Create a micro abstraction around the POSIX file APIs

This way we can start to write IO code to read and write files in the
Git object database, but provide a hook to inject native Win32 APIs
instead so libgit2 can be ported to run natively on that platform.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

.gitignore

 /apidocs
+/include/git/config.h
 *.o
 *.a

Makefile

@@ -3,6 +3,7 @@ all::
 DOXYGEN = doxygen
 
 CFLAGS = -g -O2
+OS     = unix
 
 BASIC_CFLAGS := -Iinclude
 BASIC_CFLAGS += -DGIT__PRIVATE
@@ -11,11 +12,16 @@ BASIC_CFLAGS += -fvisibility=hidden
 OBJS = $(patsubst %.c,%.o,$(wildcard src/*.c))
 HDRS = $(wildcard include/git/*.h)
 
+OBJS += src/os/$(OS).o
+HDRS += include/git/config.h
+HDRS += include/git/os/$(OS).h
+
 
 all:: libgit2.a
 
 clean:
 	rm -f libgit2.a src/*.o
+	rm -f include/git/config.h
 	rm -rf apidocs
 
 apidocs:
@@ -25,6 +31,10 @@ apidocs:
 .c.o:
 	$(CC) $(BASIC_CFLAGS) $(CFLAGS) -c $< -o $@
 
+include/git/config.h: include/git/config.h.in
+	sed 's/@@OS@@/$(OS)/g' $< >$@+
+	mv $@+ $@
+
 $(OBJS): $(HDRS)
 libgit2.a: $(OBJS)
 	rm -f libgit2.a

include/git/commit.h

@@ -28,7 +28,6 @@
 
 #include "git/common.h"
 #include "git/oid.h"
-#include <time.h>
 
 /**
  * @file git/commit.h

include/git/common.h

@@ -36,6 +36,13 @@
 # define GIT_END_DECL    /* empty */
 #endif
 
+/** Declare a public function exported for application use. */
+#ifdef __GNUC__
+# define GIT_EXTERN(type) __attribute__((visibility("default"))) type
+#else
+# define GIT_EXTERN(type) type
+#endif
+
 /**
  * @file git/common.h
  * @brief Git common platform definitions
@@ -43,14 +50,6 @@
  * @ingroup Git
  * @{
  */
-GIT_BEGIN_DECL
-
-/** Declare a public function exported for application use. */
-#ifdef __GNUC__
-# define GIT_EXTERN(type) __attribute__((visibility("default"))) type
-#else
-# define GIT_EXTERN(type) type
-#endif
 
 /** Operation completed successfully. */
 #define GIT_SUCCESS 0
@@ -69,6 +68,10 @@ GIT_BEGIN_DECL
 /** Input does not exist in the scope searched. */
 #define GIT_ENOTFOUND (GIT_ERROR - 2)
 
+#include "git/config.h"
+
+GIT_BEGIN_DECL
+
 /** A revision traversal pool. */
 typedef struct git_revp git_revp;
 

include/git/config.h.in

+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef INCLUDE_git_config_h__
+#define INCLUDE_git_config_h__
+
+#include "git/os/@@OS@@.h"
+
+#endif

include/git/odb.h

@@ -28,7 +28,6 @@
 
 #include "git/common.h"
 #include "git/oid.h"
-#include <unistd.h>
 
 /**
  * @file git/odb.h

include/git/os/unix.h

+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef INCLUDE_git_os_abstraction_h__
+#define INCLUDE_git_os_abstraction_h__
+
+#include <unistd.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <time.h>
+
+/**
+ * @file git/os/unix.h
+ * @brief Portable operating system abstractions
+ * @defgroup git_os_abstraction Portable operating system abstractions
+ * @ingroup Git
+ * @{
+ */
+GIT_BEGIN_DECL
+
+/** Descriptor to an open file in the filesystem. */
+typedef int git_file;
+
+/**
+ * Open a file by path name.
+ *
+ * Valid flags are:
+ * - O_CREAT: Create the file if it does not yet exist.
+ * - O_RDONLY: Open the file for reading.
+ * - O_WRONLY: Open the file for writing.
+ * - O_RDWR: Open the file for both reading and writing.
+ *
+ * @param path path name of the file to open.
+ * @param flags bitmask of access requested to the file.
+ * @return the opened file descriptor; <0 if the open failed.
+ */
+static inline git_file git_fopen(const char *path, int flags)
+{
+	return open(path, flags);
+}
+
+/**
+ * Close an open file descriptor.
+ * @param fd descriptor to close.
+ * @return 0 on success; <0 if the descriptor close failed.
+ */
+static inline int git_fclose(git_file fd)
+{
+	return close(fd);
+}
+
+/**
+ * Read from an open file descriptor at the current position.
+ *
+ * Less than the number of requested bytes may be read.  The
+ * read is automatically restarted if it fails due to a signal
+ * being delivered to the calling thread.
+ *
+ * @param fd open descriptor.
+ * @param buf buffer to store the read data into.
+ * @param cnt number of bytes to transfer.
+ * @return
+ *  - On success, actual number of bytes read.
+ *  - On EOF, 0.
+ *  - On failure, <0.
+ */
+GIT_EXTERN(ssize_t) git_fread(git_file fd, void *buf, size_t cnt);
+
+/**
+ * Write to an open file descriptor at the current position.
+ *
+ * Less than the number of requested bytes may be written.  The
+ * write is automatically restarted if it fails due to a signal
+ * being delivered to the calling thread.
+ *
+ * @param fd open descriptor.
+ * @param buf buffer to write data from.
+ * @param cnt number of bytes to transfer.
+ * @return
+ *  - On success, actual number of bytes written.
+ *  - On EOF, 0.
+ *  - On failure, <0.
+ */
+GIT_EXTERN(ssize_t) git_fwrite(git_file fd, void *buf, size_t cnt);
+
+/** @} */
+GIT_END_DECL
+#endif

src/os/unix.c

+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include <errno.h>
+#include "git/common.h"
+
+ssize_t git_fread(git_file fd, void *buf, size_t cnt)
+{
+	for (;;) {
+		ssize_t r = read(fd, buf, cnt);
+		if (r < 0 && (errno == EINTR || errno == EAGAIN))
+			continue;
+		return r;
+	}
+}
+
+ssize_t git_fwrite(git_file fd, void *buf, size_t cnt)
+{
+	for (;;) {
+		ssize_t r = write(fd, buf, cnt);
+		if (r < 0 && (errno == EINTR || errno == EAGAIN))
+			continue;
+		return r;
+	}
+}