Abstract all access to shares through a modular system

This patch introduces the notion of a "scheme module". Such a
module provides a "get_file" function to retrieve the contents of
a file located at a specified URI.

Currently available modules:
- the "file" module, supporting the "file://" URI scheme;
- the "libmtp" module, using the LibMTP library to support the
  "mtp://' scheme;
- the "gio" module, using the GLib-GIO library to support the
  "uuid://" and "label://" schemes.

src/Makefile.am

@@ -2,9 +2,10 @@ bin_PROGRAMS = gfsec-use
 
 gfsec_use_SOURCES = gfsec-use.c util.c util.h secret.c secret.h \
 		    secretcfg.c secretcfg.h gfsec-errors.h \
-		    schemes.h \
-		    mtp-support.c mtp-support.h \
-		    uuid-support.c uuid-support.h
+		    schemes.h scheme-module.h scheme-module.c \
+		    scheme-libmtp.c scheme-libmtp.h \
+		    scheme-gio.c scheme-gio.h \
+		    scheme-file.c scheme-file.h
 
 AM_CPPFLAGS = -I$(top_srcdir)/lib $(LIBGFSHARE_CFLAGS) $(LIBMTP_CFLAGS) $(GIO_CFLAGS)
 AM_LDFLAGS = -L$(top_builddir)/lib $(LIBGFSHARE_LIBS) $(LIBMTP_LIBS) $(GIO_LIBS)

src/gfsec-use.c

@@ -37,8 +37,7 @@
 #include "util.h"
 #include "secret.h"
 #include "secretcfg.h"
-#include "mtp-support.h"
-#include "uuid-support.h"
+#include "scheme-module.h"
 
 static void
 usage(int status)
@@ -126,37 +125,15 @@ get_config_file(const char *filename, char *buffer, size_t len)
 static int
 get_share_data(gfsec_share_t *share)
 {
-    int rc = -1;
+    int rc;
     unsigned char *data;
     char buffer[256];
     size_t len;
 
-    switch ( share->scheme ) {
-    case GFSEC_SCHEME_FILE:
-        if ( (data = read_file(share->path, &len, GFSEC_SECRET_MAX_SIZE)) )
-            rc = 0;
-        break;
-
-    case GFSEC_SCHEME_UUID:
-        if ( (data = gfsec_get_file_from_uuid(share->authority,
-                        share->path, &len)) )
-            rc = 0;
-        break;
-
-    case GFSEC_SCHEME_LABEL:
-        if ( (data = gfsec_get_file_from_label(share->authority,
-                        share->path, &len)) )
-            rc = 0;
-        break;
-
-    case GFSEC_SCHEME_MTP:
-        if ( (data = gfsec_get_file_from_mtp(share->authority,
-                        share->path, &len)) )
-            rc = 0;
-        break;
-    }
+    rc = gfsec_scheme_module_get_file(share->scheme, share->authority,
+            share->path, &data, &len);
 
-    if ( rc == 0 ) {
+    if ( rc == GFSEC_SCHEME_STATUS_SUCCESS ) {
         gfsec_share_get_uri(share, buffer, sizeof(buffer));
 
         if ( (rc = gfsec_share_set_data(share, data, len)) != 0 ) {
@@ -167,7 +144,6 @@ get_share_data(gfsec_share_t *share)
             printf("Found share data in %s\n", buffer);
     }
 
-
     return rc;
 }
 
@@ -216,7 +192,7 @@ main(int argc, char **argv)
         }
     }
 
-    gfsec_mtp_init();
+    gfsec_scheme_module_init();
 
     if ( ! gcry_check_version(GCRYPT_VERSION) )
         errx(EXIT_FAILURE, "libgcrypt version mismatch");

src/scheme-file.c

@@ -0,0 +1,53 @@
+/*
+ * gfsecret - Secret sharing tools
+ * Copyright (C) 2016 Damien Goutte-Gattat
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include "scheme-file.h"
+#include "util.h"
+
+static int
+gfsec_scheme_file_get_file(gfsec_scheme_t   scheme,
+                           const char      *authority,
+                           const char      *path,
+                           unsigned char  **buffer,
+                           size_t          *len)
+{
+    (void) authority;
+
+    if ( scheme != GFSEC_SCHEME_FILE )
+        return GFSEC_SCHEME_STATUS_UNSUPPORTED_SCHEME;
+
+    if ( (*buffer = read_file(path, len, GFSEC_SECRET_MAX_SIZE)) ) {
+        return GFSEC_SCHEME_STATUS_SUCCESS;
+    }
+    else
+        return GFSEC_SCHEME_STATUS_ERROR;
+}
+
+gfsec_scheme_module_t
+gfsec_scheme_file_init(void)
+{
+    gfsec_scheme_module_t module;
+
+    module.get_file = gfsec_scheme_file_get_file;
+
+    return module;
+}

