 	gboolean      writable;
 	guint32		jet_version;
 	guint32		db_key;
diff --git a/src/libmdb/file.c b/src/libmdb/file.c
index c6d0d83..b742b80 100644
--- a/src/libmdb/file.c
+++ b/src/libmdb/file.c
@@ -123,7 +123,7 @@ static char *mdb_find_file(const char *file_name)
  *
  * Return value: The handle on success, NULL on failure
  */
-static MdbHandle *mdb_handle_from_stream(FILE *stream, MdbFileFlags flags) {
+static MdbHandle *mdb_handle_from_stream(FILE *stream, void *data, size_t data_len, MdbFileFlags flags) {
 	MdbHandle *mdb = g_malloc0(sizeof(MdbHandle));
 	mdb_set_default_backend(mdb, "access");
     mdb_set_date_fmt(mdb, "%x %X");
@@ -140,6 +140,8 @@ static MdbHandle *mdb_handle_from_stream(FILE *stream, MdbFileFlags flags) {
 	mdb->f = g_malloc0(sizeof(MdbFile));
 	mdb->f->refs = 1;
 	mdb->f->stream = stream;
+	mdb->f->data = data;
+	mdb->f->data_len = data_len;
 	if (flags & MDB_WRITABLE) {
 		mdb->f->writable = TRUE;
     }
@@ -206,17 +208,7 @@ static MdbHandle *mdb_handle_from_stream(FILE *stream, MdbFileFlags flags) {
  * Return value: point to MdbHandle structure.
  */
 MdbHandle *mdb_open_buffer(void *buffer, size_t len, MdbFileFlags flags) {
-    FILE *file = NULL;
-#ifdef HAVE_FMEMOPEN
-    file = fmemopen(buffer, len, (flags & MDB_WRITABLE) ? "r+" : "r");
-#else
-    fprintf(stderr, "mdb_open_buffer requires a platform with support for fmemopen(3)\n");
-#endif
-    if (file == NULL) {
-        fprintf(stderr, "Couldn't open memory buffer\n");
-        return NULL;
-    }
-    return mdb_handle_from_stream(file, flags);
+    return mdb_handle_from_stream(NULL, buffer, len, flags);
 }
 
 /**
@@ -253,7 +245,7 @@ MdbHandle *mdb_open(const char *filename, MdbFileFlags flags)
 
     g_free(filepath);
 
-    return mdb_handle_from_stream(file, flags);
+    return mdb_handle_from_stream(file, NULL, 0, flags);
 }
 
 /**
@@ -354,25 +346,42 @@ static ssize_t _mdb_read_pg(MdbHandle *mdb, void *pg_buf, unsigned long pg)
 	ssize_t len;
 	off_t offset = pg * mdb->fmt->pg_size;
 
-    if (fseeko(mdb->f->stream, 0, SEEK_END) == -1) {
-        fprintf(stderr, "Unable to seek to end of file\n");
-        return 0;
-    }
-    if (ftello(mdb->f->stream) < offset) { 
-        fprintf(stderr,"offset %" PRIu64 " is beyond EOF\n",(uint64_t)offset);
-        return 0;
-    }
+	if (mdb->f->data) {
+		if ((off_t)mdb->f->data_len < offset) {
+			fprintf(stderr,"offset %" PRIu64 " is beyond EOF\n",(uint64_t)offset);
+			return 0;
+		}
+	} else {
+		if (fseeko(mdb->f->stream, 0, SEEK_END) == -1) {
+			fprintf(stderr, "Unable to seek to end of file\n");
+			return 0;
+		}
+		if (ftello(mdb->f->stream) < offset) {
+			fprintf(stderr,"offset %" PRIu64 " is beyond EOF\n",(uint64_t)offset);
+			return 0;
+		}
+	}
+
 	if (mdb->stats && mdb->stats->collect) 
 		mdb->stats->pg_reads++;
 
-	if (fseeko(mdb->f->stream, offset, SEEK_SET) == -1) {
-        fprintf(stderr, "Unable to seek to page %lu\n", pg);
-        return 0;
-    }
-	len = fread(pg_buf, 1, mdb->fmt->pg_size, mdb->f->stream);
-	if (ferror(mdb->f->stream)) {
-		perror("read");
-		return 0;
+	if (mdb->f->data) {
+		if (offset + mdb->fmt->pg_size > (off_t)mdb->f->data_len)
+			len = mdb->f->data_len - offset;
+		else
+			len = mdb->fmt->pg_size;
+
+		memcpy(pg_buf, (char*)mdb->f->data + offset, len);
+	} else {
+		if (fseeko(mdb->f->stream, offset, SEEK_SET) == -1) {
+			fprintf(stderr, "Unable to seek to page %lu\n", pg);
+			return 0;
+		}
+		len = fread(pg_buf, 1, mdb->fmt->pg_size, mdb->f->stream);
+		if (ferror(mdb->f->stream)) {
+			perror("read");
+			return 0;
+		}
 	}
     memset(pg_buf + len, 0, mdb->fmt->pg_size - len);
 	/*
diff --git a/src/libmdb/write.c b/src/libmdb/write.c
index 44a48f2..51c8f89 100644
--- a/src/libmdb/write.c
+++ b/src/libmdb/write.c
@@ -79,13 +79,20 @@ mdb_write_pg(MdbHandle *mdb, unsigned long pg)
 	off_t offset = pg * mdb->fmt->pg_size;
 	unsigned char *buf = mdb->pg_buf;
 
-    fseeko(mdb->f->stream, 0, SEEK_END);
-	/* is page beyond current size + 1 ? */
-	if (ftello(mdb->f->stream) < offset + mdb->fmt->pg_size) {
-		fprintf(stderr,"offset %" PRIu64 " is beyond EOF\n",(uint64_t)offset);
-		return 0;
+	if (mdb->f->data) {
+		if ((off_t)mdb->f->data_len < offset + mdb->fmt->pg_size) {
+			fprintf(stderr,"offset %" PRIu64 " is beyond EOF\n",(uint64_t)offset);
+			return 0;
+		}
+	} else {
+		fseeko(mdb->f->stream, 0, SEEK_END);
+		/* is page beyond current size + 1 ? */
+		if (ftello(mdb->f->stream) < offset + mdb->fmt->pg_size) {
+			fprintf(stderr,"offset %" PRIu64 " is beyond EOF\n",(uint64_t)offset);
+			return 0;
+		}
+		fseeko(mdb->f->stream, offset, SEEK_SET);
 	}
-	fseeko(mdb->f->stream, offset, SEEK_SET);
 
 	if (pg != 0 && mdb->f->db_key != 0)
 	{
@@ -94,13 +101,18 @@ mdb_write_pg(MdbHandle *mdb, unsigned long pg)
 		mdbi_rc4((unsigned char*)&tmp_key, 4, buf, mdb->fmt->pg_size);
 	}
 
-	len = fwrite(buf, 1, mdb->fmt->pg_size, mdb->f->stream);
+	if (mdb->f->data) {
+		memcpy((char*)mdb->f->data + offset, mdb->pg_buf, mdb->fmt->pg_size);
+		len = mdb->fmt->pg_size;
+	} else {
+		len = fwrite(buf, 1, mdb->fmt->pg_size, mdb->f->stream);
+	}
 
 	if (buf != mdb->pg_buf) {
 		g_free(buf);
 	}
 
-	if (ferror(mdb->f->stream)) {
+	if (!mdb->f->data && ferror(mdb->f->stream)) {
 		perror("write");
 		return 0;
 	} else if (len<mdb->fmt->pg_size) {