Move stream ops into mtar_ops_t; separate open and init

Moving stream ops into a separate struct lets them be
defined in a const object and shared between multiple
mtar_t objects.

Also provide a new mtar_init() call which accepts the
ops struct and initializes the mtar_t object properly.

3 files changed, 55 insertions, 43 deletions

diff --git a/src/microtar-stdio.c b/src/microtar-stdio.c
index 87ae4f7..4aed2a6 100644
--- a/src/microtar-stdio.c
+++ b/src/microtar-stdio.c
@@ -25,61 +25,48 @@
 #include <stdio.h>
 #include <string.h>
 
-static int file_write(mtar_t* tar, const void* data, unsigned size)
+static int file_read(void* stream, void* data, unsigned size)
 {
-    unsigned res = fwrite(data, 1, size, tar->stream);
-    return (res == size) ? MTAR_ESUCCESS : MTAR_EWRITEFAIL;
+    unsigned res = fread(data, 1, size, (FILE*)stream);
+    return (res == size) ? MTAR_ESUCCESS : MTAR_EREADFAIL;
 }
 
-static int file_read(mtar_t* tar, void* data, unsigned size)
+static int file_write(void* stream, const void* data, unsigned size)
 {
-    unsigned res = fread(data, 1, size, tar->stream);
-    return (res == size) ? MTAR_ESUCCESS : MTAR_EREADFAIL;
+    unsigned res = fwrite(data, 1, size, (FILE*)stream);
+    return (res == size) ? MTAR_ESUCCESS : MTAR_EWRITEFAIL;
 }
 
-static int file_seek(mtar_t* tar, unsigned offset)
+static int file_seek(void* stream, unsigned offset)
 {
-    int res = fseek(tar->stream, offset, SEEK_SET);
+    int res = fseek((FILE*)stream, offset, SEEK_SET);
     return (res == 0) ? MTAR_ESUCCESS : MTAR_ESEEKFAIL;
 }
 
-static int file_close(mtar_t* tar)
+static int file_close(void* stream)
 {
-    fclose(tar->stream);
-    return MTAR_ESUCCESS;
+    int err = fclose((FILE*)stream);
+    return (err == 0 ? MTAR_ESUCCESS : MTAR_EFAILURE);
 }
 
+static const mtar_ops_t file_ops = {
+    .read = file_read,
+    .write = file_write,
+    .seek = file_seek,
+    .close = file_close,
+};
+
 int mtar_open(mtar_t* tar, const char* filename, const char* mode)
 {
-    int err;
-    mtar_header_t h;
-
-    /* Init tar struct and functions */
-    memset(tar, 0, sizeof(*tar));
-    tar->write = file_write;
-    tar->read = file_read;
-    tar->seek = file_seek;
-    tar->close = file_close;
-
-    /* Assure mode is always binary */
+    /* Ensure mode is always binary */
     if(strchr(mode, 'r')) mode = "rb";
     if(strchr(mode, 'w')) mode = "wb";
     if(strchr(mode, 'a')) mode = "ab";
 
     /* Open file */
-    tar->stream = fopen(filename, mode);
-    if(!tar->stream)
+    FILE* file = fopen(filename, mode);
+    if(!file)
         return MTAR_EOPENFAIL;
 
-    /* Read first header to check it is valid if mode is `r` */
-    if(*mode == 'r') {
-        err = mtar_read_header(tar, &h);
-        if(err != MTAR_ESUCCESS) {
-            mtar_close(tar);
-            return err;
-        }
-    }
-
-    /* Return ok */
-    return MTAR_ESUCCESS;
+    return mtar_init(tar, &file_ops, file);
 }
diff --git a/src/microtar.c b/src/microtar.c
index 81e1031..2f5f781 100644
--- a/src/microtar.c
+++ b/src/microtar.c
@@ -99,7 +99,7 @@ static unsigned checksum(const mtar_raw_header_t* rh)
 
 static int tread(mtar_t* tar, void* data, unsigned size)
 {
-    int err = tar->read(tar, data, size);
+    int err = tar->ops->read(tar->stream, data, size);
     tar->pos += size;
     return err;
 }
@@ -107,7 +107,7 @@ static int tread(mtar_t* tar, void* data, unsigned size)
 
 static int twrite(mtar_t* tar, const void* data, unsigned size)
 {
-    int err = tar->write(tar, data, size);
+    int err = tar->ops->write(tar->stream, data, size);
     tar->pos += size;
     return err;
 }
@@ -216,18 +216,34 @@ const char* mtar_strerror(int err)
     }
 }
 
+int mtar_init(mtar_t* tar, const mtar_ops_t* ops, void* stream)
+{
+    memset(tar, 0, sizeof(mtar_t));
+    tar->ops = ops;
+    tar->stream = stream;
+    return 0;
+}
+
 int mtar_close(mtar_t* tar)
 {
-    return tar->close(tar);
+    int err = tar->ops->close(tar->stream);
+    tar->ops = NULL;
+    tar->stream = NULL;
+    return err;
 }
 
 int mtar_seek(mtar_t* tar, unsigned pos)
 {
-    int err = tar->seek(tar, pos);
+    int err = tar->ops->seek(tar->stream, pos);
     tar->pos = pos;
     return err;
 }
 
+int mtar_is_open(mtar_t* tar)
+{
+    return (tar->ops != NULL) ? 1 : 0;
+}
+
 int mtar_rewind(mtar_t* tar)
 {
     tar->remaining_data = 0;
diff --git a/src/microtar.h b/src/microtar.h
index d17129c..b24c8dc 100644
--- a/src/microtar.h
+++ b/src/microtar.h
@@ -57,6 +57,7 @@ enum {
 typedef struct mtar_header mtar_header_t;
 typedef struct mtar_raw_header mtar_raw_header_t;
 typedef struct mtar mtar_t;
+typedef struct mtar_ops mtar_ops_t;
 
 struct mtar_header {
     unsigned mode;
@@ -82,12 +83,17 @@ struct mtar_raw_header {
     char _padding[255];
 };
 
+struct mtar_ops {
+    int(*read)(void* stream, void* data, unsigned size);
+    int(*write)(void* stream, const void* data, unsigned size);
+    int(*seek)(void* stream, unsigned pos);
+    int(*close)(void* stream);
+};
+
 struct mtar {
-    int (*read)(mtar_t* tar, void* data, unsigned size);
-    int (*write)(mtar_t* tar, const void* data, unsigned size);
-    int (*seek)(mtar_t* tar, unsigned pos);
-    int (*close)(mtar_t* tar);
+    const mtar_ops_t* ops;
     void* stream;
+
     unsigned pos;
     unsigned remaining_data;
     unsigned last_header;
@@ -98,7 +104,10 @@ struct mtar {
 const char* mtar_strerror(int err);
 
 int mtar_open(mtar_t* tar, const char* filename, const char* mode);
+
+int mtar_init(mtar_t* tar, const mtar_ops_t* ops, void* stream);
 int mtar_close(mtar_t* tar);
+int mtar_is_open(mtar_t* tar);
 
 int mtar_seek(mtar_t* tar, unsigned pos);
 int mtar_rewind(mtar_t* tar);