src/scheme-file.h

@@ -0,0 +1,35 @@
+/*
+ * gfsecret - Secret sharing tools
+ * Copyright (C) 2016 Damien Goutte-Gattat
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef ICP20160821_SCHEME_FILE_H
+#define ICP20160821_SCHEME_FILE_H
+
+#include "scheme-module.h"
+
+#ifdef __cpluscplus
+extern "C" {
+#endif
+
+gfsec_scheme_module_t
+gfsec_scheme_file_init(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* !ICP20160821_SCHEME-FILE_H */

src/uuid-support.c → src/scheme-gio.c

@@ -20,39 +20,9 @@
 #include <config.h>
 #endif
 
-#include "uuid-support.h"
+#include "scheme-gio.h"
 
-#ifndef HAVE_GIO
-
-#include <errno.h>
-
-unsigned char *
-gfsec_get_file_from_uuid(const char    *authority,
-                         const char    *path,
-                         size_t        *len)
-{
-    (void) authority;
-    (void) path;
-    (void) len;
-
-    errno = ENOSYS;
-    return NULL;
-}
-
-unsigned char *
-gfsec_get_file_from_label(const char   *authority,
-                          const char   *path,
-                          size_t       *len)
-{
-    (void) authority;
-    (void) path;
-    (void) len;
-
-    errno = ENOSYS;
-    return NULL;
-}
-
-#else
+#ifdef HAVE_GIO
 
 #include <string.h>
 #include <gio/gio.h>
@@ -210,57 +180,46 @@ get_file_contents(GVolume          *volume,
     return rc;
 }
 
-/**
- * Gets the contents of a file on a volume identified by its UUID.
- *
- * @param[in]  authority The volume UUID.
- * @param[in]  path      Path to the file on the volume.
- * @param[out] len       Number of bytes read from the volume.
- *
- * @return A pointer to a newly allocated buffer containing
- * the file data, or NULL if an error occured.
- */
-unsigned char *
-gfsec_get_file_from_uuid(const char    *authority,
-                         const char    *path,
-                         size_t        *len)
+static int
+gfsec_scheme_gio_get_file(gfsec_scheme_t   scheme,
+                          const char      *authority,
+                          const char      *path,
+                          unsigned char  **buffer,
+                          size_t          *len)
 {
-    GVolume *volume;
-    unsigned char *blob = NULL;
+    GVolume *volume = NULL;
+    int rc = GFSEC_SCHEME_STATUS_ERROR;
+
+    switch ( scheme ) {
+    case GFSEC_SCHEME_UUID:
+        volume = find_volume(authority, 1);
+        break;
+
+    case GFSEC_SCHEME_LABEL:
+        volume = find_volume(authority, 0);
+        break;
 
-    if ( (volume = find_volume(authority, 1)) ) {
-        get_file_contents(volume, path, &blob, len);
+    default:
+        return GFSEC_SCHEME_STATUS_UNSUPPORTED_SCHEME;
+    }
+
+    if ( volume ) {
+        if ( get_file_contents(volume, path, buffer, len) == 0 )
+            rc = GFSEC_SCHEME_STATUS_SUCCESS;
         g_object_unref(volume);
     }
 
-    return blob;
+    return rc;
 }
 
-
-/**
- * Gets the contents of a file on a volume identified by its label.
- *
- * @param[in]  authority The volume label.
- * @param[in]  path      Path to the file on the volume.
- * @param[out] len       Number of bytes read from the volume.
- *
- * @return A pointer to a newly allocated buffer containing
- * the file data, or NULL if an error occured.
- */
-unsigned char *
-gfsec_get_file_from_label(const char   *authority,
-                          const char   *path,
-                          size_t       *len)
+gfsec_scheme_module_t
+gfsec_scheme_gio_init(void)
 {
-    GVolume *volume;
-    unsigned char *blob = NULL;
+    gfsec_scheme_module_t module;
 
-    if ( (volume = find_volume(authority, 0)) ) {
-        get_file_contents(volume, path, &blob, len);
-        g_object_unref(volume);
-    }
+    module.get_file = gfsec_scheme_gio_get_file;
 
-    return blob;
+    return module;
 }
 
 #endif /* HAVE_GIO */

src/uuid-support.h → src/scheme-gio.h

@@ -16,23 +16,20 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef ICP20160207_UUID_SUPPORT_H
-#define ICP20160207_UUID_SUPPORT_H
+#ifndef ICP20160207_SCHEME_GIO_H
+#define ICP20160207_SCHEME_GIO_H
 
-#include <stdlib.h>
+#include "scheme-module.h"
 
 #ifdef __cpluscplus
 extern "C" {
 #endif
 
-unsigned char *
-gfsec_get_file_from_uuid(const char *, const char *, size_t *);
-
-unsigned char *
-gfsec_get_file_from_label(const char *, const char *, size_t *);
+gfsec_scheme_module_t
+gfsec_scheme_gio_init(void);
 
 #ifdef __cplusplus
 }
 #endif
 
-#endif /* !ICP20160207_UUID_SUPPORT_H */
+#endif /* !ICP20160207_SCHEME_GIO_H */

src/mtp-support.c → src/scheme-libmtp.c

@@ -20,29 +20,13 @@
 #include <config.h>
 #endif
 
-#include "mtp-support.h"
+#include "scheme-libmtp.h"
 
-#ifndef HAVE_LIBMTP
-
-#include <errno.h>
-
-unsigned char *
-gfsec_get_file_from_mtp(const char *authority,
-                        const char *path,
-                        size_t     *len)
-{
-    (void) authority;
-    (void) path;
-    (void) len;
-
-    errno = ENOSYS;
-    return NULL;
-}
-
-#else
+#ifdef HAVE_LIBMTP
 
 #include <string.h>
 #include <splitstr.h>
+#include <libmtp.h>
 
 #define MTP_ROOT_FOLDER_ID  0xFFFFFFFF
 
@@ -183,46 +167,56 @@ getfile_cb(void            *params,
     return LIBMTP_HANDLER_RETURN_OK;
 }
 
-/**
- * Gets the contents of a file on a MTP device.
- *
- * @param[in] authority Serial number of the MTP device.
- * @param[in] path Path to the file on the MTP device.
- * @param[out] len Number of bytes read from the device.
- *
- * @return A pointer to a newly allocated buffer containing
- * the file data, or NULL if an error occured.
- */
-unsigned char *
-gfsec_get_file_from_mtp(const char *authority,
-                        const char *path,
-                        size_t     *len)
+static int
+gfsec_scheme_libmtp_get_file(gfsec_scheme_t   scheme,
+                             const char      *authority,
+                             const char      *path,
+                             unsigned char  **buffer,
+                             size_t          *len)
 {
     LIBMTP_mtpdevice_t *device;
     struct getfile_cb_data cb_data;
-    unsigned char *blob = NULL;
+    int rc;
+
+    if ( scheme != GFSEC_SCHEME_MTP )
+        return GFSEC_SCHEME_STATUS_UNSUPPORTED_SCHEME;
 
     if ( (device = find_mtp_device(authority)) ) {
         long file_id;
 
         if ( (file_id = find_mtp_file(device, 0, path, len)) != -1 ) {
-            if ( (blob = malloc(*len)) ) {
-                cb_data.buffer = blob;
+            if ( (*buffer = malloc(*len)) ) {
+                cb_data.buffer = *buffer;
                 cb_data.written = 0;
                 cb_data.expected = *len;
 
                 if ( LIBMTP_Get_File_To_Handler(device, file_id,
                             getfile_cb, &cb_data, NULL, NULL) != 0 ) {
-                    free(blob);
-                    blob = NULL;
+                    free(*buffer);
+                    *buffer = NULL;
+                    rc = GFSEC_SCHEME_STATUS_SUCCESS;
                 }
+                else
+                    rc = GFSEC_SCHEME_STATUS_ERROR;
             }
         }
 
         LIBMTP_Release_Device(device);
     }
 
-    return blob;
+    return rc;
+}
+
+gfsec_scheme_module_t
+gfsec_scheme_libmtp_init(void)
+{
+    gfsec_scheme_module_t module;
+
+    LIBMTP_Init();
+
+    module.get_file = gfsec_scheme_libmtp_get_file;
+
+    return module;
 }
 
 #endif /* HAVE_LIBMTP */

src/mtp-support.h → src/scheme-libmtp.h

@@ -16,27 +16,20 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef ICP20160207_MTP_SUPPORT_H
-#define ICP20160207_MTP_SUPPORT_H
+#ifndef ICP20160207_SCHEME_LIBMTP_H
+#define ICP20160207_SCHEME_LIBMTP_H
 
-#include <stdlib.h>
+#include "scheme-module.h"
 
 #ifdef __cpluscplus
 extern "C" {
 #endif
 
-#ifdef HAVE_LIBMTP
-#include <libmtp.h>
-#define gfsec_mtp_init()    LIBMTP_Init()
-#else
-#define gfsec_mtp_init()
-#endif
-
-unsigned char *
-gfsec_get_file_from_mtp(const char *, const char *, size_t *);
+gfsec_scheme_module_t
+gfsec_scheme_libmtp_init(void);
 
 #ifdef __cplusplus
 }
 #endif
 
-#endif /* !ICP20160207_MTP_SUPPORT_H */
+#endif /* !ICP20160207_SCHEME_LIBMTP_H */

src/scheme-module.c

@@ -0,0 +1,95 @@
+/*
+ * gfsecret - Secret sharing tools
+ * Copyright (C) 2016 Damien Goutte-Gattat
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include "scheme-module.h"
+#include "scheme-file.h"
+#include "scheme-libmtp.h"
+#include "scheme-gio.h"
+
+static gfsec_scheme_module_t *modules;
+
+/**
+ * Initializes the module system.
+ * This function should be called once, before any other
+ * function from this module.
+ */
+void
+gfsec_scheme_module_init(void)
+{
+    static gfsec_scheme_module_t mods[4];
+    gfsec_scheme_module_t dummy = { NULL };
+    int n = 0;
+
+    mods[n++] = gfsec_scheme_file_init();
+#ifdef HAVE_LIBMTP
+    mods[n++] = gfsec_scheme_libmtp_init();
+#endif
+#ifdef HAVE_GIO
+    mods[n++] = gfsec_scheme_gio_init();
+#endif
+
+    mods[n++] = dummy;
+
+    modules = mods;
+}
+
+/**
+ * Attempts to retrieve a file's contents.
+ * This function will successively ask all available modules
+ * to retrieve the file at the specified location.
+ *
+ * @param scheme[in]    The URI scheme.
+ * @param authority[in] The URI authority part.
+ * @param path[in]      The URI path.
+ * @param buffer[out]   A pointer to a buffer to store the file
+ *                      contents; will be automatically allocated.
+ * @param len[out]      The address where the count of retrieved
+ *                      bytes will be stored.
+ *
+ * @return
+ * - GFSEC_SCHEME_STATUS_SUCCESS if successful;
+ * - GFSEC_SCHEME_STATUS_UNSUPPORTED_SCHEME if no module is
+ *   available to handle the URI scheme;
+ * - GFSEC_SCHEME_STATUS_ERROR if a module supported the
+ *   URI scheme but an error occured during retrieval.
+ */
+int
+gfsec_scheme_module_get_file(gfsec_scheme_t   scheme,
+                             const char      *authority,
+                             const char      *path,
+                             unsigned char  **buffer,
+                             size_t          *len)
+{
+    gfsec_scheme_module_t *mod = modules;
+    int rc;
+
+    while ( mod->get_file != NULL ) {
+        rc = mod->get_file(scheme, authority, path, buffer, len);
+
+        if ( rc != GFSEC_SCHEME_STATUS_SUCCESS )
+            mod += 1;
+        else
+            break;
+    }
+
+    return rc;
+}

src/scheme-module.h

@@ -0,0 +1,61 @@
+/*
+ * gfsecret - Secret sharing tools
+ * Copyright (C) 2016 Damien Goutte-Gattat
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef ICP20160820_SCHEME_MODULE_H
+#define ICP20160820_SCHEME_MODULE_H
+
+#include <stdlib.h>
+
+#include "schemes.h"
+
+typedef enum gfsec_scheme_status {
+    GFSEC_SCHEME_STATUS_SUCCESS = 0,
+    GFSEC_SCHEME_STATUS_UNSUPPORTED_SCHEME = -1,
+    GFSEC_SCHEME_STATUS_ERROR = -2
+} gfsec_scheme_status_t;
+
+
+typedef int (*gfsec_scheme_get_file)(gfsec_scheme_t,
+                                     const char *,
+                                     const char *,
+                                     unsigned char **,
+                                     size_t *);
+
+typedef struct gfsec_scheme_module {
+    gfsec_scheme_get_file   get_file;
+} gfsec_scheme_module_t;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void
+gfsec_scheme_module_init(void);
+
+int
+gfsec_scheme_module_get_file(gfsec_scheme_t,
+                             const char *,
+                             const char *,
+                             unsigned char **,
+                             size_t *);
+
+#ifdef __cpluscplus
+}
+#endif
+
+#endif /* !ICP20160820_SCHEME_MODULE_H */